Electro-Osmosis of Oil : Electrical Stimulation of Oil Recovery -- Articles & patents

US7325604
Method for enhancing oil production using electricity

A method of enhancing oil production from an oil bearing formation includes the steps of providing a first borehole in a first region of the formation and a second borehole in a second region of the formation. A first electrode is positioned in the first borehole in the first region, and a second electrode is positioned in proximity to the second borehole in the second region. A voltage difference is established between the first and second electrodes to create an electric field across the plugging materials. The electric field is applied to destabilize the plugging materials and improve oil flow through the formation.

FIELD OF THE INVENTION

The present invention relates generally to oil production, and more particularly to a method for enhancing the production of oil from subterranean oil reservoirs with the aid of electric current.

BACKGROUND

When crude oil is initially recovered from an oil-bearing earth formation, the oil is forced from the formation into a producing well under the influence of gas pressure and other pressures present in the formation. The stored energy in the reservoir dissipates as oil production progresses and eventually becomes insufficient to force the oil to the producing well. It is well known in the petroleum industry that a relatively small fraction of the oil in subterranean oil reservoirs is recovered during this primary stage of production. Some reservoirs, such as those containing highly viscous crude, retain 90 percent or more of the oil originally in place after primary production is completed.

A variety of conditions in the oil-bearing formation can impede the flow of oil through interstitial spaces in the oil-bearing formation, limiting the recovery of oil. In many cases, formations become damaged during the process of drilling wells into the formation. Mud, chemical additives and other components used in drilling fluids can accumulate around the well, forming a cake that blocks the flow of oil into the well bore. Drilling fluids can also migrate and accumulate in fissures in the formation, blocking the flow of oil through the formation. Parrafins and waxes may precipitate at the interface between the well bore and the formation, further impeding the flow of oil into the well bore. Sediments and native materials in the formation can also migrate and block interstitial spaces.

Numerous methods have been used to alleviate the problems associated with plugging in oil bearing formations. Plugging is often addressed by backflushing the well to remove mud from around the well. Backflushing the well can consume significant time and energy, and has limited effectiveness in unplugging areas that are located deep within a formation and away from the well. Acidizing the well and flushing the well with solvents are also used to alleviate plugging, but these methods can create hazardous waste that is expensive and difficult to dispose of. As a result, known methods for unplugging oil bearing formations leave much to be desired.

In many cases, crude oil is extracted with high concentrations of sulfur, polycyclic aromatic compounds (PAHs) and other compounds that reduce the quality and value of the oil. The presence of undesirable compounds in the oil requires subsequent processing of the oil, increasing the time and cost of production. Therefore, there is a great need to develop oil production methods that allow oil to be treated while it is being extracted.

SUMMARY OF THE INVENTION

The foregoing problems are solved to a great degree by the present invention, which uses electrodes to enhance oil production from an oil bearing formation. A first borehole is provided in a first region of the formation, and a first electrode is positioned in the first borehole. A second electrode may be placed above ground in proximity to the formation. Alternatively, the second electrode may be installed in a second borehole. The second borehole may be positioned in a second region of the formation, or in proximity to the formation. A voltage difference is established between the first and second electrodes to create an electric field across the formation.

It has been discovered that the method of the present invention can be used to improve the condition of the oil formation and repair damaged or plugged formations where oil flow is impeded by drilling fluids, natural occlusions or other matter. The method can also be applied to pre-treat oil in the formation as it is extracted from the formation. The electric field may be applied and manipulated to destabilize occlusions and plugging materials, increase oil flow through the formation and improve the quality of the oil prior to and during extraction.

DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following description will be better understood when read in conjunction with the figures in which:

FIG. 1 is a schematic diagram of an improved electrochemical method for stimulating oil recovery from an underground oil-bearing formation;

FIG. 2 is a schematic diagram in partial sectional view of an apparatus with which the present method may be practiced;

FIG. 3 is an elevational view of an electrode assembly adapted for use in practicing the present invention;

FIG. 4 is a block flow diagram of a method for improving flow conditions and pre-treating oil in a formation;

FIG. 5 is a schematic diagram of a first alternate electrochemical method for stimulating oil recovery from an underground oil-bearing formation; and

FIG. 6 is a schematic diagram of a second alternate electrochemical method for stimulating oil recovery from an underground oil-bearing formation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the Figures in general, and to FIG. 1, specifically, the reference number 11 represents a subterranean formation containing crude oil. The subterranean formation 11 is an electrically conductive formation, preferably having a moisture content above 5 percent by weight. As shown in FIG. 1, formation 11 is comprised of a porous and substantially homogeneous media, such as sandstone or limestone. Typically, such oil-bearing formations are found beneath the upper strata of earth, referred to generally as overburden, at a depth of the order of 1,000 feet or more below the surface. Communication from the surface 12 to the formation 11 is established through on or more boreholes. In FIG. 1, communication from the surface 12 to the formation 11 is established through spaced-apart boreholes 13 and 14. The hole 13 functions as an oil-producing well, whereas the adjacent hole 14 is a special access hole designed for the transmission of electricity to the formation 11.

The present invention can be practiced using a multiplicity of cathodes and anodes placed in boreholes. The boreholes may be installed in a variety of vertical, horizontal or angular orientations and configurations. In FIG. 1, the system is shown having two electrodes installed vertically into the ground and spaced apart generally horizontally. A first electrode 15 is lowered through access hole 14 to a location in proximity to formation 11. Preferably, first electrode 15 is lowered through access hole 14 to a medial elevation in formation 11, as shown in FIG. 1. By means of an insulated cable in access hole 14, the relatively positive terminal or anode of a high-voltage d-c electric power source 2 is connected to the first electrode 15. The relatively negative terminal on the power source or cathode is connected to a second electrode 16 in producing well 13, or within close proximity of the producing well. Between the electrodes, the electrical resistance of the connate water 4 in the underground formation 11 is sufficiently low so that current can flow through the formation between the first and second electrodes 15, 16. Although the resistivity of the oil is substantially higher than that of the overburden, the current preferentially passes directly through the formation 11 because this path is much shorter than any path through the overburden to "ground."

To create the electric field, a periodic voltage is produced between the electrodes 15, 16. Preferably, the voltage is a DC-biased signal with a ripple component produced under modulated AC power. Alternatively, the periodic voltage may be established using pulsed DC power. The voltage may be produced using any technology known in the electrical art. For example, voltage from an AC power supply may be converted to DC using a diode rectifier. The ripple component may be produced using an RC circuit or through transistor controlled power supplies. Once the voltage is established, the electric current is carried by captive water and capillary water present in the underground formation. Electrons are conducted through the formation by naturally occurring electrolytes in the groundwater.

The electric potential required for carrying out electrochemical reactions varies for different chemical components in the oil. As a result, the desired intensity or magnitude of the ripple component depends on the composition of the oil and the type of reactions that are desired. The magnitude of the ripple component must reach a potential capable of oxidizing and reducing bonds in the oil components. In addition, the ripple component must have a frequency range above 2 hertz and below the frequency at which polarization is no longer induced in the formation. The waveshape of the ripple may be sinusoidal or trapezoidal and either symmetrical or clipped. Frequency of the AC component is preferably between 50 and 2,000 hertz. However, it is understood in the art that pulsing the voltage and tailoring the wave shape may allow the use of frequencies higher than 2,000 hertz.

A system suitable for practicing the invention is shown in FIG. 2. In this system, borehole 13 functions as an oil producing well which penetrates one region 17 of underground oil-bearing formation 11. Well 13 includes an elongated metallic casing 18 extending from the surface 12 to the cap rock 23 immediately above region 17. The casing 18 is sealed in the overburden 19 by concrete 20 as shown, and its lower end is suitably joined to a perforated metallic liner 24 which continues down into the formation 11. Piping 21 is disposed inside the casing 18 where it extends from the casing head 22 to a pump 25 located in the liquid pool 26 that accumulates inside the liner 24. Preferably the producing well 13 is completed in accordance with conventional well construction practice. The pump 25 is selected to operate at sufficient pumping head to draw oil from adjacent formation 11 up through metallic liner 24.

Access hole 14 that contains first electrode 15 includes an elongated metallic casing 28 with a lower end preferably terminated by a shoe 29 disposed at approximately the same elevation as the cap rock 23. The casing 28 is sealed in the overburden 19 by concrete 30. Near the bottom of hole 14, a tubular liner 31 of electrical insulating material extends from the casing 28 for an appreciable distance into formation 11. The insulating liner 31 is telescopically joined to the casing 28 by a suitable crossover means or coupler 32.

Below the liner 31, a cavity 34 formed in the oil-bearing formation 11 contains the first electrode 15. The first electrode 15 is supported by a cable 35 that is insulated from ground. The first electrode 15 is relatively short compared to the vertical depth of the underground formation 11 and may be positioned anywhere in proximity to the formation. Referring to FIG. 2, first electrode 15 is positioned at an approximately medial elevation within the oil-bearing formation 11. The first electrode may be exposed to saline or oleaginous fluids in the surrounding earth formation, as well as a high hydrostatic pressure. Under these conditions, first electrode 15 may be subject to electrolytic corrosion. Therefore, the electrode assembly preferably comprises an elongate configuration mounted within a permeable concentric tubular enclosure radially spaced from the electrode body. The enclosure cooperates with the first electrode body to protect it from oil or other adverse materials that enter the cavity.

It should be noted that FIG. 2 is not to scale, and some of the dimensions of the hole 14 and components in the hole are exaggerated. For example, the diameter of hole 14 is shown to be quite large in comparison to the cable 35 and other components. The diameter of the hole 14 may be much closer to the diameter of the cable 35. In addition, liner 31 preferably has a substantial length and a relatively small inside diameter.

Referring now to FIG. 3, a preferred assembly for the first electrode 15 is shown. The assembly comprises a hollow tubular electrode body 15 electrically connected through its upper end to a conducting cable 35 and disposed concentrically in radially spaced relation within a permeable tubular enclosure 16a of insulating material. The first electrode 15 is preferably coated externally with a material, such as lead dioxide, which effectively resists electrolytic oxidation. The assembly preferably includes means to place the internal surfaces of the first electrode 15 under pressure substantially equal to the external pressure to which the first electrode is exposed, thereby to preclude deformation and consequent damage to the first electrode. The enclosure 16a is closed at the bottom to provide a receptacle for sand or other foreign material entering from the surrounding formation.

Referring again to FIG. 2, the first electrode 15 is attached to the lower end of insulated cable 35, the other end of which emerges from a bushing or packing gland 36 in the cap 37 of casing 28 and is connected to the relatively positive terminal of an electric power source 38. The other terminal on the electric power source 38 is connected via a cable 42 to an exposed conductor that acts as a second electrode 16 at the producing well 13. The second electrode 16 may be a separate component installed in the proximity of producing well 13 or may be part of the producing well itself. In the embodiment shown in FIG. 2, the perforated liner 24 serves as the second electrode 16, and the well casing 18 provides a conductive path between the liner and cable 42.

Thus far, it has been presumed that electrodes 15, 16 are located in a formation with a suitable moisture content and naturally occurring electrolytes to provide an electroconductive path through the formation. In formations that do not have adequate capillary and captive groundwater to be electrically conductive, an electroconductive fluid may be injected into the formation through one or both boreholes to maintain an electroconductive path between the electrodes 15, 16. Referring to FIG. 2, a pipe 40 in borehole 14 delivers electrolyte solution from the ground surface to the underground formation 11. Preferably, a pump 43 is used to convey the solution from a supply 44 and through a control valve 45 into borehole 14. Borehole 14 is preferably equipped with conventional flow and level control devices so as to control the volume of electrolyte solution introduced to the borehole. A detailed system and procedure for injecting electrolyte solution into a formation is described in the aforementioned U.S. Pat. No. 3,782,465. See also, U.S. Pat. No. 5,074,986, the entire disclosure of which is incorporated by reference herein.

Referring now to FIGS. 1-2, the steps for practicing the improved method for stimulating oil recovery will now be described. An electric potential is applied to first electrode 15 so as to raise its voltage with respect to the second electrode 16 and region 17 of the formation 11 where the producing well 13 is located. The voltage between the electrodes 15, 16 is preferably no less than 0.4 V per meter of electrode distance. Current flows between the first and second electrodes 15, 16 through the formation 11. Connate water 4 in the interstices of the oil formation provides a path for current flow. Water that collects above the electrodes in the boreholes does not cause a short circuit between the electrodes and surrounding casings. Such short circuiting is prevented because the water columns in the boreholes have relatively small cross sectional areas and, consequently, greater resistances than the oil formation.

As current is applied across formation 11, electrolysis in the capillary water and captive water takes place. Water electrolysis in the groundwater releases agents that promote oxidation and reduction reactions in the oil. That is, negatively charged interfaces of oil compounds undergo cathodic reduction, and positively charged interfaces of the oil compounds undergo anodic oxidation. These redox reactions split long-chain hydrocarbons and multi-cyclic ring compounds into lighter-weight compounds, contributing to lower oil viscosity. Redox reactions may be induced in both aliphatic and aromatic oils. As viscosity of the oil is reduced through redox reactions, the mobility or flow of the oil through the surrounding formation is increased so that the oil may be drawn to the recovery well. Continued application of electric current can ultimately produce carbon dioxide through mineralization of the oil. Dissolution of this carbon dioxide in the oil further reduces viscosity and enhances oil recovery.

In addition to enhancing oil flow characteristics, the present invention promotes electrochemical reactions that upgrade the quality of the oil being recovered. Some of the electrical energy supplied to the oil formation liberates hydrogen and other gases from the formation. Hydrogen gas that contacts warm oil under hydrostatic pressure can partially hydrogenate the oil, improving the grade and value of the recovered oil. Oxidation reactions in the oil can also enhance the quality of the oil through oxygenation.

Electrochemical reactions are sufficient to decrease oil viscosities and promote oil recovery in most applications. In some instances, however, additional techniques may be required to adequately reduce retentive forces and promote oil recovery from underground formations. As a result, the foregoing method for secondary oil recovery may be used in conjunction with other processes, such as electrothermal recovery or electroosmosis. For instance, electroosmotic pressure can be applied to the oil deposit by switching to straight d-c voltage and increasing the voltage gradient between the electrodes 15, 16. Supplementing electrochemical stimulation with electroosmosis may be conveniently executed, as the two processes use much of the same equipment. A method for employing electroosmosis in oil recovery is described in U.S. Pat. No. 3,782,465.

Many aspects of the foregoing invention are described in greater detail in related patents, including U.S. Pat. No. 3,724,543, U.S. Pat. No. 3,782,465, U.S. Pat. No. 3,915,819, U.S. Pat. No. 4,382,469, U.S. Pat. No. 4,473,114, U.S. Pat. No. 4,495,990, U.S. Pat. No. 5,595,644 and U.S. Pat. No. 5,738,778, the entire disclosures of which are incorporated by reference herein. Oil formations in which the methods described herein can be applied include, without limitation, those containing heavy oil, kerogen, asphaltinic oil, napthalenic oil and other types of naturally occurring hydrocarbons. In addition, the methods described herein can be applied to both homogeneous and non-homogeneous formations.

It has been discovered that the method of the present invention can be used to improve the condition of the oil formation and repair damaged or plugged formations where oil flow is impeded. The method can also be applied to pre-treat oil in the formation as it is extracted from the formation.

Referring now to FIG. 4, a method 110 for improving flow conditions and pre-treating oil in a formation is shown in a block diagram. The method 110 is applicable to a variety of well pump installations that draw material from underground formations, including oil recovery wells. The method 110 utilizes electric current to enhance the production of oil from an oil-bearing formation and improve the flow characteristics within the formation. The improved flow characteristics increase the volume of oil that is recoverable from the formation. Electric current is also applied to modify the properties of the oil in the formation and increase the quality of oil recovered. The decomposition of long-chain compounds decreases the viscosity of the oil compounds and increases oil mobility through the formation such that the oil may be withdrawn at the recovery well. Electrochemical reactions in the formation also upgrade the quality and value of the oil that is ultimately recovered.

The components used in the present method include many of the same components described in U.S. patent application Ser. No. 10/279,431. The system generally includes two or more electrodes placed in proximity of the oil bearing formation. In systems using only two boreholes, a first borehole and a second borehole are provided within the underground formation, or in proximity of the underground formation. The first and second boreholes may be drilled vertically, horizontally or at any angle that generally follows the formation. A first electrode is placed within the first borehole and a second electrode is placed within or in proximity of the second borehole. Alternatively, the second electrode may be positioned at the earth's surface. A source of voltage is connected to the first and second electrodes. The first and second boreholes may penetrate the body of oil to be recovered, or they may penetrate the formation at a point beyond but in proximity to the body of oil. A voltage difference is applied between the electrodes to create an electric field through the oil bearing formation.

The method 110 for improving flow conditions and pre-treating oil in an underground formation will now be described in greater detail. A first borehole is provided in a first region of the formation in step 120. A second borehole is provided in a second region of the formation in step 130. A first electrode is placed in the first borehole in step 140, and a second electrode is placed in proximity of the second borehole in step 150. A voltage difference is established between the first and second electrodes to create an electric field across plugging materials in the formation in step 160. The electric field is applied across the plugging materials to destabilize the plugging materials in step 170.

The method of FIG. 4 may be applied in several ways to improve flow characteristics in a formation. For example, if a mud cake is deposited on the interface between the well bore and the formation, an electric field may be applied to loosen and remove the mud. A negative electrode is placed in the well bore that is blocked by the mud cake, and the electric field is applied across the mud cake. Formation water will can move through the well bore interface toward the negative electrode under the influence of the electric field. As the water moves through the interface, the electroosmotic forces hydrate the mud and gradually dislodge the clay from the well bore to unblock the well.

The method of FIG. 4 may also be applied to remove plugging materials from fissures within the formation. Plugging materials may include mud or residue from drilling fluid, naturally formed occlusions, or other matter that blocks flow of oil through the interstitial spaces in the formation. The electrode in the well bore may be negatively charged to draw plugging materials into the well bore and out of the formation. Alternatively, the electrode in the well bore may positively charged to repel and push the plugging materials deeper into the formation.

The electric field can be applied alone or in conjunction with other techniques for unplugging formations. For example, the present method may be used in conjunction with acidizing to dissolve and remove clay plugging materials. An unplugging acid is introduced into the formation, and an electrode in the formation is positively charged. An electric field is applied to drive the unplugging acid into the formation until the acid reaches the plugging materials. Migration of the acid is carried out by electroosmosis, but may be assisted by other means, such as well pumping. The electric field may be used to drive the acid into regions of the formation that cannot be reached through boreholes. If desired, the voltage may be increased to impart resistive heating and decrease viscosity of the plugging materials. Additives may be introduced into the formation to change the electric charge of plugging materials. Once the plugging materials are destabilized, the formation may be backflushed to remove any remnants or byproducts remaining in the formation. One or more well pumps may be operated to establish suction pressure in the well and draw the destabilized plugging materials into the well.

As noted above, the present invention promotes electrochemical reactions that upgrade the quality of the oil being recovered. For example, the electric field may be used to remove sulfur-containing compounds from crude, thereby improving the quality and value of oil as it is recovered. It has been found that superimposing a variable AC signal with a frequency between 2 Hz and 1.24 MHz on to a DC signal can induce oxidation to convert sulfur compounds to sulfates. The sulfates tend to remain in the formation as the oil is removed. The present invention may also be applied to remove polycyclic aromatic compounds (PAHS) from crude oil. Operation of the electric field to remove sulfur compounds and PAHs may take place prior to extraction of oil, or while the oil is being extracted. The electric field may be applied for a specified period of time. Alternatively, the electric field may be applied until the concentration of sulfur compounds and/or PAHs is reduced below a predetermined limit.

The present invention can be practiced using a multiplicity of cathodes and anodes placed in vertical, horizontal or angular orientations and configurations, as stated earlier. Referring now to FIG. 5, an alternate system is shown with electrodes installed in well casing 113, 114. The well casings 113, 114 extend in a generally horizontal orientation through an oil-bearing formation 111. The relatively positive terminal or anode of a high-voltage d-c electric power source 102 is connected to the first well casing 113. The relatively negative terminal on the power source or cathode is connected to the second well casing 114. In this arrangement, well casing 113 acts as a cathode producer, and well casing 114 acts as an anode. Insulating components or breaks 115 are placed in each of the well casings 113, 114 so that electricity flows between the horizontal sections of the casings within the oil-bearing formation 111. Between the well casings 113, 114, the electrical resistance of the connate water in the formation is sufficiently low so that current can flow through the formation between the casings. Although the resistivity of the oil is substantially higher than that of the overburden, the current preferentially passes directly through the formation 111 because this path is much shorter than any path through the overburden to "ground."

The present method may include one or more electrodes placed above ground, as described earlier. Referring now to FIG. 6, an alternate system is shown with a first electrode 215 placed below the earth's surface (marked "E") and a second electrode 216 placed above the earth's surface in proximity to an underground oil-bearing formation 211. The first electrode 215 is installed in a borehole 214 that penetrates the formation 211. The first electrode 215 is positioned within the formation, but may be positioned outside the formation, depending on the desired position and range of the electric field. The second electrode 216 is placed on the earth's surface. By means of an insulated cable in access hole 214, a terminal on a high-voltage d-c electric power source 202 is connected to the first electrode 215. The opposite terminal on the power source 202 is connected to the second electrode 216. A voltage difference is established between the first and second electrodes 215, 216 to create an electric field across the formation 211. It should be noted that the second electrode 216 may be installed at a shallow depth just beneath the earth's surface to produce an electric field. For example, the second electrode may be installed within fifty feet of the earth's surface to establish an electric field across the formation. Placing the second electrode 216 at a shallow depth below the earth's surface may be desirable where space above ground is limited.

Method for Increasing Bottom-Hole Formation Zone Permeability

FIELD

[0002] The invention is related to the well services in oil-field industry, particularly, to the methods for increasing permeability of a near-wellbore zone of a formation by stimulation of a fluid inflow into a wellbore.

BACKGROUND

[0003] A stimulation of a fluid inflow into a wellbore is required to recover and improve the near-wellbore zone filtration characteristics, basically through improved permeability of the near-wellbore zone and reduced fluid viscosity. Among the most efficient methods of the stimulation of fluids' influx from a formation are acid treatment and formation hydraulic fracturing (see, for example, V.I. Kudinov, Osnovy neftegazopromyslovogo dela ( Foundations of Oil and Gas Formation Industry), Moscow, 2005, pp. 428-429). Acid treatment and formation hydraulic fracturing enable stimulation of a fluid inflow into a wellbore by creating high-permeable paths for the fluid inflow into the wellbore hereby the selection of a specific treatment method and a quality of the works completed are critical for the efficiency of the future well operation. Thus, incorrectly performed fluid inflow stimulation may, for example, result in the need to completely stop the future wellbore operation. To intensify the fluid inflow during the matrix treatment and formation hydraulic fracturing various liquid and solid chemicals are injected into a wellbore. Thus, during hydraulic fracturing various substances are injected into a wellbore under large pressure which results in cracks in the rock. To prevent a closure of the cracks in the rock solid particles are injected into the wellbore using a viscous gel—propping agent (proppant). Due to high viscosity of the gel the crack becomes low-permeable and to improve its permeability, as a rule, reverse recirculation is used. To reduce the gel viscosity different chemicals—breakers—are added to the solution and, when penetrating the formation, they can reduce the gel viscosity. The chemicals being added are, as a rule, expensive, but not always efficient. Besides, engineers normally are not able to impact the breakers' activity after the chemicals have been injected into the wellbore. Therefore, among the key disadvantages of the existing methods for increasing the near-wellbore zone permeability are high costs, low speed and inability to monitor the reaction speed after the chemicals have been injected into the wellbore.

[0004] The proposed method provides for increased reliability and efficiency of stimulating a fluid inflow into a wellbore, enhanced speed of stimulating with simultaneous reduction of the risk of incorrect performing thereof as well as reduced costs.

SUMMARY

[0005] The method comprises carrying out a stimulation of a fluid flow into a wellbore comprising injecting chemical substances into a targeted zone of a formation and applying an electric field to the targeted zone of the formation.

[0006] The stimulation of the fluid flow into the wellbore is an acid formation treatment or a hydraulic fracturing of the formation.

[0007] Additional magnetic, thermal, acoustic treatment or a combination of thereof can be applied to the targeted zone of the formation zone during the stimulation.

[0008] The electric filed can be applied by electrodes. At least one of the electrodes is disposed in the wellbore on the level of the targeted zone.

[0009] One of the electrodes can be disposed in the wellbore on the level of the targeted zone and the other electrode can be disposed on the surface.

[0010] One of the electrodes can be disposed lower than the targeted zoned of the formation while the other can be disposed higher than the targeted zone of the formation being treated.

[0011] Casings and tubing can be used as the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention is explained by a drawing ( FIG. 1) showing a system providing an electric impact onto a formation in which stimulation of the fluid inflow is performed.

DETAILED DESCRIPTION

[0013] The proposed method is based on applying an electric field to a formation in which stimulation of a fluid inflow is performed. The effect of the electrical stimulation depends on physical parameters of the formation and is determined by positioning of electrodes, value and frequency of the electric field being created as well as a power of a power supply being used. The electric impact causes enhancement of physico-chemical processes in the formation and in space inside a wellbore during the stimulation of a fluid inflow into the wellbore. Thus, for example, the electric field causes the appearance of electric currents as well as an electro-kinetic, phenomena like electroosmosis or electrophoresis. These phenomena result in the motion of charged particles and the fluid and therefore result in the intensification of current physico-chemical processes. Additional application of magnetic field promotes additional motion of the charged particles. Extra temperature heating also causes the intensification of physico-chemical processes in the area being heated through intensification of the substances' thermal diffusion. Additional acoustic impact using a sound-emitting device also enhances the physico-chemical processes due to additional oscillations of the particles caused by the sound wave passage. Hereby any of the impacts above may be applied locally or directionally which enables intensification of the physico-chemical processes (such as chemical reaction speed) in the required area.

[0014] A system that allows to create an electric field inside a wellbore and a formation is shown on FIG. 1 where 1 is a current and voltage generator, 2—electrodes connected to the current and voltage generator 1, 3—a targeted zone of the formation in which stimulation of a fluid inflow is performed, chemicals have been injected into this targeted zone 3. For creating the electric field different combinations of electrodes positioning in the wellbore are possible, but at least one of the electrodes should be disposed in the wellbore at the level of the targeted zone 3 being treated. The other electrode may be located in an adjacent wellbore (see FIG. 1 a) or on the surface (see FIG. 1 b). The electrodes may also be disposed in the wellbore above and below the targeted zone 3 being treated (see FIG. 1 c). Casings and tubings may also be used as electrodes. A source of magnetic field can be placed into the wellbore at the level of the targeted zone 3 being treated. If a sound emitting device and/or a thermal heater is used they also can be disposed in the wellbore at the level of the targeted zone 3 being treated. Different components of the instruments used may be located both on the same device and on different and their power may be supplied by a cable or by batteries or accumulators.

[0015] As an example, three series of experiments were conducted in order to check the feasibility of described method. These experiments were carried out at room temperature 22° C. (72° F.). For the first experiment 750 ml of YF130LGD gel was prepared and put into a tank with plane electrodes attached thereto. The electrodes were connected to a standard power generating unit with AC output of 100V at ̃50 Hz. The distance between the electrodes was about 10 cm. After 15 minutes, only a slight gel destruction near the surface of the electrode was observed. That can be a result of local temperature increase up to 80° C. (180° F.) near the electrodes. The temperature was measured immediately after power was off.

[0016] For the second experiment two samples of YF130LGD hydraulic-fracture gel were prepared (500 ml each) and 2 g of J218 breaker was added to each gel sample. J218 breaker concentration for YF130LGD gel destruction is about 10 pounds/1000 gallons (1,2 kg/m3) that is two times lower than for carrying out this experiment. But it should be mentioned that the breaker operation temperature range is 52-107° C. (125-225° F.), moreover, the breaker is activated by adding special chemical catalysts. One sample of the prepared gel with the breaker portion was placed into a tank without electrodes and thoroughly mixed. The other sample was placed into the system with electrodes. After 7 minutes of AC applying it was detected that almost all gel (90%) in the tank under voltage was destroyed (the gel viscosity reduced to water viscosity value). In the tank without AC application only 10-15% gel was destroyed. During the second experiment the temperature value was 95° C. (200° F.) on the electrodes and 35° C. (95° F.) in the centre of the tank after 7 minutes of the AC impact.

[0017] The third experiment was performed to prove that at high temperatures there will be no gel destructions. For this purpose 500 ml of YF130LGD gel mixed with 2 g of J218 breaker was prepared and placed into a pre-heated tank, and then into an oven at 100° C. (210° F.). After 15 minutes of the temperature action destruction of maximum 25-30% of gel was noted.

[0018] Comparing the results of electrical field and temperature impact in presence of breaker, the advantage of the electrical field impact for the gel destruction becomes evident.

RU2132757
Method of Removing Hydrocarbons from Soil

FIELD: oil pollution removal. SUBSTANCE: central and peripheral electrodes are plunged into soil at area to be cleaned and voltage gradient between electrodes is created. Then, nonpolluting liquid carrier is fed into the surface region around central electrode, which carrier moves under electroosmosis effect from central electrode toward peripheral electrodes and displaces hydrocarbons in soil that are removed from peripheral electrodes. As liquid carrier, water with pH 9 prepared by cavitation effect or water with pH 5,5 prepared by heating is utilized. Utilization of water taken from bed in oil and gas deposit development is possible. EFFECT: enhanced cleaning efficiency due to accelerated movement of liquid carrier and reduced voltage gradient on electrodes.

A method for cleaning sand from petroleum products is known (as. USSR N 1629102, MKI 5: B 03 V 5/00, C 01 B 33/12, pub. 23.02.91 y. Bul-N-7-analogue.), Including sand treatment with an aqueous solution of hydrofluoric acid with a concentration of 0.5-2.0% by weight, with a ratio of the mass of solid soil to the liquid reagent as 1: (2-6) for 30 minutes.

The main disadvantage of this method is sand treatment with a chemical reagent, for neutralization it is necessary to add additional reagents and remove the reaction products of these reagents, which entails additional economic costs and does not increase the ecology of the cleaned sandy soil.

The closest in technical essence to the proposed invention is the method for removing contaminated soil (U.S. Patent No. 5,415,7774 A, MKI 6: B 01 D 61/56, published, ISM, No. 001, No. 10, 1996, p. 34 - prototype ), Including immersion in the soil on the cleared area of the central and peripheral electrodes, the creation of a voltage gradient between them, feeding the non-contaminating carrier fluid to the zone adjacent to the central one, moving the carrier fluid under the effect of the electroosmotic effect between the electrodes, displacing the carrier liquid of the contaminated Material from the soil to the peripheral electrodes and the removal of contaminated material from the latter.

This method is more ecological than the analogue. However, the motion of pure carrier fluids of the water type under the action of the electroosmotic effect is not intensive, and it is further slowed down when the carrier fluid displaces such impurities as viscous hydrocarbons such as oil, engine oil and the like. Especially large resistance to the displacement of the carrier fluid with hydrocarbons occurs in the cold season, when the viscosity of the latter increases. Therefore, to ensure the movement of the carrier fluid and viscous hydrocarbons, it is necessary to maintain a high voltage gradient, on the order of 380-500 V, depending on the soil structure, which leads to high energy costs and makes this method ineffective.

The purpose of the invention is to increase the efficiency of soil purification from hydrocarbons by accelerating the movement of the carrier fluid and reducing the voltage gradient at the electrodes.

The aim is achieved by the fact that in a method for purifying soil from hydrocarbons including immersion in the soil on the cleaning portion of the central and peripheral electrodes, creating between the first and second voltage gradients, feeding into the region adjacent to the central electrode not contaminating the carrier fluid, Carrier under the action of the electroosmotic effect from the central electrode to the peripheral electrode, displacement of hydrocarbon from the soil by the carrier fluid and their removal from the peripheral electrodes, as Carrier liquids use water in which the pH is changed to 9 by applying cavitation to it, or up to 5.5 by heating.

The use of water as the carrier fluid, in which the pH is changed to 9, by applying it to cavitation, or up to 5.5 by heating, has made it possible to increase the efficiency of soil purification at any temperatures without the use of chemical reagents and their neutralization.

The Applicant does not know how to purify soils that use water as the carrier fluid, in which the pH is changed to 9, influencing it by cavitation, or up to 5.5 by heating.

In Fig. 1 is a graph of the pH change of distilled and fresh water, depending on the time of action of cavitation.

In Fig. 2 is a plot of the pH of water versus its temperature.

In Fig. 3 is a flow diagram of an installation for implementing a method for cleaning soil from hydrocarbons.

The proposed method for cleaning soil from hydrocarbons is as follows.

Due to the action of cavitation, the water molecules dissociate into H + and OH- ions. H + ions partially leave the liquid phase, and OH- ions accumulate in the latter, raising the pH of the water. In Fig. 1 is a graph of the pH change of distilled water and fresh water taken from different sources 2 and 3, depending on the time of action of the cavitation. Water with an elevated pH has a high surface activity and has high detergent properties.

Such water in contact with hydrocarbons - destroys the viscous surface film of hydrocarbons and intensively flushes them from the soil; - increases the dynamics of mixing of leachable hydrocarbons with them and forms an emulsion, which has a small hydraulic and low electrical resistance.

These properties increase the mobility in the soil of the formed liquid system (emulsion) under the action of the electroosmotic effect, which ultimately leads to a reduction of the voltage between the electrodes to 60 V and the cost of electricity and, as a consequence, to an increase in the efficiency of the method for cleaning the soil of hydrocarbons.

When the water is heated, its pH decreases and, as a result, its electrical conductivity increases. In Fig. 2 is a plot of the pH of water versus its temperature. As the pH of the water decreases, the solubility of hydrocarbons in it increases.

Such water when in contact with hydrocarbons - reduces their surface tension and viscosity; - forms a mobile electrically conductive emulsion.

These properties intensify the joint movement of water with hydrocarbons in the soil under the effect of the electroosmotic effect from the central electrode to the peripheral, which, as a consequence, leads to a decrease in the voltage between the electrodes to 60 V and the reduction of electricity costs and increases the efficiency of the method for cleaning the soil of hydrocarbons.

The proposed method for cleaning soil from hydrocarbons is similar in its intensity to methods for cleaning soil using chemical reagents such as surfactants with pH 9 and acids pH 5.5.

However, this method is environmentally friendly, does not require additional costs for chemical reagents and for their neutralization.
Compared with the prototype, this method is more effective than the prototype for energy costs in 6-7 times.
[3]

The method can be implemented with the apparatus shown in FIG. 3. The installation consists of immersed in the soil in the cleaning area 1 of the central 2 and peripheral 3 electrodes, a water supply nozzle 4, a pump 5 serving to remove water from the peripheral electrodes with hydrocarbons, a separator 6 for separating water and hydrocarbons, a container 7 with a nozzle Venturi 8 and heater 9, a pump 10 for injecting water into the nozzles 4 and a Venturi nozzle 8. The separator 6 and the tank 7 are connected by a pipeline through the water with a check valve 11. The container 7 is additionally connected to the nozzle 4 by a high-pressure water supply pipe 12 with a pH of 5.5.

An example of the execution of the method. Water with a temperature of 17 ° C, having a pH of 7.4, is supplied by a pump 10 from the tank 7 to the Venturi nozzle 8 at a speed of 30 m / s. The pressure of water flowing through the diffuser of the Venturi 8 nozzle is reduced to 2 x 103 Pa. This causes cavitation of water. The cavitated liquid re-enters the vessel 7. The water is cavitated in this manner for 520 s, after which the water in the vessel has a pH of 9. The obtained surface active water by the pump 10 is fed through the nozzle 4 to the region adjacent to the central electrode 2. A voltage gradient of 60 V is created between the central and peripheral electrodes. Surface-active water with pH 9 under the action of the electroosmotic effect moves from the central electrode 2 to the peripheral 3. At the same time, it contacts hydrocarbons that pollute the soil, destroys their surface film and intensively flushes them from the soil. Surface-active water with pH 9 with hydrocarbons forms an emulsion that enters the peripheral electrodes 3, from where it is removed by pump 5 and fed to separator 6.

In the separator 6, the emulsion is divided into water at the bottom and hydrocarbons located at the top of the separator 6. The separated water enters the tank 7 through the check valve 11. The separated hydrocarbons are sent to storage tanks.

The described cycle is repeated until the hydrocarbons are completely removed from the soil. The process of cleaning the soil with surface active water obtained by cavitation is energetically beneficial at soil temperatures above 0oC.

In the case of soil cleaning with a temperature below 0oC from hydrocarbons, this water is used with water at pH 5.5, which is obtained by heating to 240oC in tank 7 using a heater 9. When the water in the tank 7 is heated, the pressure rises to 3.5 MPa. Under this pressure, water with a pH of 5.5 is fed, bypassing the pump 10, via the line 12 through the nozzle 4 to the work area 1. Further process of soil purification from hydrocarbons is carried out in a similar manner to the process described above.

KR20010086551
Purification Method of Contaminated Soil with Petroleum Oil

PURPOSE: A purification method of contaminated soil with petroleum oil is provided, which can purify contaminated soil by generating radical oxidant such as hydroxide radical using metal peroxide such as calcium peroxide and magnesium peroxide in the presence of a catalyst of iron and by transferring the radical to contaminated area in soil by electroosmosis. The method does not need any excavation and transportation of soil and can remove more than 99 % of contaminants. CONSTITUTION: The system comprises the followings: (i) an acrylic box (10) which has an anode chamber (16a) and a cathode chamber (16b) at both sides of the box (10); (ii) anode chamber (16a) that is made of anode diaphragm (15a), in which an anode (11a) is inserted and to which discharge line of an electrode liquid supplement tank (18) is inserted; and (iii) a cathode chamber (16b) that is made of cathode diaphragm (15b), in which a cathode (11b) is inserted and to which discharge line of an electroosmosis liquid storage tank (19) is connected.

RU2602615
Method of Soil Cleaning from Hydrocarbons

FIELD: ecology.SUBSTANCE: invention relates to environmental protection, namely to reclamation of lands, contaminated with hydrocarbons (oil products), decontamination of soil from pesticides using phenomenon of electric osmosis. Method of cleaning soil from oil products and pesticides using electroosmosis consists in immersing of central and peripheral electrodes into soil at section, undergoing cleaning, creation of non-uniform electric field between central and peripheral electrodes, supplying of non-contaminating carrier fluid into area adjoining central electrode, movement of carrier fluid under action of electroosmotic effect from central electrode to peripheral ones, removal of dirt beyond contaminated section, displacement of contaminants from soil by carrier fluid and removal thereof from peripheral electrodes, non-uniform electric field intensity value is set within 50-110 kV/m, before supplying carrier fluid soil is milled into particles of 1.0 mm in depth of 20-25 cm. Milled soil is mixed with carrier fluid to concentration of 1:6. Fluidized layer is created by device in depth of 10-12 cm with supply of compressed air of pressure 1-2 ATM. Proposed device comprises central electrode and system of peripheral electrodes, submerged into soil cleaning section, nozzle for carrier fluid supply and removal of fluid, containing contaminants, from cleaning section. Central electrode is made in form of rod with cross section in form of polygon with concave sides. System of peripheral electrodes is composed by separate rods. Rods are connected by wire conductors with sharp-pointed elements on them, point of which is directed to central electrode. Ahead of nozzles for supply of carrier fluid dispenser is placed. Above system of peripheral electrodes device for creation of fluidized layer is located, including central r-shape pipeline with compressor, connected via control valve with system of radial pipelines, at end of each of which nozzles are located, submerged into soil for depth of 10-12 cm.EFFECT: proposed method of soil cleaning from hydrocarbons and pesticides and device for it provide maximum effect of soil cleaning.

The invention relates to the protection of the environment, in particular to the reclamation of soils contaminated with hydrocarbons (oil products), the neutralization of soil from pesticides using the phenomenon of electroosmosis.

With the expansion of the use of pesticides, a number of negative consequences were identified: pollution of soils and water sources, accumulation of residues of chemicals in food. In soil, pesticides decay as a result of both physical-chemical processes and microbiological decomposition. Remnants of pesticides in the soil are washed out by storm and soil waters, gathering in natural reservoirs, polluting them, as well as surrounding land.

The problem of clearing lands and soils for agricultural purposes, the disposal of excess pollutants, especially those stored in the open way, is especially urgent for modern ecology. Currently, in the technology of agricultural production, herbicides have spread, as well as organochlorine pesticides: fusid-forte, zenkor, chistoplan, puma-super.

A method for cleaning a capillary-porous medium contaminated with oil and oil products is known, by introducing a solution of oil-oxidizing microorganisms into the cleaning zone, introducing an electroconductive liquid, passing an electric current to create an electroosmosis (RU 96115094 A, IPC B09C 1/10, publ. 27.11.1998).

There is a known method for restoring contaminated soils contaminated with different in composition and properties (heterogeneous), including applying a material for purification from contaminants to the heterogeneous soil area, passing a constant electric current between the electrodes within the contaminated heterogeneous soil, applying a hydraulic gradient across the contamination area (RU 2143954 C1, IPC B09C 1/08, publ. 10.01.2000).

The disadvantage of the above analogs is the laboriousness of their application and the insufficient degree of soil purification from contamination.

The closest analogue of the method adopted as a prototype is a method for cleaning the soil, including immersion in the soil on the cleaned portion of the central and peripheral electrodes, creating a voltage gradient between the central and peripheral electrodes, feeding into the region adjacent to the central electrode not contaminating the carrier fluid , Displacement of the carrier fluid under the effect of the electroosmotic effect from the central electrode to the peripheral electrode, displacement of the hydrocarbon carrier from the soil, removal x of the peripheral electrodes, creating an uneven electric field between the central and peripheral electrodes (RU 2508954 C1, IPC B09C 1/00, publ. 10.03.2014).

The disadvantage of the prototype is the insufficient degree of soil purification from hydrocarbons, since cleaning with the use of electroosmosis is carried out in an insufficiently strong uneven electric field, as well as the lack of effective cleaning from pesticides.

A device is known for applying a method for cleaning from contamination of a capillary-porous medium, comprising a chamber for placing a cleaned medium with electrodes connected to a DC source, a container with a liquid to be cleaned and a container for the spent liquid (RU 2106432 C1, MPC <6> C25C 1/22 , Publ. 10.03.1998).

A plant for processing soils and soils is known (RU 2330734 C1, IPC B09C 11/00, publ. 10.08.2008), containing a hopper with a stirring device, with a device for transporting liquid therefrom to the overflow tank and a device for removing solid inclusions, a washing liquid supply system, a vibrator.

The disadvantage of the above-mentioned analogue devices is also the insufficient degree of soil purification from pollution.

The closest to the proposed device for implementing the method adopted for the prototype is a device comprising a central electrode and a peripheral electrode system immersed in the soil, a nozzle for supplying the carrier liquid, pumps for injecting liquid into the nozzles and removing the contaminating liquid from the Cleaning zone, the central electrode is made in the form of a rod, the cross section of which is a polygon with concave sides (RU 2508954 C1, IPC B09C 1/00, publ. 10.03.2014).

The disadvantage of the prototype is the ineffective cleaning of the soil from hydrocarbons (oil products) and the lack of purification from pesticides.

The task of the proposed method and device for its implementation is to increase the degree of soil purification from hydrocarbons (petroleum products), as well as soil cleaning from pesticides.

The technical result of the application of the method for cleaning the soil from hydrocarbons and pesticides is achieved by including immersion in the soil on the cleanable portion of the central and peripheral electrodes, creating an uneven electric field between the central and peripheral electrodes, feeding a non-polluting liquid to the region adjacent to the central electrode Carrier, the transport of the carrier fluid under the effect of the electroosmotic effect from the central electrode to the peripheral electrode, displacement from the soil by liquid-n And, in contrast to the prototype, the magnitude of the uneven electric field strength is set in the range of 50-110 kV / m, preliminary before feeding the carrier liquid, the soil is ground by means of a standard ripper in the form of a disk cutter to the particle size 1.0 mm at a depth of 20-25 cm, the ground soil is mixed with the carrier fluid to a concentration controlled by a doser of 1: 6, by means of an additionally installed device, a fluidized bed is formed with a depth 10-12 cm with the supply of compressed air at a pressure of 1-2 atm.

The technical result of using a soil cleaning device for hydrocarbons and pesticides is achieved by including a central electrode in the form of a rod with a cross-section in the form of a polygon with concave sides immersed in the soil, and a system of peripheral electrodes made of individual rods, Liquid carrier, pumps for injecting liquid into the nozzles and removing the contaminating liquid from the cleaning zone, in contrast to the prototype, a system of peripheral electrodes of soy The foam is interconnected by wire conductors with pointed elements attached to them, the point of which is directed to the central electrode, a dispenser is installed in front of the carrier liquid injectors, and a device for creating a fluidized bed is installed above the peripheral electrode system, including a central L- Connected through a distributor with a system of radial pipelines, at the end of each of which there are nozzles immersed in the soil to a depth of 10-12 cm.

The state of the art does not know the effect of the new set of features of the claimed method and device on the achievement of a new technical result - cleaning the soil of pesticides, which makes it possible to conclude that the technical solutions meet the criteria of "novelty" and "inventive level".

Soil cleaning from hydrocarbons and pesticides is as follows. On the area to be cleaned, a voltage gradient is created between the central and peripheral electrodes, the magnitude of the uneven electric field strength is set within 50-110 kV / m, fed to the region adjacent to the central electrode, the carrier fluid, the carrier fluid is transported by the electroosmotic effect from Central electrode to the peripheral, are displaced from the soil with the help of a carrier fluid and remove oil from peripheral electrodes.

Prior to supplying the carrier fluid to increase the degree of soil purification from hydrocarbons and pesticides, the soil is ground by means of a standard ripper in the form of a disk cutter to a particle size of 1.0 mm at a depth of 20-25 cm. The depth of soil grinding depends on the depth of penetration of pesticides, and this is determined by the depth of plowing, and by the technology of processing different crops an average of 10-12 cm. To create a fluidized bed to a depth of 10-12 cm, it is necessary to grind the contaminated soil with a ripper, respectively, to a depth of two times as much, which is 20-25 cm.

If the particle size is larger than 1.0 mm, then in the formation of a fluidized (boiling) layer of soil consisting of water droplets and air bubbles, the particles will soon be sedimented and settle on the site without sufficient purification. In the event that the particle size is less than 1.0 mm, the particles will migrate in the water-air phase.

The crushed soil particles are mixed with the carrier fluid to a concentration of 1: 6, which is determined by the flow of water through the circulating pump for supplying the carrier liquid and the dispenser. If the concentration of soil particles in the liquid phase is more than 1: 6, a suspension between the solid and liquid phase is not formed. Conversely, if the concentration of soil particles in the liquid phase is less than 1: 6, then in the resulting suspension the soil particles will not be sufficient to implement the method.

If the compressed air pressure is less than 1-2 atm, the formed fluidized bed can not penetrate to a depth of 10-12 cm, if the compressed air pressure is more than 1-2 atm, the depth of the fluidized bed will be greater than 10-12 cm, which will lead to Increased consumption of compressed air and energy costs for its production.

The efficiency of soil purification from hydrocarbons and pesticides increases due to physical processes occurring during the interaction of the fluidized bed with the uneven electric field of the indicated tension, which occur as follows.

It is known that when the carrier liquid is saturated with air in a ratio of 1: 6 (in our case), air bubbles are created in the liquid phase. Under the influence of an uneven electric field between the sharpened elements of the peripheral electrodes and the central electrode, air bubbles align along the lines of force of the field, then they elongate along the lines of force and decrease in the transverse direction. Compression of a bubble in the transverse direction means that compressive forces act near its equator. In this case, the air bubble behaves like a dielectric, the field inside it is slightly distorted. Further, it increases in all directions with the formation of a primary streamer that flies out of its tip (Korobeinikov SM The role of bubbles in the electrical breakdown of liquids. Thermophysics of High Temperatures, 1998, No. 3, pp. 362-367, 1998, No. 4, p. 541-547). The streammer is an ionized channel, obtained by overlapping individual electron avalanches occurring in its path.

The formation of streamers is accompanied by shock waves, whose center is the origin of the streamers, that is, the tip of the bubble. When the streamer channel develops, the surface of the bubbles turns to be charged, a volume discharge develops over the surface of the bubbles as a result of the action of the streamers in a two-phase medium (a mixture of water and soil), ozone and a number of active particles are generated, including the OH radical, atomic oxygen, Formed ozone decomposes pesticides, up to the mineralization. In addition, the hard ultraviolet radiation of the plasma takes place. Also, during the development of electrical breakdown, a powerful shock wave is formed, which has an additional disinfection effect on the soil.

It is known that the electric field E of a charged cylinder of radius r is determined by the formula (1) (Koshkin NI Handbook on elementary physics .- M .: Nauka, 1980):

Where k is the coefficient of proportionality, k = 8.9875 * 10 <9> m / F;

Q - electric charge, q = 2,3467 * 10 <-2> Cl;

R is the radius of the cleaning zone;

Ε is the permittivity of the medium.

It is known that, depending on the amount of humus, the amount of water, the viscosity of the soil, the permittivity of the soil is ε = 19.2; 23.8; 26.7; 41,2 (Bobrov PP, Belyaeva TV Experimental check of the model of complex dielectric permittivity of soils and viscosity of soil moisture. // Natural sciences and ecology. Yearbook of the Omsk GPU. 2002. - p. 29-33).

The results of calculating the electric field strength from formula (1) for r = 10 m are given in Table. 1.

Table 1

Calculations show that for a given range from 19.2 to 41.2 changes in the dielectric permittivity of the soil, the electric field strength ranges from 50 to 110 kV / m.

In Fig. 1 is a schematic diagram of an apparatus for carrying out a process for cleaning soil from hydrocarbons and pesticides; FIG. 2 is a device for creating a fluidized bed.

FIG. 1 is a schematic diagram of an apparatus for carrying out the method,
FIG. 2 shows a fluidized bed apparatus

The scheme of the device (Figure 1) shows: the cleaning zone 1, immersed in the soil of the cleaning zone, the central electrode (anode) 2, the peripheral electrode system (cathodes) 3, the injector 4 for feeding the carrier fluid, the dispenser 5 for creating a controlled liquid concentration A pump 7 for removing liquid containing oil products from the peripheral electrodes, a pump 6 for injecting the carrier liquid into the injector 4 through a dispenser 5, a pump 9 for evacuating contaminants containing petroleum products and pesticides from the perforated pipe 8.

The system of peripheral electrodes is made of individual rods 3 connected with each other by wire conductors 11 (fig.2) with pointed elements 10 on it, the point of which is directed to the central electrode. For grinding the soil, use a standard ripper in the form of a disk cutter. A device 12 for creating a fluidized bed is provided above the peripheral electrode system including a central L-shaped conduit 13 with a compressor 14 connected through a distributor 15 to a system of radial conduits 16 at the end of which are installed injectors 17 for supplying compressed air into the fluidized bed immersed in the soil To a depth of 10-12 cm.

The proposed method for cleaning the soil is carried out using the device as follows.

A serial ripper in the form of a disk mill cuts the soil to a particle size of 1.0 mm. In soil crushed to a depth of 20-25 cm, the pump 6 is fed through a nozzle 4 with a carrier fluid.

Turn on the pumps 6 and 7. The ground soil is then mixed with the carrier fluid by means of a pump 6 and a dispenser 5 to a concentration of 1: 6. Electrodes 2 and 3 are supplied with a voltage, the value of which is set within 50-110 kV / m, as a result, an uneven electric field is created between the protrusions of the central electrode and the pointed elements. The carrier fluid under the effect of the electroosmotic effect flows from the central electrode 2 to the peripheral electrode system 3, sorbing oil products or pesticides in its path, then the impurities are removed by the pump 7.

The fluidized bed using the device is constructed as follows. From the compressor 14, compressed air is injected through a central L-shaped conduit connected through a distributor 15 and a system of radial conduits 16 with injectors 17 at a pressure of 1-2 atm. And air bubbles appear. In this case, under the influence of an uneven electric field between the sharpened elements of the peripheral electrodes 3 and the central electrode 2, air bubbles are aligned along the lines of force. Further on, at the tip of the bubble, the formation of a streamer takes place, which flies into the cleaning zone. As a result of the action of streamers in a two-phase medium, ozone and a number of active particles are generated (OH radical, atomic oxygen, etc.). The ozone formed decomposes pesticides up to their mineralization.

As a result, the degree of soil purification from hydrocarbons (oil, oil, fuel oil, etc.) and pesticides rises to 98-99%.

KR101464878
Remediation System for Multi-Contaminated Soils

An aspect of the present invention provides a remediation system for complexly contaminated soil using a combined chemical oxidation and soil flushing method by electrokinetic remediation that increases the remediation efficiency of complexly contaminated soil as a treatment region is formed by hydrogen peroxide inserted into one side of a soil cell from an anode cell to induce the oxidation and decomposition of oil contaminants and the oil contaminants are oxidized and decomposed by being flushed and adsorbed by an anionic surface active agent inserted into the other side of the soil cell from a cathode cell to be moved into the treatment region. The remediation system for complexly contaminated soil using a combined chemical oxidation and soil flushing method by electrokinetic remediation according to an embodiment of the present invention comprises: a soil cell complexly contaminated by oil contaminants and heavy metal contaminants; an anode cell having an anode inserted into one side of the soil cell; a cathode cell having a cathode inserted into the other side of the soil cell to be separated from the anode by a certain distance; a hydrogen peroxide supply cell connected to the anode cell to supply hydrogen peroxide to one side of the soil cell; a first anionic surface active agent supply cell connected to the cathode cell to supply a first anionic surface active agent to the other side of the soil cell; and a power supply device for flushing and adsorbing oil contaminants via electric ion movement using the first anionic surface active agent to be moved from the cathode to the treatment region while simultaneously forming the treatment region, which is defined by the flowing distance of hydrogen peroxide, so that oil contaminants can be oxidized and decomposed as hydrogen peroxide is moved from the anode to the cathode via electroosmosis by supplying power to the anode and the cathode.

US4645004
Electro-Osmotic Production of Hydrocarbons Utilizing Conduction Heating of Hydrocarbon Formations

An electro-osmotic method for the production of hydrocarbons utilizes in situ heating of earth formations having substantial electrical conductivity. A particular volume of an earth formation is bounded with a waveguide structure formed of respective rows of discrete elongated electrodes in a dense array wherein the active electrode area and the row separation are chosen in reference to the deposit thickness to avoid heating barren layers. Electrical power is applied at no more than a relatively low frequency between respective rows of electrodes to deliver power to the formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent regions to less than a predetermined amount. At the same time the temperature of the electrodes is controlled near the vaporization point of water to maintain an electrically conductive path between the electrodes and the formation. A heat sink is provided by supplying aqueous liquid electrolyte to space between the electrodes and the adjacent formation, thereby maintaining the temperature thereat no greater than about the boiling point of water and maintaining a conductive path between said formation. A d.c. polarized potential is applied to enhance flow of reservoir fluid into a preselected row of electrodes, and collected reservoir fluids are removed from the electrodes in the preselected row.

BACKGROUND OF THE INVENTION

This invention relates generally to the exploitation of hydrocarbon-bearing formations having substantial electrical conductivity, such as tar sands and heavy oil deposits, by the application of electrical energy to heat the deposits. More specifically, the invention relates to the delivery of electrical power to a conductive formation at relatively low frequency or d.c., which power is applied between rows of elongated electrodes forming a waveguide structure bounding a particular volume of the formation, while at the same time the temperature of the electrodes is controlled.

Materials such as tar sands and heavy oil deposits are amenable to heat processing to produce gases and hydrocarbons. Generally the heat develops the porosity, permeability and/or mobility necessary for recovery. Some hydrocarbonaceous materials may be recovered upon pyrolysis or distillation, others simply upon heating to increase mobility.

Materials such as tar sands and heavy oil deposits are heterogeneous dielectrics. Such dielectric media exhibit very large values of conductivity, relative dielectric constant, and loss tangents at low temperature, but at high temperatures exhibit lower values for these parameters. Such behavior arises because in such media ionic conducting paths or layers are established in the moisture contained in the interstitial spaces in the porous, relatively low dielectric constant and loss tangent rock matrix. Upon heating, the moisture evaporates, which radically reduces the bulk conductivity, relative dielectric constant, and loss tangent to essentially that of the rock matrix.

It has been known to heat electrically relatively large volumes of hydrocarbonaceous formations in situ. Bridges and Taflove U.S. Pat. No. Re. 30,738 discloses a system and method for such in situ heat processing of hydrocarbonaceous earth formations wherein a plurality of elongated electrodes are inserted in formations and bound a particular volume of a formation of interest. As used therein, the term "bounding a particular formation" means that the volume is enclosed on at least two sides thereof. The enclosed sides are enclosed in an electrical sense with a row of discrete electrodes forming a particular side. Electrical excitation between rows of such electrodes established electrical fields in the volume. As disclosed in such patent, the frequency of the excitation was selected as a function of the bounded volume so as to establish a substantially nonradiating electric field which was confined substantially in the volume. The method and system of the reissue patent have particular application in the radio-frequency heating of moderately lossy dielectric formations at relatively high frequency. However, it is also useful in relatively lossy dielectric formations where relatively low frequency electrical power is utilized for heating largely by conduction. The present invention is directed toward the improvement of such method and system for such heating of relatively conductive formations at relatively low frequency and to the application of such system for heating with d.c.

SUMMARY OF THE INVENTION

For electrically heating conductive formations, it is desirable to utilize relatively low frequency electrical power or d.c. to achieve relatively uniform heating distribution along the line. At low frequency, it is necessary that conductive paths remain conductive between the subsurface electrodes and the formation being heated. It is also desirable to heat the formation as fast as possible in order to minimize heat outflow to barren regions. This presents certain inconsistent requirements, as fast heating requires a large amount of heat at the electrodes, and the resultant high temperatures boil away the water needed to maintain the conductive paths. On the other hand, if the heating proceeds slowly, excessive temperatures leading to vaporization of water and consequent loss of conductivity are avoided, but there is economically wasteful loss of heat to the barren formations in the extended time needed to heat the deposit of interest.

It is a primary aspect of the present invention to provide compromises to best meet such disparate requirements in the in situ heating of earth formations having substantial conductivity. A waveguide structure as shown in the reissue patent is emplanted in the earth to bound a particular volume of an earth formation with a waveguide structure formed of respective rows of discrete elongated electrodes wherein the spacing between rows is greater than the distance between electrodes in a respective row and in the case of vertical electrodes substantially less than the thickness of the hydrocarbonaceous earth formation. Electrical power at no more than a relatively low frequency is applied between respective rows of the electrodes to deliver power to the formation while producing relatively uniform heating thereof and limiting the relative loss of heat to adjacent barren regions to less than a tolerable amount. At the same time the temperature of the electrodes is controlled near the vaporization point of water thereat to maintain an electrically conductive path between the electrodes and the formation. A d.c. polarized potential is applied to enhance flow of reservoir fluid toward at least one preselected electrode.

A waveguide electrical array which employs a limited number of small diameter electrodes would be less expensive to install than an array using more electrodes but would result in excess electrode temperature and nonuniform heating and consequently inefficient use of electrical power. On the other hand, a dense array, that is, one in which the spacing s between rows is greater than the distance d between electrodes in a row, would be somewhat more costly, but would heat more uniformly and more rapidly and, therefore, be more energy efficient.

A key to optimizing these conflicting factors is to control the temperature of the electrodes and the resource immediately adjacent the electrodes by properly selecting the deposit gas pressure, heating rates, heating time, final temperature, electrode geometry and positioning and/or cooling the electrodes.

These and other aspects and advantages of the present invention will become more apparent from the following detailed description, particularly when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view, partly diagrammatic, of a preferred embodiment of a system for the conductive heating of an earth formation in accordance with the present invention, wherein an array of electrodes is emplaced vertically, the section being taken transversely of the rows of electrodes;

FIG. 2 is a diagrammatic plan view of the system shown in FIG. 1;

FIG. 3 is an enlarged vertical sectional view, partly diagrammatic, of part of the system shown in FIG. 1;

FIG. 4 is a vertical sectional view, partly diagrammatic, of an alternative system for the conductive heating of an earth formation in accordance with the present invention, wherein an array of electrodes is emplaced horizontally, the section being taken longitudinally of the electrodes;

FIG. 5 is a vertical sectional view, partly diagrammatic of the system shown in FIG. 4, taken along line 5--5 of FIG. 4;

FIG. 6 is a vertical sectional view comparable to that of FIG. 4 showing an alternative system with horizontal electrodes fed from both ends;

FIG. 7 is a plan view, mostly diagrammatic, of an alternative system comparable to that shown in FIG. 3, with cool walls adjacent electrodes;

FIG. 8 is a vertical sectional view, partly diagrammatic of the system shown in FIG. 7, taken along line 8--8 of FIG. 7;

FIG. 9 is a set of curves showing the relationship between a time dependent factor c and heat loss and a function of deposit temperature utilizing the present invention;

FIG. 10 is a set of curves showing the temperature distribution at different heating rates when heat is delivered to a defined volume;

FIG. 11 is a set of curves showing the relationship between time and temperature at different points when a formation is heated by a sparse array;

FIG. 12 is a set of curves showing the relationship between time and temperature at different points when a formation is heated in accordance with the present invention with electrode diameters of 32 inches; and

FIG. 13 is a set of curves showing the relationship of time and temperature at the same points as in FIG. 12 in accordance with the present invention with electrode diameters of 14 inches.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

FIGS. 1, 2 and 3 illustrate a system for heating conductive formations utilizing an array 10 of vertical electrodes 12, 14, the electrodes 12 being grounded, and the electrodes 14 being energized by a low frequency or d.c. source 16 of electrical power by means of a coaxial line 17. The electrodes 12, 14 are disposed in respective parallel rows spaced a spacing s apart with the electrodes spaced apart a distance d in the respective rows. The electrode array 10 is a dense array, meaning that the spacing s between rows is greater than the distance d between electrodes in a row. The rows of electrodes 12 are longer than the rows of electrodes 14 to confine the electric fields and consequent heating at the ends of the rows of electrodes 14.

The electrodes 12, 14 are tubular electrodes emplaced in respective boreholes 18. The electrodes may be emplaced from a mined drift 20 accessed through a shaft 22 from the surface 24 of the earth. The electrodes 12 preferably extend, as shown, through a deposit 26 or earth formation containing the hydrocarbons to be produced. The electrodes 12 extend into the overburden 28 above the deposit 26 and into the underburden 30 below the deposit 26. The electrodes 14, on the other hand, are shorter than the electrodes 12 and extend only part way through the deposit 26, short of the overburden 28 and underburden 30. In order to avoid heating the underburden and to provide the power connection, the lower portions of the electrodes 14 may be insulated from the formations by insulators 31, which may be air. The effective lengths of the electrodes 14 therefore end at the insulators 31.

FIGS. 4 and 5 illustrate a system for heating conductive formations utilizing an array 32 of horizontal electrodes 34, 36 disposed in vertically spaced parallel rows, the electrodes 34 being in the upper row and the electrodes 36 in the lower row. The upper electrodes 34 are preferably grounded, and the lower electrodes 36 are energized by a low frequency or d.c. source 38 of electrical power. The electrodes 34, 36 are disposed in parallel rows spaced apart a spacing s, with the electrodes spaced apart a distance d in the respective rows. The electrode array 32 is also a dense array. The upper row of electrodes 34 is longer than the lower row of electrodes 36 to confine the electric fields from the electrodes 36. The electrodes 34 extend beyond both ends of the electrodes 36 for the same reason. Grounding the upper electrodes 34 keeps down stray fields at the surface 24 of the earth.

The electrodes 34, 36 are tubular electrodes emplaced in respective boreholes 40 which may be drilled by well known directional drilling techniques to provide horizontal boreholes at the top and bottom of the deposit 26 between the overburden 28 and the underburden 30. Preferably the upper boreholes are at the interface between the deposit 26 and the overburden 28, and the lower boreholes are slightly above the interface between the deposit 26 and the underburden 30.

FIG. 6 illustrates a system comparable to that shown in FIGS. 4 and 5 wherein the array is fed from both ends, a second power source 42 being connected at the end remote from the power source 38.

FIGS. 7 and 8 illustrate a system comparable to that of FIGS. 1, 2 and 3 with an array of vertical electrodes. In this system the rows of like electrodes 12, 14 are in spaced pairs to provide a low field region 44 therebetween that is not directly heated to any great extent.

The deposit thickness h and the average or effective thermal diffusion properties determine the uniformity of the temperature distribution as a function of heating time t and can be generally described for any thickness of a deposit in the terms of a deposit temperature profile factor c, such that
c=kt/(h/2)@2

where k is the thermal diffusivity. FIG. 9 presents a curve A showing the relationship between the factor c and the portion of a deposit above 80% of the temperature rise of the center of the deposit for a uniform heating rate through the heated volume. Note that at c=0.1, about 75% of the heated volume has a temperature rise greater than 80% of the temperature rise of the center of the heated volume.

FIG. 10 illustrates the heating profiles for three values of the factor c as a function of the distance from the center of the heated volume, the fraction of the temperature rise that would have been reached in the heated volume in the absence of heat outflow. Note that where c=0.1 or c=0.2, the total percentage of heat lost to adjacent formations is relatively small, about 10% to 15%. Where low final temperatures, e.g., less than 100 DEG C., are suitable, c up to 0.3 can be accepted, as the heat lost, or extra heat needed to maintain the final temperature, is, while significant, economically acceptable. FIG. 9, curve B, showing percent heat loss as a function of the factor c, shows percent heat loss to be less than 25% at c=0.3. On the other hand, if higher temperatures (e.g., about 200 DEG C.) are desired to crack the bitumen, then higher central deposit temperatures above the design minimum are needed to process more of the deposit, especially if longer heating times are employed. Moreover, the heat outflows at these higher temperatures are more economically disadvantageous. Thus a temperature profile factor of c less than about 0.15 is required. In general the heating rate should be great enough that c is less than 30 times the inverse of the ultimate increase in temperature AT in degrees celsius of the volume:
c.ltoreq.0.3(100/.DELTA.T)

The lowest values of c are controlled more by the excess temperature of electrodes and are discussed below.

The electrode spacing distance d and diameter a are determined by the maximum allowable electrode temperature plus some excess if some local vaporization of the electrolyte and connate water can be tolerated. In a reasonably dense array, the hot regions around the electrodes are confined to the immediate vicinity of the electrodes. On the other hand, in a sparse array, where s is no greater than d, the excess heat zone comprises a major portion of the deposit.

FIG. 11 illustrates a grossly excessive heat build-up on the electrodes as compared to the center of the deposit for a sparse array. In this example row spacing s was 10 m, electrode spacing d 10 m, electrode diameter a 0.8 m, and thermal diffusivity 10@-6 m@2 /s, with no fluid flow.

FIG. 12 shows how the electrode temperature can be reduced by the use of a dense array. In this example row spacing s was 10 m, electrode spacing d 4 m, electrode diameter a 0.8 m, and thermal diffusivity 10@-6 m@2 /s, with no fluid flow.

FIG. 13 illustrates the effect of decreasing the diameter of the electrodes of the dense array of FIG. 12 such that the temperature of the electrode is increased somewhat more relative to the main deposit. In this example row spacing s was 10 m, electrode spacing d 4 m, electrode diameter a 0.35 m, and thermal diffusivity 10@-6 m@2 /s, with no fluid flow. The region of increased temperature is confined to the immediate vicinity of the electrode and does not constitute a major energy waste. Thus, varying the electrode separation distance d and the diameter of the electrode a permit controlling the temperature of the electrode either to prevent vaporization or excessive vaporization of the electrolyte in the borehole and connate water in the formations immediately adjacent the electrode.

The electrode spacing d and diameter a are chosen so that either electrodetemperature is comparable to the vaporization temperature, or if some local vaporization is tolerable (as for a moderately dense array), the unmodified electrode temperature rise without vapor cooling will not significantly exceed the vaporization temperature.

The means for providing water for both vaporization and for maintenance of electrical conduction is shown in the drawings, particularly in FIG. 3 for vertical electrodes and in FIG. 4 for horizontal electrodes. As shown in FIG. 3, a reservoir 46 of aqueous electrolyte provides a conductive solution that may be pumped by a flow regulator and pump 47 down the shaft 22 and up the interior of the electrodes 12 and into the spaces between the electrodes 12 and the formation 26. A vapor relief pipe 48, together with a pressure regulator and pump 50 returns excess electrolyte to the reservoir 46 and assures that the electrolyte always covers the electrodes 12. Similarly, a reservoir 52 provides such electrolyte down the shaft 22, whence it is driven by a pressure regulator and pump 53 up the interior of the electrodes 14 and into the spaces between the electrodes 14 and the formation 26. In this case the electrodes are energized and not at ground potential. The conduits 54 carrying the electrolyte through the shaft 22 are therefore at the potential of the power supply and must be insulated from ground, as is the reservoir 52. The conduits 54 are therefore in the central conductor of the coaxial line 17. The electrodes 14 have corresponding vapor relief pipes 56 and a related pressure regulator and pump 58.

As shown in FIG. 4, electrolyte is provided as needed from reservoirs 60, 61 to the interior tubing 62 which also acts to connect the power source 38 to the respective electrodes 34, 36, the tubing being insulated from the overburden 28 and the deposit 26 by insulation 64. The electrolyte goes down the tubing 62 to keep the spaces between the respective electrodes 34, 36 and the deposit 26 full of conductive solution during heating. The tubing to the lower electrode 36 may later be used to pump out the oil entering the lower electrode, using a positive displacement pump 66.

In either system, the electrolyte acts as a heat sink to assure cool electrodes and maintain conductive paths between the respective electrodes and the deposit. The water in the electrolyte may boil and thereby absorb heat to cool the electrodes, as the water is replenished.

The vaporization temperature is controlled by the maximum sustainable pressure of the deposit. Typically for shallow to moderate depth deposits the gauge pressure can range from a few psig to 300 psig with a maximum of about 1300 psig for practical systems. The tightness of adjacent formations also influences the maximum sustainable vapor pressure. In some cases, injection of inert gases to assist in maintaining deposit pressure may be needed.

Another way to keep the electrodes cool is to position the electrodes adjacent a reduced field region on one side of an active electrode row. This reduces radically the heating rate in the region of the diminished field, thus creating in effect a heat sink which radically reduces the temperature of the electrodes, in the limiting case to about half the temperature rise of the center portion of the deposit.

As shown in FIGS. 7 and 8, in the case of vertical arrays, pairs of electrodes 12, 14 can be installed from the same drift and the same potential is applied to each pair, thus the regions 44 between the pairs become low field regions. By proper selection of heating rates and pair separation, it is possible to control the temperature of the electrode at slightly below that for the center of the deposit. The thickness of the cool wall region 44 can be sufficiently thin that the cool wall region can achieve about 90% of the maximum deposit temperature via thermal diffusion from the heated volume after the application of power has ended.

As shown in FIGS. 4, 5 and 6 in the case of a horizontally enlarged biplate, a nearly zero field region exists on the barren side of the row of grounded upper electrodes 34 and a nearly zero field region exists on the barren side of the row of energized electrodes 36. Such low field regions act as the regions 44 in the system shown in FIGS. 7 and 8.

The arrangement of FIGS. 4, 5 and 6 with the upper electrodes grounded is superior to other arrangements of horizontal electrodes in respect to safety. No matter how the biplate rows are energized and grounded (such as upper electrode energized and lower electrode grounded, vice versa or both symmetrically driven in respect to ground) leakage currents will flow near the surface 24 that may be small but significant in respect to safety and equipment protection. These currents will create field gradients which, although small, can be sufficient to develop hazardous potentials on surface or near-surface objects 68, such as pipelines, fences and other long metallic structures, or may destroy operation of above-ground electrical equipment. To mitigate such effects, ground mats can be employed near metallic structures to assure zero potential drops between any metallic structures likely to be touched by anyone.

These safety ground mats as well as electrical system grounds will collect the stray current from the biplate array. These grounds then serve in effect as additional ground electrodes of a line. Leakage currents between the grounding apparatus at the surface and the biplate array also heat the overburden, especially if the uppermost row is excited and the deposit is shallow. Thus biplate arrays, although having two sets of electrodes of large areal extent, also implicitly contain a third but smaller set of electrodes 68 near the surface at ground potential. Although this third set of electrodes collects diminished currents, the design considerations previously discussed to prevent vaporization of water in the earth adjacent the other electrodes must also be applied.

The near surface ground currents are minimized if the upper electrodes 34 are grounded and the lower electrodes 36 are energized. Also the grounded upper electrodes 34 can be extended in length and width to provide added shielding. This requires placing product collection apparatus at the potential of the energized lower set of electrodes by means of isolation insulation. However, this arrangement reduces leakage energy losses as compared to other electrodes energizing arrangements. Such leakage currents tend to heat the overburden 28 between the row of upper electrodes 34 and the above-ground system 68, giving rise to unnecessary heat losses.

Short heating times stress the equipment, and therefore, the longest heating times consistent with reasonable heat losses are desirable. This is especially true for the horizontal biplate array. The conductors of an array in the biplate configuration, especially if it is fairly long, will inject or collect considerable current. The amount of current at the feed point will be proportional to the product of the conductor length l, the distance d between electrodes within the row, and the current density J needed to heat the deposit to the required temperature in time t. Thus the current I per conductor becomes at the feed point (assuming small attenuation along the line):
I=(J) (l) (d) ##EQU1## where

.sigma. is the conductivity of the reservoir and joules-to-heat is the energy required to heat a cubic meter to the desired temperature. Thus the current carrying requirement of the conductors at the feed points is reduced by increasing the heat up time t as determined by the maximum allowable temperature profile factor c and deposit thickness h. Further, making the array more dense, that is, decreasing d, also reduces the current carrying requirements as well as decreasing l. If conductor current at the feed point is excessive, heat will be generated in the electrode due to I@2 R losses along the conductor. The power dissipated in the electrode due to I@2 R losses can significantly exceed the power dissipated in the reservoir immediately adjacent the electrode. This can cause excessive heating of the electrode in addition to the excess heat generated in the adjacent formation due to the concentration of current near the electrode. Thus another criterion is that the I@2 R conductor losses not be excessive compared to the power dissipated in the media due to narrowing of the current flow paths into the electrodes. Also the total collected current should not exceed the current carrying rating of the cable feed systems.

Another cause of excess temperature of the electrodes over that for the deposit arises from fringing fields near the sides of the row of excited electrodes. Here the outermost electrodes (in a direction transverse to the electrode axis) carry additional charges and currents associated with the fringing fields. As a consequence, both the adjacent reservoir dissipation and I@2 R longitudinal conductor losses will be significantly increased over those experienced for electrodes more centrally located. To control the temperature of these outermost electrodes, several methods can be used, including: (1) increasing the density of the array in the outermost regions, (2) relying on additional vaporization to cool these electrodes, and (3) the enlarging the diameter of these electrodes. Some cooling benefit will also exist for the cool-wall approach, especially in the case of the vertical electrode arrays if an additional portion of the deposit can be included in the reduced field region near the outermost electrodes. Applying progressively smaller potentials as the outermost electrodes are neared is another option.

In the case of the biplate array, especially if it extends a great length into the deposit, such as over 100 m, special attention must be given to the path losses along the line. To alleviate the effects of such attenuation, the line may be fed from both ends, as shown in FIG. 6. At the higher frequencies, these are frequency dependent and are reduced as the frequency is decreased. Perhaps not appreciated in earlier work, is that there is a limit to how much the path attenuation can be reduced by lowering the frequency. The problem is aggravated because, as the deposit is heated, it becomes more conducting.

A buried biplate array or triplate array exhibits a path loss attenuation .alpha. of
.alpha.=8.7[(R+j.omega.L)(G+j.omega.C)]@1/2 dB/m

where

R is the series resistance per meter of the buried line, which includes an added resistance contribution from skin effects in the conductor, if present,

L is the series inductance per meter of the buried line,

G is the shunt conductance over a meter for the line and is directly proportional to .sigma., the conductivity of the deposit,

C is the shunt capacitance over a meter for the line. Where conduction currents dominate, G>>j.omega.c, so that the attenuation .alpha. becomes
.alpha.=8.7[(R+j.omega.L)(G)]@1/2 dB/m

If the frequency .omega. is reduced, j.omega.L is radically reduced, R is partially decreased (owing to a reduction in skin effect loss contribution) and G tends to remain more or less constant. Eventually, as frequency .omega. is decreased, R>>j.omega.L, usually at a near zero frequency condition, so that
.alpha.=8.7[(R)(G)]@1/2 dB/m

If thin wall steel is used as the electrode material, unacceptable attenuation over fairly long path lengths could occur, especially at the higher temperatures where conductance G and conductivity .sigma. are greater. If thin walled copper or aluminum is used for electrodes (these may be clad with steel to resist corrosion), the near zero-frequency attenuation can be acceptably reduced so that
.alpha.l=8.7[(R)(G)]@1/2 (l).ltoreq.2dB

for the single end feed of FIG. 4 and less than 8 dB for the double end feed of FIG. 6.

When d.c. power is applied, advantage may be taken of electro-osmosis to promote the production of liquid hydrocarbons. In the case of electro-osmosis, water and accompanying oil drops are usually attracted to the negative electrodes. The factors affecting electro-osmosis are determined in part by the zeta potentials of the formation rock, and in some limited cases the zeta potentials may be such that water and oil are attracted to the positive potential electrodes.

Electro-osmosis can also be used to cause slow migration of the reservoir water toward one of the sets of electrodes preferentially. This preferential migration will be toward the cathode for typical reservoirs. However, depending upon the salinity of the reservoir fluids and the mineralogy of the reservoir matrix, the net movement under application of d.c. can be toward the anode. Remote ground can be used as an opposing electrode to facilitate this. This can be used to replenish conductivity in formations around the desired electrodes of sets of electrodes by resaturating the formation using reservoir fluids. This will permit resumption of heating.

In some cases, the presence of water fills the available pore spaces and thereby suppresses the flow of oil. Also in the case of a heavy oil deposit, influx of water from the lower reaches of the deposit may reach the producing electrodes such as electrodes 36 (FIG. 6). Therefore, in some cases it may be desirable to place a potential onto both sets of electrodes 34, 36 such that water is drawn away from the array. This may be done by modifying the source 38 such that the ground electrode array 68 near the surface is placed at a negative potential with respect to the entire set of deep electrodes 34, 36.

D.C. power applied for electro-osmosis can cause anodic dissolution of the metal electrodes, and hence, it will be preferable to keep the d.c. power levels just high enough to cause migration of fluids. Such required d.c. power can either be added as a bias to a.c. power which provides the bulk of the energy required to heat the formation or be applied intermittently.

While the use of electro-osmotic effects to enhance recovery from single wells or pairs of wells has been described, the employment of the dense array offers unique features heretofore unrecognized. For example, in the case of a pair of electrodes widely separated, the direct current emerges radially or spherically from the electrode. The radially divergent current produces a radially divergent electric field, and since the electro-osmotic effect is proportional to the electric field, the beneficial effects of electro-osmosis are evident only very near the electrode. Furthermore, the amount of current which can be introduced by an electrode is restricted by vaporization consideration or, if the deposit is pressurized, by a high temperature coking condition which may plug the producing capillary paths. On the other hand, with the arrangement of the present invention, the large electrode surface area and the controlled temperature below the vaporization point allows substantially more d.c. current to be introduced. Further, the effects of electro-osmosis are felt throughout the deposit, as uniform current flow and electric fields are established throughout the bulk of the deposit. Thus an electro-osmotic fluid drive phenomenon of substantial magnitude can be established throughout the deposit which can substantially enhance the production rates.

Further, electrolyte fluids will be drawn out of the electrodes which are not used to collect the water. Therefore, means to replace this electrolyte must be provided.

Production of liquid hydrocarbons using electro-osmosis can also be practiced in combination with conventional recovery techniques such as gravity drainage. Electro-osmosis can be used to increase the rate of production of liquid hydrocarbons by gravity drainage. For example, the polarity of the electrode rows shown in FIG. 5 can be so chosen such that reservoir water will slowly move toward the upper row of electrodes 34. This will cause a simultaneous increase in saturation of hydrocarbons toward the bottom row of electrodes 36. The rate of flow of hydrocarbons toward these bottom electrodes 36 is directly proportional to the permeability of the formation near the electrodes to flow of hydrocarbons. This in turn increases with increase in hydrocarbon saturation. Thus, the rate of hydrocarbon production can be increased by forcing the reservoir water to move toward the upper part of the formation by electro-osmosis.

Although various preferred embodiments of the present invention have been described in some detail, various modifications may be made therein within the scope of the invention.

Several methods of production are possible beyond the unique features of electro-osmosis. Typically, the oil can be recovered via gravity or autogenously generated vapor drives into the perforated electrodes, which can serve as product collection paths. Provision for this type of product collection is illustrated in FIG. 4, where a positive displacement pump 66 located in the lowest level of electrode 36 can be used to recover the product. Product can be collected in some cases during the heat-up period. For example, in FIG. 4 the reservoir fluids will tend to collect in the lower electrode array. If those are produced during heating, those fluids can provide an additional or substitute means to control the temperature of the lower electrode. On the other hand, it may not be desirable to produce a deposit, if in situ cracking is planned, until the final temperature is reached.

Various "hybrid" production combinations may be considered to produce the deposit after heating. These could include fire-floods, steam floods and surfactant/polymer water floods. In these cases, one row of electrodes can be used for fluid injections and the adjacent row for fluid/product recovery.

In contrast with polarizing the electrodes so as to suppress the production of water, the electro-osmotic forces can be used as a drive mechanism which exists volumetrically throughout the deposit for a fluid replacement type flood. The principal benefits of using the electro-osmotic drive in conjunction with the electrode arrays discussed here is that the volumetric drive can be maintained without excessive heat being developed near the electrode or without excessive electrolysis as might occur in a simple five-spot well arrangement.

The fluids injected at the electrodes can contain surfactants such as long chain sulfonates or amines or polymers such as polyacrylamides. The presence of surfactants will reduce the interfacial tension between the injected fluids and the liquid hydrocarbons and will help in recovering the liquid hydrocarbons. Addition of polymers will increase the viscosity and cause an improvement in sweep efficiency. The applied d.c. power can act as the driving force for the migration of fluids toward the other set of eIectrodes, whereby the accompanying liquid hydrocarbons can be produced along with the drive fluid.

The foregoing discussion, for simplicity, has limited consideration to either vertical or horizontal electrode arrays. However, arrays employed at an angle with respect to the deposit may be useful to minimize the number of drifts and the number of boreholes. In this case, the maximum row separation s is chosen to be midway between the vertical or horizontal situation, such that if largely vertical, the row separation s is not much greater than that found for the true vertical case. On the other hand, if the rows are nearly horizontal, then a value of s closer to that chosen for a horizontal array should be used.

WO2012158145
Method for Electrokinetic Prevention of Scale Deposition in Oil Producing Well Bores

Method of using direct current (DC) electrokinetics to alleviate and prevent scale deposition in and around well bores, e.g., the well bores of oil producing wells.

FIELD OF THE INVENTION

The present invention relates generally to the prevention of mineral scale deposition in a well bore, and more particularly to a method for electrokinetically preventing mineral scale deposition in oil well bores with the aid of DC electric current.

BACKGROUND OF THE INVENTION

The waterflood, a secondary enhanced oil recovery process/<11> is a simple, low cost, and proven approach for pressure maintenance and for driving oil towards a production well.

Though initial waterflooding attempts were used to rectify plugged wells or casing leaks, the apparent benefits led to broader applications <pl>. Waterflood efficiency depends on oil viscosity, permeability, wettability, structural considerations, uniformity of reservoir rock, and type of flood<[2]>. The volume of liquid produced partly determines the volume of water required for injection<111>. For economic reasons nearby seawater is commonly used, where available, as the injection water type to save money on water transportation. The mixing of incompatible injection seawater and formation water frequently produces mineral scale deposits, one of the most significant and costly problems encountered in oilfield operations <[3> Water flooding operations conducted in the Abu Dhabi oilfields often result in the formulation of BaS04, CaS04 and SrS04 deposits. The S04<2"> and Ba<2+> ion content in both seawater and formation water, respectively, can easily reach the solubility product (Ks) causing accumulation of BaS04 scale on surface and subsurface equipment. This is recognized as a major cause of formation damage in production or injection wells. Inorganic scale contributes to wear, corrosion, and flow restriction, resulting in a decrease of oil and gas production. This scale also deposits in downhole pumps, tubing, casing, flow lines, heaters, treaters, tanks and other production equipment and facilities<131>. Barium sulfate (BaS04) scale is among the toughest to remove either by mechanical or chemical means. BaS04 is typically removed by mechanical tools that involve abrasion, such as gauge cutters, nipple brushes and spinning wash tools. Chemical removal methods utilizing ethylenediaminetetraacetic acid (EDTA) are also available<[3>

Unfortunately, current scale inhibitor applications incur high costs due to conventional chemical dissolution. Scale inhibitor treatment is limited by its "squeeze efficiency" into the formation, which results in limited penetration as well as quick consumption in the reservoir. A squeeze usually involves the application of pump pressure to force a treatment fluid or slurry into a planned treatment zone (Schlumberger Oilfield Glossary). The problem is that scale inhibitors do not move deeply into the reservoir, hence only a small volume can be squeezed before being rapidly consumed. A need exists for a new methodology to prevent scale formation which is both economical and effective.

While electrically enhanced techniques for promoting oil recovery are known, including those described in United States Patent Nos. 5,614,077 and 7,325,604, such techniques have not been applied in the fashion described herein for preventing mineral scale deposits.

SUMMARY OF THE INVENTION

The method of the invention involves the application of electrokinetics for mitigating mineral scale formation. In one embodiment, the present invention provides an electrokinetic method for preventing mineral scale deposition in an oil well, having a well bore in fluid communication with an oil-bearing formation in which water and positively and negatively charged scale-forming species are present. The method comprises the steps of:

a) positioning at least one first electrode adjacent to a well bore;

b) positioning at least one second electrode at a location spaced apart from the first electrode and within electrical current conducting proximity of the first electrode;

c) applying a potential difference between the first electrode(s) and the second electrode(s) using a direct current (DC) power source, the potential difference producing an electrical current flow between the first electrode(s) and the second electrode(s), whereby the positively charged scale-forming species are caused to migrate toward one of the first and the second electrode(s), and the negatively charged scale-forming species are caused to migrate toward the other of the first and second electrode(s). In an aspect of this method, the potential difference is applied such that the first electrode(s) serves as one or more cathodes and the second electrode(s) serves as one or more anodes.

In another aspect of this method, at least one of the positively and negatively charged scale-forming species is introduced into the formation from an external source such as waterflooding. When waterflooding is the source of the scale-forming species, the method may be performed using an electrically conducting aqueous solution, e.g., a prepared or manmade aqueous salt solution, or alternatively, an aqueous solution selected from the group consisting of seawater, groundwater, surfacewater, and wastewater.

In a further aspect of the method, the positively and negatively charged scale-forming species include at least one alkaline earth metal ion and sulfate or carbonate ions.

In still a further aspect of the electrokinetic method, multiple cathodes are positioned in the vicinity of the well. Additionally, multiple anodes may be positioned at locations spaced apart from the cathodes and beyond the well, and in preferred installations the number of anodes exceeds the number of cathodes.

In yet another embodiment, the present invention provides an electrokinetic method for preventing mineral scale deposition in an oil well, and the vicinity of the well, with the well having a well bore in fluid communication with an oil-bearing formation in which water and positively and negatively charged scale-forming species are present, the method comprising the steps of:

a) positioning at least one cathode adjacent to the well bore;

b) positioning a plurality of anodes at a location spaced apart from the at least one cathode and within electrical current conducting proximity of the at least one cathode, wherein the number of anodes exceeds the number of cathodes;

c) applying a potential difference between the at least one cathode and each individual anode of the plurality of anodes; whereby electrical current flow between the at least one cathode and each individual anode of the plurality of anodes causes the positively charged scale-forming species to migrate toward the at least one cathode, and the negatively charged scale-forming species to migrate toward each individual anode of the plurality of anodes.

In another aspect, the method further comprises the step of providing a switch between the at least one cathode and each individual anode of the plurality of anodes, wherein the switch is adapted to be opened to interrupt application of the potential difference between the at least one cathode and each individual anode of the plurality of anodes, or closed to apply the potential difference between the at least one cathode and each individual anode of the plurality of anodes.

In a further aspect of the method of the invention, the step of applying a potential difference between the at least one cathode and each individual anode of the plurality of anodes further comprises the step of providing a DC power source between the at least one cathode and each individual anode of the plurality of anodes.

The method described herein is believed to be the first use of direct current to prevent scale deposition in a well bore in fluid communication with an oil bearing formation. The electrokinetic method for preventing scale deposition described herein may be categorized as a green technology, since there is no water consumption, and no air, water, or formation pollution. The technology can be applied without depth limitations in situ, thereby making it an attractive option in remote or environmentally challenging operating locations.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will be more easily understood when read in conjunction with the accompanying figures in which:

FIGURES 1A-C are circuit diagrams representing cathode and an anode configurations where the number of anodes exceeds the number of cathodes.

FIGURE 2 is a graphical representation of the pressure across the core versus time in experiment 1 of Example 1.

FIGURES 3A-C are a set of graphs showing the barium concentration profiles of the experiments in Example 1 ; Figure 3A is a graphical representation of the concentration profile of barium found in the tested electrode configuration (++--) for all tested salinity and

composition waters against the blank at the five strategic sampled positions across the 18 cm sand specimen of Example 1; Figures 3B-C are graphs representing the concentration profile of barium remaining after application of DC current; where Figure 3B includes the average of experiments 1 and 10 in addition to experiments 2, 5, 8 - seawater/formation composition water (SW/FW) and 11 of Experiment 1; and Figure 3C includes experiments 5, 8, 9 and 12 of Example 1. FIGURE 4 is a graph of the current across the core as a function of time for experiment 2 of Example 1.

FIGURES 5A-C are a set of graphs showing current as a function of time across the core for several experiments of Example 1 ; Figure 5A is a graph of the current across the core as a function of time for experiment 3 of Example 1; Figure 5B is a graph of the current across the core as a function of time for experiment 5 of Example 1 ; and Figure 5C is a graph of the current across the core versus time for experiment 8 of Example 1.

FIGURES 6A-C are a set of graphs showing pressure as a function of current across the core for several experiments of Example 1; Figure 6A is a graph of the pressure versus current for experiment 2 of Example 1 ; Figure 6B is a graph of the pressure as a function of current for experiment 3 of Example 1 ; and Figure 6C is a graph of the pressure as a function of current for experiment 8 of Example 1.

FIGURE 7 is a graph of the standardized concentration profile of barium with and without DC current - No salinity and actual seawater/formation composition water (SW/FW) of Example l(see Table 3).

FIGURE 8 is a graphical representation of the change in permeability with respect to the pore volume in the blank experiment of Example 2.

FIGURE 9 is a schematic illustration of a consolidated sand cell shown, in cross-section, with an electrode positioned at each of the production water outlet and the sea water inlet.

FIGURES 10A-B are schematic illustrations of the electrokinetic cell utilized in

Example 2; Figure 10A is a schematic illustration of a consolidated sand cell showing, in cross- section, the distribution of anodes and cathodes in a first configuration (AAACC), and Figure 10B is a schematic illustration of a consolidated sand cell shown, in cross-section, a distribution of anodes and cathodes in the second configuration (AAAAC).

FIGURE 11 is a graphical representation of the effect of pH on BaS04 solubility.

FIGURES 12 A-F are a set of graphs showing permeability as a function of pore volume for several experiments of Example 2; Figure 12A is a graphical representation of permeability reduction with respect to the pore volume in experiment 5 of Example 2; Figure 12B is a graphical representation of permeability reduction with respect to the pore volume in experiment 6 of Example 2; Figure 12C is a graphical representation of permeability reduction with respect to the pore volume in experiment 7 of Example 2; Figure 12D is a graphical representation of permeability reduction with respect to the pore volume in experiment 8 of Example 2; Figure 12E is a graphical representation of permeability reduction with respect to the pore volume in experiment 9 of Example 2; and Figure 12F is a graphical representation of permeability reduction with respect to the pore volume in experiment 10 of Example 2.

WO2012158145a