RU2124118C1 - Method for increasing oil recovery from low-permeable oil bed - Google Patents

Abstract

FIELD: oil production industry. SUBSTANCE: this can be used in oil wells at zones with low permeability. According to method, drilled from main well is additional bore-hole which is angled in relation to main well. Installed in main well and in additional bore-hole are electrodes connected to source of direct current, thus creating electroosmotic motion of liquid. Beside that, additional bore-hole can be provided with metal casing pipe located above oil bed level or with dielectric casing pipe which is perforated in zone of location of additional electrode. Focusing electrodes can be installed above and below additional electrode. Section of casing pipe located above oil bed can be removed. Beside that, additional bore-hole can be drilled from main well or from other additional bore-hole. In this case, main electrode is installed in other additional bore-hole. Voltage and amperage of direct current are determined according to mathematical relations. Application of aforesaid method improves efficiency of oil recovery from beds. EFFECT: higher efficiency. 10 cl, 8 dwg

Description

 The invention relates to oil production technology and can be used in oil wells in areas with low soil permeability.

 To assess the novelty and inventive step of the claimed solution, we consider a number of well-known technical means of a similar purpose.

 There is a method of electrolytic increase in downhole oil production rate, according to which the enhanced oil recovery is achieved due to the effect of electroosmosis under various modes of electric processing, including using pulsed electric current, see, US patent N 2.799.641.

 The disadvantage of this method is that it can be implemented only in open-hole wells.

 There is a known method of processing a well using electroosmosis, in which the anode and cathode electrodes are lowered into the well with an open bottom hole, the anodes being located in the oil-saturated layer and the cathodes below this layer, see US Patent No. 3.417.823.

 The disadvantages of this method include the small extent of the electroosmotic zone.

 A known method of electroosmotic processing, in which rows of long electrodes are used, between which DC and AC potentials are applied, see, U.S. Patent No. 4,645.004.

 The disadvantages of this analogue are the high energy costs for conducting conductive heating of the reservoir and the high cost of arranging rows of wells.

 A known method of developing an oil reservoir, including the impact on the reservoir at the same time lowering pressure and direct current, for which the first electrode located in the well, the flow rate of which they are trying to increase, is connected to the negative pole of the direct current source, and then, when an influx of hydrocarbons appears, the polarity of the electrode is changed see A.S. USSR N 1670109.

 The disadvantages of this analogue are the high costs of electroosmotic treatment of the formation due to current leakage from the surface ground electrode to the upper part of the casing and from the armor of the connecting cable through the water to the casing and then to the soil layers located above the oil reservoir.

 There is a method of increasing oil recovery in a low-permeability oil reservoir, including creating a vibration in the reservoir with a frequency close to the resonant frequency of the reservoir and performing simultaneous electrical stimulation of the reservoir by means of two electrodes located at the level of the oil reservoir in neighboring wells, see PCT / NO 86/00080, according to which the patent of the Russian Federation N 1838594, E 21 B 43/24 is issued.

 By the greatest number of similar features and achieved by using the result, this technical solution is selected as a prototype of the claimed invention.

 The disadvantages of the prototype, which does not allow us to achieve our goal, is the need to drill a neighboring well to the level of the oil reservoir, which must be close to the main well to ensure the required current density, which in some cases leads to the need for a break in the main production well and reduces the efficiency formation processing technologies.

 The objective of the invention is the use of electroosmosis to increase oil recovery in a low-permeable oil reservoir by the most efficient arrangement of electrodes and create the necessary current density at any ratio of the electrical resistivity of the reservoir and adjacent soil layers, as well as reduce the cost of drilling additional wells and eliminate interruptions in the operation of the producing well .

 The essence of the claimed invention is expressed in the following set of essential features, sufficient to achieve the above technical result.

 According to the invention, a method of increasing oil recovery of a low-permeability oil reservoir, comprising placing in the wells at the level of the oil reservoir the main and additional electrodes connected to a constant current source and transmitting between the constant current electrodes to create electroosmotic fluid movement, characterized in that previously in the casing of the main well form a window through which additional wells are drilled at an angle to the production well to the level of the oil reservoir a.

 This is the totality of essential features that provides a technical result in all cases to which the requested amount of legal protection applies.

In addition, the claimed solution has optional features characterizing its particular cases, specific forms of its material embodiment or special conditions for its use, namely:
- an additional well is equipped with a metal casing, the end of which is placed above the level of the oil reservoir.

 - an additional well is equipped with a dielectric casing, in which perforation is performed in the area where the additional electrode is located.

 - Above and below the additional electrode set focusing electrodes connected to a constant current source.

- an additional electrode is placed symmetrically relative to the interface between the oil reservoir and the overlying soil layer, while the current value is set by the expression
I = I ₁ (1 + ρ ₁ / ρ ₂ ),
where I ₁ is the specified current necessary for the occurrence of electroosmotic fluid movement in the oil reservoir, A;
ρ ₁ and ρ ₂ - electrical resistivity of the oil reservoir and the overlying soil layer, respectively, Ohm • m
- pre-remove the casing section of the main well above the oil reservoir.

 - carry out the sinking of the second additional well to the level of the oil reservoir, while the primary and secondary electrodes are installed in additional wells.

 - sinking of the second additional well is carried out through a window previously formed in the casing of the main well, at an angle to the main well.

 - sinking the second additional well is carried out from the first additional well at an angle to it.

 - electroosmotic effect is carried out with a change in the polarity of the current.

где
ρ - удельное электрическое сопротивление нефтяного пласта, Ом•м,
λ - удельная теплопроводность нефтяного пласта, Вт/м•с,
ΔT - максимально допустимое увеличение температуры на поверхности обсадной трубы основной скважины, при которой пластовая жидкость еще не закипает, ^oC.- the voltage of the DC source is selected from the condition

Where
ρ - electrical resistivity of the oil reservoir, Ohm • m,
λ is the specific thermal conductivity of the oil reservoir, W / m • s,
ΔT is the maximum allowable temperature increase on the surface of the casing of the main well, at which the reservoir fluid does not boil, ^o C.

 The claimed technical solution is new, as it is characterized by the presence of a new set of features that is absent in all objects of equipment of a similar purpose known to us.

 The immediate technical result that can be obtained by implementing the claimed combination of features is to reduce the cost of installing an additional well that provides the most efficient arrangement of electrodes.

 This technical result is a property of the entire set of features declared in the first paragraph of the formula, including such completely new features as the penetration of an additional well through a window in the casing of the main well.

 The receipt of the aforementioned technical result ensures that the object of the invention as a whole has a number of new useful properties, namely, it is possible to obtain oil from low permeability formations, and the efficiency of electroosmotic treatment is increased.

 This allows you to recognize the claimed technical solution meets the criterion of "inventive step".

 The invention is illustrated in the drawing, where in FIG. 1 presents a general diagram of the implementation of the method, FIG. 2 is an embodiment of a method with a metal casing in an additional well; FIG. 3 is a variant with a dielectric casing in an additional well with perforation, FIG. 4 is an embodiment with focusing electrodes, in FIG. 5 is a variant with the location of the additional electrode symmetrically with respect to the interface between the oil reservoir and the overlying soil layer, in FIG. 6 is a variant with a remote section of the casing of the main well; in FIG. 7 is a variant with two additional wells passed through windows in the main well; FIG. 8 is an illustration of a second additional well passed from a first additional well.

 In the main producing well 1, the main electrode 2 is installed with a contactor 3, which ensures its electrical contact with the surface of the metal casing 4. The main electrode 2 is installed at the level of the oil reservoir 5 and is connected by a conductor 6 to a direct current source 7.

 In the casing 4 of the well 1, for example, a window is formed, through which an additional well 8 is drilled, at an acute angle to the well 1 to the level of the oil reservoir, in which an additional electrode 9 is placed at the level of the oil reservoir, 10 connected to the source 7 by a current path 10 .

 The additional well 8 may be equipped with a metal casing 11 (Fig. 2), the lower end of which is located above the level of the oil reservoir 5, or a dielectric casing 12 (Fig. 3), which is provided with a perforation 13 at the level of the oil reservoir 5. Above and below an additional electrode 9 can be placed focusing electrodes 14 and 15, respectively connected by current conductors 16 and 17 with a source 7 (Fig. 4).

 An additional electrode 9 can be placed symmetrically relative to the interface between the oil reservoir 5 and the overlying soil layer (Fig. 6).

 In the casing 4, a portion 18 (FIG. 6) located above the oil reservoir 5 can be removed.

 In the casing 4 of the main well 1, a second window may be formed through which the second additional well 19 may be drilled to the level of the oil reservoir 5 (FIG. 7). When this electrode 2 is installed in the second additional well 19.

 The second additional well 19 may be passed from the first additional well 8 (FIG. 8).

 The method is as follows.

 From the source 7, through the conductors 6, 10, power is supplied to the electrode 2, which is located in the main well 1 at the level of the oil reservoir 5, and to the electrode 9, which is also located in the oil reservoir in the additional well 8 in the immediate vicinity of the electrode 2. minus is supplied to the main electrode 2, and plus to the additional electrode 9. Electro-osmotic treatment of the oil reservoir 5 is carried out and the production rate of production well 1 is measured. When the production rate increases above the minimum predetermined value, a signal is sent to power off the electrodes and on the inclusion of pumping equipment.

 With a positive potential difference between the electrodes 2 and 9, cathodic corrosion protection of the casing 4 is simultaneously provided.

 If during the electroosmotic treatment of an oil reservoir within a few days the well production rate does not increase significantly, then the polarity of the supply of electrodes is changed.

 When equipping an additional well 8 with a metal casing 11, the additional well may also be a production well made with an open bottom.

 When the additional well 8 is equipped with a casing 12 of dielectric material with perforations 13 in the zone of the oil reservoir, reliable electrical contact of the additional electrode 9 with the medium is ensured and it becomes possible to use the additional well as a production well.

 Additional focusing electrodes 14 allow you to shield the current in the oil reservoir 5 from the soil layers located above and below the reservoir. The signs of the potential of the focusing electrodes are the same as those of the additional electrode 9, and their values are determined experimentally. If there is a casing dielectric pipe in the area where the focusing electrodes are located, perforation is performed.

 When the additional electrode is located symmetrically relative to the interface between the oil reservoir 5 and the overlying soil layer, this interface is impermeable to the current flowing through the oil reservoir 5 and, at any ratio of the electrical resistances of the soil layer and the reservoir 5, a predetermined current value in the oil reservoir 5 is provided for conducting its effective electroosmotic treatment.

 If a section above the oil reservoir 5 is cut out in the casing 4, the current leakage to the upper part of the casing 4 is reduced.

 If both electrodes 2 and 9 are located in additional wells 8 and 19, the influence of the casing 4 on the current distribution in the oil reservoir 5 is minimal.

 In all variants of the method, the electroosmotic treatment can be carried out with a change in the polarity of the current. At the same time, two physical phenomena are successively used to increase oil recovery and increase well production: the flow of water and oil from the anode to the cathode and a significant increase in the permeability of the formation in the anode zone.

 The possibility of industrial application of the claimed technical solution is not in doubt, because it can be implemented using well-known technological equipment. The power source, as well as control and switching units, are performed using a well-known element base.

 The use of the claimed solution in comparison with all known means of a similar purpose significantly increases the efficiency of oil recovery in low-yield wells in reservoirs with low permeability.

Claims (11)

 1. A method of increasing oil recovery low-permeability oil reservoir, including the placement in the wells at the level of the oil reservoir of the main and additional electrodes connected to a constant current source to create electroosmotic fluid movement, characterized in that the additional electrode is placed in an additional well, passed at an angle to the main well through a window formed in the casing of the main well.  2. The method according to claim 1, characterized in that the additional well is equipped with a metal casing, the end of which is placed above the level of the oil reservoir.  3. The method according to claim 1, characterized in that the additional well is equipped with a dielectric casing, in which perforation is performed in the area where the additional electrode is located.  4. The method according to any one of claims 1 to 3, characterized in that focusing electrodes connected to a direct current source are installed in the additional well above and below the additional electrode. 5. The method according to any one of claims 1 to 4, characterized in that the additional electrode in the additional well is placed symmetrically relative to the interface between the oil reservoir and the overlying soil layer, while the current value is set by the expression
I = I ₁ (1 + ρ ₁ / ρ ₂ ),
where I ₁ is the specified current required for the occurrence of electroosmotic fluid movement in the oil reservoir, A;
ρ ₁ and ρ ₂ - electrical resistivity of the oil reservoir and the overlying soil layer, respectively, Ohm • m.  6. The method according to any one of claims 1 to 5, characterized in that pre-remove the section of the casing of the main well above the oil reservoir.  7. The method according to any one of claims 1 to 6, characterized in that the second additional well is drilled to the level of the oil reservoir, while the primary and secondary electrodes are installed in additional wells.  8. The method according to claim 7, characterized in that the drilling of the second additional well is carried out through a window previously formed in the casing of the main well, at an angle to the main well.  9. The method according to claim 7, characterized in that the drilling of the second additional well is carried out from the first additional well at an angle to it.  10. The method according to any one of claims 1 to 9, characterized in that the electroosmotic effect is carried out with a change in the polarity of the current. 11. The method according to any one of claims 1 to 10, characterized in that the voltage of the DC source is selected from the condition

where ρ is the electrical resistivity of the oil reservoir, Ohm • m;
λ is the specific thermal conductivity of the oil reservoir, W / m • s;
ΔT - the maximum allowable temperature increase on the surface of the casing of the main well, at which the reservoir fluid does not boil, ^o C.

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