RU2086758C1 - Method for development of oil reservoir - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this relates to development of oil reservoir to reduce permeability of flooded reservoir and to involve in development less flooded reservoirs or part of reservoir. According to method, injected into flooded reservoir are alkali reagent, mineralized water, and clay solution. Used as alkali reagent are compounds of first-group metals. Clay solution is delivered in mixture with alkali reagent. Directly after injection of alkali reagent, injected is solution of chlorous or hydrochloric aluminium. This method can be applied at beginning of flooding process, but most suitable objects are deposits with flooding of 80 % and larger and current oil productivity coefficient less than 0.7. Methods allows for reduction of product watering by 19-49%. Application of clay suspension reduces consumption of reagent by 5-7 times with obtaining same technological effect and this gives overall economy. EFFECT: high efficiency. 3 cl, 1 tbl

Description

 The present invention relates to the oil and gas industry, in particular, to methods that reduce the permeability of flooded formations and involving less flooded formations or parts of the formation in the development.

 A known method of developing a field by injecting into the formation through an injection well an aqueous solution of a mixture of ethoxylated alkyl phenol, polyacrylamide and water glass. (USSR author's certificate N 1736228, Е 21 В 43/22, 1990). This method does not provide an effective reduction in the permeability of highly porous fractured reservoirs due to the insufficient volume of precipitated sediment. The sediment volume is negligible with a low content of calcium and magnesium ions in the injected water. The complexity of the preparation of the solution in the field and the high cost of the reagents are the disadvantages of the method.

 The closest in technical essence and the effect obtained to the proposed technical solution is a method of developing oil fields, including the sequential injection of an aqueous polymer solution, concentrated alkali solution and mineralized water. However, the practical application of the method is limited by the insufficient efficiency of clogging the collectors, especially with desalinated formation water and the high cost of the polymer (RF patent N 2004782, Е 21 В 43/22, 1991).

 To reduce the permeability of the flooded reservoir, an alkaline reagent and mineralized water are sequentially injected, an additional clay solution is injected, and a metal compound of the first group is used as an alkaline reagent, while the clay solution is mixed with an alkaline reagent, and immediately after the alkaline reagent is injected, a solution is supplied aluminum chloride or hydrochloride.

 The concentration of alkaline reagent, aluminum chloride, hydrochloride chloride varies depending on the permeability of the formation, the injectivity of the well from 0.5% to the concentration of saturated solution. The volume of solutions is calculated by the pore volume of the reservoir.

The volume of the solution of aluminum chloride, hydroxychloride should contain 0.2-0.4 equivalents of the theoretically necessary amount for the complete precipitation of the alkaline reagent. Precipitation of alkaline reagents will also occur with the ions contained in the wastewater. The concentration of clay in the suspension is selected depending on the permeability of the formation, that is, the injectivity of the injection well, and it can vary from 0.5 to 25.0%
The sequence of operations reduces or stops the filtration through the flooded part of the reservoir, as high-permeability sections of the reservoir become clogged, a transition to new filtration zones occurs, that is, the displacement front is regulated.

 As alkaline reagents, sodium liquid glass according to GOST 13078-81, water-soluble sodium silicate powder according to TU 2145-015-13002578-94, aqueous solutions of sodium silicates according to TU 2145-014-13002578-94, soda ash according to GOST 5100-85 can be used , technical caustic soda according to GOST 2263-79 or 11078-78, ammonia (aqueous solution) according to GOST 9-92.

 For alkaline reagents, solutions of spent aluminum chloride according to TU 38.102163-84 or aluminum hydroxyl chloride according to TU 38.302163-94 are pumped.

 Along with the target industrial chemical products, spent alkaline waste products that have the appropriate permit for use in oil production processes can also be used.

The density of mineralized water should exceed 1050 kg / m ³ , it is allowed to use a solution of calcium chloride according to GOST 450-86 of the corresponding density.

The effectiveness of reducing the permeability of a waterlogged formation by the proposed and known methods was determined by laboratory experiments on filtering the applied solutions through an artificial core sample. The sample is a cemented quartz sand with a diameter of 39-40 mm, a length of 52-56 mm, a pore volume of 13.2-17.5 cm ³ . The experiments begin with the installation of the sample in the core holder, saturation of it with formation water with a density of 1050 k / m ³ , and the initial permeability is determined with a constant pressure drop of 0.01 MPa.

 In order to reduce permeability, alternating rims of 2 ml of fresh water, 5 ml of the first precipitating gel-forming composition, 2 ml of fresh water, 5 ml of a solution of aluminum chloride or hydrochloride, 2 ml of fresh water, 20 ml of waste water are filtered through a sample. Residual permeability was determined by filtering waste water in the forward and reverse directions. The degree of decrease in the permeability of samples characterizes the effectiveness of the applied method of pumping solutions.

 In addition to water glass, solutions of ammonium or sodium hydroxide mixed with polyacrylamide can be used. The efficiency of sequential filtration of aluminum chloride and wastewater for solutions of ammonium or sodium hydroxide is 6-14% compared with well-known methods (Russian Patent N 2004782 Е 21 В 43/22) (experiments 19-22).

 The best results were obtained by filtering a clay suspension containing 4% liquid glass or sodium hydroxide, the effectiveness of the proposed method with a 6% clay suspension reaches 8-9% (experiments 23, 24, 27, 28), with a clay powder concentration of 12% in a liquid glass solution the effect of reducing permeability is 13% (experiments 25, 26). A comparison of experiments 23-26 and 29-32 shows that the proposed method can significantly increase the effectiveness of reducing the permeability of the flooded reservoir by pumping a clay suspension containing a small proportion of the reagents.

 The method is as follows.

Example 1. The experimental section of the oil deposits is represented by coal-bearing horizons СI and СII with a sand reservoir. The site is operated by 2 injection and 10 production wells. The depth of the deposit is 1639-1631 m. The injectivity of injection wells at 10.2 MPa is 380 and 620 m ³ / day. The water cut of production wells is 79-93% oil production rate of 1.5-37.8 m ³ / day.

8 m ^{3 of} clay solution in fresh water with a density of 1200 kg / m ³ , 12 m ^{3 of an} aqueous solution containing 21% sodium hydroxide and 14% sodium silicate, 24 m ^{3 of} mineralized water with a density of 1178 kg / m ^{3 are} sequentially pumped into each injection well.

For 7 months after injection of reagents, the decrease in water cut in production of producing wells was 0.6-2.1% or an average of 0.7% in the area, the volume of produced water decreased by 89498 m ³ , due to the application of the technology 2988.8 tons of oil were additionally produced .

Example 2. The test object is selected sandstone of a coal-bearing horizon, operated by 1 injection and 6 production wells. The perforation interval of the injection well is 1347.2-1352.4 m. The average thickness of the formation is 5.2 m. The density of injected water is 1118 kg / m ³ , the injectivity of the well at 9.5 MPa is 535 m ³ / day, the permeability of the formation is 0.18-0 , 22 μm ² , porosity 0.23-0.26, water cut in production of producing wells 92-96% oil production rate 0.6-1.7 m ³ / day.

After a set of preparatory and research works, 3 m ^{3 of} fresh water is pumped into the injection well, followed by 24 m ^{3 of an} alkaline suspension containing 8.5% sodium silicate and 6% clay powder, another 3 m ^{3 of} fresh water. The process of improving oil displacement is achieved by subsequent injection of 2.3 m ^{3 of a} 27% solution of aluminum chloride and 20 m ^{3 of} waste water with a density of 1118 kg / m ³ . The solutions are pressed with 15 m ^{3 of} waste water. The volume of injected solutions is about 0.013 pore volume. The well is stopped for 72 hours to respond.

Within 2 months, the water cut of 5 production wells decreased to 63-87% at 1 well to 47%; the oil production rate of 2 wells did not change, 3 wells increased to 4.1-13.6 m ³ / day, 1 well from 1, 3 m ³ / day reached 19.2 m ³ / day. The injectivity of the injection well remained the same.

Example 3. The reservoir D1 is operated by 3 producing and 1 injection wells. The depth is 1472-1485 m, the effective thickness of the formation is 6.7 m. The perforation interval of the injection well is 1473.2-1478.2. The density of the injected water is 1156 kg / m ³ , the injectivity of the well at 10.5 MPa is 243 m ³ . Permeability 0.37-0.45 μm ² , porosity 0.22-0.28. The water cut of production wells 96-98% oil production rate of 1.3-4.5 m ³ / day.

3 m ^{3 of} fresh water, 32 m ^{3 of a} 9.5% sodium silicate solution are sequentially pumped into the injection well. 3 m ^{3 of} fresh water, 3 m ^{3 of a} 27% solution of aluminum hydroxychloride, 40 m ^{3 of} waste water with a density of 1156 kg / m ³ . The volume of injected solutions is 0.017 pore volume. The well is stopped for 72 hours to respond.

 After injecting the solutions for 1 month, the water cut of the production of 2 producing wells decreased by 28 and 37%; the decrease in water cut of 1 well by the end of 2 months reached 48%. The oil production rate of 2 wells increased by 1.5 and 12.4 times. The flow rate of 3 wells remained unchanged. The injectivity of the injection well after injection of the reagents decreased by 25% and was fully restored within 1 month.

Example 4. The reservoir is operated by 1 producing and injection wells. The deposit is represented by sandstone of the SP formation, the depth of the deposit is 1758-1764 m, the permeability is 0.24-0.26. The injectivity of the injection well at 9.4 MPa 670 m ³ / day. The density of the injected water is 1104 kg / m ³ . The water cut of production wells 86% oil flow rate of 5.6 m ³ / day.

3 m ³ fresh water, 36 m ³ alkaline clay slurry containing 6% clay powder, 4% sodium hydroxide, 3 m ³ fresh water, 40 m ³ waste water with a density of 1104 kg / m ^{3 are} pumped into the injection well. The volume of injected solutions is 0.014 pore volume. The well is stopped for 72 hours.

The decrease in water cut in production wells amounted to 8% oil production rate reached 17.2 m ³ / day.

 Examples of the method are shown in the table.

Concentrated solutions with a total volume of liquids used up to 100 m ³ can be pumped directly from tankers, large volumes of diluted solutions are pumped using existing SPS equipment.

The method can be applied from the very beginning of the waterflooding process, but the most suitable objects are deposits with a water cut of more than 80% and a coefficient of current oil recovery of less than 0.7. When wells are injected more than 500 m ³ / day, saturated solutions of the first group of metal compounds mixed with 5-25% clay slurry are used as the first portion, more dilute solutions are used with less injectivity, and it is advisable to control the displacement front for less than 500 m ³ / day with solutions of lower concentration.

Claims (4)

 1. A method of developing an oil reservoir, including the injection of a filler solution, an alkaline reagent and mineralized water, characterized in that a clay solution is used as a filler solution, and a solution of metal compounds of the first group as an alkaline reagent.  2. The method according to claim 1, characterized in that the clay solution is served in a mixture with an alkaline reagent.  3. The method according to claim 1, characterized in that immediately after the injection of the alkaline reagent, a solution of aluminum chloride or hydrochloride is fed.  4. The method according to claim 1, characterized in that the clay solution, alkaline reagent and saline water are pumped sequentially.

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