RU2213215C1 - Method of development of nonuniform permeable formations - Google Patents

Abstract

FIELD: oil producing industry. SUBSTANCE: method includes alternating injection into producing formation between fringes of displacement fluid of suspension of water-soluble polymer in inert fluid carrier and aqueous solution with pH below 5.0 or above 8.0. Suspension of water-soluble polymer in inert fluid carrier additionally contains substances crystallizing in aqueous medium in amount of 0.5-50 wt.p.p. per 100 vol.p.p. of suspension. Displacement fluid is used in form of alcohols, glycols, ethers and other fluids preventing contact of isolating composition with aqueous solution and formation water in wellbore. Inert fluid carrier is used in form of pure oil, gasoline, gas-oil, hexane, diesel fuel, distillate, kerosene, condensate, natural bitumen or compositions on their base. Substances crystallizing in aqueous medium are used in form of cement or cement-limestone mixture. EFFECT: higher efficiency of development of nonuniform permeable formations due to increased reliability of isolation of water-encroached interlayers. 4 cl, 2 tbl, 2 ex

Description

 The invention relates to the oil industry and can be used in the development of heterogeneous permeability formations.

 A known method for the development of heterogeneous permeability of oil reservoirs, including the injection into the reservoir of a suspension of a water-soluble polymer in highly mineralized formation water (RF Patent 2158824, class E 21 B 43/22, publ. 10.11.2000).

 The disadvantage of this method is the low efficiency due to the destruction of the polymer in a highly mineralized dispersion medium and the clogging of the perforation holes of oil-saturated intervals with particles of partially hydrolyzed polymer.

 Closest to the invention in technical essence is a method of developing heterogeneous permeability of oil reservoirs, comprising alternating injection into a reservoir of a suspension of a water-soluble polymer in an inert carrier fluid and an aqueous solution (USSR Author's Certificate 1501597, class E 21 B 43/22, publ. 10.23.91 - prototype).

 The disadvantage of this method is its low efficiency due to the lack of static shear stress in a highly concentrated polymer solution formed in the formation from a suspension of a water-soluble polymer, as a result of which the insulating composition is forced back into the well and does not create the necessary resistances in the water filtration channels.

 The objective of the invention is to increase the efficiency of development of heterogeneous permeability formations by increasing the reliability of the isolation of waterlogged layers.

 The problem is solved in that in a method for developing heterogeneous permeability formations, comprising alternately injecting a suspension of a water-soluble polymer in an inert carrier fluid and an aqueous solution into the reservoir, according to the invention, a suspension of a water-soluble polymer in an inert carrier fluid is pumped between the rims of the buffer fluid, wherein the suspension a water-soluble polymer in an inert carrier fluid additionally contains substances that crystallize in an aqueous medium, in an amount of 0.5-50 wt. hours per 100 parts suspension of a water-soluble polymer in an inert carrier liquid, and the value of the hydrogen ion index of the aqueous solution is below 5.0 or above 8.0.

 Alcohol, glycols, ethers and other liquids that prevent the contact of the insulating composition with an aqueous solution and produced water in the wellbore are used as a buffer fluid.

 As an inert carrier liquid, anhydrous oil, gasoline, gas oil, hexane, diesel fuel, distillate, kerosene, condensate, natural bitumen or compositions based on them are used.

 As substances that crystallize in an aqueous medium, cement or a cement-lime mixture is used.

The features of the invention are:
1) injection into the reservoir of a suspension of a water-soluble polymer in an inert carrier fluid;
2) injection of an aqueous solution;
3) injection of a suspension of a water-soluble polymer in an inert carrier fluid between the rims of the buffer fluid;
4) the content in the suspension of a water-soluble polymer in an inert carrier fluid of substances crystallizing in an aqueous medium;
5) the same in the amount of 0.5-50 wt.h. for 100 rpm suspensions of a water-soluble polymer in an inert carrier fluid;
6) the value of the indicator of hydrogen ions of an aqueous solution below 5.0 or above 8.0;
7) the use of alcohols, glycols, ethers and other liquids as a buffer fluid to prevent the insulating compound from contacting with the aqueous solution and produced water in the wellbore;
8) the use of anhydrous oil, gasoline, gas oil, hexane, diesel fuel, distillate, kerosene, condensate, natural bitumen or compositions based on them as an inert carrier fluid;
9) the use of substances that crystallize in an aqueous medium, cement or cement-lime mixtures.

 Signs 1, 2 are common with the prototype, signs 3-6 are the essential distinguishing features of the invention, signs 7-9 are particular features of the invention.

SUMMARY OF THE INVENTION
When developing reservoirs of heterogeneous permeability, a significant part of the oil reserves remains undeveloped. The objective of the invention is to increase the efficiency of development of heterogeneous permeability formations by increasing the reliability of the isolation of waterlogged layers. The problem is solved as follows.

 When developing heterogeneous permeability formations, alternating injection of a suspension of a water-soluble polymer in an inert carrier fluid and an aqueous solution with a hydrogen ion index (pH) below 5.0 or above 8.0 is carried out between the rims of the buffer fluid. A suspension of a water-soluble polymer in an inert carrier liquid contains substances that crystallize in an aqueous medium in an amount of 0.5-50 parts by weight. for 100 rpm suspensions in an inert carrier fluid. Alcohol, glycols [diethylene glycol (DEG), triethylene glycol (TEG)], ethers and other liquids that prevent the contact of the insulating composition with the aqueous solution and produced water in the wellbore are used as a buffer fluid. As an inert carrier fluid, anhydrous oil, gasoline, gas oil, hexane, diesel fuel, distillate, kerosene, condensate, natural bitumen (PB) or compositions based on them are used. As substances that crystallize in an aqueous medium, use cement or a cement-lime mixture.

 Polyacrylamide (PAA), hydroxyethyl cellulose (OEC), carboxymethyl cellulose (CMC), etc. are used as a water-soluble polymer.

 The method provides a selective reduction in the permeability of highly permeable water-saturated intervals due to the formation of a viscous, subsequently hardening composition in them, and connection to the development of less permeable sections of the reservoir containing mobile oil.

Case Studies
Example 1. Determination of the effectiveness of the method in conditions of heterogeneous permeability of the formations was carried out in laboratory conditions on bulk linear models of the reservoir simulating high and low permeability portions of the reservoir, with permeability respectively (1000-3000) • 10 ^-3 μm ² and (200-600) • 10 ^-3 μm ² . The permeability of the models was achieved by varying degrees of core grinding of real oil fields.

Then, through hydrodynamically connected models, the formation water, model oil and injected water were sequentially filtered in the amount of 5 pore volumes (V _p ) each. Simulated conditions are close to real for heterogeneous oil reservoirs that are at a late stage of development.

Next, rims of the buffer fluid (anhydrous oil, oil products, alcohols, glycols, ethers), a suspension of water-soluble polymer and Portland cement (or cement-lime mixture) in oil in a volume of 0.3 V _p , buffer fluid and 0.15 V _p an aqueous solution of alkaline runoff production of caprolactam with a pH of 8.1 as an aqueous solution. The volume of the rims of the buffer fluid was 0.1 V _p .

 After pumping the calculated volumes of the initial reagents, an exposure was carried out in time for 24 hours and water was pumped to a complete water cut of the selected liquid. Next, the growth of the oil displacement coefficient was determined as the difference between the final oil displacement coefficient when using the proposed method and the water displacement coefficient until a 99% water cut of the produced oil is reached.

 The research results are shown in table 1.

 According to table 1 it is seen that the use of the method in the development of heterogeneous permeability formations can significantly increase the recovery factor by 24.6-29.5%.

Example 2. We treated a well operating carbonate deposits lying at a depth of 837-845 m. The fluid rate at the time of the method implementation was 6.0 m ³ / day, oil - 0.1 t / day, water cut - 99%.

A suspension of 0.25 tons of PAA and 3.0 tons of Portland cement in 6.0 tons of natural bitumen was pumped into the well with preliminary and subsequent injection of rims of buffer liquid - natural bitumen with a volume of 0.5 tons and 6 m ^{3 of} produced water were pushed.

 The pressure at the beginning of the injection was 6 MPa, at the end of the injection it was 8.0 MPa, which indicates the placement of the suspension in the highly permeable fractured zone of the formation. Next, the well was closed for response for 24 hours.

 After the time required for the formation of a waterproofing composition in the reservoir, the well was put into operation. Monthly well operation parameters are presented in table 2.

 From table 2 it follows that as a result of a field experiment, both the limitation of water inflow from highly permeable water-saturated sections of the reservoir as a result of their isolation and an increase in well productivity by oil by 3.5-5.1 tons per day were achieved. Over 6 months of well operation, additional oil production in the amount of 740.2 tons was obtained.

 The application of the proposed method will improve the efficiency of development of heterogeneous permeability formations.

Claims (4)

 1. A method of developing heterogeneous permeability formations, comprising alternately injecting a suspension of a water-soluble polymer in an inert carrier fluid and an aqueous solution into the reservoir, characterized in that the suspension of the water-soluble polymer in the inert carrier fluid is pumped between the rims of the buffer fluid, while the suspension of the water-soluble polymer in an inert carrier fluid additionally contains substances that crystallize in an aqueous medium, in an amount of 0.5-50 wt. hours per 100 vol. including a suspension of a water-soluble polymer in an inert carrier liquid, and the value of the hydrogen ion index of the aqueous solution is below 5.0 or above 8.0.  2. The method according to p. 1, characterized in that alcohols, glycols, ethers and other liquids are used as the buffer fluid to prevent the insulating compound from contacting the aqueous solution and produced water in the wellbore.  3. The method according to p. 1, characterized in that as an inert carrier liquid anhydrous oil, gasoline, gas oil, hexane, diesel fuel, distillate, kerosene, condensate, natural bitumen or compositions based on them are used.  4. The method according to p. 1, characterized in that as the substances crystallizing in the aquatic environment, use cement or cement-lime mixture.

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