RU2298088C1 - Method for non-uniform oil reservoir development - Google Patents

Abstract

FIELD: oil production, particularly enhanced recovery methods for obtaining hydrocarbons with the use of chemicals or bacterial activity to increase oil output from non-uniform reservoirs and to isolate drowned wells.

SUBSTANCE: method involves injecting dispersion of colloid polyacrylamide or polysaccharide particles, or cellulose ester particles including aluminum poly-oxychloride in reservoir. Above components are taken in the following amounts (% by weight): polyacrylamide or polysaccharide, or cellulose ester - 0.005-0.5, aluminum poly-oxychloride - 0.0015-0.1, remainder is water. Volume of above dispersion is determined as V=π·R²mh, where R is radius of dispersion penetration in reservoir, m, m is mean porosity, parts, h is summary thickness of accommodating intervals, m.

EFFECT: increased reservoir coverage by injection of colloid particle dispersion obtained by intromolecular cross-linking of aqueous suspension of polyacrylamide or polysaccharide, or cellulose ester and aluminum poly-oxychloride, and, as a result, filtering and oil-sweeping properties change in non-uniform reservoir, improved ecological safety and technological efficiency.

1 ex, 2 tbl

Description

The invention relates to the oil industry, in particular to methods for developing oil from a heterogeneous oil reservoir, and can be used to increase oil recovery of heterogeneous reservoirs and isolate watered wells.

A known method of oil production by sequentially injecting into the formation solutions of polyacrylamide and aluminum salt, characterized in that between the rims of the polyacrylamide and aluminum salt, a rim of fresh water is pumped. The disadvantage is that a concentrated polymer solution is prepared on the surface, which is diluted, moving along the formation, and does not always reach the necessary degree of gelation (RF patent No. 2086757, publ. 08/10/1997).

A known composition for injection into the reservoir, comprising a mixture of an anionic polymer and a salt of a polyvalent cation and water in the following ratio of components, wt.% (RF patent No. 2215870, publ. 10.11.2003):

anionic polymer 0.001-0.08 polyvalent cation salt 0.0005-0.002 water rest

The disadvantage of this composition is that it is not effective in highly permeable formations due to the insufficient content of polymer and salt of the polyvalent cation in the mixture. As a result, the number of encapsulated systems formed and their sizes are insufficient to clog highly permeable formation zones. As a result, there is no redistribution of the filtration flow of the water injected after the water and the coefficient of formation coverage by the impact is reduced.

A method for changing the permeability of an underground formation is also known, which consists in injecting a gelling composition into the subterranean formation, wherein said gelling composition contains an encapsulated crosslinking agent, a second polymer and a liquid. A crosslinking agent is a multivalent metal compound or an organic crosslinking agent. The crosslinking agent is encapsulated by the first polymer (a homopolymer or copolymer of glycolate and lactate, polycarbonate, polyanhydride or a mixture thereof) using double emulsion technology or by spray drying. The encapsulation method complicates and increases the cost of this method (RF patent No. 2250987, publ. 04/27/2005).

A known method of developing a heterogeneous formation, including the injection into the formation of a dispersion of colloidal particles of a polymer and a salt of a polyvalent cation (RF patent No. 2167281, publ. 05.20.2001). As the polymer, an aqueous solution of polyacrylamide, polysaccharide, polymethacrylamide and cellulose derivatives are used. According to this method, the polymer reacts with a polyvalent cation with the formation of transverse chemical bonds between macromolecules, leading to the formation of polymers with a reticulated spatial structure. This process occurs in time, i.e. an induction period is necessary for gelation (crosslinking). The hydrogels formed in the formation as a result of crosslinking have a rather high initial gradient of shear pressure in pores and fractures, and very low mobility. In addition, before injection of the dispersion, a polymer solution is first prepared on the surface, which requires additional time and the availability of special equipment. When applying this method, it is often necessary to remove the gel-forming composition from the wellbore, and after gel formation in the formation, to restore the permeability of oil-saturated interlayers.

As salts of polyvalent cations, acetate, tartrates, citrates, chromium and dichromate of ammonium and alkali metals, chromium and potassium alum, in particular chromium acetate, are used. Weak knowledge of ecosystems in terms of the possibility of oxidizing the trivalent form of chromium to a more toxic hexavalent form (maximum permissible concentration - MPC = 0.1 mg / L), as well as the possible presence of Cr ⁺⁶ in a marketable product containing chromium salts in trivalent form, led certain restrictions on the use of technologies based on chromium compounds in a number of Western countries and in some regions of Russia. Potassium alum has limited solubility and is poorly combined with wastewater, and aluminum hydroxide precipitates upon contact with them. Dissolution occurs over time.

In order to improve the filtration properties of polymer systems, dispersions of gel particles (DHP) are added, swelling 100-5000 times, but not soluble in water, which leads to the formation of a dispersion of colloidal particles with the following concentration of components, wt.%:

water soluble polymer 0.1-1.0 polyvalent cation salt 0.001-0.5 gel dispersion 0.001-0.1.

Particles of acrylate monomers with cellulose ethers, methylene bisacrylamide, etc., partially crosslinked by intramolecular bonds, are used as gel particles. These gel particles begin to swell rather quickly in the injected solution, which leads to an increase in the injection pressure of the dispersed system. This complicates the process, it is becoming more expensive due to the use of expensive reagents.

The method is effective in formations with high permeability with the presence of a developed system of fractures. In heterogeneous terrigenous reservoirs, the swollen gel particles clog the pores at the inlet and prevent the crosslinked sedentary polymer solution from penetrating into the depth of the formation, which reduces the coverage of the formation by displacement and the efficiency of the process as a whole.

The closest is a method of developing a heterogeneous oil reservoir, including injecting into the reservoir an aqueous dispersion of colloidal particles of polyacrylamide, or polysaccharide, or cellulose ether containing aluminum chloride (US patent No. 4009755, published. 01.03.1977).

EFFECT: increased formation coverage by injection by dispersion of colloidal particles formed by intramolecular crosslinking of an aqueous suspension of polyacrylamide, or polysaccharide, or cellulose ether and polyoxychloride of aluminum, which leads to a change in the filtration and oil-displacing parameters of the heterogeneous formation, as well as an increase in the processability and environmental friendliness of the method .

A method of developing a heterogeneous oil reservoir, including injecting into the reservoir an aqueous dispersion of colloidal particles of polyacrylamide, or polysaccharide, or cellulose ether containing aluminum chloride, characterized in that aluminum polyoxychloride is used as aluminum chloride in the following ratio of components of the specified dispersion, wt.%:

polyacrylamide, or polysaccharide, or cellulose ether 0.005-0.5 aluminum polyoxychloride 0.0015-0.1 water rest

the volume of the specified dispersion is calculated by the formula

V = πR ² mh, where

R is the radius of penetration of the dispersion into the reservoir, m,

m - average porosity, fraction of units,

h is the total thickness of the receiving intervals, m

As a result of the interaction of the polymer solution and the salt of the polyvalent cation, three types of bonds are formed.

The first - crosslinking of several polymer chains - is called intermolecular or interchain crosslinking, with the formation of a network structure, which refers to a coherent dispersed type of dispersion of colloidal particles. In the prototype, crosslinking occurs according to this type.

The second type of bond — polyvalent cation ions interact with only one unit of the polymer macromolecule.

The third type of bond is called long-range intramolecular crosslinking; in this case, two polymer segments located at a certain distance from each other are crosslinked. Crosslinking of this type does not lead to meshing.

The introduction of aluminum polyoxychloride into an aqueous suspension of polyacrylamide, or polysaccharide, or cellulose ether in the optimal ratio allows to obtain a dispersion of colloidal particles based on heterophase crosslinking according to the third type. The inner part of the colloidal particles contains water, and the shell consists of polymer molecules connected to each other by aluminum polyoxychloride. Colloidal particles are freely located in the aqueous phase and are not related to each other. This type of dispersed system is called free-dispersed.

The dispersion of colloidal particles (DCF) formed on the basis of the proposed method based on a suspension of polyacrylamide, or polysaccharide, or cellulose ether and aluminum polysichloride (POCHA) is capable of moving deep into the heterogeneous formation over considerable distances, gradually accumulating in the pores and isolating them. Due to this, there is a redistribution of the flows of the oil-displacing agent filtered through the formation, which contributes to an increase in the coverage of the formation by exposure and leads to an increase in the oil recovery coefficient of the method of developing oil from a heterogeneous formation. The size of the colloidal particles is 0.1-5.0 microns.

The technological process of pumping DCC is carried out without first dissolving the polymer. The powder of polyacryamide (PAA), or polysaccharide (PS), or cellulose ether (EC) is fed by a screw batcher into the jet apparatus, where it is mixed with water and in the form of a suspension enters the pressure pipe, where it is mixed with aluminum polyoxychloride solution and sent through the discharge line to injection well. This method of injecting into the formation an aqueous suspension of polyacrylamide, or polysaccharide, or cellulose ether and aluminum polyoxychloride is much more technologically advanced, and its implementation time is significantly reduced.

Using aluminum polyoxychloride as a crosslinker has several advantages: domestic production, low cost, environmental friendliness - these aluminum salts are used as a coagulant in water treatment in the drinking water supply system. The sanitary and environmental advantage of aluminum polyoxychloride over chromium salts and other aluminum salts is manifested in a lower content of residual aluminum in the water. In the case of using POHA for crosslinking polymer molecules, the residual content of aluminum oxide is 0.6 g / l, i.e. approaching the maximum permissible concentration of aluminum MPC, which corresponds to 0.5 mg / l for Al ₂ O ₃ .

The composition of commercial aluminum polyoxychloride with sufficient completeness is described by the combined chemical formula in the hydroxide-chloride form:

where a = 1.2-1.4; b = 3-a = 1.8-1.6; n = 2.4-4.5; m is 3-5;

x = 1, 2, 3 ... - repeating trimeric-tetrameric-pentameric units.

When mixing it with water it dissolves almost immediately and completely.

The choice of the concentration of an aqueous suspension of polyacrylamide, or polysaccharide, or cellulose ether and aluminum polyoxychloride was determined by the following criteria. Its upper boundary is the production of relatively homogeneous, kinetically and aggregatively stable dispersed systems when polyacrylamide, or polysaccharide, or cellulose ether of aluminum polyoxychloride is introduced into an aqueous suspension. The lower concentration boundary is to obtain the effect of improving the technological properties of the dispersion of colloidal particles.

It was found that the optimal content of the mass fraction of PAA, or PS, or EC from the point of view of obtaining a dispersion of colloidal particles is 0.005-0.5%, and the mass fraction of POHA is 0.0015-0.1%, while the sizes of the resulting colloidal particles satisfy conditions for leveling the reservoir heterogeneity of the formation. In this concentration range, the most durable, time-stable dispersions of colloidal particles are obtained.

When applying this method in areas with high heterogeneity of the formation, when choosing the injection volume of the dispersion of colloidal particles, it is necessary to take into account the total thickness of the intervals of the formation receiving the injected water, which is determined by the results of geophysical studies of the injectivity profile. The radius of penetration of the dispersion of colloidal particles into the formation during equalization of the permeability heterogeneity of the formation should be 15-20 m at an injection pressure not exceeding the pressure of the hydraulic fracturing. The volume of injected dispersion is calculated by the formula

V = πR ² mh,

where R is the radius of penetration of the dispersion into the reservoir, m;

m - average porosity, d.ed .;

h is the total thickness of the receiving intervals, m

Comprehensive laboratory tests and tests of the proposed method were carried out.

The size of the resulting colloidal particles was determined as follows. The same dispersion was sequentially filtered through a system of filters arranged in decreasing order of their pore size. Cascade filtration was carried out through the following filters: ordinary filter paper (d _nop = 5-10 μm) → paper filter "white tape" (d _pore = 3-5 μm) → paper filter "blue tape" (d _pore = 1-2, 5 μm) → Vladipor membrane filter No. 8 (d _por = 0.751-0.850 μm) → Vladipor membrane filter No. 4 (d _por = 0.351-0.450 μm) → Vladipor membrane filter No. 3 (d _por = 0.251-0.350 μm). The filter cake was washed with distilled water, after which the filters were dried to constant weight at a temperature of 80 ° C (membrane filters) and 105 ° C (paper filters). According to the data obtained, the weight and percentage contents of each fraction of colloidal particles were calculated. As a result, it was found that the size of the colloidal particles lies in the range of 0.1-5.0 microns.

The parameter characterizing the ability of particles to penetrate and accumulate in the pores of the formation is the ratio proposed by A.N. Patrashev of the average pore diameter of the formation rock to the particle size:

η ₀ = D / d,

where η ₀ is the filtration coefficient;

D is the averaged pore diameter of the formation rock;

d is the diameter of the encapsulated systems.

In turn, the permeability of the porous medium depends on the pore size:

,

,

where K is the permeability of the formation, μm ² ,

m - porosity, d.ed.

Substituting the values of the sizes of colloidal particles into these equations, we find the values of the permeability of the formation, in which the injected dispersion of colloidal particles will show maximum efficiency in the displacement of oil. These values of the permeability of the reservoir are in the range of 0.01-5 microns.

The study of the influence of this method on the change of filtration and oil-displacing parameters characterizing the change in the coverage of the formation by displacement, as well as comparison with the prototype was carried out using physical models of layered inhomogeneous porous media with impermeable interfaces.

Laboratory bulk models are two identical stainless steel tubes with a length of 150 cm, an inner diameter of 2.7 cm, densely filled with ground quartz sand, with a common entrance and separate exits. In this case, one tube (more permeable interlayers) contains sand, the oil permeability of which is several times higher than the permeability of sand in another tube (less permeable interlayers).

As displaced oil, degassed Devonian oil with the Karabash gas treatment unit viscosity at a temperature of 20 ° C of 13-19 MPa · s is used.

The polymer used was DP 9-8177 grade polyacrylamide with a molecular weight of 6.7 million units, xanthan polysaccharide, and Polycell Cell-1 cellulose ether.

As the salt of the polyvalent cation, the following were used:

- aluminum polyoxychloride produced by the chemical plant named after Voikov (OAO Aurat), Moscow, under the trade name Aqua-Aurat ™ -30 (TU-6-09-05-1456-96);

- chromium acetate (AX), which is a solid crystalline substance, is produced in the form of a 50% aqueous solution with a density of 1300 kg / m ³ (TU 2499-001-50635131-00).

As a dispersion of gel particles, a water-swelling polymer AK-639 with a concentration of 0.01%.

Primary oil displacement was carried out to a total water content of residual oil of 95-99%. After that, the dispersion of colloidal particles was pumped into the general input of the model according to the proposed method at different concentrations of the components and according to the prototype.

As a filtration parameter characterizing the unevenness of the displacement process in two differently permeable tubes, we used the partial (relative) flow rate of the liquid of the less permeable interlayer q before and after displacement of the rim. Moreover, the more the partial production rate of a less permeable formation increases, the more effective this method of oil displacement from the point of view of exposure to inhomogeneous permeability formations.

The main conditions and average results of oil displacement on two-layer models according to the proposed and known methods are presented in table. one.

Table 1 Name One meas. 0.2% PAA 0.02% POHA 99.78% water 0.1% PAD, 0.02% FISH 99.88% water 0.5% xanthan gum 0.025% PHA 99.475% water 0.2% PAA, 0.02 AH, 0.01 DHA known 99.77% water The number of experiments 5 5 5 3 The content of clay powder in a porous medium MPa · s 5 3 5 3 Oil permeability: more permeable tube μm ² less permeable tube μm ² 3.82 0.46 4.02 0.24 4.66 0.69 15.4 0.43 Permeability ratio grandfather 8.3 16.7 6.75 35.8 Water displacement: Relative liquid output ΣV spore 11.0 7.06 12.16 8.31 The final water cut of the liquid at the outlet of the two-layer medium % 98.5 98.0 99.6 99.0 Oil displacement coefficient % 49.9 37.5 49.0 47.0 Partial fluid flow rate: less permeable tube q ' grandfather. 0,074 0.006 0,101 0,070 Retrieval with dispersion (10% ΣVpor): The relative amount of filtered fluid (OKPZH) ΣV spore 14.2 11.52 11.28 Final oil displacement rate % 64.6 50,4 62.3 55.1 The growth rate of oil displacement % 14.7 12.9 13.3 8.1 Partial fluid flow rate: q '' less permeable tube grandfather. 0.348 0.059 0.535 0.12 The rate of increase in the partial flow rate of a less permeable tube b / r 4.7 9.8 5.3 1.7

As can be seen from the table. 1, the partial flow rate of a less permeable tube during the implementation of the proposed method increased by an average of 6.6 times, and by a known method by 1.7 times, and the increase in oil displacement ratio was 13.6% and 8.1%, respectively.

The effectiveness of the proposed method for developing oil from a heterogeneous oil reservoir in laboratory conditions was determined by testing the filtration and oil-displacing properties of dispersions of colloidal particles on Devonian cores using the Core Lab installation using a special technique.

The analysis of the test results was carried out on the example of the main filtration parameter - residual resistance factor (OFS), which shows how many times the filtration resistance increased during water filtration after injection of a dispersion of colloidal particles compared to the initial filtration resistance during filtration of water before injection of a dispersion of colloidal particles. With an increase in the resistance factor and especially the residual resistance factor, the coefficient of formation coverage by the impact increases.

The selection of the polymer concentration was carried out taking into account the permeability of the core. The main conditions and test results on Devonian cores of disperse systems are presented in table. 2.

table 2 Test methods n CRM., Microns ² m,% Qu.,% FS OFS Proposed 0.5% Polycell + 0.1% POHA, 99.4% water 3 2,456 17.7 75.3 53.6 88.4 0.1% PAA + 0.01% POHA, 99.89% water 3 0.254 18.3 57.4 16.1 19.5 0.1% PAA + 0.02% POHA, 99.88% water 3 0.258 18.0 68.6 39,4 52.9 0.05% Polysaccharide, 0.025% POHA, 999.125% water 3 0.377 15.1 52,5 23.6 42.8 0.01% PAA, 0.01% POHA, 99.98% water 3 0.236 18.8 55.9 4.24 6.38 0.005% PAA, 0.005% POHA, 99.99% water 3 0.161 18.1 54.9 2.68 5.02 Famous 0.15% PAA, 0.02% AH, 0.001% DHA, 99.729% water 3 0.512 18.2 52.9 3,1 6.6 0.2% PAA, 0.005% ACC, 0.001% DHA, 99.794% water 3 9,470 20.1 56.2 12.3 16.1

Where

n is the number of experiments,

KPR - core permeability,

m is the core porosity,

Quit. - displacement coefficient,

FS - resistance factor,

AX - chromium acetate

ACC - potassium alum.

As can be seen from the table. 2, the OFS value of the proposed method (average value of 35.8) exceeds the OFS value of the known method (average value of 11.4) 3.1 times. The oil displacement coefficient is 60.8% and 54.6%, respectively. The known method works well in highly permeable formations, and the proposed one works in heterogeneous permeability formations. With low core permeability, the proposed method is effective even with a component ratio of 0.005% PAA + 0.005% POHA, it is well known that when the SFC is greater than 2, the displacing composition works to increase the coverage of the formation. Therefore, the proposed method allows you to adjust the coverage of the formation by exposure by determining the optimal concentration of components depending on the permeability of the formation.

Example.

In the method for developing a heterogeneous oil reservoir, an aqueous dispersion of colloidal particles is pumped into the reservoir in the following ratio of components, wt.%: Carboxymethyl cellulose 0.4, POHA 0.05, water 99.55. The volume of this dispersion is calculated by the formula V = πR ² mh. R = 20 m, h = 3 m, m = 0.2, V = 753.6 m ³ .

The application of the proposed method for the development of a heterogeneous oil reservoir allows to increase the coverage of the reservoir by injection of a dispersion of colloidal particles formed by intramolecular crosslinking of the polymer and the salt of the polyvalent cation, which leads to a redistribution of the filtration flow of the oil displacing oil and to an increase in oil displacement coefficient, as well as improved manufacturability and environmental friendliness way.

Claims (1)

A method of developing a heterogeneous oil reservoir, including injecting into the reservoir an aqueous dispersion of colloidal particles of polyacrylamide, or polysaccharide, or cellulose ether containing aluminum chloride, characterized in that aluminum polyoxychloride is used as aluminum chloride in the following ratio of components of the specified dispersion, wt.%: Polyacrylamide, or polysaccharide, or cellulose ether 0.005-0.5 Aluminum polyoxychloride 0.0015-0.1 Water Rest the volume of the specified dispersion is calculated by the formula V = πR ² mh, where R is the radius of penetration of the dispersion into the reservoir, m, m - average porosity, fraction of units, h is the total thickness of the receiving intervals, m