RU2159325C1 - Oil-forcing reagent for inhomogeneous flooded pools - Google Patents

Abstract

FIELD: oil industry, increase of oil recovery form carbonate and terrigenous flooded inhomogeneous pools under conditions of limit water content at latest stage of exploitation of oil fields. SUBSTANCE: technical objective of invention lies in rise of rheological properties of oil-forcing reagent under high shearing stresses and high degrees of mineralization of stratal water and in increase of its thermal oxidizing stability in sweet and highly mineralized water. Oil-forcing reagent for inhomogeneous flooded pools includes, per cent by mass: cross-linked polyacrylamide with molecular mass not less than 1,10⁶•50-98 and carboxymethylcellulose with substitution degree of 0.65- 1.45 in carboxylmethyl groups and polymerization degree of 600-1600•2-50. EFFECT: raised rheological properties of oil-forcing reagent. 2 tbl

Description

 The invention relates to the field of oil production and can be used to increase oil recovery of carbonate and terrigenous flooded heterogeneous formations in conditions of maximum water cut in the late stages of oil field development.

 Known reagents for enhancing oil recovery in productive formations, which are water-soluble non-cross-linked polymer systems (M.L. Surguchev et al. Methods of oil recovery, M: Nedra, 1991, p. 117). The positive effect of the use of aqueous polymer non-crosslinked systems is achieved due to their special rheological and filtration properties in porous media, due to the non-Newtonian type of flow. The nature of the flow of polymer solutions is affected primarily by shear stress, the elastic properties of macromolecules, adsorption and mechanical capture of polymer particles by a porous medium.

 Also known are reagents for enhancing oil recovery based on crosslinked polymer systems, which, due to the presence of gel fractions in them, form elastoplastic particles uniformly distributed in water. When injected into the formation, these particles fill the largest pores and cracks and easily overcome the narrowing of the pore channels of inhomogeneous high-permeability formations and block (clog) them. Less permeable areas of formations are generally not exposed to these particles. This makes it possible in the future, when water is injected into the formation, to more fully cover less permeable areas of the reservoirs, which leads to a decrease in oil water cut, increased production and enhanced oil recovery (M. L. Surguchev et al. Methods for oil recovery, M .: Nedra, 1991 ., p.123).

 However, most water-soluble crosslinked and non-crosslinked polymer systems that effectively block highly permeable reservoir areas suffer from a serious drawback, namely, at high shear stresses and high degrees of mineralization of formation waters, they practically lose their viscosity characteristics and have insufficient thermal oxidative stability in fresh and highly mineralized produced waters, which leads to in most cases, to the loss of their effectiveness.

 An oil-displacing reagent based on radiation-treated amyl compounds, for example polacrylamide, is also known. The specified reagent with a degree of hydrolysis from 4 to 40% wt. obtained by treating powdered polymers or copolymers of acrylic series with ionizing radiation at an absorbed dose of 0.5-3.0 Mrad (Russian Pat. N 2069256, class: E 21 B 33/138, 11/20/1996 g).

 The closest to the proposed reagent in technical essence and the achieved result is an oil displacing reagent, which includes polyacrylamide (non-crosslinked) 0.005-0.5% wt., Hydroxyethyl cellulose 0.05-1.5% wt., Water the rest (see patent RF N 2072034, class E 21 B 43/22 from 01.20.1997).

The disadvantage of this reagent is insufficiently high rheological characteristics and thermo-oxidative stability in fresh and highly mineralized waters at temperatures above 80 ^o With high shear stresses.

 The objective of the present invention is to improve the rheological properties of the oil-displacing reagent at high shear stresses and at high degrees of mineralization of formation water, as well as increasing its thermo-oxidative stability in fresh and highly saline produced waters.

The problem is solved in that the oil-displacing reagent for heterogeneous flooded formations, including polyacrylamide with a molecular weight of at least 1 • 10 ⁶ and a water-soluble cellulose ether, contains the specified polyacrylamide crosslinked, and as a water-soluble cellulose ether, carboxymethyl cellulose with a degree of substitution with degree 0 65-1.45 and a degree of polymerization of 600-1600 with the following content of components, wt.%:
The specified polyacrylamide crosslinked - 50-98
Specified carboxymethyl cellulose - 2-50
The choice of carboxymethyl cellulose to obtain an effective water-displacing reagent is due to the fact that it has a high thermal oxidative stability, forms gels rather quickly in fresh and mineralized water, and the resulting solutions have high viscosities, including at high shear stresses. In addition, carboxymethyl cellulose can be used as a flocculant (A.F. Nikolaev, GI Okhrimenko "Water-soluble esters" L-, Chemistry, 1979, p. 29). Polyacrylamide also has flocculating properties, and it is the sol fraction that possesses these properties (A.F. Nikolaev, G.I. Okhrimenko "Water-soluble esters" L-, Chemistry, 1979, p. 71). Oxyethyl cellulose does not possess such properties due to its nonionicity. At certain ratios of CMC with crosslinked PAA, a synergistic phenomenon is observed. This leads to an increased blocking ability of the reagent and an increase in thermo-oxidative stability in fresh and highly mineralized produced water at temperatures above 80 ^o C at high shear stresses.

The specified reagent is prepared by uniform mixing of cross-linked polyacrylamide (PAA), obtained under the influence of ionizing radiation by conventional doses or cross-linking chemicals (molecular weight 5 • 10 ⁶ , basic substance content 98% wt., Particle size less than 0.25 mm 8.5 % wt., gel time 20 min), with a water-soluble cellulose ether, for example CMC (basic substance content 99.5% wt., degree of substitution for carboxymethyl groups 1.3, sodium content 10.2% wt.). The resulting reagent is given the name "Ritin-10".

To check the effectiveness of reagent samples, their viscosity was determined on a Reotest-2 rotational viscometer at various strain rates. In a beaker with a capacity of 150 cm ^3, crosslinked powdered PAA with the above characteristics is weighed and dissolved in fresh water (distilled) with constant stirring at room temperature for 30 minutes. Then, at room temperature, powdered CMC with the above characteristics is added to the glass and dissolved with constant stirring until a viscous transparent liquid is formed. After dissolving the CMC, in the case of studying the thermal oxidative stability of the reagent, the resulting solution is kept in a thermostat at temperatures of 80-100 ^o C with an accuracy of (± 1 ^o C) for 2 hours, or a certain amount of saline water is added to the resulting solution with constant stirring (formation water East Perevalnoye field, mg / l: chlorine-ion-219, bicarbonate-ion-427, calcium-ion-100.2, magnesium-ion-146, Na + K-ion - 5016, total salinity 13465.2, pH 6, 3), incubated for 4 hours at room temperature or at temperatures of 95 ^o C with a point nosti (± 1 ^o C).

 The compositions of the reagent samples and their test conditions are presented in table 1.

As can be seen from the presented test results, the use of water-soluble CMC cellulose ethers in a mixture with crosslinked PAA (examples 3-5) makes it possible to increase the viscosity of the solutions of the obtained system in fresh water at the ratios PAA: CMC = 50-98: 2-50%, and increase resistance to the action of mineralization and temperatures above 80 ^o C (examples 8-9) compared with the prototype. At a low strain rate, 3 s ^-1 , the viscosity of the solution of the compositions PAA: CMC (example 4) is 20% higher than that of the prototype. At a high strain rate, 1312 s ^-1 (examples 3-5), by 34-41%. This is explained by the presence in the crosslinked PAA of both sol and gel fractions with flocculating and blocking properties, respectively. The use of CMC enhances the flocculating properties of the composition and, in addition, due to synergism, the rheological properties are at a higher level.

In order to determine the oil-displacing properties of the proposed reagent, comparative studies were conducted on bulk models of a two-layer heterogeneous permeability formation, which are two parallel metal tubes with a diameter of 3.2 • 10 ^-2 m filled with various fractions of sand. The permeability ratio was 4.56-5.06. The research results are presented in table.2. The research methodology was as follows: the reservoir models were evacuated, saturated with mineralized water, then oil was supplied, and then oil was displaced by mineralized water under vacuum. Next, a polymer solution or a mixture of polymers in mineralized water was pumped and the polymer rim was displaced by mineralized water, and then the oil recovery coefficient was calculated.

The results show a high efficiency of oil displacement from the reservoir model by the rims of a mixture of PAA with CMC. The increase in oil recovery ratio amounted to:
1) 35% compared to pure water flooding (experiment 1, table 2);
2) 11-22% compared with the individual use of the rims of the solutions of PAA or CMC (experiment 2-3, table 2);
3) 11% compared with the prototype (experiment 4, table 2).

Claims (1)

An oil-displacing reagent for heterogeneous flooded formations, including polyacrylamide with a molecular weight of at least 1 • 10 ⁶ and a water-soluble cellulose ether, characterized in that it contains the specified polyacrylamide crosslinked, and carboxymethyl cellulose with a degree of substitution of 5 with a degree of substitution of 5 for carboxymethyl cellulose with a degree of substitution of 5 for ⁵ -1.45 and a degree of polymerization of 600-1600 with the following content of components, wt.%:
The specified polyacrylamide crosslinked - 50 - 98
Specified carboxymethyl cellulose - 2 - 50

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