RU2396419C1 - Method for isolation of water production to producing oil wells - Google Patents

Abstract

FIELD: oil and gas production. ^ SUBSTANCE: invention refers to oil industry, particularly to a method for isolation of water production to production wells. In the method for isolation of water production to the producing oil wells, including injection of a gelling compound prepared by mixing polyacrylamide, carbamide, aluminium salt and water, said aluminium salt is solid aluminium pentahydroxychloride S-APHC containing low-molecular electrolyte - magnesium chloride, and when mixing, APHC and carbamide in the ratio 1:0.5 to 1:4 are mixed with 0.3% aqueous polyacrylamide - PAA taken in amount 0.35-0.5 wt %. ^ EFFECT: higher nonuniform reservoir recovery. ^ 3 ex, 3 tbl, 2 dwg

Description

The invention relates to the oil industry, in particular to the use of gelling compositions that occur in situ upon the introduction of polymer-colloidal complexes into the reservoir, and can be used to increase oil recovery of heterogeneous formations and isolate watered production wells.

Compositions of various chemical reagents are known, including polymeric ones, which form suspensions of dispersed particles in highly flooded interlayers, or visco-elastic, or gel-like systems, clogging washed channels and thus connecting oil-saturated zones to development [Manyryn V.N., Shvetsov I .BUT. Physico-chemical methods for flooding. ROING, Samara. 2002].

However, most of them have significant disadvantages, such as insufficient efficiency and a high concentration of expensive reagents in the injected solutions, the use of environmentally unsafe crosslinking agents, the rapid loss of viscoplastic properties in highly mineralized formation waters, and others. A progressive method of selective formation waterproofing is the use of gel-forming compositions using water soluble polymers.

A known composition injected into the reservoir, comprising a mixture of an anionic polymer and a salt of a polyvalent metal in an aqueous solution [US Pat. RF 2215870. Cl. 6 ЕВВ 43, publ. 2003], forming a dispersed system with small particle sizes in encapsulated form.

The disadvantage of this composition is the low concentration of the dispersed phase, its low efficiency in highly permeable zones of the formation.

A known method of developing a heterogeneous formation, which consists in injecting into the formation a dispersion of colloidal polymer particles and a crosslinking agent in the form of a salt of a polyvalent metal [US Pat. RF 2167981. Cl. 6 ЕВВ 43/22, publ. 2001].

As a result of the reaction between the components, a cross-linked polymer system of a spatial structure appears. Such a system eliminates, if necessary, the removal of the gel-forming composition from the wellbore (for example, in the case of premature formation of a crosslinked hydrogel). In addition, the use of chromium salts as a crosslinking agent, capable of oxidizing to the highly toxic form of Cr ⁺⁶ , imposes serious environmental restrictions on this composition.

There is a method of developing a heterogeneous oil reservoir by pumping dispersions of colloidal particles (hydrogel) formed by intramolecular crosslinking of polyacrylamide or polysaccharide or cellulose ether with aluminum polyoxychloride, which leads to a change in the filtration characteristics and oil-producing parameters of the heterogeneous reservoir, as well as to a method for improving manufacturability and processability [Pat. RF 2298088, Е21В, С09К. Publ. 2007].

The disadvantage of this method is that the composition is injected into the injection well not in the form of a solution, but in the form of a suspension of polymer powder and a solution of aluminum polyoxychloride. The resulting suspension is a free-dispersed system with a wide range of particle sizes of 0.1-5.0 microns. Because of this, it acts by purely mechanical blocking of channels of a certain size and does not have selectivity to water-saturated and oil-saturated zones. Such systems are notable for their low strength and low resistance to leaching. In addition, this method relates to injection wells, contributing to the alignment of the profile and increase the coverage of the formation during flooding, without affecting the water content of production wells.

A known method of regulating the development of a heterogeneous oil reservoir by sequentially injecting into the reservoir through injection wells the rims of fresh water, an aqueous solution of an alkaline reagent, fresh water, an aqueous solution of aluminum hydroxychloride and a water-soluble polymer - polydimethyldiallylammonium chloride [Pat. RF 2224092. Cl. ЕВВ 43. Publ. 2004]. The latter, when interacting with an aluminum salt, forms a hydrogel that fills cracks in the highly permeable intervals of the formation in the bottom-hole zone of injection wells. In this case, the permeability of the oil-saturated zone of the reservoir does not decrease, i.e. the gel has selectivity.

However, the gel-like precipitate formed as a result of the interaction of the components is a free-dispersed system with low strength, as evidenced by a decrease in viscosity from 4.5 to 0.2 Pa · s at a relatively small shear stress of ~ 10 Pa. The method involves a 4-fold sequential download of the components of the composition, which significantly lengthens and complicates the process. In addition, the method is intended to reduce the water cut of oil by increasing the coverage of the reservoir and regulating the profile of the injectivity of the well, without directly affecting the waterproofing of producing wells.

Closest to the proposed is a method in which to isolate water inflow to producing oil wells using a composition containing an aqueous solution of aluminum pentahydroxochloride, an aqueous solution of polyacrylamide with a polymer concentration of 0.1-1.0 wt.% And urea [Pat. RF 2348792. Cl. ЕВВ 33/138. Publ. 03/10/2009. Bull. No. 7]. In this case, the components are mixed and receive an aqueous solution of the composition in ratios, wt.%:

aluminum pentahydroxochloride 3-6 polyacrylamide 0.25-0.5 urea 7-14 water rest

The initial aqueous solution is pumped into the washed zones of the formation, where, under the influence of high temperature, an aluminum hydroxide gel is formed, which reduces the rock's phase permeability to water, while slightly changing the oil permeability, i.e. the composition has selectivity.

The disadvantages of this method include the following:

firstly, the initial working solution is prepared on the basis of an aqueous solution of aluminum salt - aluminum pentahydroxochloride, which is a colloidal solution with a basic substance content of 35-40%, the rest is water [Coagulant polyaluminium chloride “BOPAK-E, TU-216350-002- 39928758-02, Ecological Fund "Water of Eurasia", Yekaterinburg; Aluminum oxychloride. TU-2152-164-05763458-93 OJSC "Khimprom", Volgograd].

The production of this product is located at considerable distances from oil-producing enterprises, and therefore unproductive transportation costs arise for the transportation of actually ballast water;

secondly, the majority of oil producing enterprises are located in the Northern and Polar regions, which limits the possibility of delivering aqueous solutions of aluminum pentahydroxochloride during periods of low temperature seasons;

thirdly, the use of this composition containing aluminum pentahydroxochloride leads to a "decrease in the phase permeability" of water to production wells, however, water filtration does not stop completely.

The objective of the invention is to increase oil recovery by reducing water cut in produced products by selectively isolating water inflow in producing wells using a gel-forming composition with improved consumer properties.

When implementing the proposed method, the following technical result is obtained: firstly, a composition based on solid highly basic aluminum pentahydroxochloride (PHHA-T) having magnesium chloride [Pat. RF 2210539. MKP 6 С01, F 7/00, 08.20.03, “Aluminum oxychloride-T”, produced according to TU 2152-3120576 3458-04, AOOT “Khimprom”, Volgograd], polyacrylamide (PAA) and carbamide ( KA) forms a stable gel in a wide range of reservoir temperatures (60-95 ° C), which has a "locking" effect in the pore space with respect to water and causes the filtering of water to cease in highly permeable zones to production wells;

secondly, to prepare the working solution of the composition before injection into the well, solid components are used - dry PHHA-T, urea and granular polyacrylamide, which suggests the possibility of delivery of these reagents to their destination in any season, including at subzero temperatures;

thirdly, a solution of the composition can be prepared in any water (technical, produced, produced) and has a near-neutral reaction of the medium (pH = 5.5-6.0), therefore, it will not adversely affect the carbonate reservoir and metal production well equipment;

The technical result achieved is achieved in a method of isolating water inflow to producing oil wells, including pumping a gelling composition obtained by mixing polyacrylamide, carbamide, aluminum salt and water, characterized in that the solid aluminum pentahydroxochloride PHHA-T containing low molecular weight is used as an aluminum salt the electrolyte is magnesium chloride, and when mixed, PHHA-T and urea in a ratio of 1: 0.5 to 1: 4 are mixed with a 0.3% aqueous solution of polyacrylamide - PAA with a PAA content of Leave 0.35-0.5 wt.%.

The specified method provides the formation in reservoir conditions of a structured combined gel, in which the amphoteric aluminum hydroxide gel, structured by a polymer-colloidal complex, is distributed in the pore space of the water-saturated zone of the formation, blocking water-permeable channels and cracks, thereby preventing water from filtering into the producing well and contributing to connecting new oil-saturated zones of the reservoir to the displacement of oil from them.

The mechanism of formation of the polymer-colloidal complex (PAC) [I.A. Novakov, F.S. Radchenko, I.M. Papisov. High molecular weight compounds, 2003. T.A 45, No. 8. P.1340] consists in the intermolecular interaction of the polyacrylamide polymer chains with the surface of colloidal particles of the alumoxane structure (> A1-O-), with sizes of 10-40 nm, formed under certain conditions in aqueous solutions of aluminum pentahydroxochloride. The strength of such complexes is explained by the cooperative nature of the intermacromolecular bonds and depends on the specific surface of alumoxane particles of 1.7 · 10 ² m ² / g sol [Ozerin AS, Radchenko FS, Timofeeva GI, Novakov I. BUT. // Russian nanotechnology. 2009. V.4, No. 1-2, p.145], and the presence of interacting reaction centers in the polymer macromolecule (-COOH) and on the surface of alumoxane particles (> Al ⁺ -O-). The second important factor affecting the strength of the PAC is the conformation (form) of polyacrylamide macromolecules in solution. As is known, in aqueous solutions, PAA undergoes partial hydrolysis [Polyacrylamide. Ed. V.F. Kurenkova, M., 1992], as a result of which ionized carboxyl groups appear in the polymer chain. Because of this, even with their small amount, the polymer acquires the properties of a polyelectrolyte, the conformational behavior of which in solution is determined by ionic strength, i.e. the presence in the solution of low molecular weight inorganic salt ions. The solid PHHA used in the proposed method contains a low molecular weight electrolyte MgCl ₂ , which changes the ionic strength of the solution. This leads to the fact that the conformational set of macromolecules with unfolded tangles increases and the number of cooperative bonds with the surface of positively charged alumoxane particles increases. As a result of this, the density of the network of physical bonds of the amorphous gel that arises during the hydrolysis of PAC increases and the gel passes from a free-dispersed state to a structured system. Such a structured combined gel, being in the pore space of the water-saturated zone of the formation, not only reduces its phase permeability to water, but completely blocks the pore channels, stopping the filtration, i.e. has a "locking effect."

The invention is illustrated by the following examples.

Example 1. In this example, the effect of the type of aluminum salt and its ratio with urea on the microstructure of the gel and its viscoelastic properties is determined. Dry solid PHCA-T and urea are loaded into a 0.3% solution of polyacrylamide in the ratios indicated in Table 1 and in amounts that provide a total composition concentration of 16.7 wt.%. The prepared solution is poured into a recess in the form of transparent polystyrene with a diameter of 30 mm and a depth of 5 mm. Hermetically sealed form is placed in a thermostat and heated at 75 ° C until gelation is observed by the loss of fluidity of the composition. After cooling, disk-shaped samples are removed from the mold and transferred to the lower plate of the MFR-2000 vibration micro-Fourier rheometer (GBS, Australia), with which dynamic viscosity, elastic modulus and loss tangent are determined (Table 1). At the same time, microphotography of the surface of the samples was carried out using an optical modular motorized microscope Olimpus BX-61 C with fixation of KM microstructures using a digital microscope camera DP-12.

Figure 1 presents a micrograph of the surface of the gel based on PHCA-liquid, and figure 2 presents a micrograph of the surface of the gel based on PHCA-solid, magnification × 500. From microphotographs it follows that, in contrast to amorphous gels based on PHCA-liquid (figure 1), gels using PHCA-solid (figure 2) have a pronounced anisometric structure. This is due to the orienting effect of polyacrylamide macromolecules in a certain conformation caused by the presence of a low molecular weight polyelectrolyte in PHCA-T - MgCl ₂ .

From the data of Table 1 it follows that the gels based on PHCA have predominantly elastic properties (tgα = 0.05 ÷ 0.10), however, when using solid PHCA, the elastic modulus and viscosity of the gels are 2 or more times higher than for compositions with based on liquid PGA. An increase in the content of urea in the composition leads to a decrease in the gelation time and a certain decrease in the viscoelastic properties of the gels.

Example 2. In this example, the effect of gelation temperature and the ratio of PHCA-T: urea on the gelation time is determined. The calculated PHCA-T and urea weights in the weight ratios indicated in Table 2 are loaded into glass tubes and an aqueous 0.3% (wt.) Solution of polyacrylamide is added based on the formation of a concentration of the composition of 16.7 wt.%. After the formation of a clear solution, the contents of the tubes are heated in a thermostat at a temperature of 65, 70, 75, 80, 85, 90 ° C, fixing the moment of gel formation by yield loss.

table 2 The effect of the ratio of PHCA-T: KA (mass.) And temperature on the gelation time No. p / p Gelation temperature, ° С PHHA-T: KA (wt.) Gelation time, h one 65 1: 3 18.0 2 70 1: 2 7 3 75 1: 2 6.0 four 80 1: 0.5 11.0 5 80 1: 1 6.0 6 80 1: 2 3.0 7 80 1: 3 2.0 8 80 1: 4 1,5 9 85 1: 2 1.3 10 90 1: 2 1,2

From the data of the table it follows that the time of gelation or the viability of the solution of the composition depends on the amount of hydrolyzing agent - urea. The temperature determines the rate of urea hydrolysis and, as a result, the time until gel formation. Thus, at a given temperature, the PHCA-T: KA ratio necessary for delivering a solution of the composition to the water-saturated interval of the formation in which the gel appears can be selected.

Example 3. In this example, the dependence of the filtration ability of the formation model on the composition of the gel-forming composition is determined, in which physical and chemical processes occur under conditions of the formation at elevated temperatures and pH, accompanied by the formation of a dispersed aluminum hydroxide system as a result of hydrolysis of aluminum salt - aluminum pentahydroxochloride in accordance with the equation:

Al ₂ (OH) ₅ Cl + H ₂ O → 2Al (OH) ₃ ↓ + HCl

The waterproofing properties of aluminum hydroxide gels were studied on a bulk model of the formation in the form of a layer of quartz sand, as one of the natural layers of terrigenous sedimentary rocks that are part of oil-saturated reservoirs. Permeability was used as the main parameter evaluating the effect on the waterproofing properties of aluminum hydroxide gels. Permeability - the ability of a porous body, penetrated by many capillaries and cracks, to pass fluids through itself, in this case water. The study of the waterproofing properties of aluminum hydroxide gels was carried out in a glass column with a heated jacket filled with a layer of sand, in which the required temperature was maintained using a thermostat. The sand was pre-fractionated using sieves and a fraction with a grain size of 0.32 mm was used. All experiments were carried out at a temperature of T = 75 ° C. A solution of the composition was poured into the column and, after gel formation in the entire volume of sand filling in the bottom column, water was taken through a tap to the measuring cylinder, while water was supplied to the column from above, through a dropping funnel at a rate that ensured a constant liquid level above the sand. The process of filtering water in a porous medium is due to the presence of cracks and washed capillary channels in it. The structured gel filling them during the well treatment with the proposed composition and representing a non-fluid body with a high modulus of elasticity causes a “blocking effect” in the pore space. As follows from the data in Table 3, the rate of water filtration through the bulk model processed by the proposed composition is 50-150 times lower than for the prototype composition, which practically means the complete cessation of water filtration through the bulk model.

Table 3 Filtration characteristics of a reservoir model treated with various compositions No. p / p The composition, wt.% The volume of filtered water, cm ³ Filtration time through the model processed by the composition, min * Filtration rate, cm ³ / min Waterproofing effect 1 prototype PGA - 3 (liquid)
KA - 7
PAA - 0.25 Water - the rest one hundred 94 1.05 Permeability limitation 2 PGA - 2 (solid)
KA - 4
PAA - 0.25 Water - the rest 2,5
stop filtering 120 0.02 Locking effect 3 PGA - 4 (solid)
KA - 8
PAA - 0.50 Water - the rest 1,0
stop filtering 120 0.008 Locking effect * Filtration time of 100 cm ^{3 of} water through an unprocessed model - 1, 2 min

Claims (1)

A method of isolating water inflow to producing oil wells, including pumping a gelling composition obtained by mixing polyacrylamide, carbamide, aluminum salt and water, characterized in that the aluminum pentahydroxychloride PHHA-T, which contains a low molecular weight electrolyte - magnesium chloride, is used as an aluminum salt, and when mixed, PHCA-T and urea in a ratio of 1: 0.5 to 1: 4 are mixed with a 0.3% aqueous solution of polyacrylamide - PAA with a PAA content of 0.35-0.5 wt.%.

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