RU2440485C1 - Insulation method of water influx to production oil wells - Google Patents

Abstract

FIELD: oil and gas industry. ^ SUBSTANCE: insulation method of water influx to production oil wells involves pumping of gel-forming compound prepared by introducing the carbamide to polymer-colloidal complex obtained by mixing of water colloidal solution of aluminium pentahydroxochloride with 0.20.3 wt % of water solution of polymer; at that, as polymer there used is weakly charged cationic polyelectrolyte with molecular weight of 6106-20106 and content of cationic groups of 1.65 to 9.20% molar. ^ EFFECT: increasing oil production owing to reducing water content of extracted products. ^ 4 tbl, 5 ex, 1 dwg

Description

The invention relates to the oil industry, in particular to the use of gelling compositions that create a water insulating screen in highly permeable washed zones of the formation, preventing the penetration of water into production wells.

Usually inorganic salts, acids and bases (chromium and aluminum salts, sodium silicate, etc.) are used as components of gel-forming compositions, reacting in situ with alkaline reagents to form gel-like precipitates that reduce phase permeability in water [N. Surguchev. Residual oil recovery methods. M .: Subsoil. 1993; Mamyrin V.N., Shvetsov I.A. Physico-chemical methods for flooding. Samara ROING. 2002].

Limiting water inflow, these gel-like precipitations are characterized by low rheological properties, which is why they have insufficient efficiency and low durability. Improving the operational properties of the gels is achieved through the introduction of special additives - surfactants, polyglycerols and water-soluble polymers [USSR Patent 1654554, MKI E21B 43/22, publ. 1998; G. Oilfield business. 2002. No. 4, p.11; Altunina L.K., Kuvshinov V.A. Physicochemical technologies for enhanced oil recovery (review). Chemistry for sustainable development. 2001. No. 9. P.331]. However, in all these cases, the gel-like precipitate that arises under certain conditions is a free-dispersed system with particle sizes of 20–25 μm and is characterized by a low static shear resistance, which results in its relatively rapid washing out of channels and fractures in the formation.

Improving the properties of gel-forming compositions can be achieved by introducing into their composition water-soluble polymers and their crosslinking salts of chromium and aluminum.

A known method of developing a heterogeneous formation by injecting into it a dispersion of polymer particles and a crosslinking agent, which is used as salts of a polyvalent metal [RF Patent 2167981, MKI E21B 43/22. Publ. 2001]. As a result of the reaction between the components, a chemically cross-linked polymer system with increased strength arises.

However, such a system eliminates the possibility of removing, if necessary, a gel-like composition from the wellbore in case of premature formation of a crosslinked hydrogel. In addition, the oxidation of chromium salts to the highly toxic form of Cr ^{+6 over time} limits the practical use of this composition for environmental reasons.

There is a method of developing an inhomogeneous formation by injecting into it particles of hydrogel formed during intramolecular crosslinking of polyacrylamide and cellulose ether with aluminum polyoxychloride, which is accompanied by a change in the filtration characteristics of the inhomogeneous formation and increasing the processability and environmental friendliness of the method [RF Patent 2298088, MKI E21B, C09K, publ. 2007].

The disadvantage of this method is the injection into the injection well of not a reagent solution, but a suspension of polymer powder and a solution of aluminum polyoxychloride, resulting in a free-dispersed system with a wide range of different particle sizes from 0.1 to 5.0 microns, the action of which reduces to mechanical blockage of the channels a certain size without pronounced selectivity to water-saturated zones of the reservoir. In addition, this method relates to injection wells, is designed to align the profile and increase the coverage of the formation by water flooding and does not affect the water cut of production wells.

A known method of regulating the development of a heterogeneous formation of sequential injection of rims of fresh water, an aqueous solution of aluminum hydroxychloride, an alkaline reagent, fresh water and a water-soluble polymer - polydimethyldiallamonium chloride [RF Patent 2224092, MKI E21B 43, publ. 2004].

The disadvantage of this method is that the gel-like precipitate formed is a free-dispersed system with low strength, as evidenced by a drop in the gel viscosity from 4.5 Pa · s to 0.2 Pa · s with a small shear stress of 10 Pa. The method involves the separate injection of reagents, in which the process of mixing them in the well becomes uncontrolled, and the polymer used, which acts as a flocculant, under such conditions cannot guarantee the formation of a uniform and dense deposit. In addition, this method is intended to increase the coverage of the formation by water flooding and does not directly affect the water cut of production wells.

Closest to the proposed is a method in which to isolate water inflow to producing oil wells, a gel-forming composition is injected containing an aqueous solution of aluminum pentahydrochloride, an aqueous solution of polyacrylamide and urea. In this case, the components are mixed in proportions, wt.%:

Aluminum pentahydrochloride 3-6 Polyacrylamide 0.25-0.50 Urea 7-14 Water Rest

[RF patent 2348792, MKI E21B 33/138, publ. 2009].

The solution obtained by mixing is pumped into the washed zones of the formation, where, under the influence of temperature, an aluminum hydroxide gel is formed, which reduces the rock phase permeability of the rock to water, while slightly changing the oil permeability, thus ensuring the selectivity of the action.

The disadvantages of this method include the following:

First, the polyacrylamide used in this composition is characterized by a relatively low molecular weight (1 ÷ 2 · 10 ⁶ ) and is characterized by low resistance to hydrolysis. Already in the process of acrylamide polymerization, the obtained commercial product polyacrylamide contains a small amount of carboxyl groups [Abramova LN, Bayburdov TA, Grigoryan E.P. et al. Polyacrylamide. Ed. V.F. Kurenkova. M .: Chemistry. 1992]. In dilute aqueous solutions, their content increases and the “nonionic” (by brand) polyacrylamide becomes weakly anionic. At the same time, it was shown that the interaction of aluminum pentahydroxyl chloride with anionic polyelectrolytes leads to the formation of insoluble polycomplexes [Novakov IA, Radchenko FS, Ozerin AS, Rybakova EV Bulletin of Volgograd State Technical University. Interuniversity. Sat Ser. chemistry and technology of organoelement monomers and polymeric materials. AT 5. 2008. No. 1. P.150] not suitable for use as a waterproofing gelling composition.

Secondly, the molecular weight of the polycrylamide used is relatively low, while at the same time it plays a large role in the formation of coagulation structure gels, the higher it is, the lower the dosage of polymer and the stronger the network of intermolecular bonds.

Thirdly, the use of this composition based on polyacrylamide leads to a "decrease in the phase permeability" of water to production wells, however, water filtration does not stop completely and can lead to gradual leaching of the gel and a decrease in the filtration resistance of the waterproofing screen, i.e. reducing the durability of the gel composition.

The objective of the invention is to increase oil recovery by reducing water cut of produced products by isolating water inflow to production wells using a gel-forming composition with improved technological properties, as well as expanding the range of water-soluble polymers suitable for use in this composition.

When implementing the proposed method receive the following technical result:

firstly, a composition based on aluminum pentahydroxochloride (PHCA), carbamide (KA) and a water-soluble polymer forms a stable structured gel in a wide range of reservoir temperatures (65–85 ° C), which has a “blocking effect” in the pore space of the terrigenous reservoir with respect to water and causes the cessation of water filtration through highly permeable zones to production wells;

secondly, to prepare the working solution of the composition before injection into the well, a water-soluble polymer is used, which is a high molecular weight, low-charged cationic polyelectrolyte (SCPE) with a cationic charge of +1.65 to + 9.20 mol.%, showing high adhesion to terrigenous rocks of the formation in permeable areas;

thirdly, as SKPE use the so-called widely used and produced by domestic and foreign manufacturers high molecular weight flocculants (“superflocculants”) with a wide range of specific properties, which allows optimizing the composition of the composition taking into account the characteristics of the rocks of oil-saturated reservoirs;

fourthly, the initial solution of the composition can be prepared in any water (natural, technical, commercial, formation) with a salt content of up to 40 g / l and has a near-neutral reaction of the medium (pH 5.5-7.0), which does not render negative corrosive effects on the metal equipment of wells;

fifthly, the use of high molecular weight SLE with a molecular weight of 6 · 10 ⁶ -20 · 10 ⁶ determines a high degree of cooperative bonds in the polymer-colloidal complex and the associated high strength of the structured gel formed from it (“in situ”).

The technical result achieved is achieved in a method of isolating water inflow to production wells by pumping a gelling composition obtained by mixing aluminum pentahydroxochloride, urea and an aqueous polymer solution, the mixture being carried out by introducing urea into a polymer-colloidal complex obtained by mixing an aqueous colloidal solution of aluminum pentahydroxochloride with 0.2 ÷ 0.3 wt.% - with an aqueous solution of the polymer, and a weakly charged cationic polyelectrolyte with a molecular m ssoy 6 x 10 ⁶ -20 x 10 ^6, and the content of cationic groups of from 1.65 to 9.20 mol.%.

The specified method provides the formation in the water-saturated zone of the formation of a structured gel in which an inorganic amphoteric aluminum hydroxide gel, enhanced by bonds of dispersed particles with polyelectrolyte macromolecules, is distributed in the pore space of the rock, not only reducing its phase permeability to water, but almost completely stops water filtration , i.e. has a "locking effect."

The mechanism of formation of the polymer-colloidal complex (PAC) that arises in the initial solution when pentahydroxochloride is mixed with a solution of a polyelectrolyte consists in the intermolecular interaction of colloidal aluminum hydroxide particles with polymer macromolecules due to non-covalent bonds of various nature (hydrophobic, donor-acceptor, hydrogen). In this case, the most long-range - ionic, depending on the sign of the charge (opposite or the same) will enhance this interaction or counteract it. The interaction of positively charged colloidal particles of PHA with negatively charged macromolecules (polyanionites) is very strong, leading to a sharp compaction of macromolecules and the loss of their affinity for the solvent in water. The result is the formation of strong, but insoluble polycomplexes. The interaction of these particles with positively charged macromolecules (polycationites) leads to the opposite effect - repulsion of the same charged particles and polymer macromolecules, as a result of which the formation of PAC becomes impossible. A characteristic feature of these PACs is that they are prepared using cationic polyelectrolytes with a molecular weight (6 · 10 ⁶ -20 · 10 ⁶ ) and cationic groups from +1.65 to + 9.20% molar, preferably acrylamide copolymers are used - lightly charged with the content of cationic groups from +1.65 to +9.20 mol.%). With a high molecular weight of such polymers (6 · 10 ⁶ -20 · 10 ⁶ ) and a rare arrangement of cationic groups in the polymer chain, the latter contains extended regions without ionogenic groups that form non-covalent bonds with the surface of colloidal PHCA particles. The resulting PAC, which contains positively charged groups, has a high affinity for the negatively charged surface of silica, which is part of terrigenous rocks. The consequence of this is the increased adhesion of the structured gel to the rock, which determines its resistance to leaching from fractures and pores of the formation.

Example 1. In this example, the effect of the type of polyelectrolyte on its adsorption properties with respect to silica is due to. As a material containing silica (SiO ₂ ), use quartz sand, specially processed according to the method [Persiyantsev M.N., Kabirov M.M., Lenchenkova L.E. Enhanced oil recovery in heterogeneous formations. Orenburg Orenburg Book Publishing House. 1999] and fractionated (0.30-0.40 μm).

Solutions of polymers of various concentrations in a volume of 100 cm ^{3 are} poured into conical flasks with 20 g of quartz sand and placed on a shaker.

Periodically, samples of solutions were taken from the flasks, clarified in a centrifuge (n = 6000 s ^-1 ), and the viscosity was measured on a capillary viscometer. Samples are taken to a constant viscosity, i.e. before the onset of static adsorption equilibrium. Preliminary build calibration graphs of the dependence of viscosity on concentration for each test copolymer. Based on these graphs, the residual polymer concentration in the solution after adsorption and the adsorption value are determined:

where A is an indicator of polymer adsorption, mg / g;

With _about - the initial concentration of the polymer, g / DL;

C is the concentration after adsorption, g / dl;

V is the volume of the solution, l;

m is the mass of quartz sand, g.

The drawing shows the dependence of adsorption on the concentration of polymers in the solution: 1 - Praestol 851BC, 2 - PAA, 3 - Superfloc / V 300 LMW, from which it follows that the weakest cationic Praestol 851 BC copolymer has the maximum adsorption rate and its ultimate value. Non-ionic PAA and anionic Superfloc / V 300 LMW are significantly inferior to it in adsorption properties.

Example 2. In this example, due to the influence of the concentration of SCPE in the composition on its waterproofing properties. As SCPE, Praestol 851BC is used, which has a high molecular weight and a small cationic charge of +6.9 mol%. As a model of the formation, quartz sand processed according to Example 1 is used, which is poured onto the porous bottom of a glass column with a jacket heated from an external thermostat.

A solution of the composition in the amount of 1 pore volume of the bulk model is poured into a column of silica sand and kept at a given temperature until gel forms in the entire volume of the model. To determine the gelation time in parallel in glass tubes, compositions of similar composition are heated, visually (by loss of fluidity) fixing the moment of the transition of the solution into gel. After gel formation, water is supplied to the column from the top from a dropping funnel, maintaining its constant level above the surface of the sand, while simultaneously taking water from the bottom of the column into a measuring cylinder.

Permeability is used as the main parameter that evaluates the waterproofing properties of the model treated with the composition.

Permeability coefficient:

where Q is the flow rate of water passing through the bulk model (m ³ · s ^-1 );

L is the height of the model layer (m);

µ is the viscosity of water (Pa · s);

Δp is the pressure drop in the model layer (Pa);

S is the cross-sectional area of the bulk model (m ² ).

, %The waterproofing effect is calculated by the formula:

%

where k _o is the permeability of the model in the initial state (μm ² );

k _o - the same after treatment with the composition (μm ² ).

Table 1 The effect of the concentration of SKPE (Praestol 851 BC) in the composition on the effect of waterproofing. The ratio of PGA: KA = 1: 1 (wt.), Temperature 80 ° C No. p.p. The concentration of SKPE, wt.% Filtration rate, cm ³ / s k penetration. (μm ² ) W% one 0 0.139 11.10 0 2 0.05 0.134 10.70 33.00 3 0.10 0,057 4,54 68.00 four 0.12 0.018 1,50 90.50 5 0.15 0.003 0.24 97.80 6 0.20 1.3 · 10 ^-4 0.011 99,99 7 0.30 1.1 · 10 ^-4 0.009 99,99

From the data of table 1 it follows that the resistance to water filtration through the model processed by the composition depends on the amount of polymer in the composition, which is associated with the amount of PAC formed from this polymer. The maximum decrease in the rate of water filtration corresponds to the concentration of SCPE in the solution of 0.2 wt.% And higher.

Example 3. In this example, the effect of the amount of PHCA in the composition as a source of the dispersed phase in the resulting gel, which provides resistance to water filtration through the reservoir model, is determined. The experiment is carried out analogously to example 2, using a 0.2% solution of Praestol 851BC, preparing a composition with different content of PHA, as shown in table 2.

table 2 The effect of the concentration of PHCA in the composition on the effect of waterproofing. The concentration of Praestol 851BC is 0.2 wt.%, The ratio of PHCA: KA = 1: 1 (wt.), Temperature 80 ° С No. p.p. The concentration of PHA, wt.% Filtration rate, cm ³ / s k penetration. (μm ² ) W% one 0 0,069 5.55 50.00 2 4.0 0,041 3.27 70.50 3 5.3 0.003 0.25 97.70 four 6.0 1.2 · 10 ^-4 0.01 99,99 5 8.3 0.6 · 10 ^-4 0.005 99,99

As follows from the data in Table 2, the rate of water filtration decreases significantly with an increase in the content of PHCA in the composition, and at a concentration of 6.0% or more, the filtration completely stops.

Example 4. In this example, the influence of temperature and mass ratio (PHCA: KA) on the gelation time (time of the transition of the solution of the composition into a gel state) is determined. In the experiment, the calculated weights of PGA and KA corresponding to the given ratios (Table 3) were loaded into glass tubes, a 0.2% Praestol 851BC solution was added. The contents of the tubes are heated in a thermostat at a given temperature, fixing the moment of gel formation by yield loss.

Table 3 The effect of the ratio of PGA: CA and temperature on the gelation time. The concentration of PHA - 6.0 wt.% No. p.p. The ratio of PHA: KA, wt. Gelation time at temperature, (hour) ° С 65 70 75 80 85 one 1: 0.3 52.0 24.0 16,0 10.0 8.0 2 1: 0.5 42.0 16,0 12.0 6.5 5,0 3 1: 1 20,0 11.5 8.0 4,5 3.0 four 1: 2 18.0 10.0 6.0 4.0 2.5 5 1: 3 14.0 9.0 5.5 2.2 2.0 6 1: 4 12.0 8.0 5,0 2.1 1.8

From the data of table 3 it follows that the gelation time is determined by temperature and depends on the amount of hydrolyzing agent - urea. Thus, for each temperature in the reservoir conditions, it is possible by selecting the PGA: KA ratio to select the desired technological time for delivering the composition to a given interval of the reservoir.

Example 5. In this example, the effect of the type of polyelectrolyte on the possibility of the formation of soluble PAC and on the waterproofing properties of the structured gel obtained on its basis is determined. As water-soluble polymers, copolymers of acrylamide with cationic and anionic comonomers in the form of commercial products of the Praestol, Organopol, Zetag, Superfloc series, as well as nonionic polyacrylamide and 100% polycationic CF-99 are used. The experiment is carried out by analogy to example 2, using 0 , 2% polymer solution at a concentration of PHCA 4.0 wt.%, The ratio of PHCA = 2: 1 (wt.) And a temperature of 80 ° C.

Table 4 The influence of the type of water-soluble polymer on the formation of the polymer-colloidal complex and the waterproofing properties of the gel based on it No. p.p. Type of polymer The content of cationic groups, mol.% The formation of polymer-colloidal complex Filtration rate, cm ³ / s k penetrators. (microns) W% one Pure SiO ₂ - - 0.139 11.10 0.00 2 Gel PHHA - - 0,028 2.22 80.00 3 PAA (prototype) 0 soluble 0.009 0.72 93.50 four Organopol 6400 +1.65 soluble 1.4 · 10 ^-4 0.01 99,99 5 Organopol 6405 + 2.94 soluble 1.3 · 10 ^-4 0.01 99,99 6 Praestol 611BC +6.52 soluble 1.4 · 10 ^-4 0.01 99,99 7 Praestol 851BC +6.90 soluble 1.3 · 10 ^-4 0.01 99,99 8 Zetag 92 + 9.20 soluble 1.4 · 10 ^-4 1.12 89.80 9 Praestol 650 +19.20 not formed 0,020 1.13 85.60 10 KF-99 +100.0 not formed 0,030 2,4 78.30 eleven Praestol 2500 -1.10 partially formed 0.012 0.96 91.35 soluble 12 Superfloc N 300 -3.73 insoluble 0,025 1.92 82.70

From the data in Table 4 it follows that the anionic copolymers (11 and 12) form insoluble polymer-colloidal complexes that precipitate from the solution before the gelation process, as a result of which hydrolysis in the presence of urea produces an amphoteric aluminum hydroxide gel with a low waterproofing effect at the level of PHCA and PAA (2 and 3). Polymer-colloidal complexes based on cationic copolymers are formed to a certain maximum content of cationic groups (6.9 mol%) in them, above which complexes are not formed due to strong electrostatic repulsion between positively charged colloidal particles of PHA and macromolecules of polycationionite. The gel arising in this case during hydrolysis is a mechanical mixture of an amphoteric gel of aluminum hydroxide and a copolymer solution with low waterproofing properties (8, 9, 10). Copolymers with a low content of cationic groups (4-7) form stable soluble polymer-colloidal complexes with colloidal particles of PHCA, which upon hydrolysis with urea give structured gels with high waterproofing properties. The permeability coefficient of a saturated model treated with such compositions is reduced by more than 1000 times, which leads to a blocking effect of such compositions when the water filtration practically stops. A positive point is also a fairly wide range of suitable for these purposes commercial copolymers with a low content of cationic groups.

Claims (1)

A method of isolating water inflow to producing oil wells, including pumping a gelling composition obtained by mixing aluminum pentahydroxochloride, urea and an aqueous polymer solution, and mixing by introducing urea into a polymer-colloidal complex obtained by mixing an aqueous colloidal solution of aluminum pentahydroxochloride with 0.2-0, 3 wt.% - aqueous solution of the polymer, characterized in that the polymer is used lightly charged cationic polyelectrolyte with a molecular weight of 6 · 10 ⁶ -20 · 10 ⁶ and holding cationic groups from 1.65 to 9.20 mol.%.

Images