RU2348792C1 - Method of selective water shut-off within producing oil wells - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil-producing industry, specifically to method of selective water shut-off within producing oils well with using gelling compositions. According to method of selective water shut-off within producing oils well by pumping-in gelling composition produced from mixed polyacrylamide, carbamide, aluminium salts and water. Aluminium salt is aluminium pentahydroxocloride. The specified mixture is carried out while carbamide is introduced into polymer- colloidal complex produced from mixed aqueous solution of polyacrylamide and aqueous colloidal solution of aluminium pentahydroxocloride is ratio as follows, wt %: aluminium pentahydroxocloride 3-6, polyacrylamide 0.25-0.5, carbamide 7-14, water - the rest.

EFFECT: higher reservoir recovery.

2 dwg, 5 ex, 4 tbl

Description

The invention relates to the oil industry, in particular to the use of gelling compositions that occur in situ when polymer-colloidal complexes are introduced into the reservoir through production wells.

The vast majority of enhanced oil recovery methods are based on water flooding. A breakthrough of injected and produced water in zones with high filtration characteristics leads to the formation of washed areas through which water is subsequently filtered, bypassing low-permeable oil-containing areas of the reservoir. At the same time, the proportion of oil recovered from the reservoir decreases, and its degree of water cut increases.

Known methods and reagents used to increase oil recovery, the essence of which is to pump reagents into the formation, forming a waterproofing screen in a highly flooded layer that prevents the penetration of water into production wells [Manyryn V.N., Shvetsov I.A. Physico-chemical methods for flooding. ROING. Samara 2002].

However, most of them have significant disadvantages, such as the high cost of the reagents used, the deterioration of the environmental situation in ground and surface waters, poor manufacturability and low durability of the formed protective screens. A progressive method of selective water isolation of formations is the use of gelling compositions of an organic, inorganic or mixed organomineral nature.

Known gel-forming compositions based on polyacrylamide and crosslinkers - salts of trivalent chromium [US Pat. 2180039 RF, class Е21В 43/22, 2002], for which the gel time is preliminarily calculated according to a mathematical model that describes the behavior of the polyacrylamide-potassium alum-mineralized water system. This time should be longer than the injection time of the composition into the well.

However, it is necessary to take into account many parameters (molecular weight of polyacrylamide, its degree of hydrolysis, polymer and crosslinker concentration, temperature and pH of the medium, porosity and permeability of the rock, etc.), to determine the kinetic parameters of the gelation process. In addition, the disadvantage of the composition is the presence in it of chromium salts, which are a highly toxic component.

Known methods of oil production with insulation work using a mixture of a solution of polyacrylamide and a crosslinker - aluminum salts [Surguchev ML et al. Methods for the extraction of residual oil. M .: Subsoil. 1993]. Aluminum salts are cheap and environmentally friendly, but the rate of crosslinking of polyacrylamide with aluminum is much higher than the crosslinking of chromium, which makes it difficult to control the gelation time. In addition, one more drawback is characteristic of both compositions: high salt and mechanical degradation of polyacrylamide, which leads to a decrease in gel strength and its rapid washing out of the interlayer.

A well-known inorganic gel used for waterproofing washed zones of a formation: namely, an aluminum hydroxide gel, which is formed by interaction with formation water of aluminum sulfate [Ibragimov G.E., Khisamutdinov N.I. A reference guide on the use of chemicals in oil production. M .: Subsoil. 1983] or when aluminum-containing wastes are injected into the formation [A. p. 1550107 USSR, cl. ЕВВ 43/22].

However, the resulting gel has low strength and adhesion to the formation rock and, as a result, is not effective enough. There is a method of developing oil fields by flooding it with the injection of an aqueous solution of chloride or aluminum nitrate, while carbamide is added to the solution [Application 93007659 of the Russian Federation, 1995]. Instead of aluminum salts, it is also proposed to use aluminum-containing waste from petrochemical industries [Pat. 2120544 RF, class ЕВВ 43/22, 1998].

However, the method requires a strict sequence of technological methods, is accompanied by the release of a large amount of heat and gaseous hydrogen chloride and is not effective enough. In addition, the use of aluminum-containing wastes from chemical industries carries the risk of contamination of produced and surface waters with highly toxic organic substances.

Closest to the proposed is a method in which to isolate water inflow to wells, a composition is used containing aluminum chloride with a concentration of 0.4-17.0 wt.%, Urea with a concentration of 1.5-30.0 wt., Polyacrylamide with a concentration of 0, 5-2.5 wt., So that the viscosity of the composition was not less than η> 10 · 10 ^-3 Pa · s, and water up to 100%. The initial composition is pumped into the washed zones of the formation, where, under the influence of high temperature, an aluminum hydroxide gel is formed, the viscosity of the medium increases, which leads to "attenuation" of the fluid filtration through the highly porous zone (Pat. 2076202 RF, class E21B 49/22, publ. 03/27/97.)

The disadvantages of this method include the following:

firstly, the urea hydrolysis reaction leading to an increase in the pH of the solution and the formation of an aluminum hydroxide gel proceeds at 90 ° C. It is also known that a decrease in temperature for every 10 ° C leads to an increase in gelation time by a factor of 2–3. Even the 36 hours provided in this method for gel formation is a long period during which the well must be withdrawn from the main production cycle;

secondly, the initial injected composition has a pH of 3.4 and, in the case of a carbonate reservoir, can lead to a violation of the protolytic balance in the formation rock and negative consequences in the permeability and filtration characteristics of the latter;

thirdly, the resulting aluminum hydroxide gel is a polydisperse system with low and uneven adhesion to the formation rock, although the introduction of polyacrylamide improves the adhesion characteristics, however, in general, the resulting system is freely dispersed and can be gradually washed out from the reservoir by injection or formation water ;

fourthly, the waterproofing effect of this composition is not high enough, as evidenced by the data on the redistribution of injected water flows through core-filled columns before and after their treatment with the proposed composition. The maximum achieved value is 55 with a very high content of the composition in solution (30% urea, 17% AlCl ₃ and 2.5% polyacrylamide), which is not economically viable. At lower reagent contents (19.1% and 2.4%), water filtration is reduced by only 8-12 times.

The objective of the invention is to increase oil recovery by reducing the water content of produced products by selective isolation of water inflow in producing wells.

When implementing the proposed method receive the following technical result:

firstly, the gel-forming composition based on aluminum pentahydroxochloride (PHCA) has a higher pH value (4.5-5.5) compared to compositions based on aluminum chloride (pH 3.4), therefore, it will have a less negative effect on carbonate reservoir and low corrosive effects on the equipment of production wells;

secondly, a stable long-lived gel is formed at relatively low temperatures (70 ° C or less) in a relatively short period of time (6-8 hours), sufficient to reach the initial solution of the isolated zones of the collector;

thirdly, during the interaction of PHCA with polyacrylamide in the initial solution, a polymer-colloidal complex (PAC) is formed almost instantly, and the urea introduced during the preparation of the initial solution does not affect this process. The resulting homogeneous solution has a low viscosity (~ 20 MPa · s) and is easily pumped into the well by conventional pumping equipment;

fourthly, the hydrolysis of urea and the hydrolysis of aluminum salt caused by it occurs according to the usual mechanism in reservoir conditions [Altunina L.K., Kuvshinov V.A. Inorganic gels to increase oil recovery from high temperature formations / Oil industry. 1995. No. 4, p. 36-38], however, the polymer-colloidal complex gel is already present in the system, as a result of which there is a stable dispersed gel-in-gel system (combined gel), which is characterized by high strength and resistance to leaching;

fifthly, the combined gel is characterized by high hydrophilicity and affinity for water-saturated interlayers, which leads to its strong fixation in these areas, at the same time it has low adhesion to low-permeable oil-saturated layers of the formation and practically does not change their permeability, which determines the selective effect of this composition, resulting to increase oil recovery.

The technical result achieved is achieved by the fact that in the method of selective isolation of water inflow to an oil well by pumping a gelling composition obtained by mixing polyacrylamide, urea, aluminum salt and water, aluminum pentahydroxochloride is used as the aluminum salt, and this mixing is carried out by introducing urea into the polymer colloidal the complex obtained by mixing an aqueous solution of polyacrylamide with an aqueous colloidal solution of aluminum pentahydroxochloride in the following ratio and components in wt.%:

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

The specified composition in the formation water turns into a combined gel, in which the amphoteric aluminum hydroxide gel is distributed in the network structure of the polymer-colloidal complex gel, which leads to its hardening and resistance to leaching from the water-saturated zone of the formation.

The isolation selectivity is achieved due to the fact that the formed long-lived gel is fixed in the water-saturated part of the collector, and almost the entire gel is washed out of the oil-saturated part. At the same time, conditions are created for the well to work with increased depressions, which contributes to a more complete extraction of oil.

The polymer-colloidal complex is obtained by mixing a 0.1-1% aqueous solution of polyacrylamide with an aqueous colloidal solution of aluminum pentahydroxochloride at a molar ratio of Al ³⁺ : polyacrylamide unit is equal to (2-4): 1 at a temperature of 20-30 ° C. The reason for the formation of the polymer-colloidal complex is the intermolecular interaction of the polymer flexible chains of polyacrylamide with the surface of the colloidal particles of aluminum pentahydroxochloride. The strength of such complexes is explained by the cooperative (summarized) nature of this interaction and is associated with the polymer nature of aluminum pentahydroxochloride particles. In contrast, other aluminum salts or low-basic aluminum chlorides are not capable of forming durable polycomplexes [Novakov I.A., Radchenko F.S., Papisov I.M. High molecular weight compounds. 2003.v.4b. Number 8. p.1340].

The high stability and selectivity of isolation of the water inflow of the proposed gel is explained by the combined nature of gelation, which consists in the fact that when preparing the initial composition when mixing aqueous solutions of PHCA and polyacrylamide, a polymer-colloidal complex arises almost instantly, which is a dispersed system with a uniformly distributed macromolecular network of physical bonds - gel . Due to the low concentration of the dispersed phase, the gel has a fluidity and low viscosity, which does not interfere with its delivery to the water-saturated zones of the formation. Under reservoir conditions, an amorphous aluminum hydroxide gel is formed by increasing the pH during the hydrolysis of the urea present in the composition. In this case, the nature of the physical bonds of aluminum hydroxide particles with polyacrylamide macromolecules remains the same. The result is a hardened gel-to-gel structure. Due to the high hydrophilicity of fragments of the polymer-colloidal complex (aluminum hydroxide groups and amide groups of polyacrylamide), the gel is firmly fixed on the rock surface in the water-saturated part of the formation and, on the contrary, has low adhesion to oil-saturated zones of the formation, which determines its selectivity in the isolation of water inflow.

Moreover, the more water-saturated the formation, the more firmly the gel is fixed in it, and therefore, a variation in the concentration of gel-forming components in the composition of the injected composition is required. In more permeable areas with high water saturation, the composition should contain up to 6 wt.% Aluminum pentahydroxochloride and up to 14 wt.% Urea. In low-permeable areas, for economic reasons, it is sufficient to use a composition with 3 wt.% Aluminum pentahydroxochloride and 7 wt.% Urea (example 4). The amount of polyacrylamide is determined by its molar ratio to aluminum salt, which should be 1: 2, which is expressed in a mass content of 0.25-0.5%.

Example 1

In this example, the effect of the nature of the aluminum salt on the microstructure of the amorphous aluminum hydroxide gel resulting from the hydrolysis of the aluminum salt in the presence of urea is determined. The ability of the gel to waterproof the formations depends on their microstructure, i.e. on the shape, size and relative position of the colloidal particles of aluminum hydroxide, as well as on the thickness of the liquid layers separating them. At large distances and high polydispersity of the gel particles, low-strength structures appear in the system that are capable of peptization and syneresis, which will affect the durability of the gel and its filtration characteristics when the fluid flows through the washed sections of the oil reservoir. In this regard, the dispersed composition of the aluminum hydroxide gel was studied using an Olimpus-BX-61c motorized microscope in transmitted light with microstructure fixation using a digital camera of the DP-12 microscope. Particle size, number, and shape were determined by direct measurement using Analysis software by counting method. To calculate the dispersion characteristics of the gels of aluminum hydroxide used the formula:

average particle size for each fraction:

where x is the grid division price;

m is the integer number of divisions for a given fraction.

The main hydrodynamic characteristics:

number average radius:

mass average radius:

where n _i is the number of particles of a given fraction with radius r _i ;

Σn _i is the total number of particles in the system.

For a monodisperse system, r _n = r _m ,

for a polydisperse system r _n > r _m ,

polydispersity coefficient K _n = r _n / r _m .

Figure 1, 2 shows micrographs of the structure of the gel of aluminum hydroxide formed during the hydrolysis of PHA (Figure 1) and AlCl ₃ (Figure 2), and table 1 shows the dispersion characteristics of the gels.

Table 1
The dispersion characteristics of the studied gels formed during the hydrolysis of an aluminum salt in the presence of urea (KA) Al salt g _p · 10 ⁶ , m g _m · 10 ⁶ , m Polydispersity coefficient The most probable size, g _p · 10 ⁶ , m PGA 17.6 18.0 0.98 22.5 AlCl ₃ (prototype) 15.6 22.8 0.68 22.4

As follows from the data presented, the gels obtained from PHCA are close to monodisperse and have a denser packing of particles of the dispersed phase than gels based on AlCl ₃ .

Example 2

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 physicochemical 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 the 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 to pass liquids 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, 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 performed at a reservoir temperature of T = 75 ° C. A solution of the composition was poured into the column and, after gel formation in the entire column volume from below, water was taken through a tap into 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.

Water filtration through gel models obeys the well-known relation for viscoplastic bodies with a limiting (initial) pressure gradient G: G = ατ _s / (k) ^0.5 , where

α is a dimensionless constant;

k is the permeability of the porous medium.

Aluminum hydroxide gel particles are able to move in a porous medium (quartz sand) and, therefore, take part in all hydrodynamic processes occurring in the formation.

Since the process of water isolation is carried out in the porous medium of the formation, the gel of aluminum hydroxide, which is a thixotropic pseudoplastic body of the coagulation structure, will reduce the phase permeability of the rock in the liquid due to the adsorption of gel particles in the porous medium.

Table 2 shows the time of water flow through the backfill treated with various compositions.

table 2
Filtration characteristics of a reservoir model treated with various compositions. Songs Water filtration time through an unprocessed model, min Water filtration time through the processed model after gel formation, min The permeability of the model, microns ² PHHA + CA + PAA 1,1 94 6.54 AlCl ₃ + KA + PAA (prototype) 1,0 twenty 30.76

From the table it follows that the time of water filtration through a layer of quartz sand after the formation of a gel in it increases sharply. For AlCl _3, the filtration rate decreases by a factor of 20, while for PLCA, it decreases by a factor of 96. The permeability coefficient of the medium decreases, respectively, by a factor of 20 for a gel based on AlCl ₃ and by a factor of 85 for PHCA.

Example 3

In this example, the dependence of the stability of the gel on the operating time is determined. The experimental conditions are similar to example 2. The resulting gel from the composition (PGA + KA + PAA) was kept in a model unit for a long time (45 days) in a stationary state, periodically passing water through the backfill and measuring its flow rate (table 3).

Table 3
The results of the study of the stability of the gel over time. The number of days after gel formation from the composition (PGA + KA + PAA) 3 6 9 12 22 26 35 37 40 45 The outflow time of 100 cm ^{3 of} water through the treated model, hour 1,5 2.5 6.3 7.2 7.5 7.7 8.1 8.2 8.4 8.5

From this table it follows that the processes that destroy it (syneresis or peptization) do not occur in the gel, the gel hardens, and its insulating properties increase.

Example 4

In this example, an experimental study of gelling compositions for selective waterproofing is due. The composition: PHCA - 3.0 wt.%, KA - 7.0 wt.%, PAA - 0.25 wt.% Water - 89.75%. Studies of the effect of gel-forming solutions on the permeability of a rock saturated with formation fluids (oil, formation water) were carried out at the UIPK installation. For research, samples were taken from the producing wells of deposits with a carbonate reservoir. Preliminary preparation (extraction, drying) was carried out in accordance with OST 39-195-86. The core material was divided into two groups to simulate the water-saturated and oil-saturated zone of the reservoir.

As reservoir fluids, water and oil were used, selected from the Upper Devonian sediments in the above wells. Preparation of reservoir fluids was carried out in accordance with OST 39-235-89. During experimental studies, thermobaric conditions were simulated: reservoir pressure 31 MPa and temperature 76 ° С. Sample preparation was carried out by saturating it with formation fluid (oil or produced water) to simulate one of the zones with subsequent measurement of the main capacitive parameters (porosity and pore volume). Absolute permeability was determined by the studied fluid while maintaining reservoir conditions. Then, a gelling composition in the form of a 10% aqueous solution was injected into a water or oil-saturated sample at an excess pressure of 10-15 MPa in the amount of one pore volume, followed by exposure for 24 hours while maintaining reservoir pressure and temperature, after which permeability was measured by reservoir fluid (oil or water). At the final stage, the resistance of the gel to leaching out of the rock by back pumping of the initial formation fluid (oil or water) of 10-15 pore core volumes with subsequent measurement of permeability for this fluid in the forward direction was determined.

During the washing process (gel resistance to leaching), the pressure drops on oil-saturated samples were 18.8-21.9 MPa, and on water-saturated samples 0.5-1.1 MPa, which is due to the composition of reservoir oils taken for testing as highly resinous and highly paraffinous. The results of experimental studies are shown in table 4 (No. of samples 1 and 1A).

Table 4
The results of experimental studies of the effect of the composition of the gel-forming composition on the filtration properties of the oil-saturated formation rock. Sample Number Plast Coring Depth, m The composition of
position, wt.% Porosity Kp,% Simulated Saturation Zone The permeability coefficient KPR, 10 ^-3 μm ² Pressure drop during "flushing", ΔР MPa * The effect of waterproofing,% source after gel injection after washing the gel 1A D3fm-iii 2337.0-3237.2 PGA-3
KA-7
PAA - 0.25
water - stop 13.1 water pump 33,640 0,034 0,084 1,1 99.90 / 99.75 one 10.22 oil-filled 0,060 0.014 0,045 27.5 76.6 / 25.00 2A 3293.0-3293.8 Pgha-6
KA-14
PAA-0.5
water - stop 16.1 water pump 939.34 0,098 0.147 0.5 99.99 / 99.98 2 14.8 oil-filled 28.31 0.13 0.19 1.4 99.5 / 99.30 * in the numerator - after injection of the gel-forming composition; in the denominator - after "washing" the gel

Example 5

It is carried out analogously to example 4, but with the composition of the composition PHA - 6.0 wt.%, KA - 14.0 wt.%, PAA - 0.5 wt.% Water - the rest. The results of the study are shown in table 4 (No. of samples 2 and 2A).

The experimental data shown in Table 4 showed a significant decrease in water permeability when treating both low permeability (1 and 1a) and highly permeable (2 and 2a) rocks with a gel-forming composition (1000 times with respect to the initial one). A gelling composition based on aluminum chloride - carbamide - polyacrylamide (prototype) reduces water permeability by 12-55 times. The analysis of the gel retention ability in the rock showed a slight increase in permeability by 1.5-2.5 times, on the basis of which we can conclude that the gel is well resistant to leaching.

Ultimately, the treatment of the water-saturated zone with the composition: PGA - 3-6 wt.%, KA - 7-14 wt.%, PAA - 0.25-0.5 wt.%, The rest of the water, reduces the permeability as a result of mudding of 400 times i.e. the waterproofing effect is 99.3%.

Claims (1)

A method of selectively isolating water inflow to a producing oil well by pumping a gelling composition obtained by mixing polyacrylamide, carbamide, aluminum salt and water, characterized in that aluminum pentahydroxochloride is used, and this mixing is carried out by introducing carbamide into the polymer-colloidal complex obtained by mixing an aqueous solution of polyacrylamide with an aqueous colloidal solution of aluminum pentahydroxochloride, in the following ratio, in wt.%:
aluminum pentahydroxochloride 3-6 polyacrylamide 0.25-0.5 urea 7-14 water rest

Images