EA038656B1 - Method to level the injectivity profile of an injection well - Google Patents

Abstract

The invention relates to oil production industry, in particular to methods for improving oil recovery by leveling the injectivity profile of injection wells. The aim of the invention is to increase effectiveness of oil displacement conforming the profile log of water injection wells via partial or full blocking of high permeability oil saturated laminations and deviating the injected water to oil saturated laminations of low permeability and reduce the cost of implementing the technique. To solve the task within the scope of leveling the injectivity profile of injection wells that includes pumping an aqueous solution of gel-forming material containing preformed gel-forming particles of adjustable swellability into the reservoir, a composition consisting of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, polyvinylpyrrolidone, bentonite clay, gallic acid, N,N'-methylene bisacrylamide, ammonium peroxidesulfate and fresh water is injected whereas the aqueous solution of the gel-forming composition containing preformed gel-forming particles with adjustable swelling is injected into the formation rim in the amount of 10% of pore volume of the formation, and then water is injected to push the gel-forming composition further.

Description

The invention relates to the oil industry, in particular to methods for enhancing oil recovery by leveling the injectivity profile of injection wells.

There is a known method for leveling the injectivity profile of an injection well, including injecting a sediment-forming reagent containing an aqueous solution of calcium chloride into the formation, while preliminarily preparing a reagent that causes sedimentation in reservoir conditions at a temperature of at least 80 ° C, into which sulfamic acid or its ester is additionally introduced general formula RO-SO ₃ -NH ₄ , where R-CH3, C2H5 or C3H7, by preparing a 20-50 wt.% aqueous solution of a mixture of calcium chloride and sulfamic acid or its ester, taken in the ratio (30-70) :( 70-30) [1].

The disadvantage of this method is that in reservoir conditions at a temperature not lower than 80 ° C, the reagent causes sedimentation, i.e. hydrolysis of sulfamic acid and its ester occurs with the formation of poorly soluble calcium sulfonates, which precipitate and the method will be ineffective in wells with temperatures below 80 ° C.

There is also a known method for leveling the injectivity profile of injection wells, including the injection into the injection well of an aqueous solution of a crosslinkable polymer composition containing polyacrylamide with a molecular weight of 5 to 15 million and a degree of hydrolysis of 5-30% and chromium acetate. In this case, before pumping the polymer solution at a minimum speed, injects a rim of an aqueous solution of chromium acetate with a concentration of not more than 0.1% in a volume equal to the volume of the specified solution, and after pumping the polymer solution, water is pumped to push it to the required depth and leave the well for reaction [ 2].

The disadvantage of this method is that when the polymer solution is pumped behind the crosslinker solution, they are not uniformly mixed due to the fact that the viscosity of the polymer solution is much higher than the viscosity of the crosslinker solution and its almost piston displacement occurs. As a result of the implementation of the method, the resulting gel has a low strength. In addition, the method does not allow one to control the strength of the resulting gel. The proposed gel is unstable in reservoir conditions at temperatures above 80 ° C, i.e. decomposes. And also the decomposition process is influenced by the high mineralization of water, which speeds up this process. Consequently, this gel is not suitable for reservoirs with high temperature and salinity and is not capable of effectively blocking channels with increased permeability.

It should be noted that in both of these methods, sedimentation and gelation occurs in the formation near the injection well, which leads to a significant increase in injection pressure. In addition, the formation of an insulating plug near the well significantly reduces the amount of additional oil production due to the rapid bending of the pumped water around the installed plug. This disadvantage is overcome in the methods of leveling the injectivity profile based on the depth deviation of the injected fluid, in particular using aqueous solutions of preformed gel-forming particles with controlled swelling.

Closest to the proposed invention is a method for leveling the injectivity profile of an injection well, comprising injecting into the formation an aqueous solution of a gelling material containing pre-formed gelling particles with controlled swelling of the following composition: acrylamide; 2-acrylamido-2-methylpropane sulfonic acid sodium salt; polyethylene glycol diacrylate; N.N'-methylenebisacrylamide; sodium bromate and sodium bisulfite [3].

The disadvantage of the invention is that the gel formed in the formation has low thermal stability, low swelling, leading to a decrease in the insulating ability, which is expressed in a low coefficient of residual resistance, as well as the high cost of implementing the method due to continuous injection of a gel-forming composition containing pre-formed gel-forming particles.

The objective of the invention is to improve the efficiency of displacing oil from the reservoir by leveling the injectivity profile of injection wells by partially or completely blocking high-permeability flooded layers and deflecting the injected water into low-permeable oil-saturated layers, as well as reducing the cost of implementing the method.

The problem is solved by the fact that in the method of leveling the injectivity profile of injection wells, including the injection into the formation of an aqueous solution of a gel-forming material containing pre-formed gel-forming particles with controlled swelling, a composition consisting of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid is pumped into the formation, polyvinylpyrrolidone, bentonite clay, gallic acid, Ν, Ν'-methylenebisacrylamide, ammonium peroxodisulfate and fresh water in the following ratio of components:

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Acrylamide 15-30% 2-acrylamido-2-methylpropanesulfonic acid 20-30% Polyvinyl pyrrolidone 10-15% bentonite clay 0-10% gallic acid 0.2-0.5% Ν, Ν'-methylenebisacrylamide 0.5-1% Ammonium peroxodisulfate 0.05-0.1% water rest

In this case, an aqueous solution of a gel-forming composition containing pre-formed gel-forming particles with controlled swelling is pumped into the formation in the form of a rim in an amount of 10% of the pore volume of the formation, then water is injected to push the gel-forming composition.

Acrylamide (79-06-1 MSDS) was used to prepare a gelling composition containing pre-formed gelling particles with controlled swelling in order to level the injection profile of the injection well; 2-acrylamido-2-methylpropane sulfonic acid (15214-89-8MSDS); polyvinylpyrrolidone (GOST 30333-2007); bentonite clay (GOST 28177-89); gallic acid (GOST 30333-2007); N, N'-methylenebisacrylamig (110-26-9 MSDS); ammonium peroxodisulfate (7727-54-0 MSDS) and fresh water. The aqueous phase of the gelling composition is prepared by adding the calculated amount of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, polyvinylpyrrolidone and N, N'-methylenebisacrylamide to the clay solution in fresh water. To improve the thermal stability of the synthesized gel, a certain amount of gallic acid is added during the synthesis, the initiator of ammonium peroxodisulfate is slowly added to the solution with strong stirring at a temperature of 50-60 ° C, the reaction is completed due to the self-acceleration reaction in a short time.

The essence of the invention lies in the fact that the effectiveness of the proposed method for leveling the injectivity profile of injection wells in fractured reservoirs is increased by injecting into the formation a gel-forming material containing pre-formed gel-forming particles with increased thermal, swelling and insulating capacity.

Preformed gelling particles with controlled swelling and high thermal stability have preferred size ranges from 0.1 μm to 5 mm. These expandable and hydrophilic polymer particles are manufactured in a non-emulsion system. In reservoir conditions, until a certain time, they have the ability to retain their swollen state in fresh or salt water. An increase in the efficiency of oil displacement from the reservoir by the proposed method occurs due to the alignment of the injectivity profile of injection wells by partial or complete blocking of highly permeable flooded interlayers and deviation of the injected water into low-permeable oil-saturated interlayers due to an increase in the thermal stability and insulating capacity of the gel formed in the formation.

The method has been tested in laboratory conditions. To illustrate the proposed method, samples of a gelling material were prepared, which consisted of pre-formed gelling particles with ratios of components wt.%: Pre-formed gelling particles 1-2%; water - the rest is PPG1, PPG2, PPG3, PPG4, PPG5, PPG6, PPG7, PPG8, prototype and pumped into bulk models (Table 1).

Sample 1: prepare a prototype gel of the following composition, wt.g:

Acrylamide 8.25 AMPSNa 21.75 polyethylene glycol diacrylate-200 0.386 Ν, Ν'-methylenebisacrylamide 0.0004 sodium bromate 20 μl sodium bisulfite 20 μl water 30.6

In this example, an aqueous phase was prepared by adding 8.25 g of acrylamide, 21.75 g of sodium salt of 2-acrylamido-2-methylpropanesulfonic acid, 0.386 g of polyethylene glycol diacrylate-200 and 0.0004 g of N, N'-methylenebisacrylamide to 30.6 g of deionized water. An initiator mixture of 400 μL of 5% sodium bromate and 400 μL of 5% sodium bisulfite was slowly added to the solution with vigorous stirring at a temperature of 15-30 ° C; the reaction was completed in 5 min.

Sample 2: prepare a gel (PPG1) of the following composition, wt%:

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Acrylamide

2-acrylamido-2-methylpropanesulfonic acid

Polyvinylpyrrolidone

Gallic acid

Ν, Ν'-methylenebisacrylamide ammonium peroxodisulfate water

0.2

0.5

0.05 rest

In this example, an aqueous phase was prepared by adding 9.35 g of acrylamide, 11.45 g of 2-acrylamido-2-methylpropanesulfonic acid, 4.25 g of polyvinylpyrrolidone (K30) and 0.586 g of N, N'methylenebisacrylamide to 26.8 g of water. To improve the thermal stability of the synthesized gel, 0.05 g of gallic acid was added during the synthesis, the initiator ammonium peroxodisulfate was slowly added to the solution with vigorous stirring at a temperature of 50-60 ° C, the reaction was completed due to the self-acceleration reaction in a short time.

Other samples of a gelling material consisting of pre-formed gelling particles PPG2, PPG3, PPG4, PPG5, PPG6, PPG7, PPG8 are made in a similar way.

Experience 1.

The thermal stability of samples of preformed gel-forming particles has been studied. A differential scanning calorimeter (model: DSCQ10, manufactured by TA Instrument) was used to study the thermal stability of the samples in a nitrogen atmosphere. For the analysis, 9 samples were used (PPG1-PPG8 and prototype). Swollen gels (7-13 mg) were taken for measurements, stored in aluminum containers and sealed. A thermogram for each sample was obtained for a temperature range from 40 to 200 ° C at a heating rate of 2 ° C / min and a nitrogen purge rate of 20 cm ³ / min (the results of the experiment are shown in Table 2).

As you can see from the table. 2, thermal decomposition of preformed gel-forming particles containing 1% bentonite clay occurs in the range from about 170 to 174 ° C, with a content of 3% bentonite clay, decomposition occurs at temperatures of 175-178 ° C, and at 5% content of bentonite clay, the process decomposition occurs at higher temperatures of 180-183 ° C. Thermal decomposition of the prototype varies in the range of 118-121 ° C.

Thus, an increase in the content of bentonite clay leads to an improvement in the stability of preformed gel-forming particles due to the existence of chemical and physical interactions between polymers and the surfaces of bentonite clay layers, which can occur through the hydrogen bonding of polymer groups and Si-O-Si groups of bentonite clay with groups of polymer chains and their dipole-dipole bonding.

It was found that with an increase in the percentage of bentonite clay content to 7 and 10%, the opposite process occurs, i.e. thermal stability decreases. This is due to the agglomeration of clay particles with an increase in its concentration, leading to a decrease in the total surface area of the clay particles.

Experience 2.

The swelling and insulating capacity of preformed gelling particles has been studied.

For each sample, a weighed amount of dry PPG powder (Wd-dry weight) is carefully poured into a 50 ml tube filled with water for testing at room temperature.

After a certain time, the hydrogels were removed from the tubes. In this case, excess water was removed with filter paper, after which the swollen mass of the hydrogel was determined (W _s . The mass of the hydrogel after swelling).

The swelling factor was calculated as follows:

Ws —Wd

Swelling coefficient = ———

Wd

Here, bentonite clay acts as a crystalline nucleus of the former and miter for the chains of 2-acrylamido-2-methylpropanesulfonic acid and acrylamide. This means that if a large amount of bentonite clay is added to the monomer matrix, the number of crosslinking points of the monomer network increases, which leads to an increase in the density of crosslinking of the network and greater entanglement of the chains. An increase in the crosslinking points leads to a decrease in the free pore volume in the preformed gel-forming particles due to the mass transfer of water molecules by the inclusion of bentonite clay in its matrix. The obtained values of swelling of compositions containing 1-5% bentonite clay are explained by ionic dissociation of sodium montmorillonite (polycationic clay) and its strong swelling in water. The limitation of free pore volume is the most important factor in reducing the swelling of formulations containing more than 5% bentonite clay. An increase in the content of bentonite clay leads to a decrease in the swelling coefficient.

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The research results (Table 2) showed that the swelling capacity of the samples varies in the range 73-160 g / g, and the swelling capacity of the prototype is 71.

The effectiveness of the insulating ability of the proposed method for leveling the injectivity profile of an injection well has been proven by laboratory studies.

All experiments were carried out on a Strata-SlimTube with an absolute water permeability of 0.5-1D. The general setup is shown in Fig. 1.

Sand fractions ranging in size from 45 to 75 microns were used to obtain the required permeability. Sand carryover from the bulk model was prevented by installing a fiberglass screen at the inlet and outlet. A weighting method based on the difference between dry and water-saturated mass of the bulk model was used to determine the porosity. After preparing the model, the prepared samples were injected into the formation and the resistance factor (RF _zak ) and the residual resistance factor (RRF _oct ) were determined.

When conducting experiments evaluating the effectiveness of basic performance is the resistance factor in the injection solution (RF _zak), the initial shear gradient of pressure _(nach LR) and the residual resistance factor solutions preformed gelling particles (RRF _oct).

The results of the experiments showed that the residual resistance factor for the developed gel (RRF _oct ) increases by 300-500% in comparison with the prototype (Table 2).

Experience 3.

To study the effect of the volume of the rim of the injected reagents on the displacement efficiency of residual oil from the flooded formations, experimental studies were carried out on a layered-inhomogeneous bulk model of the formation, where the permeability of the low-permeability layer was 0.5 μm, and the high-permeability layer was 1 μm. The geometrical dimensions of the model are as follows: length - 0.8 m, inner diameter - 0.04 m. The model was filled with quartz sand. The general setup is shown in Fig. 2, where 1 is a registrar; 2 - source; 3 - manometer; 4 - column with a porous medium; 5 - load cell Sapphire; 6-PVT camera; 7 - compensator; 8 - ultrathermostat; 9-way manifold and pressure regulator; 10 - dosing pump; 11 - shut-off valves; 12 - resistance box.

Porosity and pore volume were calculated from the difference in weight between the wet and dry reservoir models. After piping the unit, at a constant temperature (30 ° C) and flow rate, the models were saturated with formation water, then the water was displaced by oil with a viscosity of 8 centipoise (cP). To create a model of a watered reservoir, oil was displaced by formation water until it was not included in the filtrate at the exit from the model. Next, rims of the prepared PPG4 sample of various volumes were injected (in the amount of 2-20% of the pore volume). Then, water was injected until the oil production stopped. The results of experimental work are shown in table. 3.

The results of the experiments (Table 3) showed that the maximum increase in the oil displacement coefficient (24.3%) was obtained when injecting a rim of an aqueous solution of a gel-forming composition in an amount of 10% of the pore volume of the formation. With a further increase in the rim volume, the increase in the value of the oil displacement coefficient was insignificant (0.7-1.6%) and is economically inexpedient due to a significant increase in the consumption of chemical reagents.

In field conditions, the method of leveling the injectivity profile of injection wells is carried out in the following sequence: a complex of geophysical and hydrodynamic studies is carried out in the selected area of the oil reservoir before the event. Based on the data from these studies, the required edging volume is calculated. At the wellhead, the proposed gel-forming material is prepared, containing pre-formed gel-forming particles, and it is pumped through the injection well into the formation in the form of a rim in an amount of 10% of the pore volume, then it is pumped with water to push the gel-forming material.

Table 1

Samples The composition of the gelling material,% Acrylamide 2-acrylamido-2methylpropane sulfonic acid Polyvinyl pyrrolidone Bentonite clay Gallic acid N, Ν'-methylene bisacrylamide Ammonium peroxodisulfate water PPG1 15 twenty ten 0 0.2 0.5 0.05 rest PPG2 15 twenty ten 1 0.2 0.5 0.05 rest PPG3 15 twenty ten 3 0.2 0.5 0.05 rest PPG4 15 twenty ten 5 0.2 0.5 0.05 rest PPG5 15 twenty ten 7 0.2 0.5 0.05 rest PPG6 15 twenty ten ten 0.2 0.5 0.05 rest PPG7 twenty 25 12 5 0.5 1 0.1 rest PPG8 thirty thirty 15 5 0.5 1 0.1 rest

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table 2

Samples RF RRF Thermal destruction ° C swelling ratio (g / g) PPG 1 6.5 500 165-168 73 PPG 2 6.5 650 170-174 85 PPG3 6.9 700 175-178 BUT PPG 4 7 750 180-183 160 PPG 5 6.8 630 168-171 80 PPG 6 6.7 450 160-163 60 PPG7 7.2 630 176-179 130 PPG8 7.3 620 172-175 125 Prototype nine 150 118-121 71

Table 3

Model no. Oil recovery factor before sample injection,% Injected PPG4 volume,% of pore volume Oil displacement coefficient after sample injection,% Displacement coefficient increase,% 1 53.8 2 59.4 5.6 2 53.4 5 64.8 11.4 3 52.9 7 71.8 18.9 4 53.9 ten 78.2 24.3 5 53.9 twenty 78.3 24.4 6 53.8 continuously 78.3 24.5 Prototype 53.7 continuously 65.0 10.5

Literature:

1) Patent RU 2633466, Е21В 43/32, С09К 8/42, publ. 12.10.2017

2) Patent RU 2648399, Е21В 43/22, СО9К 8/512, publ. 03/26/2018

3) Application US 20070204989, E21B 43/22, 33/138, 33/128, publ. 06.09.2007.

Claims (1)

CLAIM A method for leveling the injectivity profile of an injection well, comprising injecting into the formation an aqueous solution of a gelling material containing preformed gelling particles with controlled swelling, characterized in that, as a gelling material containing preformed gelling particles with controlled swelling, a composition consisting of acrylamide, 2-acrylamido-2methylpropane sulfonic acid, polyvinylpyrrolidone, bentonite clay, gallic acid, N, N'-methylene bisacrylamide, ammonium peroxodisulfate and fresh water with the following ratio of components: acrylamide - 15-30%; 2-acrylamido-2-methylpropanesulfonic acid - 20-30%; polyvinylpyrrolidone - 10-15%; bentonite clay up to 10%; gallic acid - 0.2-0.5%; N, N'methylenebisacrylamide - 0.5-1%; ammonium peroxodisulfate - 0.05-0.1%; water - the rest; while an aqueous solution of a gelling composition containing pre-formed gelling particles with controlled swelling is pumped into the formation in the form of a rim in an amount of 10% of the pore volume of the formation, then water is injected to push the gel-forming composition.