RU2562642C1 - Reagent for oil production and oil production method using it - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: reagent for oil production containing powdered polyacrylamide (PAA) treated with ionising irradiation contains powdered PAA with molecular weight of 14-25 mln. units and degree of hydrolysis of 20-30% treated with ionising irradiation with doze of 3-20kGy by accelerated electrons with energy of 5-10 MeV with compound containing additionally 5-20 wt % of PAA stabiliser weight - powder of aluminium sulphate or potash alum. Oil production technique that includes injection into the well of bank containing aqueous solution of sodium and calcium chloride with mineral content of 4-40 g/l or brine water with the same mineral content and the above reagent at concentration of 0.5-2.0 wt %.

EFFECT: increased temperature range of the reagent operability at maintenance of operating easiness.

2 cl, 4 tbl, 4 ex

Description

The invention relates to the field of oil production and can be used in the development of oil fields with high reservoir temperature, including in the late stages of development.

When developing reservoirs using reservoir pressure maintenance systems by injecting water into the reservoir, injection of rims of hydrophilic polymer systems, in particular based on polyacrylamide - PAA, is widely used. The mechanism of action of these systems is based on a change in the direction of flow of water injected into the oil reservoir, which leads to an increase in the coverage of the reservoir by flooding, drainage of the stagnant zones of the oil reservoir and, as a result, to obtain additional oil.

The known method [1], in which caustic soda is added to a solution of PAA and chromium acetate to a pH of 8.0 and sodium carbonate in an amount of 2.48 wt.%. The disadvantage of this method is its complexity and the use of environmentally harmful salts of heavy metals.

There is a known method of oil production, in which aluminum salts are used as a crosslinker [2]. The method consists in alternately injecting rims from a polymer solution, aluminum salt and fresh water, the volume of which is calculated by a special formula that takes into account the geological characteristics of the formation (porosity, thickness of the highly permeable section, distance from the bottom to the place of formation of the viscoelastic composition). The disadvantage of this method is the preliminary conduct of a large amount of geophysical work to determine the specific parameters of the formula used.

The closest in technical essence and the achieved effect are a gel-containing reagent - an additive to water to increase oil production, which is crosslinked by ionizing radiation in the solid phase of PAA, and a method of oil production using it [3]. This reagent, unlike other crosslinked systems, is a single component product. Its use in the well is limited to mixing it with water, as a result of which a suspension of particles of soft gels (polymer-gel system) is formed, which is easily pumped into the reservoir and gives a significant increase in oil production. However, this reagent and the oil production method using it are applicable only in the case of formation temperatures not exceeding 60-70 ° C.

The aim of the invention is to increase the temperature limit of the health of the reagent while maintaining the inherent simplicity of the technological operations of the prototype.

The goal is achieved in that the reagent for oil production containing powdered polyacrylamide - PAA, treated with ionizing radiation, contains powdered PAA with a molecular weight of 14-25 million units. and a degree of hydrolysis of 20-30%, treated with ionizing radiation at a dose of 3-20 kGy of accelerated electrons with an energy of 5-10 MeV in a composition containing an additional 5-20 wt.% from the mass of PAA stabilizer - powder of aluminum sulfate or potassium alum.

This goal is also achieved by the fact that the oil production method includes injecting into the injection well a rim containing an aqueous solution of sodium and calcium chlorides with a salinity of 4-40 g / l or produced water of the same mineralization and the above reagent at a concentration of 0.5-2, 0 wt.%

The essence of the invention consists in the interaction of particles of polyacrylamide and aluminum sulfate, treated together in the solid phase with accelerated electrons with an energy of 5-10 MeV in a dose of 3-20 kGy, in an aqueous medium with the formation of a dispersed polymer-gel system based on a metal-polymer composite. This product retains the rheological properties of the polymer-gel system inherent in the prototype, but has a higher thermal stability. The combined processing of polyacrylamide and aluminum salt allows you to get a ready-to-use product immediately after treatment with ionizing radiation and at the same time save the radicals initiated by the ionizing radiation both in the polymer and in the aluminum salt until the reactant is in direct contact with the aqueous medium. In this case, the joint dissolution of polyacrylamide and aluminum salt in water does not lead to a rapid increase in the effective viscosity of the dispersed polymer-gel system, since the reaction proceeds inside the gel particle and its rheological properties are almost unchanged. The effectiveness of the reagent can be improved if water with a mineralization of 4-40 g / l, which can be prepared by adding sodium chloride and calcium chloride to fresh water or using produced water with the same mineralization, is used as water for the preparation of the indicated polymer-gel system. An increase in the reagent efficiency occurs due to a decrease in the volume of gel particles of crosslinked hydrolyzed polyacryamide, which occurs due to a decrease in the effective charge of the ionic units (carboxyl groups) of polyacrylamide, caused by an increase in the electrical conductivity of the aqueous solution with the addition of sodium and calcium salts.

When injecting a polymer-gel system using the proposed reagent, its optimal concentration in water is 0.5-2 wt.%. At a concentration of more than 2%, the system cannot be injected into the reservoir due to its high viscosity. At a concentration of less than 0.5%, the effectiveness of the application is reduced due to the fact that further dilution does not lead to an increase in the volume of gel injected into the formation.

The technical result is to increase the temperature stability of the gel-like metal-polymer composite, which results in the ability to use it at reservoir temperatures of 60-100 ° C, including in formations with low permeability of the reservoir, in the late stages of development.

Example 1

In laboratory conditions, a study was made of the filtration properties of polymer-gel systems obtained by mixing the inventive reagent with fresh (mineralization 0.5 g / l) and formation (mineralization 20 g / l) water during filtration through nets with pore sizes close to pore sizes channels of reservoir rocks of oil fields. For this purpose, a laboratory bench was made, including a flow-through filtration cell, on one side of which replaceable filter screens are attached, and on the other hand, the cell is connected to a syringe pump, which pumps air into the cell with a constant volume velocity, creating pressure. Under the influence of gas pressure, the sample began to be filtered through a grid. Thermostability was calculated by changing the residual hydraulic resistance of a strainer with a diameter of 10 mm after filtering through it a fixed volume of a polymer-gel system with a volume of 40 ml before and after heat treatment it at a temperature of 95-100 ° C for 20 and 72 hours. During filtration, the filtrate volume, time and gas pressure, under the action of which the sample was filtered through a grid, were measured. A mesh with a cell diameter of 50 μm, 100 μm and 300 μm, close in cell size to the pore size of the formation rocks, which simulates the filtration conditions in the formation. When filtering gels through a strainer, part of the gels clogs the grid cells, which leads to an increase in hydraulic resistance. The stability of the gels was evaluated by the value of the residual resistance on the grid, created by gel particles that did not collapse during heat treatment. The value of destruction (D) was calculated by the change in the residual hydraulic resistance on the mesh filter after filtering the gel system in the interval of the heat treatment time between the beginning and end of the heat treatment stage according to the formula:

Where ΔP1, ΔP2 is the residual resistance, measured in kPa, on the grid, respectively, at the beginning and end of the heat treatment stage.

Samples were prepared as follows: powdered polyacrylamide with a molecular weight of 20 million units. mixed with 10 wt.% (by weight of polyacrylamide) potassium alum and treated with accelerated electrons with an energy of 8 MeV dose of 12 kGy. The resulting product in an amount of 0.5 wt.% Was mixed with fresh or produced water, and after swelling and the formation of a polymer-gel system, its filtration properties were studied on the stand described above. Some samples were placed in a thermostat with a temperature in the range of 95-100 ° C and kept for 20 or 72 hours. Further investigated their filtration properties. The measurement results for the case of polymer-gel systems prepared as using accelerated electron processing with an energy of 8 MeV, a dose of 12 kGy with the addition of stabilizers - potassium alum and aluminum sulfate. The properties of polymer-gel systems prepared in fresh and produced water are presented in table 1.

From the data presented in table 1, it follows that both the starting polyacrylamide and the polyacrylamide treated with accelerated electrons (experiments No. 1-3, No. 7-9) are not thermally stable and degrade in less than 20 hours. A sample of PAA with the addition of alum has limited stability, its destruction is in the range of 23-95%. The destruction of PAA processed by ionizing radiation (accelerated electrons) together with potassium alum does not exceed 15% under comparable conditions.

From the analysis of the same data, it follows that less degradation is observed on grids of 50 microns in size than on grids of 100 and 300 microns, which means more efficient operation of systems (experiment No. 4) in reservoirs with low permeability.

Example 2

It was prepared 7 samples of powdered polyacrylamide of 100 g with a molecular weight in the range of 14-25 million units. and the degree of hydrolysis of 20-30%. From 5 to 20 (5-20 wt.%) Grams of potassium alum were added to each sample. After mixing, the compositions were processed at an electron accelerator with accelerated electrons with energies in the range from 5 to 10 MeV with doses in the range of 3-20 kGy. Next, the samples were mixed with water having a salinity of 15 g / l until a homogeneous polymer-gel system with a reagent concentration of 1 wt.% Was formed. This system was tested for thermal stability at a temperature of 95-100 ° C for 20 and 72 hours by analogy with example 1. The results of determining the thermal stability in terms of residual resistance created by intact gel particles on a filter with 100 μm cells are presented in table 2. There the calculated gel degradation indices in the heat treatment time interval of 20-72 hours are also presented. The data obtained show the preservation of gels for at least 72 hours of treatment under these conditions under the selected conditions for the preparation of the reagent and composition using it.

Example 3

The reagent for oil production, studied in example 1, after mixing with water forms a polymer-gel system, the rheological properties of which vary widely. At sufficiently high polymer concentrations — more than 2 wt.% — Its viscosity can increase so much that it cannot be pumped into the well by existing technological equipment. The viscosity of this system depends on the concentration of the polymer and the salinity of the water. In this example, experimental data on the viscosity of this system depending on the concentration of the polymer and the salinity of the water are given. Model systems with different salinity were prepared on the basis of sodium and calcium chlorides, the main components of formation water. The ratio of sodium chloride and calcium chloride, typical for these waters, was 9: 2 and mineralization in the range of 4–40 g / l. The prepared samples of the polymer-gel system were investigated for rheological properties and thermal stability. For comparison, the properties of similarly prepared systems based on polyacrylamide, not subjected to processing by accelerated electrons, with and without the addition of a stabilizer, were studied. To determine the rheological properties, we measured the relative viscosity in a funnel viscometer with a drain pipe diameter of 15 mm. In this case, the nominal viscosity was calculated as the ratio of the time of expiration of the mixture of reagent and water in the indicated concentrations to the time of expiration of water. Thermal stability was determined by the value of residual resistance on a mesh filter with a pore size of 100 μm after heat treatment for 72 hours at 95-100 ° C. The fact of the presence of residual resistance and its value is evidence of the existence of gel particles in the test sample. The test results are presented in table 3. From these data it can be seen that samples of systems based on the proposed reagent in the declared ranges of reagent concentrations and mineralization of water (see experiments 1-10) combine moderate viscosity and the presence of residual resistance on the strainer after heat treatment for 72 hours at 95-100 ° C. Comparison with similar systems based on unprocessed accelerated electrons polyacrylamide shows that the latter have too high viscosity to be pumped into the well.

Example 4

The proposed reagent and oil production method using it were tested at the Priobskoye oil field, which is characterized by high reservoir temperature and low permeability of the reservoir. As the test object, a pilot section with an injection well at the Priobskoye field was selected with the characteristics shown in table 4.

For testing, a reagent was prepared in an amount of 900 kg by treating a mixture of 810 kg of polyacrylamide with a molecular weight of 14-24 million units. and the degree of hydrolysis of 25% with 90 kg of potassium alum (10 wt.%) accelerated electrons with 8 MeV dose of 12 kGy. At the experimental facility - the injection well - this reagent was mixed with 180 m ^{3 of} produced water with a salinity of 4 g / l and the resulting polymer-gel system was pumped into the injection well. After that, the injection well was put into operation.

Observation of the environment from producing wells in the mentioned area over the course of 3 months established an increase in additional production in the amount of 800 tons. This confirms the results of laboratory experiments and proves the applicability of the reagent and the proposed method of oil production for reservoirs with high temperature and low permeability of the reservoir.

Information sources

1. RU 2352771, E21B 43/22, 01.29.2007.

2. RU 2086757, E21B 43/22, 02.21.1995.

3. SU 1669404, E21B 43/22, 04/03/1989.

Claims (2)

1. The reagent for oil production containing powdered polyacrylamide - PAA, treated with ionizing radiation, characterized in that it contains powdered PAA with a molecular weight of 14-25 million units and a degree of hydrolysis of 20-30%, treated with ionizing radiation at a dose of 3-20 kGy of accelerated electrons with an energy of 5-10 MeV in a composition containing an additional 5-20 wt.% from the mass of PAA stabilizer - powder of aluminum sulfate or alum-potassium alum. 2. The method of oil production, including the injection into the injection well of the rim containing an aqueous solution of sodium and calcium chlorides with a salinity of 4-40 g / l or produced water of the same mineralization and the reagent according to claim 1 at a concentration of 0.5-2.0 wt .%.