RU2352771C2 - Method of applying modified polymer compositions for increased oil withdrawal of formations - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention can be applied at development of oil deposits at late stage of development an also for increased oil withdrawal of formations at development of deposits with high level of watering. The method of applying modified polymer compositions to increase oil withdrawal of formations consists in pumping water solution of polyacrylamide and chromium acetate into the formation; the said solution is prepared on formation water with addition of caustic soda to pH=8.0 and additional with acidic sodium carbonate at amount of 2.48 wt % and dosing of polyacrylamide at amount of 1.33 wt % and chromium acetate at amount of 0.47 wt %.

EFFECT: increased hardness of gel, reduced time for gel forming.

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Description

The invention relates to the oil industry and can be used in the development of oil deposits that are in the late stages of development, and can also be used to increase oil recovery in the development of fields with a high degree of water cut. It can be used for waterproofing in vertical and horizontal production wells, to increase the coverage by injection and to smooth the injectivity profile of injection wells.

Background to the invention

Analysis of the current level of technology in this field showed the following.

Today, there are numerous methods for creating gel-forming systems based on water-soluble polymers:

ATP - cross-linked polymer systems (patent No. 2167281 dated 08/04/1999 "Method for the development of a heterogeneous reservoir"). The method is based on the injection of a composition from a mixture of an aqueous solution of an anionic polymer (polyacrylamides, polysaccharides) and salts of the polyvalent cation (acetates, chromates and dichromates of alkali metals).

ShchPK - alkaline-polymer composition (patent No. 2136871 dated 02/01/1999 "Method for the development of oil deposits"). The method is based on the injection of an aqueous solution of polyacrylamide and alkali metal hydrate.

VUS - the method of viscoelastic systems (patent No. 2180039 from 02/14/2000 "Method for the selection of gel-forming compositions to increase oil recovery"). The method is based on the injection of a concentrated aqueous mixture of polyacrylamide and a crosslinker (chromium acetate, chromium potassium alum, etc.).

When substantiating the use of these compounds, viscosity, pressure, and flow rate of injected solutions are generally taken into account with the properties of the solution itself unchanged. Also taken into account lithology, fracturing, hydrodynamic connection of aquifers, etc.

These methods have a number of disadvantages that limit their use:

1) a large volume of injected solutions and, as a result, chemical reagents;

2) a significant gelation time is the loss from down time of the well stock;

3) instability of the formed structures - over time, complete or partial destruction of the resulting gel systems.

In the process of field work, questions arise about the influence on the gelation process of such a factor as the content in the waste water used for the preparation of solutions of various impurities that can especially affect the gelation process, worsening or improving it.

The presence in water of various impurities of metals and salts, as well as corrosion inhibitors and demulsifiers, most negatively affects the process.

Field studies of gel-forming systems (the so-called cross-linked polymer systems, viscoelastic systems) revealed a number of features, namely, that the structure of the resulting system is very dependent on the physicochemical properties of the water used to prepare the composition.

A significant content of various impurities (metals, carbonates, etc.) in the wastewater used to implement these technologies seriously impairs the parameters of the gel system formed due to incomplete crosslinking of polyacrylamide molecules (most likely, crosslinking chromium molecules are replaced by other less stable to physical exertion), as a result of which, under reservoir conditions, when sampling from reservoir conditions, the gel may partially or to a large extent be destroyed or not crosslinked.

The closest in physical parameters of the process is the method of viscoelastic systems based on crosslinked polyacrylamide molecules, which we have chosen as the closest analogue, that is, a prototype.

The disadvantages of the prototype include the fact that the AK-642 polyacrylamide used in the WCS technology is rather poorly soluble in water - prolonged mixing is necessary.

Along with this, the indicated method works effectively only with certain parameters of the injection object and the absence of foreign impurities in the composition of the water used. In real conditions, creating such conditions is extremely difficult. Therefore, during the injection process of viscoelastic systems, problems arise due to incomplete crosslinking of polyacrylamide molecules and, as a result, gel formation with characteristics different from those specified.

The aim of this invention is to improve the technology of gelation through the use of physical processes that accelerate gelation, and the method of separation (sedimentation) from the composition of the solvent (formation, waste water) insoluble compounds (salts), which in the dissolved form prevent the formation of strong gel-forming compounds, and as a result - obtaining a gel with desired strength characteristics.

The goal is achieved by the proposed method of using modified polymer compositions to increase oil recovery by converting the impurities dissolved in the formation and pumped water into a strengthening structure of the resulting gel. It is the combination of essential features of the invention that provides the above technical result.

A method of using modified polymer compositions to enhance oil recovery involves injecting an aqueous solution of polyacrylamide and chromium acetate into the formation, the solution being prepared in produced water with the addition of caustic soda to pH 8.0 and additionally sodium carbonate in an amount of 2.48 wt.% And a dosage of polyacrylamide in an amount of 1.33 wt.% and chromium acetate in an amount of 0.47 wt.%.

The dosage of the components (polyacrylamide and chromium acetate) is reduced by 5% from the components used in the WCS method. The final pH of the composition is 11.7-13.8.

It is also new that the application of the method is carried out without adding fillers to the gel structure, which are mechanical impurities and insoluble compounds present in the formation (waste) water.

The method of preparation of the composition is quite simple and does not require special devices for the preparation of the gel, allowing you to use existing installations for the injection of polymer compositions.

Next, we consider the information confirming the possibility of carrying out the invention with obtaining the desired technical result.

In order to assess the influence of mechanical impurities, corrosion inhibitors and de-emulsifiers on the gel formation process, work was carried out in the analytical laboratory of the chemical products workshop No. 1 of the Neftekhimservice department to assess the possibility of obtaining a universal composition suitable for use in both production and injection wells (vertical and horizontal). Experiments were conducted using various grades of polyacrylamides (PAA), a crosslinker, and various additives. Work on the proposed method was carried out on real - formation (waste) - water NGDU "Nurlatneft" and NGDU "Almetyevneft".

The results of water analyzes from the fields of NGDU “Nurlatneft” and NGDU “Almetyevneft” are shown in Table 1.

The components for the syntheses were taken in the following quantities (for comparison):

PAA 0.85 g

Chromium Acetate 0.3 g

Water 58 g

Samples were mixed on a magnetic stirrer until a thick liquid formed. The gelation time was determined taking into account the mixing time.

The results are presented in table.2.

table 2 Water sampling point Laboratory samples with PAA-DP-9 with PAA-D-1 with PAA-AK-642 Water from the Kamyshlinskoye field with a pH of 5.56 The gel formed after 49 h 30 min The gel formed after 50 hours The gel formed after 146 hours water from the Vishnevo-Polyanskoye field with a pH of 6.61 The gel formed after 52 h 30 min The gel formed after 53 hours The gel formed after 144 hours Water from the Yuzhno-Nurlatskoye field with a pH of 6.48 The gel formed after 53 hours The gel formed after 53 hours The gel formed after 170 hours Water with NGDU Almetyevneft with pH 5.2 The gel formed after 63 hours The gel formed after 72 hours The gel formed after 153 hours

Gelation in real water did not occur in 48 hours.

Work was continued with the preliminary alkalization of the water used in the technology to a pH of 8.0; 10.0

The test results of laboratory samples are shown in table.3.

Table 3 Water sampling point Laboratory samples with PAA-DP-9 with PAA-D-1 with PAA-AK-642 water from the Kamyshlinskoye field with a pH adjusted to 8.0 The gel formed after 37 hours The gel formed after 42 hours The gel formed after 138 hours water from the Vishnevo-Polyanskoye field with a pH adjusted to 8.0 The gel formed after 21 hours The gel formed after 41 hours The gel formed after 63 hours water from the Yuzhno-Nurlatskoye field with a pH adjusted to 8.0 The gel formed after 16 hours The gel formed after 40 hours The gel formed after 61 hours Water with NGDU Almetyevneft with a pH adjusted to 8.0 The gel formed after 17 hours The gel formed after 41 hours The gel formed after 60 hours water from the Kamyshlinskoye field with a pH adjusted to 10.0 The gel formed after 5 hours The gel formed after 5 hours 25 minutes. The gel formed after 23 hours

To increase the gelation efficiency by the proposed method, it was decided to conduct tests with the addition of sodium carbonate (soda).

The tests were carried out on real water NGDU "AN".

The following laboratory samples were prepared:

1) water (adjusted to pH 8.0) + 2.48 wt.% Sodium carbonic acid + PAA-DR-9 + chromium acetate;

2) water with a pH of 5.2 + 2.48 wt.% Sodium carbonate + PAA-DR-9 + Chromium acetate;

3) water with a pH of 5.2 + 10 wt.% Sodium carbonic acid + PAA-DR-9 + Chromium acetate.

The components for the syntheses were taken in the following quantities (for comparison):

PAA 0.85 g

Chromium Acetate 0.3 g

Water 58 g

Samples were mixed on a magnetic stirrer until a thick liquid formed. The gelation time was determined (taking into account the mixing time).

The results are shown in table 4.

Table 4 No. p / p Name of the laboratory sample Gelation one. Water adjusted to pH 8.0 + 2.48% sodium carbonate + PAA-DP-9 + Chromium acetate The gel formed after 12 hours 2. water with a pH of 5.2 + 2.48% sodium carbonate + PAA-DP-9 + Chromium acetate The gel formed after 12 hours 3. water with a pH of 5.2 + 10% sodium carbonic acid + PAA-DP-9 + chromium acetate Gelation did not occur (in 96 hours).

The tests on the proposed method continued:

No. 1. The dosage of the components PAA-DR-9 and chromium acetate decreased by 5%. The dosage of sodium carbonic acid (soda) is 2.48 wt.%.

PAA-DP-9 0.8075 g

Chromium Acetate 0.285 g

Real water 58 g

Sodium carbonate, 1.5 g

No. 2. The dosage of the components remained unchanged, but the dosage of sodium carbonate was reduced.

PAA-DP-9 0.85 g

Chromium Acetate 0.3 g

Real water 58 g

Sodium carbonate, sour 0.75 g

Number 3. Real water, the pH of the water was adjusted to 7.0.

PAA-DP-9 0.85 g

Chromium Acetate 0.3 g

Water 58 g

Number 4. Real water, the pH of the water was adjusted to 8.0. The dosage of the components PAA-DR-9 and chromium acetate decreased by 5%. The dosage of sodium carbonic acid (soda) is 2.48 wt.%.

PAA-DP-9 0.8075 g (1.33 wt.%)

Chromium acetate 0.285 g (0.48 wt.%)

Real water 58 g

Sodium carbonate, acid 1.5 g (2.48 wt.%)

Samples were mixed on a magnetic stirrer until a thick liquid formed. The gelation time was determined (taking into account the mixing time). The results are shown in table.5.

Table 5 No. p / p Name of the laboratory sample Gelation one. Laboratory sample No. 1 The gel formed after 36 hours, in the upper part a weak gel. 2. Laboratory sample No. 2 The gel formed after 27 hours, in the upper part a weak gel. 3. Laboratory sample No. 3 The gel formed after 36 hours, in the upper part a weak gel. four. Laboratory sample No. 4 The gel formed after 16 hours

The result of the work was the selection of components with more efficient gelation. Laboratory tests were conducted with various brands of PAA, namely DP-9, AK-642, D-1.

DP-9 grade polyacrylamide has the best solubility, at the same time it gives better gelation compared to the other two PAA grades.

As a result of tests of laboratory samples by the proposed method, it was found that the most effective gelation is provided by the technology of preliminary alkalization of real water to a pH of 8.0, the addition of sodium carbonic acid (soda) in an amount of 2.48 wt.% And the dosage of the main PAA reagents grade DP- 9 1.33 wt.% (0.8075 g) and chromium acetate 0.48 wt.% (0.285 g).

Thus, if during the gelation process the influence of impurities (metals, dissolved salts) is eliminated, then a gel with specified strength characteristics can be obtained. Due to the fact that when adding crosslinkers, such as alkali (caustic soda) and sodium carbonic acid (soda), insoluble metal and carbonate salts are formed in the composition of the already crosslinked polymer system, which give additional elastic properties to the gel formed.

The injection time of the gelling composition was calculated by the following formula:

T = 16V / Q,

where V is the zone of the reservoir, processed gelling composition;

Q - injectivity of the treated formation.

A decrease in gelation time compared with other methods has a positive effect on reducing the negative effect of formation fluids on the polymer crosslinking process.

It is also necessary to take into account factors affecting the gelation rate in real formation conditions (temperature, rock composition, salinity and density of formation water).

Laboratory studies found that a change in the quantitative composition of PAA in solution does not lead to a change in the structure of the resulting gel and its crosslinking time. Basically, the concentration of the alkaline solution used to prepare the composition affects the gelation time. Strengthening the strength of the gel and the time of its formation depends on a certain concentration of sodium carbonate (soda) introduced into the sodium solution.

The regulation of the gelation rate can be carried out in two known ways:

1) regulation of the concentration of crosslinkers and precipitating components;

2) the injection into the reservoir separately of rims of cross-linking elements and sediment-forming compounds to accelerate the speed of the gel-forming process, combined with sedimentation.

For a more effective application of the technology, it is possible to pump certain concentrations of gel-forming and sediment-forming compositions together with a further sharp increase in their concentrations to speed up the process and reduce the time of work on the well.

Sedimentary elements act as natural fillers to strengthen the structure of this composition.

The proposed gelation method takes into account not only the physicochemical parameters of the polymer composition, but also eliminates negative factors (the presence of impurities in the injected water and the content of chemical elements in the formation) that affect the following parameters:

1) The volume of chemicals and the final product - the polymer composition necessary for the implementation of the technology.

2) The lack of influence of chemical elements in reservoir conditions and in the water used to prepare the compositions.

3) The use of the same dissolved elements as a filler for the formation of a strong gel structure in reservoir conditions.

4) After carrying out the proposed method of water isolation, the non-reactive crosslinker molecules (alkali and soda) in the solution when the water enters the gelation zone (injection into the injection or breakthrough, pull-ups in the extraction), due to the additional reaction with the dissolved elements in the water will only strengthen the gel structure . So, we can talk about the possibility of changing the educated composition in the process of well development after treatment. This also plays a positive role, since the application of significant elastic impacts on the formation creates a risk of destruction of the resulting composition. In our case, over time, the strength of the resulting polymer composition will only increase.

The main difference and advantage of the proposed method from previously known is that it becomes inappropriate to cement with cement to strengthen the strength of the formed composition, since you can get almost any strength parameters of the gel, especially resistant to destruction.

We consider it possible to use this composition to isolate watering sources in horizontal wells, since the number of effective methods of water isolation is insignificant.

It is worth noting that all the chemicals used are relatively inexpensive and common when carrying out work to increase oil recovery. It should also be repeated that for the injection of the composition does not require special equipment and it is possible to carry out work already available equipment for the preparation and injection of polymer compositions.

The method is promising, since it is possible to further change the complex of crosslinkers and to obtain new types of polymer gels with specified parameters.

Thus, the use of the proposed method of using modified polymer compositions to increase oil recovery allows to increase the production rate of producing wells and reduce the amount of produced water, to improve the quality and duration of waterproofing. In addition, the method is technologically simple, reliable, does not require a large consumption of scarce and expensive materials.

Claims (1)

A method of using modified polymer compositions to increase oil recovery, including the injection into the formation of an aqueous solution of polyacrylamide and chromium acetate, characterized in that the solution is prepared in produced water with the addition of caustic soda to pH 8.0 and additionally sodium carbonate in an amount of 2.48 wt.% and a dosage of polyacrylamide in an amount of 1.33 wt.% and chromium acetate in an amount of 0.47 wt.%.