RU2342418C2 - Oil displacing reagent for non-uniform watered formations - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil extraction and can be employed for raising oil yield from carbonate and terrygenous water-flooded non-uniform formations under conditions of critical watering at late stages of oil deposits development. Oil displacing reagent for non-uniform watered formations includes water, polyacrylamide and additionally metal-indicator, grafted to polyacrylamide, at a following ratio of components, wt %: polyacrylamide 0.5-2.0, metal-indicator 0.0005-0.05, water - the rest. Also as metal indicator a reagent contains polyvalent metals - nickel or cobalt, or vanadium or aluminium or chromium.

EFFECT: increased efficiency of well development.

2 cl, 8 ex, 9 tbl

Description

The invention relates to the field of oil production and can be used to increase oil recovery of carbonate and terrigenous flooded heterogeneous formations in conditions of maximum water cut in the late stages of oil field development.

Known reagents for enhancing oil recovery in productive formations, which are water-soluble non-cross-linked polymer systems (M.L. Surguchev et al. Methods for oil recovery. M.: Nedra, 1991, p. 117). The positive effect of the use of aqueous polymer non-crosslinked systems is achieved due to their special rheological and filtration properties in porous media, due to the non-Newtonian type of flow. The nature of the flow of polymer solutions is affected primarily by shear stress, the elastic properties of macromolecules, adsorption and mechanical capture of polymer particles by a porous medium.

Also known are reagents for enhanced oil recovery based on crosslinked polymer systems, which, due to the presence of gel fractions in them, form elastoplastic particles uniformly distributed in water. When injected into the formation, these particles fill the largest pores and cracks, easily overcome the narrowing of the pore channels of heterogeneous high-permeability formations and block (clog) them. Less permeable areas of formations are generally not exposed to these particles. This makes it possible in the future, when water is injected into the formation, to more fully cover less permeable areas of the reservoirs, which leads to a decrease in oil water cut, increased production and enhanced oil recovery (M.L.Surguchev et al. Methods for oil recovery. M .: Nedra, 1991 ., p.123).

These reagents are taken as a prototype. However, all known reagents have the following disadvantage.

When polymer is injected into the formation, it enters the most washed, i.e. most permeable formation zones. Subsequently, water injected deviates into less permeable zones and displaces oil from them. At the same time, under the influence of a pressure gradient, the polymer rim moves along the formation from the bottom of the injection well to the bottom of the producing well. At the same time, all new formation zones are covered by water flooding.

In the process of polymer movement through the formation, its destruction occurs. The destruction process is very difficult to predict. The destruction proceeds under the influence of formation temperature, mineralization of formation water, oxygen dissolved in the injected water, and, in addition, the polymer is mechanically destroyed when it is moved across the formation.

As the process of polymer degradation proceeds, its viscosity decreases, and the rate of movement of the polymer rim increases. There comes a moment when the polymer rim no longer provides increased resistance when moving along the formation and the process of increasing the coverage of the formation by water flooding stops, i.e. there comes a moment of termination of the technological effect of processing.

In time, this process can be represented as an increase in production after processing, the output of oil production to a maximum and a smooth decrease in oil production.

As shown by many years of experience, the maximum result can be achieved if, during the period when the production level reaches the maximum value, the well is re-treated with polymer.

However, it is not possible to predict the time to reach the maximum level of production from processing. This will lead to the fact that when the production level reaches a maximum, preparatory work begins for the re-injection of the polymer. As a result, processing is done when oil production levels begin to decline. Thus, reprocessing does not produce the desired result.

The objective of the present invention is to increase the efficiency of well treatments.

The problem is solved in that the proposed oil displacing reagent for heterogeneous flooded formations, including polyacrylamide, according to the invention further comprises a metal indicator grafted onto polyacrylamide, with the following components, wt.%:

polyacrylamide 0.5-2.0 metal indicator 0.0005-0.05 water rest.

Moreover, as an indicator metal, it contains polyvalent metals - nickel, or cobalt, or vanadium, or aluminum, or chromium.

This allows you to detect the appearance of a metal indicator in them by sampling and analyzing fluid samples in production wells.

Physically, the time of the indicator metal entering the production well coincides with the time of polymer destruction and its washing out of the formation, and, consequently, with the time the technological effect begins to cease (production reaches its maximum level).

Thus, there is a margin of time for the design and reprocessing before the reduction of the technological effect.

An example of the preparation of the proposed oil-displacing reagent.

PAA brand Akkotrol S622 in an amount of 250 kg is pre-irradiated with gamma rays at a source of ⁶⁰ to a dose of 0.05 Mrad. Separately, a solution of aluminum sulfate is prepared, for which 6 kg of AL ₂ (SO ₄ ) ₃ 18H ₂ O is dissolved in 60 l of water. The process of polymer modification is carried out in a technological reactor with a mixing device and controlled heating by spraying a dosed aqueous salt solution with stirring the entire mass. In the same reactor, subsequent drying of the product to a moisture content of 10-12% is carried out. The resulting product contains about 0.2 wt.% Grafted aluminum in terms of metal.

The following are examples of laboratory tests of a prepared oil displacing reagent.

Example 1

Mutiflock-231 grade PAA was used, irradiated to a dose of 0.05 Mrad with gamma rays. For modification, NiSO ₄ 7H ₂ O was used, 100 g of PAA powder was treated with stirring 30 ml of an aqueous solution of nickel sulfate. The concentration of the solution is 30 g / dl. The resulting sample was dried at a temperature of 40 ° C until free flowing. After drying, 0.5 g of powder was mixed with 100 ml of water until gel formation. To control the completeness of grafting Ni, the resulting gel was washed with water (1 L). The metal content was determined separately in the gel and water from washing the gel. Used the method of x-ray fluorescence analysis. The measurement was carried out on a Spectroscan X-ray spectrometer. The results of the analysis are presented in table 1.

Table 1 Object of analysis The content of Ni, wt.% Gel before contact with water 0.0270 Gel after contact with water at 20 ° C, 24 hours 0.0204 Water phase Not found

It is seen that upon contact of the gel with water, nickel is retained in the gel, i.e. nickel entered the gel structure.

Example 2

The preparation of powder samples of modified PAA and gel, as well as analysis was carried out in the same way as in example 1, but the gel was in contact with water at 60 ° C. The results are shown in table 2.

table 2 Object of analysis The content of Ni, wt.% Gel before contact with water 0.0243 Gel after contact with water at 60 ° C, 24 hours 0.0194 Water phase Not found

It can be seen that at elevated temperatures, nickel is retained in the gel, i.e. metal-gel bonding is heat-resistant.

Example 3

The preparation and analysis of the samples was carried out in the same way as in example 1, but mineralized water containing 20 g / l of sodium, calcium, and magnesium salts was used to wash the gel. The results of the analysis are presented in table 3.

Table 3 Object of analysis The content of Ni, wt.% Gel before contact with water 0.0185 The gel after contact with a solution of salts of 20 g / l at 20 ° C, 24 hours 0.0150 Water phase Not found

It is seen that upon contact of the gel with mineralized water, nickel is retained in the gel, i.e. metal-gel bonding is salt tolerant.

Example 4

Nickel and gel grafted PAA samples were prepared and analyzed in the same manner as in Example 1, but nickel sulfate solutions of different concentrations were used. The metal content was determined in dry powders of the obtained reagent and in gels. In addition, the volume of the gel was measured using a measuring cylinder. The volume of the gel reflects the degree of crosslinking of the polymer. The results are presented in table 4.

Table 4 No. Powder, Ni, wt.% Gel, Ni, wt.% The volume of the gel, cm ³ one 0.144 0.0002 one hundred 2 0.36 0.0017 120 3 1.19 0.0058 130 four 1.57 0.0081 one hundred 5 2.33 0.0114 70 6 3.0 - Does not swell

It can be seen that, at a high nickel concentration, the polymer swells poorly. This is due to a significant increase in crosslink density. The lower concentration limit is limited by the sensitivity of the metal detection method. The optimal limits for nickel concentration are 0.1-2.3% in the mass of the reagent powder.

Example 5

This example illustrates the use of grafted metal to study the movement of a gel (reagent) in a formation.

According to the measured value of the metal, the concentration of the reagent in the samples of produced water is estimated. Used reagent containing 1.0277 wt.% Grafted Ni. The reagent powder was mixed with saline water in various ratios. Received model samples of produced water with different concentrations of reagent (table 5, column 1).

Water was evaporated in an open container on a heating plate until a wet mass was obtained, which was then annealed in a muffle furnace at 800 ° C to a dry residue.

The mass of solids and the nickel content in it were determined. Weighing was performed on an VLR-200 analytical balance, and nickel analysis on a Spectroscan X-ray spectrometer.

Based on the measured values of the mass of solids and nickel, the concentration of the reagent in model samples of produced water was estimated. The evaluation was carried out according to the formula:

C (g / l) = M (g / l) × Cr (%) / Co (%),

Where:

C is the concentration of the reagent;

M is the mass of dry residue, this value mainly depends on the salinity of the water;

Cg is the measured value of the metal in the dry residue;

Co - grafted on PAA amount of metal.

Table 5 (column 2) presents the calculation results.

Table 5 Reagent concentration, g / l, in samples of produced water one 2 Introduced Found 1.0356 1.2215 0.1035 0.0943 0.0542 0.0330

The table shows that the concentration of the reagent, embedded and calculated according to the measured values of the hemmed metal, is consistent within an error of 20%. The calculation method can be used for indicator studies using the proposed reagent.

Example 6

The preparation and analysis of the samples was carried out in the same way as in examples 1-3, but instead of nickel sulfate, cobalt acetate Co (CH ₃ COO) ₂ 4H ₂ O was used. The results are presented in table 6.

Table 6 Object of analysis Co content, wt.% Gel before contact with water 0.0150 Gel after contact with a salt solution of 20 g / l at 60 ° C, 24 hours 0.0161 Water phase Not found

It is seen that after washing with water, the metal remains in the gel.

Example 7

Used PAA brand Akkotrol S622. Dose 0.1 Mrad. For metal modification, the technical salt Al ₂ (SO ₄ ) ₃ 18H ₂ O was used.

The metal was grafted to the polymer, as in Example 1. The modified PAA was stirred in water at the rate of 0.5 g of powder per 100 ml of water. After powder swelling (2-3 hours), a gel was obtained. To control the completeness of grafting of aluminum and bond strength, the resulting gel was washed with water. The gel was topped up with one liter of water containing 20 g of NaCl and stored at 60 ° C for 24 hours. The aluminum content in the gel samples was determined before and after contact with water, as well as in wash water. A chemical analysis method was used. The results are presented in table 7.

Table 7 Object of analysis Al content, wt.% Gel before contact with water 0.080 Gel after contact
Mineralization of NaCl water,
Temperature 60 ° С
24 hours time 0.085 Water phase Not found

It can be seen that in the contact of the gel with water, the mineralization is 20 g / l, at a temperature of 60 ° C, aluminum remains in the gel, therefore, the bond of the metal with PAA is strong. The proposed reagent passed field tests.

Example 8

An injection well was processed at an oil field, around which there are three production wells. The daily water injection into the injection well was 450 m ³ . Daily fluid withdrawals from surrounding producing wells - 400 m ³ . The water content of the extracted products is 83%. The permeability of the formation in thickness varies from 100 to 800 mD.

In order to reduce water cut in the produced products and increase oil recovery, it was decided to periodically pump cross-linked solutions of polyacrylamide into the formation through an injection well. To control the movement of polyacrylamide prepared polyacrylamide in accordance with example 1.

One month after the injection of polyacrylamide, weekly sampling of produced products from producing wells began. The results of the analysis of samples taken in production wells are shown in table 8.

Table 8 Sample No. The indicator content in the samples, wt.% No. 1 Number 2 Number 3 one 0 0 0 2 0 0 0 3 0 0 0 four 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 8 0 0 0 9 0 0.00031 0 10 0 0.00052 0 eleven 0.00015 0.00028 12 0.00033 0 0 13 0.00005 0 0 fourteen 0 0 0 fifteen 0 0 0.00006 16 0 0 0.00012 17 0 0 0.00004 eighteen 0 0 0

Analysis of the samples was carried out according to the method described in example No. 1 and example No. 5.

The dynamics of changes in the water cut of the extracted products is given in table 9. The determination of the water content of the extracted products was carried out simultaneously with the determination of the presence of an indicator in it.

Table 9 Sample No. Water cut of extracted products,% No. 1 Number 2 Number 3 one 71 68 76 2 71 68 76 3 71 68 76 four 71 68 76 5 71 68 76 6 71 68 76 7 71 68 76 8 71 71 76 9 71 71 76 10 75 71 76 eleven 77 72 76 12 77 73 76 13 77 73 76 fourteen 77 73 78 fifteen 78 73 78 16 78 73 78 17 78 73 78 eighteen 78 73 78

As can be seen from tables 8 and 9, the arrival of the indicator coincided with the beginning of a decrease in the technological effect of processing. However, 19 weeks after the first injection of polyacrylamide into the reservoir, the necessary forces and equipment were prepared (the necessary volume of chemicals was brought into the well and the equipment necessary for injecting polyacrylamide was delivered). This allowed, without waiting for the complete cessation of the technological effect of the treatment, to re-treat the formation with a solution of polyacrylamide and get the maximum technological effect.

Claims (2)

1. Oil-displacing reagent for heterogeneous flooded formations, including water, polyacrylamide, characterized in that it further comprises an indicator metal grafted onto polyacrylamide, with the following components, wt.%: polyacrylamide 0.5-2.0 metal indicator 0.0005-0.05 water rest 2. The oil-displacing reagent according to claim 1, characterized in that as an indicator metal it contains polyvalent metals nickel, or cobalt, or vanadium, or aluminum, or chromium.