RU2217575C2 - Way to seal off flooded sections of formation - Google Patents

Abstract

FIELD: oil and gas industry, blocking-off water inflow in production wells and equalization of intake profile in injection wells. SUBSTANCE: way to seal off flooded sections of formation includes consistent pumping of gel-forming and sludge-forming compounds based on aqueous solution of sodium silicate and calcium chloride, in additional pumping of aqueous solution of polymer into formation. Aqueous solution of polymer is pumped in alternation with compounds and/or in mixture with at least one of them and the amount ensuring 0.05-1.5% consumption of polymer to volume of gel-forming compound. EFFECT: reduced water content in sections of formation, increased oil output. 1 tbl

Description

The invention relates to the oil and gas industry and can be used to isolate the influx of water in producing oil or gas wells to create waterproof screens, as well as to align the injectivity profile in injection wells.

A known method of isolating flooded sections of a formation, used to even out injectivity profiles of injection wells, involves sequentially injecting a sediment forming composition containing sodium silicate (potassium), calcium chloride, sodium chloride and water, and a gelling composition containing sodium silicate (potassium), chloride calcium and water [1].

The effectiveness of the known method is reduced due to the uneven distribution in the reservoir of injected compositions, which leads to increased water cut and reduced oil production.

The technical challenge facing the invention is to reduce water cut and increase oil production.

The problem is solved in that in the method of isolating waterlogged sections of the formation, including sequentially injecting sediment-forming and gel-forming compositions into the formation, prepared on the basis of an aqueous solution of sodium silicate and calcium chloride, an additional aqueous polymer solution is pumped into the formation, while the aqueous polymer solution is pumped in alternation with compositions and / or in a mixture with at least one of them and in an amount providing a polymer consumption of 0.05-1.5% by volume of the gelling composition.

In this case, an aqueous polymer solution can be pumped in the following options:

before injection of the gelling composition;

simultaneously with the injection of a gelling composition;

after injection of the gelling composition;

before and simultaneously with the injection of a gelling composition;

before and after injection of the gelling composition;

simultaneously and after injection of the gelling composition;

before, simultaneously and after injection of the gelling composition.

As a polymer, PAA (polyacrylamides of the brands Accotroll S-622, PDA-1040, etc.), CMC, and others can be used.

According to the data of geophysical studies of the reservoir and the current state of its development, the volume (V) of the injected composition is determined, depending on the processing radius (R), interlayer thickness (h) and porosity (m): V = πR ² hm.

The preparation of sediment-forming and gel-forming compositions is carried out by known technologies described, for example, in the prototype.

To implement the option, when the polymer is pumped simultaneously with the gelling composition, simultaneously in separate containers a solution of calcium chloride (GOST 450-77) and a solution of sodium silicate (GOST 13078-81) are prepared, and a water-soluble polymer, for example, carboxymethyl cellulose (TU 6-55-40 -990), added to both or to one of the containers. Mixing of the solutions is carried out at the wellhead during their injection into the formation. Water can be used both fresh and mineralized.

It was experimentally established that with any variant of adding water-soluble polymers, the rheological properties of the silicate gel solution change significantly, which becomes more viscous and plastic, and the gel structure becomes more stable. It was noted on the reservoir models that due to the increased viscosity, the injected composition penetrates mainly into highly permeable water-washed layers and to a much lesser extent penetrates into zones with low permeability.

A tangible effect is manifested when at least 0.05% of the polymer is introduced into the formation relative to the volume of the gel-forming composition, containing, wt.%: Sodium silicate 5-10; calcium chloride 0.2-2; water is the rest.

With the addition of polymer in excess of 1.5%, the effectiveness of the impact on the formation does not change significantly.

The polymer-treated gel-forming composition, when heated in a formation having a higher temperature, forms a strong gel that prevents further penetration of water.

An insignificant part of the gel-forming composition can penetrate into low-permeability zones. In this case, a caustic soda solution is pumped into the well and soaked for a time sufficient to destroy the gel that has penetrated into the low-permeability zone.

The method of isolation of waterlogged sections of the reservoir is illustrated by the following examples.

Example 1. In the experimental section of the oil reservoir with a permeability of 167 mD, which is at a late stage of development, there was a progressive increase in water cut in the produced fluid. The current oil recovery factor was 23.1%. It was proposed according to the method to process a focal injection well with an injection rate of 470 m ³ / day.

30 m ^{3 of a} 0.1% polymer solution were sequentially injected into the reservoir, then 60 m ^{3 of a} sediment-forming composition based on sodium silicate and calcium chloride, and then a gelling composition based on sodium silicate and mineralized water, additionally containing 0.05% polymer (polyacrylamide grade RDA-1040).

After treatment, the injectivity of the well decreased by 27%, and after 5 months at the experimental site, the water cut of the produced fluid decreased by 4.8%, the oil production rate increased by 1.6 tons / day, and the well response coefficient was 0.73. The predicted duration of the technological effect will be at least 11 months.

Example 2. In the experimental section of the oil reservoir with a permeability of 138 mD, a progressive increase in water cut of the produced products was observed. For individual wells in the area, water cut growth averaged 1.4% per month. The current oil recovery factor was 17.2%. To eliminate the water breakthrough, it is proposed according to the method to treat a focal injection well with an injectivity of 535 m ³ / day.

25 m ^{3 of a} 0.3% polymer solution were sequentially injected into the formation, then 70 m ^{3 of a} sediment-forming composition based on sodium silicate and calcium chloride and an additional 25 m ^{3 of a} 0.3% polymer solution, after which the gel-forming composition was pumped onto based on sodium silicate and calcium chloride, optionally containing 0.1% polymer. The polymer used was carboxymethyl cellulose KMC-500.

After treatment, the injectivity of the well decreased by 16%, the increase in water cut stopped. After 2 months at the experimental site, the water cut of the produced liquid decreased by 3.4%, oil production increased by an average of 1.22 tons / day. The predicted duration of the technological effect will be at least 9 months.

The effectiveness of the developed and known methods was investigated in laboratory conditions. Their insulating effect and their influence on the filtration process of the fluid pumped through an inhomogeneous model of the oil reservoir are evaluated. Efficiency assessment was carried out by changing the filtration rate through a highly permeable and low permeable interlayers and by an increase in oil displacement coefficients.

The studies were conducted on a modernized installation of the “UIPK” type, which simulates reservoir conditions and allows maintaining the necessary pressure and temperature, as well as controlling the flow of water and oil that are filtered through a reservoir model.

Two steel columns 60 cm long and 3.7 cm in diameter, filled with disintegrated core and simulating interlayers of various permeability, were used as a reservoir model. The permeability of the columns ranged from 147 to 848 mD; the permeability ratio in the model was 2.7–4.2. Preparation of the reservoir model and the fluids for the experiment was carried out in accordance with STP 0148070-013-91 “Methodology for laboratory studies on the displacement of oil by reagents”.

A reservoir model with a column permeability ratio of 2.9 is sequentially saturated with water with a content of calcium and magnesium salts of 2.5 g / l and sodium salts of 18 g / l, and then with oil. Next, the model is thermostated at a temperature of 75 ° C and oil is displaced by mineralized water up to 100% watering of the extracted liquid. At the end, they measure the rate of fluid filtration through the columns, the pressure in the system and calculate the coefficient of oil displacement by water.

In accordance with the method, 0.1 pore volume (V _pore ) of a 0.3% polymer solution was subsequently pumped into the reservoir model, then 0.2 V _{pore of a} sediment-forming composition based on sodium silicate and calcium chloride and an additional 0.1 V _pore 0 , 3% polymer solution. Next, a gel-forming composition based on sodium silicate and calcium chloride with a volume of 0.1 V _pore was added, additionally containing 0.1% polymer, which was used as CMC-500 carboxymethyl cellulose. At the end of the treatment, mineralized water was pumped through the reservoir model until the oil production ceased. The rates of fluid filtration through the columns and the pressure in the system were measured. The increase in oil displacement coefficient is calculated.

Similarly, tests were carried out with other ratios of reagents. The effectiveness of the prototype method is evaluated in the same conditions. The results of the experiments are presented in the table.

The results show that the use of the proposed method allows to achieve a more significant redistribution of the speeds of the filtration flows in heterogeneous formations in comparison with the method of the prototype. This is due to the formation in a porous medium of a polymer gel structured with an inorganic (silicate) precipitate and / or gel. Moreover, such a gel-like system is more intense

interacts with the formation rock and can withstand higher pressure gradients during water injection, which allows to increase the efficiency and duration of the impact on the reservoir model. Ultimately, this leads to an increase in the oil displacement coefficient.

Sourse of information

1. RF patent No. 2087698, MKI ⁷ E 21 V 43/32, 1995.

Claims (1)

A method of isolating flooded sections of a formation, comprising sequentially injecting sediment-forming and gel-forming compositions into the formation, prepared on the basis of an aqueous solution of sodium silicate and calcium chloride, characterized in that an additional aqueous polymer solution is pumped into the formation, while the aqueous polymer solution is pumped in alternation with the compositions and / or in a mixture with at least one of them and in an amount providing a polymer flow rate of 0.05-1.5% by volume of the gelling composition.