RU2542059C2 - Method of increase of reservoir recovery by injection of water-gas mixture - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to oil and gas production industry and, in particular, to field development by means of water and gas injection into injection wells and withdrawal of oil through production wells. The method includes the preparation of the water-gas mixture within the range of gas content values, ensuring the operational stability of the pumping unit, injection of the mixture into one or more wells using the unit with a centrifugal pump and displacement of oil from the formation with the tank pressure maintaining system. Meanwhile before injection of the water-gas mixture into the formation, the correlation of oil displacement coefficient with the gas content in the water-gas mixture at formation conditions is determined. On the basis of the obtained correlation the optimum value of the gas content is selected. In the well itself the correlation between the injection capacity and the gas content is determined. The working relation of water and gas discharge values upstream the mixer is identified. Further, with the advancing of displacement front located between injection and production wells, the current value of the gas content at the displacement front is calculated with the pressure correlation. After that the gas content in the water-gas mixture is decreased, maintaining it at the optimum level.

EFFECT: simplification of technology with simultaneous decrease of expenses for its implementation due to more thorough consideration of the factors influencing the efficiency of oil recovery increase measures.

1 ex, 1 dwg

Description

The invention relates to the oil and gas industry, in particular to methods for developing fields by injecting water and gas into injection wells and extracting oil through the production.

A known method of developing an oil reservoir, including the selection of fluid through production wells and injection into the injection wells of a water-gas mixture, which is obtained at the mouth of these wells by gas ejection in a jet pump, while the water-gas mixture (hereinafter HCV) is dispersed and homogenized, for which this mixture is fed by jet pump into a hydrodynamic cavitation unit and then into a jet disperser to convert the energy of the jets into the energy of acoustic waves and the formation of pulsating cavitation (RF patent No. 2266396).

The disadvantage of this method is: low coefficient of oil displacement, a complex system for the preparation of a water-gas mixture does not allow for regulation (change) of the gas content of the injected agent during the development of the reservoir, which leads to an increase in the cost of gas compression and difficulties in the operation of production wells.

The closest technical solution to the claimed method relates to a method of increasing oil recovery with a system for maintaining reservoir pressure by injecting a water-gas mixture into a formation, including preparing a water-gas mixture, pumping it into one (or more) wells using a centrifugal pump, allowing free water-gas mixture to be present gas in the range of gas concentrations, ensuring stable operation of the pump, and the displacement of oil from the reservoir by the injected water-gas mixture. The effective displacement of oil from the reservoir during its oil recovery and exposure to it with a water-gas mixture with a gas content in this mixture in the range from 30 to 75% of the volume of the mixture under oil displacement conditions. To create the necessary gas content in the mixture before injecting the water-gas mixture into the wells at the outlet of the centrifugal pumping unit, an excess amount of water is separated from the water-gas mixture using a separator, and the water-gas mixture with the necessary gas content is fed to the suction manifold of the centrifugal pumping unit (RF Patent 2357074, 2007 .).

The disadvantage of this method is the lack of a criterion for choosing the optimal gas content value for a particular oil production object, which determines the irrational use of the injected gas, which leads to a complication of the technology and an increase in the cost of its implementation.

The technical task of the invention is to simplify the technology while reducing the cost of its implementation due to more complete consideration of factors affecting the effectiveness of measures to increase oil recovery.

The problem is achieved in that in a method of increasing oil recovery by injecting a water-gas mixture into a formation, including preparing a water-gas mixture in a range of gas contents, ensuring a stable operation of a pumping unit, pumping it into one or more wells using a centrifugal pump installation, and displacing oil from formation with a system for maintaining reservoir pressure, according to the invention before the injection of the water-gas mixture into the formation experimentally determine the dependence of the coefficient in tightening oil from gas content in a water-gas mixture under reservoir conditions, based on the obtained dependence, choose the optimal gas content value, determine the dependence of the formation injectivity on gas content directly at the well, establish the working ratio of water and gas flow rates at the inlet to the mixer, then, as the displacement front advances located between the injection and production wells, calculate the current gas content at the displacement front depending on the pressure, p follows that reduce the gas content in the water-gas mixture, keeping it at the optimum level.

Thus, according to the invention, it is proposed:

- before injection of HCV, using core material and oil selected from a specific reservoir, the dependence of the displacement coefficient of oil displacement on gas content in the HCV under its thermobaric conditions is experimentally determined;

- based on the obtained dependence, the optimal gas content value is selected (taking into account the costs of preparing the HCV and the increase in the displacement coefficient);

- determine the dependence of the injectivity of the well from gas content. The dependence of the injectivity of the well on the gas content is determined directly at the well by pumping the HCV with different flow rate and gas content in the HCV;

- establish the working ratio of the flow of water and gas at the inlet to the mixer to obtain a HCV with optimal gas content;

- then periodically determine the position of the displacement front and the pressure value in this area and calculate the current value of gas content at the displacement front using the dependence of gas content on pressure. The position of the displacement front is determined either by calculation or by geophysical methods. The dependence of gas content on pressure is determined by any known method;

- using these data reduce the gas content in the HCV at the inlet to the mixer, maintaining it at the optimum level.

The drawing shows the experimentally obtained dependence of the displacement coefficient on the gas content in the injected HCV under displacement conditions.

Here is an example of the implementation of the proposed method, indicating the actual parameters of the process.

There is an oil field being developed with a reservoir pressure maintenance system. The object of development of the oil field is a layer lying at a depth of 3000 m, with a reservoir pressure of 30 MPa and a temperature of 90 ° C.

Associated petroleum gas and water come from the oil treatment unit at a pressure of 0.5 MPa. Water at the inlet to the mixer (ejector) comes from the pumping unit ANT 150 with a pressure of 20 MPa. The pressure at the outlet of the ejector (pressure at the inlet to the pump unit) is 4 MPa.

The volume of water injection before applying the gas treatment is 140 m ³ / day at wellhead pressure of 20 MPa. The viscosity of oil in reservoir conditions is 1 MPa * s.

a) Before injection of HCV, experimentally determine the dependence of the displacement coefficient of oil displacement on gas content in the HCV under reservoir conditions.

b) Analysis of the presented dependence (graph) shows that when choosing a gas content in the injected mixture of more than 20-25%, there is no significant increase in the efficiency of oil displacement, which will lead to unreasonable overstatement of the volume of injected gas. Then, according to the obtained dependence, the gas content at the bottom of the well should be 20%.

c) determine the dependence of the change in injectivity of the well from gas content.

The estimated pressure at the bottom of the well at a wellhead pressure of 20 MPa and gas content at the bottom of the well, equal to 20%, will be P = 48 MPa. The injectivity of the well during HCV injection (determined for each specific well and reflected in the technical documentation) was 100 m ³ / day. Then the gas content (calculations of the gas content are carried out without taking into account the compressibility) at the bottom of the well at a pressure of 48 MPA will be:

Г = Qг / (Qг + Qв) = 0.2

Gas consumption (Qg) under these conditions will be 20 m ³ / day, water (Qв) - 80 m ³ / day.

) при давлении Р_с=0,5 МПа составит:Then the gas flow rate at the inlet to the mixer ( $$Q_g^{\mathrm{one}}$$

) at a pressure P _c = 0.5 MPa will be:

$${\text{Q}}_{\text{g}}^{\text{one}}=\text{Qg}\cdot {\text{P / p}}_{\text{from}}=\text{twenty}\cdot \text{48 / 0.5}={\text{1920 m}}^{\text{3}}/\mathrm{from}\mathrm{at}t$$

Water consumption will remain the same - 80 m ³ / day.

d) establish the initial working ratio of the flow of water and gas at the inlet to the mixer.

The gas content at the inlet to the mixer will be:

G ₁ = 1920 / (1920 + 80) = 0.96

d) As the displacement front advances, its position is periodically determined, the pressure in the area occupied by the water-gas mixture and the dependence of gas content on pressure are adjusted for gas content.

In a year, the displacement front will be at a distance of 50 m from the bottom of the injection well. The reservoir pressure in the zone occupied by the HCV will be P _p = 35 MPa. Given the change in pressure, the gas flow rate at the inlet to the mixer is adjusted, which will now be:

. $${\text{Q}}_{\text{g}}^{\text{one}}=\text{Qg}\cdot {\text{P / p}}_{\text{from}}=\text{20-35 / 0.5}={\text{1400 m}}^{\text{3}}/\mathrm{from}\mathrm{at}t$$

.

A new gas content at the inlet to the mixer is set equal to:

G ₁ = 1400 / (1400 + 80) = 0.945

Therefore, the gas flow (and therefore the costs of its compression) should be reduced by 520 m ³ / day, or by 27%.

When using the proposed method, the role of such a factor as the change in gas content as the HCV moves in the reservoir is taken into account. It is well known that the greatest pressure in the reservoir exists near the bottom of the injection well, and the minimum - near the bottom of the producing well. As the HCV rim moves from the injection to the production well, a change in pressure will lead to an increase in gas content in the HCV rim. It also makes it necessary to adjust the gas content in the injected HCV taking into account the position of the displacement front.

The simplification of the technology is achieved by optimizing (minimizing) the gas content, to values that ensure the maximum economic effect due to the injection of a smaller, but sufficient to increase oil recovery, gas volume. In addition, since the high gas content in the produced products can lead to a disruption in the supply of working downhole pumps, which will require replacement of the downhole equipment, the implementation of the proposed approach will reduce the cost of subsequent gas recovery and utilization, due to the minimization of gas content in the produced products.

Claims (1)

A method of increasing oil recovery by injecting a water-gas mixture into a formation, including preparing a water-gas mixture in a gas content range that ensures stable operation of a pumping unit, injecting it into one or more wells using a centrifugal pump, and displacing oil from the reservoir, with a reservoir maintenance system pressure, characterized in that before the injection of the water-gas mixture into the reservoir, the dependence of the oil displacement coefficient on the gas content is experimentally determined water in a gas-gas mixture under reservoir conditions, on the basis of the obtained dependence, the optimal gas content is selected, the dependence of changes in the injectivity of the formation on gas content is determined directly at the well, the working ratio of water and gas flow rates at the inlet to the mixer is established, then, as the displacement front located between injection and production wells, calculate the current value of gas content at the displacement front depending on pressure, and then reduce the content e gas to water-gas mixture, keeping it at the optimum level.

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