RU2096588C1 - Method for recovery of liquid from underground reservoir - Google Patents

Abstract

FIELD: oil and gas industry. SUBSTANCE: this can be used for recovery of hydrocarbon liquid from depleted oil reservoirs in oil and gas production industry. According to method, producing string is run down with lift of smaller diameter pipes and high-pressure chamber. This chamber is made of larder diameter pipes which are fastened on lift by means of adapter. Gas is injected into underground reservoir through inter-string space. Liquid is displaced from inter-string space and annular passage of high-pressure chamber. Gas is delivered from inter-spring space and reservoir to lift through high-pressure chamber. Liquid is recovered from gas lift. Upper part of high-pressure chamber is located above level of liquid in reservoir and is connected with reservoir. Gas is delivered from high-pressure chamber to lift through non-return valve. Created behind high-pressure chamber is column of liquid, and injection pressure and gas flow rate are maintained constant. EFFECT: high efficiency. 1 cl, 3 dwg

Description

 The invention relates to the selection of fluid from an underground reservoir and can be used to extract hydrocarbon fluid from depleted oil reservoirs in the oil and gas industry.

A known method of selecting liquid from an underground reservoir with a gas lift using couplings with holes along the length of the elevator to allow gas to pass from the annular space to the elevator [1]
The disadvantages of this method:
the need to create high overpressure in the annular space of the well and in the reservoir, increased specific gas flow rate for lifting fluid from the reservoir, in the presence of highly permeable reservoirs and low reservoir pressures, it is possible to push oil from the well into the reservoir.

 A known method of fluid selection from the reservoir, which consists in the descent of a two-row elevator into the production casing of the well with a stepped injection column: in the lower part of a smaller diameter, in the upper - a larger one.

High-pressure gas is fed into the annular space between the two columns to create a gas-liquid mixture in the elevator with the fluid coming from the reservoir under reservoir pressure [1]
The disadvantages of this method:
increased metal consumption of the gas-liquid hoist design, the impossibility of increasing the immersion of the lifting pipes by tolerance, to raise the fluid it is necessary to have a power reserve of the compressor unit to create starting pressure, in the presence of low-permeability reservoirs and insignificant inflows of reservoir fluid, it is impossible to operate a well with constant fluid withdrawal from the reservoir.

Closest to the proposed gas-lift method of fluid withdrawal from the reservoir using a replacement chamber [2] It provides for the selection of fluid from the reservoir at very low reservoir pressures. A hoist is lowered into the production casing for fluid extraction, in the lower part of which a replacement chamber is installed. The method of fluid selection is to inject high-pressure gas into the well and then into the substitution chamber with a cut-off of the injected gas either at the wellhead or at the bottom near the substitution chamber. The replacement chamber is equipped with a check valve to allow fluid to flow from the formation to the elevator and to prevent the transfer of pressure of the injected gas into the formation. The selection of fluid is carried out on the principle of periodic gas supply to the replacement chamber and periodic filling of the lift with extractable liquid, followed by its displacement in the form of a gas-liquid mixture to the surface at atmospheric pressure at the wellhead:
The disadvantages of this method:
the impossibility of constant fluid withdrawal from the reservoir, it is necessary to have a power reserve of the compressor unit, increased gas flow during periodic shutdowns and starts of the well for fluid extraction, the need for complex automatic devices for periodic gas supply to the lift.

 The purpose of the invention is to increase the efficiency of liquid withdrawal from an underground reservoir and reduce energy consumption.

 To achieve this goal, a production casing is lowered into the well with a hoist inside it from pipes of smaller diameter and a high-pressure chamber from pipes of larger diameter mounted on the hoist by a sub, pumping gas into the underground tank through the annular space, squeezing the fluid out of it through the annular channel of the high-pressure chamber into the elevator, gas supply from the annular space and the reservoir to the elevator and the selection of liquid from the reservoir by a gas lift, for which the upper part of the high-pressure chamber placed above the liquid level in the tank and communicate it with the tank, and the gas supply from the high-pressure chamber to the lift is carried out through a check valve.

 The selection of fluid is carried out by the following steps.

 Gas under the working pressure of a compressor unit or other high-pressure gas source is injected into the well into the annulus, creating excess pressure in the underground reservoir. The injected gas into the well also enters through the open part of the pipe string of larger diameter into the high-pressure chamber and then through the check valve to the lift. The gas, mixing with the liquid inside the lift, forms a two-phase gas-liquid mixture, the density of which becomes lower than the density of the liquid. This phenomenon leads to a pressure drop determined by the difference in the statistical pressures created by the columns of one liquid located in the underground reservoir and the gas-liquid mixture in the elevator. Due to this, the liquid is displaced from the underground reservoir into the elevator, the gas-liquid mixture is further formed and, under the influence of excess pressure in the reservoir, this mixture is lifted along the elevator to the day surface.

 This method is carried out using the device.

 The device is a high-pressure chamber 1 (see Fig. 1), consisting of pipe columns of larger 2 and smaller 3 diameters. The inner pipe string of a smaller diameter is a gas-liquid mixture hoist, and the outer pipe string 2 serves to create a channel through which gas flows in a free state from the wellhead to the lowest part of the lift 3. For this, the upper part of the high-pressure chamber 1 is open and the lower plugged by a sub 4 connecting both columns of pipes 2 and 3. In a sub 4 there is an inlet 5 with a check valve 6 and an outlet 7 for passing gas from the chamber 1 into the interior of the elevator 3. Translated Nike also has a passage channel 8 for collecting fluid from the underground reservoir.

 The technological scheme of the method of liquid selection from the underground reservoir (see Fig. 2) includes an underground reservoir 1, a high pressure chamber 2, a lift 3, a liquid 4, a liquid level 5, a sub 6, a check valve 7, an inlet 8 for supplying gas to well, removal of a two-phase flow of gas-liquid mixture 9 from the lift 3.

 The incoming gas to the underground reservoir is spent only on creating a two-phase flow inside the elevator and moving it to the day surface, provided that the upper part of the high-pressure chamber 2 is located above the liquid level 5.

Case Studies
Example 1

The underground tank is filled with condensate with a density of 800 kg / m ³ . The condensate level is 800 m below the wellhead. A lift consisting of tubing and a high-pressure chamber was lowered into the production casing. The elevator is lowered into the underground reservoir to a depth of 1000 m, and the upper part of the chamber is set 5 m above the liquid level. A gas was injected into the well at a constant flow rate from a factory gas source with a working pressure of 3 MPa. First, condensate was taken with a flow rate of 400 m ³ / day. Then, after emptying the annular space, the condensate flow rate decreased to 100 m ³ / day and continued to remain almost constant until the very end of the process of its selection from the underground reservoir (see Fig. 3).

 Compared with the known condensate extraction method [1], the gas flow rate decreased by more than 6 times with a lower discharge pressure of 2 MPa.

 Example 2

The liquid level is in the underground tank. An elevator with a high-pressure chamber was lowered into the underground reservoir, the upper part of which is located in the production string 40 m above the liquid level. First, the necessary gas flow rate was determined at a given working discharge pressure of 3 MPa to achieve the maximum possible condensate extraction. It was found that this design of the lift can work with a gas flow rate of 40,000 m ³ / day. By injecting gas into the well, we obtained a condensate extraction of 450 m ³ / day, which is more than 4 times higher than the condensate extraction in a known manner [2]
It can also be seen from the above examples that with any other method, the initial gas injection pressure should be at least 8 MPa for a liquid with a density of 800 kg / m ³ and a sampling depth of 1000 m, i.e. the same conditions as in the above examples.

 Thus, the increase in efficiency from the introduction of the proposed method consists in increasing the productivity of the gas-lift installation while reducing gas consumption and in the presence of lower gas injection pressures into the annulus of the well.

 Sources of information.

1. The exploitation of oil and gas fields. I.A. Muravyov, M. Nedra, 1978, p. 199, [1] [2]
2. Theory and practice of gas lift. Yu.V. Zaitsev. M. Nedra, 1987, p.90 [3] - prototype.

Claims (2)

 1. A method of taking liquid from an underground reservoir, including lowering a production casing with an elevator from pipes of smaller diameter and a high-pressure chamber from pipes of larger diameter mounted on an elevator by a sub, pumping gas into the underground reservoir through the annular space, extruding liquid from it and the annular chamber channel high pressure, gas supply from the annular space and the tank to the lift through the high pressure chamber and the selection of liquid from the tank with a gas lift, characterized in that the top the lower part of the high-pressure chamber is placed above the liquid level in the reservoir and communicates with the reservoir, and gas is supplied from the high-pressure chamber to the lift through a non-return valve, while a liquid column is created behind the high-pressure chamber and the discharge pressure and gas flow are kept constant.  2. The method according to p. 1, characterized in that by supplying gas to the lift form a gas-liquid mixture in it and create an additional pressure drop between this mixture, which is formed in the lift immediately after the start of the gas supply, and the liquid located behind the high pressure chamber.

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