What Is an Airlift Pump?

Gas lift means that when the energy supplied by the local area is not enough to lift crude oil from the bottom of the well to the surface, the well will stop self-injecting. In order to make the oil well continue to produce oil, a method of oil recovery is to artificially press the gas (natural gas or air) into the bottom of the well and eject the crude oil from the surface.

The principle of gas lift oil recovery is a type of oil recovery that relies on the mixing of high-pressure gas injected from the surface into the well with the fluid produced in the wellbore by the expansion of the gas to reduce the density of the mixed liquid in the wellbore and lift the crude oil flowing into the well to the surface. the way.

When the formation energy cannot lift the liquid to the surface or cannot meet the production requirements, artificially inject high-pressure gas (natural gas, N2, CO2) into the well, and rely on the gas to reduce the flow pressure gradient (gas-liquid mixture density) in the lift pipe. And use its energy to lift liquid artificial lifting method.

Gas lift oil recovery is based on the "U" tube principle, injecting high pressure gas through the annulus (back lift) or tubing (forward lift) of the oil jacket through the ground, mixing it with the formation fluid, reducing liquid column density and returning to the bottom of the well. Pressure (bottom flow pressure) to increase well production.

Air lift is divided into continuous air lift and intermittent air lift. Continuous gas lift is the continuous injection of high-pressure gas into the well and draining the liquid from the wellbore. It is suitable for oil wells with better liquid supply capacity and higher production. Intermittent gas lift is the periodic injection of gas into the wellbore, which pushes the plug of the oil layer fluid accumulated in the wellbore during the injection stop to the surface, thereby draining the liquid in the well. Mainly used in oil wells with poor supply capacity and low production.

Wellhead and downhole equipment for gas lift oil production are relatively simple, easy to manage, and the volume of fluid changes is large. For deep wells, oil and gas are relatively high, sand production wells, inclined wells, etc. have advantages over pumping methods. However, gas-lift oil recovery methods require sufficient high-pressure gas sources. The bottom-hole back pressure of gas-lift wells is high, and the temperature of the injected gas is low, which can cause wellbore waxing. ^[1]

Gas lift oil recovery can be subdivided into two ways: continuous gas lift and intermittent gas lift.

Continuous gas lift

The so-called continuous gas lift is to continuously inject high-pressure gas into the gas lift pipe to inflate the liquid in the well to reduce the density of the mixture, until a sufficient production pressure difference is formed at the bottom of the well due to the pressure drop at the bottom of the well to reach the required index. For this purpose, flow and regulating valves are used. The former uses the available gas injection pressure to inject the gas into the tubing as deep as possible at a single point; the latter functions as a variable orifice plate, which can adjust the volume of gas injection on the ground according to the pressure of the tubing pressure (oil pressure). This continuous gas lift method is used for oil wells with high production index and excessive bottomhole pressure due to well depth.

Intermittent gas lift

This method involves the expansion of high-pressure gas after rising to a low-pressure outlet. The valve aperture used in intermittent gas lift is very large, so that all the gas can enter the oil pipe, and the expansion of the gas can be controlled by pressure. This can adjust the maximum flow rate to lift the liquid column collected at the upper part of the valve, so that slippage is minimized. Or control the amount of liquid leakage so that all the liquid enters the oil tank with minimal gas content. For intermittent gas lift, the ground is generally equipped with an intermittent gas lift controller (cycle-time controller).

Intermittent gas lift can be used in both low-production wells and

1.Classification

According to the pressure control method, it is divided into throttle valve, pneumatic valve or sleeve pressure operation valve, hydraulic valve or oil pressure operation valve and compound control valve.

According to the role played by the gas lift valve in the well, it is divided into unloading valve, working valve and foot valve.

According to the loading method of the gas lift valve, it is divided into inflatable bellows valve and spring gas lift valve.

According to the installation method of gas lift valve, it is divided into fixed gas lift valve and fishing gas lift valve. The fixed gas lift valve is connected with a wire buckle, and the gas lift valve is fixed outside the gas lift cylinder. To replace

The range of production changes is very wide, the operation cost is low, and it is suitable for wells with large angles, wells with large dog legs, sand production wells, high gas-oil ratio oil wells, and wax and scaling wells.

(1) Gas source: Gas-lift oil production must have sufficient gas volume to support the entire production process. The oilfield itself must have a minimum amount of dissolved gas (at least equal to 10% of the gas volume required for normal gas lift) to start gas lift recovery. Otherwise, gas lift oil recovery cannot be used.

(2) Bottom-hole flow pressure: gas-lift oil production must have a certain bottom-hole flow pressure, and cannot reach the minimum bottom-hole flow pressure like other artificial lifting methods. May not be adapted for low pressure wells.

(3) Oil wells producing heavy oil and emulsion are not suitable for gas-lift oil production. ^[3]

(1) During normal gas lift production, all the discharge valves are closed. Only the designed working valve is open for gas injection, and the production is continuous and stable.

(2) There are two independent parameters of gas lift, which have a great impact on gas lift production, namely the gas injection depth and the flow pressure gradient above the gas injection point. In gas lift wells, controlling changes in these two parameters can control changes in downhole flow pressure and production.

(3) The depth of the gas injection point means that the gas lift efficiency is high. The maximum depth of the gas injection point is mainly determined by the maximum gas injection pressure on the ground. The gas injection pressure on the ground depends on the level of the gas compressor. At a certain depth, the pressure in the casing is equal to the flow pressure in the tubing. This point is called the pressure equilibrium point. In consideration of the pressure drop of the gas injection valve, the gas injection point is set slightly above the equilibrium point, so that the sum of the pressure of the oil pipe and the pressure drop of the gas injection valve is equal to the casing pressure.

(4) The flow pressure gradient above the injection point is mainly determined by the injection amount. Increasing the amount of gas injected will increase the gas-liquid ratio in the oil pipe; within a certain limit, increasing the gas-liquid ratio will reduce the flow pressure gradient; beyond this limit, the flow pressure gradient will increase as the gas-liquid ratio increases. The lowest flow pressure gradient means the lowest downhole flow pressure and the highest production. Therefore, increasing the amount of injected gas can increase the output until it reaches the highest output value; but beyond this point, increasing the amount of injected gas will decrease the output. ^[2]

There are many factors affecting gas lift production, including the reservoir, the well completion itself, and the surface production system. The main factors are summarized as follows:

(1) Production capacity and formation pressure of oil wells

Gas lift completion is designed based on this. If the actual production capacity, formation pressure of the oil well is different from the production capacity and formation pressure selected for the design, it will cause abnormal gas lift operation. When the actual production capacity and formation pressure are higher than the design value, high tubing pressure will cause insufficient air intake, increased casing pressure, upward movement of the working valve and multi-point gas injection, which will reduce gas lift efficiency. In serious cases, the upper-stage gas lift valve may be opened and closed intermittently, resulting in unstable production. When the actual production capacity and formation pressure are lower than the design value, more gas will be consumed than designed to meet the production requirements; gas lift efficiency is low. In severe cases, excessive gas injection and dry gas injection may be caused, affecting gas lift production in other wells.

(2) Oil well temperature.

When the actual temperature is lower than the design value, the actual air bag pressure is low, and the drain valve is not closed, resulting in shallow gas injection or multi-point gas injection, which wastes pressure resources. When the actual well temperature is higher than the design value, if the working valve is a gas lift valve, the working valve cannot be opened, and the gas injection valve is a higher level valve, the gas injection depth cannot be reached, the production is low, and the efficiency is low.

(3) Wellhead pressure

When the wellhead pressure is high, the back pressure is high and the gas injection depth is shallow. If you want to obtain the same output, you must inject more gas, and the gas lift efficiency is low; or the oil jacket pressure difference is small, the gas injection volume is small, and the output is low, which cannot meet the production requirements. Conversely, when the wellhead pressure is low, the injection depth increases, the same gas injection volume can get higher production, and the same gas production requires less gas lift. Therefore, in oil fields with gas lift wells, the surface processing system and the oil well itself should try to reduce the wellhead pressure and back pressure to maximize production.

(4) Gas injection pressure

The higher the gas injection pressure, the greater the depth of gas injection, a better yield can be obtained with less gas volume, and the gas lift effect is high.

(5) Gas injection volume

When the gas injection volume is lower than the designed gas volume, the output cannot meet the requirements. When it is serious, it will cause intermittent gas injection to the working valve, and gas lift.

Production is unstable. Only by increasing the gas volume and lowering the density of the liquid in the wellbore, can the back pressure of the liquid column to the formation be reduced, and the required bottom-hole lift pressure is also reduced, so that higher production can be obtained. But it is not that the larger the gas injection volume is, the better. When the gas injection volume is larger than a certain value, if the gas injection volume is continuously increased, the increase value of the liquid production volume will be smaller and smaller, up to a certain maximum liquid volume point. If you continue to increase the gas injection volume, the output will not only increase, but will decrease. In severe cases, the gas source will be wasted, which may cause dry gas injection without oil production.

(6) Gas lift valve

The design of the gas lift valve (including the position of the working valve and the setting value of the air lift valve air bag) is different from the actual requirements, or even very different. If the difference is small, the problem can usually be solved by adjusting the gas volume to meet the production requirements. But sometimes it is very different, and adjusting the gas volume cannot solve the problem.

(7) Unstable production

That is, the wellhead pressure is unstable, the oil production is unstable, and the gas volume is unstable. In severe cases, intermittent gas lift occurs. When the production of an oil well is unstable, it not only affects the production of the oil well, causes sand to the oil layer, but also causes damage to the surface treatment facilities. For example, sometimes the output is low and the liquid level of the separator is very low, and sometimes the output of the well is high and the liquid level is high. This not only affects the normal operation of the separator, but also the entire production system is often closed due to the high or low liquid level. Therefore, in gas lift production, it is not only necessary to maintain high oil well production, but it is also important to maintain stable production of the oil well.

If various methods cannot be used to make the oil well in stable production, you can move the gas injection valve up, increase the oil jacket pressure difference, and keep the gas lift valve in a throttled state, so that production can be stabilized. ^[2]