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1. Principle of gas lift oil production: The principle of gas lift oil production relies on the injection of high-pressure gas from the surface into the well, where it mixes with the fluids produced from the oil reservoir in the wellbore. The expansion of this gas reduces the density of the mixture in the wellbore, thereby enabling the fluids to be lifted out of the well. 2. Air lift method: (1) Based on the air injection method, air lift can be divided into continuous air lift and intermittent air lift. Continuous gas lift involves continuously injecting high-pressure gas into the well from the annulus between the oil and casing (or through the tubing), in order to remove the liquid from the wellbore. Continuous gas lift is suitable for oil wells with good liquid supply capacity and high production rates. Intermittent gas lift is a lifting method that involves periodically injecting gas into the annulus between the oil and casing. The gas quickly enters the tubing, forming a gas plug that pushes up the segments of oil-bearing fluid that have accumulated in the wellbore during periods when injection stops, thereby removing the liquid from the well. Intermittent gas lift is mainly used in oil wells with low bottom hole flow pressure, a low liquid production index, and low production rates. (2) The gas lift method is classified into an annular space gas inlet system and a central gas inlet system based on the channel through which the compressed gas enters. Annular space gas inlet refers to the situation where compressed gas is injected from the annular space, while crude oil is lifted out through the oil pipes ； The central air intake method is the opposite of the annular space air intake method

Definition of gas lift: A artificial lifting method that uses high-pressure gas injected from the surface into the wellbore to lift crude oil to the surface. The principle of gas lift oil production relies on the injection of high-pressure gas from the surface into the well, where it mixes with the fluids produced by the oil reservoir. The expansion of this gas reduces the density of the mixture in the wellbore, thereby lifting the crude oil flowing into the well to the surface. There are two main methods of gas lift oil production: continuous gas lift and intermittent gas lift. Intermittent gas lift further includes conventional intermittent gas lift, plunger gas lift, and chamber gas lift. 1. Continuous gas lift: Continuous gas lift is the most commonly used method for gas lift oil production. Its lifting principle is similar to that of self-priming wells; high-pressure gas is injected into the wellbore through the annulus between the oil and casing (or through the tubing), and enters the tubing or the annulus via the gas lift valve installed on the tubing. This helps to reduce the pressure exerted by the liquid column at the bottom of the well. When the flow pressure in the tubing is lower than the flow pressure at the bottom of the well, the liquid is lifted to the wellhead. Continuous gas lift is suitable for oil wells with strong liquid supply capacity and high formation permeability. 2. Pulsating air lift: Pulsating air lift involves periodically injecting high-pressure gas into the wellbore from the surface; the injected gas enters the tubing rapidly through large-diameter air lift valves, where it forms an air plug that pushes the liquid to the surface. Intermittent gas lift is mainly applied to wells with low bottom hole pressure and low liquid production index, or wells with high liquid production index but low bottom hole pressure. For such oil wells, using intermittent gas lift can significantly reduce the amount of gas required for lifting and improve the lifting efficiency compared to continuous gas lift. The disadvantage of intermittent air lifting is that the wellhead equipment is relatively complex. In a closed-loop system, when a certain proportion of wells use intermittent air lifting, it can easily cause fluctuations in the pressure of the gas injected at the surface, affecting the normal operation of other air-lifting wells. 3. Plunger air lift: Plunger air lift is a type of intermittent air lift. In this process, the plunger acts as a fixed interface between the liquid column and the lifting gas, serving to seal the gap and prevent gas from leaking in while reducing slippage losses. Plunger gas lift is mainly suitable for wells with low bottom hole pressure and low fluid production capacity, as well as wells with high bottom hole pressure and low fluid production capacity. It can also be used for water drainage and gas production in gas wells. The surface equipment for plunger gas lift is more complex than that of other gas lift methods; its operation and management present certain difficulties, and it can easily cause significant pressure fluctuations in the surface gathering and transportation pipelines during production. 4. Cavity air lift: Cavity air lift is a type of closed intermittent air lift system that features a \"cavity\" at the lower part of the tubing string used for this purpose. Since the volume of this cavity is greater than that of the oil tubes at the same height, when a certain volume of fluid is located above the fixed valve in the cavity air lift device, the pressure head generated is significantly lower than that produced by the same volume of fluid in conventional intermittent air lift systems. This helps to minimize the resistance to the flow of fluid from the production layer to the bottom of the well. Chamber air lifting is a method of using air lifting to produce depleted low-pressure wells, and it is particularly suitable for low-production wells as well as high-production low-pressure wells.

Principle of gas lift oil production: It relies on the injection of high-pressure gas from the surface into the well, where it mixes with the fluids produced from the oil reservoir in the wellbore. The expansion of this gas reduces the density of the mixture in the wellbore, thereby enabling the lifting of the fluids out of the well. 1) Gas lift can be divided into continuous gas lift and intermittent gas lift according to the gas injection method. 2) The gas lift method is divided into an annular space air intake system and a central air intake system, depending on the channel through which the compressed gas enters

Principle of gas lift oil production: It relies on the injection of high-pressure gas from the surface into the well, where it mixes with the fluids produced from the oil reservoir in the wellbore. The expansion of this gas reduces the density of the mixture in the wellbore, thereby enabling the fluids to be lifted out of the well

Gas lift is a type of artificial lifting method; it involves injecting high-pressure gas into the annulus between the oil and casing (or into the tubing) in order to reduce the density of the fluids in the wellbore. Under the action of the flow pressure at the bottom of the well, these fluids are then pumped out to the surface. At the same time, as the injected gas rises up the wellbore, its volume gradually increases, and the expansion work of the gas also helps to carry the liquid along. Therefore, gas lift is a mechanical oil production method used to restore spontaneous flow in oil wells after production stops, and it can also serve as an energy source to supplement spontaneous production in such wells. Gas lift for oil production mainly includes two methods: continuous gas lift and intermittent gas lift. Intermittent gas lift further comprises conventional intermittent gas lift, plunger gas lift, chamber gas lift, etc.

Principles and Equipment of Gas Lift Oil Production I. Characteristics and Operation Modes of Gas Lift Oil Production (1) Characteristics of Gas Lift Oil Production Gas lift oil production is a type of artificial lifting method; it involves injecting high-pressure gas into the annulus between the oil and casing (or into the tubing), thereby reducing the density of the liquid in the wellbore. Under the action of the flow pressure at the bottom of the well, this liquid is pushed out to the surface. At the same time, as the injected gas rises up the wellbore, its volume gradually increases, and the expansion work of the gas also helps to carry the liquid along. Therefore, gas lift is a mechanical oil production method used to restore spontaneous flow in oil wells after production stops, and it can also serve as an energy source to supplement spontaneous production in such wells. 　　Gas lift oil production has the following characteristics: (1) High lifting capacity, with the lifting depth capable of reaching over 3600 meters. (2) It has a wide range of adaptability regarding fluid production volume, and can be applied to oil wells with different production levels. (3) Suitable for inclined wells and directional wells. (4) Particularly suitable for wells with a high gas-to-oil ratio. (5) Suitable for wells with corrosive media in the fluid and sand-producing wells. (6) Simple operation and management, with flexible adjustment of working hours. (7) The initial investment is high, mainly due to the costs of building compressor stations; however, since the maintenance costs for gas lift wells are low, their overall production cost is relatively lower compared to other mechanical oil extraction methods. (8) There must be an adequate supply of gas, mainly natural gas; injecting nitrogen is costly. (9) Suitable for centralized production in a single oil field or block, and not suitable for decentralized extraction. (10) Its safety is inferior to that of other oil extraction methods. Although gas lift oil production has the aforementioned advantages, it has not been widely adopted in China due to the lack of sufficient gas sources in domestic oil fields as well as high construction costs. At present, it is only used in oil fields with high gas saturation ratios and deep reservoirs, such as those in the Central Plains, Tuha, and Tarim regions. (II) Gas lift oil production method Gas lift oil production mainly includes two approaches: continuous gas lift and intermittent gas lift. Intermittent gas lift further comprises conventional intermittent gas lift, plunger gas lift, chamber gas lift, etc. 1. Continuous gas lift Continuous gas lift is the most commonly used method for gas lift oil production. Its lifting principle is similar to that of self-priming wells; high-pressure gas is injected into the wellbore through the annulus between the oil and casing (or through the tubing), and it enters the tubing (or the annulus) via the gas lift valve installed on the tubing. This helps to reduce the pressure exerted by the liquid column at the bottom of the well. When the pressure in the tubing is lower than the pressure at the bottom of the well, the liquid is lifted to the wellhead. Continuous gas lift is suitable for oil wells with strong liquid supply capacity and high formation permeability. 2. Pulsating gas lift Pulsating gas lift involves periodically injecting high-pressure gas into the wellbore from the surface; the injected gas enters the tubing rapidly through large-diameter gas lift valves, where it forms a gas plug that pushes the liquid to the surface. Intermittent gas lift is mainly applied to wells with low bottom hole pressure and low liquid production index, or wells with high liquid production index but low bottom hole pressure. For such oil wells, using intermittent gas lift can significantly reduce the amount of gas required for lifting and improve the lifting efficiency compared to continuous gas lift. The disadvantage of intermittent air lifting is that the wellhead equipment is relatively complex. In a closed-loop system, when a certain proportion of wells use intermittent air lifting, it can easily cause fluctuations in the pressure of the gas injected at the surface, affecting the normal operation of other air-lifting wells. 3. Plunger air lift Plunger air lift is a type of intermittent air lift in which a plunger acts as a fixed interface between the liquid column and the lifting gas during the intermittent air lift process, serving to seal against the intrusion of gas and reduce slippage losses. Plunger gas lift is mainly suitable for wells with low bottom hole pressure and low fluid production capacity, as well as wells with high bottom hole pressure and low fluid production capacity. It can also be used for water drainage and gas production in gas wells. The surface equipment for plunger gas lift is more complex than that of other gas lift methods; its operation and management present certain difficulties, and it can easily cause significant pressure fluctuations in the surface gathering and transportation pipelines during production. 4. Cavity air lift Cavity air lift is a type of closed intermittent air lift system. At the lower part of the tubing string used in this system, there is a \"cavity.\" Since the volume of this cavity is greater than that of the oil tubing at the same height, when a certain volume of liquid is located above the fixed valve in the cavity air lift device, the pressure head generated is significantly lower than that produced by the same volume of liquid in conventional intermittent air lift systems. This helps to minimize the resistance to the flow of fluid from the production layer to the bottom of the well. Chamber air lifting is a method of using air lifting to produce depleted low-pressure wells, and it is particularly suitable for low-production wells as well as high-production low-pressure wells. (III) Pneumatic lift string structure 1. Single-string structure The single-string structure includes open-string systems, semi-closed string systems, closed-string systems, and chambered string systems; Figure 1 shows the structural diagrams of open-string systems, semi-closed string systems, and closed-string systems. (1) Open tubular string. 　　In an open tubing string configuration, the oil tubing does not have a seal and is suspended directly within the wellbore. Open tubing strings are only suitable for continuous gas lift wells with a high liquid level, as shown in Figure 1 – the single-tubing string structure of a gas lift well. Since the oil casing in such strings are connected to each other, in low-production wells, when the liquid level drops to the bottom of the tubing, the gas injected will flow from the casing into the tubing, resulting in uncontrolled gas injection rates. Another drawback of open tubing strings is that whenever a gas lift well is shut down and then restarted, the liquid level rises again, requiring the liquid above the working valve to be drained off. This not only prolongs the time it takes to get the well operational again, but the repeated flow of liquid through the gas lift valve can also cause erosion of the valve, reducing its service life. Therefore, open tubing strings are typically used in continuous gas lift wells where packers cannot be installed due to casing damage, deformation, corrosion, or other reasons. (2) Semi-closed string. 　　It features an open tubing string structure, with a packer installed below the final gas lift valve to separate the space between the tubing and the casing. This prevents the injected gas from leaking into the tubing due to a drop in liquid level, and it also eliminates the need for repeated fluid drainage each time the well is shut down and then reopened. The semi-closed tubing string is suitable for both continuous and intermittent air lifting, and it is the most commonly used tubing string configuration in air-lifted wells. (3) Closed tubing string. 　　A closed tubing string is based on the semi-closed tubing string structure, with a fixed valve installed at the bottom of the tubing; its function is to prevent the pressure inside the tubing from acting on the formation during intermittent air lifting. Closed tubing strings are generally used in gas lift wells with gaps. (4) Chamber stringer. 　　Figure 2 shows the two most basic structures for chamber air lift strings: the packer-type chamber string and the inserted-type chamber string. The packer-type chamber string structure consists of two packers that form a \"chamber\" above the oil layer; its volume is greater than that of a tubing column of the same height. As a result, the height of the liquid column inside the tubing **decreases**, which reduces the pressure acting on the check valve and helps to restore the oil well’s fluid level. The insert-type chamber air lift string involves inserting the tail end of the tubing into a \"chamber\" that is lowered into the oil reservoir in order to achieve the maximum possible production pressure difference. With this insert-type chamber air lift system, even when the pressure at the bottom of the well is very low, the liquid can flow into the chamber due to its own gravity, and then be lifted to the wellhead. Figure 2 Structure of the chamber air lift string 　　　　　　　a — Septum-type chamber structure ； b — Inserted chamber structure 2. Multi-string structure The multi-string structure enables the gas lift production of two or more oil layers simultaneously, with the fluid from each layer flowing to the surface through its own channel. In multi-pipe string structures, the double-pipe string air lift structure is commonly used; this structure can be composed of two parallel pipe strings or of concentric pipe strings. The parallel tube string structure is relatively widely used, generally in large-diameter cased wells ； The concentric tubing string structure is mainly used in oil wells with smaller casing diameters. The multi-string structure is relatively complex, making downhole operations difficult and increasing construction costs. The design and configuration of gas lift valves are challenging, which is why they are used less frequently. II. Gas lift oil production equipment (I) Continuous gas lift oil production equipment Figure 3 shows the continuous gas lift oil production equipment, which mainly consists of two parts: the wellhead equipment and the downhole tubing string. The wellhead equipment is basically similar to that of a self-flowing well; the gas injection pipeline is connected to the casing valves of the production tree, and a gas flow control valve is installed outside these casing valves to regulate the amount of gas. The gas-liquid mixture produced by the gas lift well is transported to the processing station via collection pipelines. The downhole string of a continuous gas lift system generally adopts a semi-closed design, consisting mainly of a gas lift valve and a packer. To facilitate the testing of wells equipped with gas lifting, a flare device can be installed at the tubing shoe. Figure 3 Continuous air lift oil production unit 　　　1—Inflation pipeline ； 2—Flow control valve ； 3—Thermometer ； 4—Valves ； 5—Pitching Summary ； 6—Sampling valve ； 　　　7—Transport pipelines ； 8—Fixed air lift valve ； 9—For submersible air lift use ； 10—Packer ； 11—Piping Shoes (II) Intermittent Air Lift Oil Production Equipment The intermittent air lift equipment mainly consists of wellhead devices, time controllers, pneumatic diaphragm valves, and downhole tubing strings. High-pressure gas is periodically injected into the wellbore through a pneumatic diaphragm valve, under the control of a time controller. Time controllers come in mechanical and electronic types. Mechanical time controllers are primarily composed of a pressure reducing valve, a filter, a timing wheel, and a needle valve. During operation, the interval at which air is injected is set on the timing wheel according to design specifications; the rotation of this timing wheel drives a lever that controls the opening and closing of the needle valve. The high-pressure air is reduced to low pressure through the pressure reducing valve and filter before entering the pneumatic diaphragm valve, thereby controlling its opening or closing and achieving intermittent air injection. 　　The working principle of an electronic time controller is the same as that of a mechanical one; the difference lies in the use of electronic components to control the opening and closing of the pneumatic diaphragm valve. A time setting button is available on its panel, allowing the control time to be set according to the intermittent air injection cycle. Used in conjunction with a time controller, the pneumatic diaphragm valve serves as the switch for controlling the injection of gas in intermittent air lifting. Pneumatic diaphragm valves are mainly composed of a diaphragm box and a valve body, and are available in two types: normally open and normally closed. The normally open type remains in an open state when there is no control air pressure, while the normally closed type remains in a closed state under the same conditions. During operation, low-pressure air controlled by a time controller acts on the membrane, forcing it to move downward and thereby pushing the valve stem downward to open or close the valve seat. When there is no air pressure, the valve moves upward due to the force of the spring, reopening or closing the valve. (III) Plunger air lift oil production device The plunger air lift oil production device is mainly composed of a time controller, a pneumatic diaphragm valve, a catcher, a blowout preventer, a plunger, buffer springs, and an oil pipe retainer. Under the control of the time controller, injection gas periodically enters the tubing through the gas lift valve, pushing the plunger upward (or using the gas present in the well itself to push the plunger upward), thereby displacing the liquid above the plunger out of the wellhead. When the plunger reaches the wellhead, it hits the shock absorbing spring of the blowout preventer, which opens the valve inside the plunger; once the pressures on both sides of the plunger are balanced, the plunger falls back down into the wellbore due to its own weight. After hitting the shock absorbing spring on the tubing holder, the valve inside the plunger closes, and the process begins again with another upward movement, repeating in this cycle. (IV) Chamber air lift oil production device The chamber air lift oil production device is mainly composed of a chamber packer, a unloading air lift valve, a chamber air lift valve, a fixed valve, an immersion tube, and a screen. Figure 4 shows the structure of the chamber air-lift packer, which is a compressed setting and anchoring type packer equipped with a bypass. Its feature is that there is a bypass hole on the outside of the packer, used to inject high-pressure gas into the chamber. For unloading air lift valves and chamber air lift valves, either type of injection pressure control valve suitable for intermittent air lifting can be used; the bore diameter of the valve seat should be large enough to ensure a high gas injection rate. The function of the chamber air lift check valve is to prevent liquid from flowing back, thereby avoiding backpressure on the formation. Sieve tubes are used in dual-packer-type chamber airlift devices to connect the chamber annulus of the dual packers with the immersion tube, while also linking the fixed valve seat sub to the immersion tube. Figure 4 Structure of chamber air-lift packer　　　　　　　1—Body ； 2—Bypass inflation port ； 3—Rubber tube ； 4—Bypass Set (Source: Handbook of New Technologies and Standards for Oil Extraction)

Principle of gas lift oil production: It relies on the injection of high-pressure gas from the surface into the well, where it mixes with the fluids produced from the oil reservoir in the wellbore. The expansion of this gas reduces the density of the mixture in the wellbore, thereby enabling the lifting of the fluids out of the well. Gas lift methods: There are mainly two types, namely continuous gas lift and intermittent gas lift. Intermittent gas lift further includes conventional intermittent gas lift, plunger gas lift, chamber gas lift, etc.