Drainage gas recovery device and method for last-stage natural gas well

Abstract

The invention relates to a water drainage and gas production device and method for a last-stage natural gas well, and belongs to the technical field of water drainage and gas production. A gas injection pipe is arranged in a gas production oil pipe, the gas injection pipe sequentially penetrates through a gas production tree, an oil pipe head assembly and a casing head assembly from top to bottom, and the lower end of the gas injection pipe directly reaches accumulated water in the natural gas well; a surfactant or gas is injected through the gas injection pipe, and the drainage annulus between the gas injection pipe and the gas production oil pipe is used for drainage, so that the foam drainage operation requirement of a last-stage natural gas well is met, and the utilization rate of natural gas resources is effectively improved. Meanwhile, the length of the gas injection pipe can be set according to the water level of accumulated water in the natural gas well, operation is easy and convenient, and safety is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of water drainage and gas production, and in particular relates to a water drainage and gas production device and method for a terminal natural gas well. Background Art

[0002] As natural gas wells are mined, a certain amount of water and mud and sand also seep out along with the natural gas. As the energy of natural gas in the formation gradually decays, the water column at the bottom of the well gradually rises. The use of fracturing gas production technology can maintain normal production needs to a certain extent, but the decrease in gas production is accompanied by an increase in water production. When the mining is close to the end, after multiple fracturing and production increases, the natural gas content in the natural gas formation being mined is not much, and it is difficult to meet the drainage and gas production requirements through conventional fracturing procedures. For terminal wells, although some natural gas resources are still retained (usually hundreds of thousands to tens of millions of cubic meters), the liquid column pressure formed by the accumulated liquid in the barrel is greater than the reservoir natural gas pressure, resulting in the natural gas in the gas layer no longer entering the wellbore. Even after fracturing again, the energy of the reservoir natural gas is not enough to lift the water in the well to the ground, that is, the remaining natural gas resources in the well cannot meet the requirements of gas lift drainage operations. This situation where natural gas resources are retained but difficult to exploit due to drainage problems undoubtedly causes a waste of resources. Therefore, a drainage gas production device and a gas production method are needed for terminal natural gas wells. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, the present invention provides a drainage gas production device and method for terminal natural gas wells. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0004] The present invention provides a drainage gas production device for a terminal natural gas well, which is arranged on a wellhead gas production equipment. The wellhead gas production equipment comprises, from top to bottom, a gas production tree, a tubing head assembly and a casing head assembly in sequence. The drainage gas production device comprises: an injection pipe, which passes through the gas production tree, the tubing head assembly and the casing head assembly in sequence from top to bottom; the injection pipe is coaxially arranged in the gas production oil pipe, and a drainage annulus is formed between the injection pipe and the gas production oil pipe; the injection pipe comprises: a plurality of injection pipe units, which are coaxially arranged in sequence and threadedly connected; a lifting and injection device, which is arranged on the gas production tree and connected to the injection pipe, and is used to assemble or disassemble a plurality of injection pipe units, and to lift or lower the injection pipe as a whole; a blowout prevention assembly, which comprises: a top wellhead valve and a bottom one-way valve; the top wellhead valve is arranged at the upper end of the injection pipe, and the bottom one-way valve is arranged at the lower end of the injection pipe, both of which are used to prevent the natural gas in the natural gas well from spraying out from the injection pipe.

[0005] In one embodiment of the present invention, the lifting injection equipment includes: a lowering and lifting gas injection pipe assembly, a suspension assembly, a sealing assembly and a blowout preventer box assembly; the lowering and lifting gas injection pipe assembly, the suspension assembly, the sealing assembly and the blowout preventer box assembly are arranged in sequence from top to bottom and are respectively connected to the gas injection pipe; wherein, the lowering and lifting gas injection pipe assembly is used to assemble or disassemble a plurality of gas injection pipe units and to lift or lower the gas injection pipe from the natural gas well; the suspension assembly is used to suspend the gas injection pipe; the sealing assembly is used to seal the outside of the gas injection pipe; the blowout preventer box assembly is used to prevent the natural gas in the natural gas well from spraying out from the outside of the gas injection pipe.

[0006] In one embodiment of the present invention, the blowout prevention assembly further comprises: a rubber seal, which is arranged between the inner end face of the top wellhead valve and the end face of the gas injection pipe unit at the upper end of the gas injection pipe, and is used to seal the top wellhead valve and the gas injection pipe.

[0007] In one embodiment of the present invention, the rubber sealing member is an inner V-shaped rubber sealing ring, an inner U-shaped rubber sealing ring or an O-shaped rubber sealing ring.

[0008] In one embodiment of the present invention, the top wellhead valve is a ball valve or a needle-type stop valve.

[0009] In one embodiment of the present invention, the size of the gap of the drainage annulus ranges from 10 to 18 mm.

[0010] The present invention also provides a water drainage gas production method for a terminal natural gas well, the gas production method comprising:

[0011] S1: closing the valves on both sides of the Christmas tree, detecting the water level in the natural gas well by pressure gradient or ultrasonic wave, and obtaining the first length according to the water level;

[0012] S2: After closing the valve at the bottom of the main path of the gas tree in sequence, opening the valves at the top and middle of the main path of the gas tree and opening the blowout preventer assembly, a plurality of gas injection pipe units are sequentially connected by lifting the injection equipment to form a gas injection pipe, and the gas injection pipe is synchronously lowered into the natural gas well until the total length of the gas injection pipe is greater than or equal to the first length and less than the depth of the natural gas well;

[0013] S3: Open the top wellhead valve of the gas injection pipe, inject the pressurized surfactant into the accumulated water in the natural gas well through the top wellhead valve from the gas injection pipe by applying external pressure, and then close the top wellhead valve;

[0014] S4: Open the top wellhead valve, and inject pressurized nitrogen or air into the natural gas well through the gas injection pipe or repeat several times until the water in the natural gas well is foamed, then close the top wellhead valve, open the valve on one side of the gas tree, and drain the foamed water through the drainage annulus between the gas injection pipe and the gas production oil pipe to complete the foaming and drainage operation;

[0015] S5: After the water drainage operation is completed, open the valve on the other side of the gas tree to carry out gas production operation.

[0016] In one embodiment of the present invention, S2 includes:

[0017] S2.1: Close the valve at the bottom of the main flow path of the gas tree in sequence, open the valves at the top and middle of the main flow path of the gas tree, and open the blowout preventer assembly;

[0018] S2.2: Install a bottom check valve on the lowest gas injection pipe unit, install a top wellhead valve on the highest gas injection pipe unit, keep the top wellhead valve in a closed state, connect the lower gas injection pipe unit and the upper gas injection pipe unit, and hang and lock them through the hanging assembly;

[0019] S2.3: First gradually open the valve at the bottom of the main bore of the gas tree, then gradually open the top wellhead valve to verify that the sealing performance of the bottom one-way valve is intact, then remove the top wellhead valve and install it on another gas injection pipe unit;

[0020] S2.4: Loosen the suspension assembly, and slowly lower the connected gas injection pipe unit into the natural gas well by lowering and lifting the gas injection pipe assembly. During the lowering process, observe the sealing performance of the sealing assembly to the gas injection pipe unit. If there is leakage, immediately close the lowering and lifting gas injection pipe assembly, and at the same time, lock the gas injection pipe by the suspension assembly and close the blowout prevention box assembly. Adjust the packing gland of the sealing assembly until the sealing performance of the sealing assembly is intact;

[0021] S2.5: Repeat S2.3 and S2.4 to connect several gas injection pipe units in sequence, keeping the top wellhead valve always installed on the upper gas injection pipe unit, until the total length of the gas injection pipe composed of the connected several gas injection pipe units is greater than or equal to the first length and less than the depth of the natural gas well.

[0022] In one embodiment of the present invention, after S5, the method further includes:

[0023] S6: Assemble or disassemble several injection pipe units by lifting the injection equipment to extend or shorten the lowering length of the injection pipe, and repeat S3 and S4 until the accumulated water in the natural gas well is discharged through the drainage annulus between the injection pipe and the gas production oil pipe. After the bubble drainage operation is completed, open the valve on the other side of the gas tree to achieve repeated gas production.

[0024] In one embodiment of the present invention, after S5, the method further includes:

[0025] S7: After the gas production operation is completed, the gas injection pipe is lifted by the lifting injection equipment and split into several gas injection pipe units. When the bottom one-way valve of the gas injection pipe unit at the lower end leaves the valve at the bottom end of the main path of the gas production tree, the valve at the bottom end is immediately closed and the lifting injection equipment is removed.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The drainage and gas production device for terminal natural gas wells of the present invention lowers a gas injection pipe into the gas production oil pipe by lifting the injection equipment. The gas injection pipe is connected in sequence by a plurality of gas injection pipe units without couplings, and the gas injection pipe units are connected by threads. A one-way valve is provided at the lower end of the gas injection pipe, and a wellhead valve is provided at the upper end of the gas injection pipe, which ensures the safety of the gas injection pipe lowering and gas injection and drainage operations. The lower end of the gas injection pipe directly reaches the natural gas well, and surfactants or gas injection are injected through the gas injection pipe, and the drainage annulus between the gas injection pipe and the gas production oil pipe is used for drainage, which meets the requirements of the bubble drainage operation of the terminal natural gas well and effectively improves the utilization rate of natural gas resources.

[0028] The drainage and gas production method for terminal natural gas wells of the present invention can set the length of the gas injection pipe according to the water level in the natural gas well, has high adaptability, is simple and convenient to operate, and has good safety, thus meeting the requirements for the drainage operation of terminal natural gas wells.

[0029] The drainage and gas production method for terminal natural gas wells of the present invention can, after lowering the gas injection pipe and achieving drainage and production, retain the gas injection pipe for multiple gas injections, drainage and step-by-step production in combination with the actual natural gas reserves and water level in the natural gas well; and in the case of one-time production completion, the gas injection pipe can also be recycled.

[0030] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following specifically cites a preferred embodiment and describes it in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of a water drainage and gas production device for a terminal natural gas well provided by an embodiment of the present invention;

[0032] Figure 2 is a structural schematic diagram of a lifting injection device provided by an embodiment of the present invention;

[0033] Figure 3 The embodiment of the present invention provides Figure 2 A partial enlarged view of the middle A;

[0034] Figure 4 is a schematic structural diagram of a gas injection pipe provided in an embodiment of the present invention;

[0035] Figure 5The present invention provides a flow chart of a method for water drainage and gas production in a terminal natural gas well.

[0036] Icons: 1-gas tree; 10-gas production tubing; 20-production casing; 2-tubing head assembly; 3-casing head assembly; 100-gas injection pipe; 200-lifting injection equipment; 210-lowering and lifting gas injection pipe assembly; 220-suspension assembly; 230-sealing assembly; 240-blowout preventer box assembly; 300-blowout preventer assembly; 310-top wellhead valve; 320-bottom check valve; 330-rubber seal. DETAILED DESCRIPTION

[0037] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a drainage and gas production device and method for terminal natural gas wells proposed in accordance with the present invention in combination with the accompanying drawings and specific implementation methods.

[0038] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0039] Embodiment 1

[0040] like Figure 1 As shown, the present invention provides a drainage gas production device for terminal natural gas wells, which is arranged on a wellhead gas production equipment, wherein the wellhead gas production equipment includes, from top to bottom, a gas production tree 1, a tubing head assembly 2 and a casing head assembly 3.

[0041] In this embodiment, if Figure 1 and Figure 2 As shown, the drainage gas production device for terminal natural gas wells of this embodiment includes: a gas injection pipe 100 and a lifting injection device 200; wherein the gas injection pipe 100 passes through the gas tree 1, the tubing head assembly 2 and the casing head assembly 3 from top to bottom in sequence; the lifting injection device 200 is arranged on the gas tree 1 and connected to the gas injection pipe 100, and is used to assemble or disassemble a plurality of gas injection pipe units, and lift or lower the gas injection pipe 100 as a whole.

[0042] In this embodiment, the gas injection pipe 100 is coaxially disposed in the gas production oil pipe 10 , and a drainage annulus is formed between the gas injection pipe 100 and the gas production oil pipe 10 .

[0043] Exemplarily, the size of the gap of the drainage annulus ranges from 10 to 18 mm.

[0044] It can be understood that, since the gas injection pipe 100 is arranged in the gas production oil pipe 10, the width of the drainage annulus formed between the gas injection pipe 100 and the gas production oil pipe 10 is smaller than the width and area of ​​the annulus formed between the production casing 20 and the gas production oil pipe 10, and since the lower end of the gas injection pipe 100 penetrates into the accumulated water of the natural gas well, the length of the gas injection pipe 100 is set, which is also conducive to the gas injection operation and drainage operation. In other words, compared with the large annulus, the small annulus has a stronger liquid carrying capacity.

[0045] In this embodiment, if Figure 3 As shown, the gas injection pipe 100 includes: a plurality of gas injection pipe units, and the plurality of gas injection pipe units are coaxially arranged in sequence and threadedly connected.

[0046] In an optional embodiment, the lifting injection equipment 200 includes: a lowering and lifting gas injection pipe assembly 210, a suspension assembly 220, a sealing assembly 230 and a blowout preventer box assembly 240; the lowering and lifting gas injection pipe assembly 210, the suspension assembly 220, the sealing assembly 230 and the blowout preventer box assembly 240 are arranged in sequence from top to bottom and are respectively connected to the gas injection pipe 100; wherein, the lowering and lifting gas injection pipe assembly 210 is used to assemble or disassemble a plurality of gas injection pipe units and lift or lower the gas injection pipe 100 from the natural gas well; the suspension assembly 220 is used to suspend the gas injection pipe 100; the sealing assembly 230 is used to seal the outside of the gas injection pipe 100; the blowout preventer box assembly 240 is used to prevent the natural gas in the natural gas well from spraying out from the outside of the gas injection pipe 100 when the sealing of the sealing assembly 230 fails.

[0047] like Figures 1 to 4 As shown, the drainage and gas production device for the terminal natural gas well of this embodiment also includes: a blowout prevention assembly 300; the blowout prevention assembly 300 includes: a top wellhead valve 310 and a bottom one-way valve 320; the top wellhead valve 310 is arranged at the upper end of the gas injection pipe 100, and the bottom one-way valve 320 is arranged at the lower end of the gas injection pipe 100, both of which are used to prevent the natural gas in the natural gas well from spraying out from the gas injection pipe 100.

[0048] It is worth noting that several gas injection pipe units all adopt a non-hoop structure, and adjacent gas injection pipe units are connected by threads, which is not only conducive to reducing the total weight of the gas injection pipe 100, but also conducive to connecting the gas injection pipe units by lifting the injection equipment 200, thereby improving work efficiency. In addition, a bottom one-way valve 320 is arranged in the gas injection pipe unit at the lowest end, which ensures that the gas flow path in the gas injection pipe 100 is one-way, that is, when the lower pipe is lowered and pressurized nitrogen or air is injected from top to bottom, natural gas or injected gas is prevented from flowing back along the gas injection pipe 100, thereby improving safety. Furthermore, two bottom one-way valves 320 are arranged in series in the gas injection pipe unit at the lowest end. When one of the bottom one-way valves 320 fails (such as sealing failure), the other bottom one-way valve 320 can still work normally, thereby further improving reliability. Furthermore, the two bottom one-way valves 320 can also be respectively arranged in different gas injection pipe units, and it is only necessary to ensure that the conduction paths of the two bottom one-way valves 320 are both conducted from top to bottom and sealed from bottom to top.

[0049] On this basis, if Figures 2 to 4 As shown, a top wellhead valve 310 is provided in the gas injection pipe unit at the uppermost end, corresponding to the bottom non-return valve 320. The bottom non-return valve 320 is used as a passive safety structure, while the top wellhead valve 310 is used as an active safety structure. By manually closing the top wellhead valve 310, the safety of the gas injection pipe 100 during lowering and gas injection is further ensured. It can be understood that, taking the lower pipe operation as an example, the gas injection pipe unit at the lowermost end is first lowered into the natural gas well. At this time, there is a risk of sealing failure of the bottom non-return valve 320. The opening and closing of the top wellhead valve 310 are both manually controlled, and the opening of the top wellhead valve 310 can also be linear. Therefore, by gradually opening the top wellhead valve 310, the sealing performance of the bottom non-return valve 320 can be verified, thereby improving the safety and controllability of the operation.

[0050] Exemplarily, the top wellhead valve 310 may be a ball valve or a needle stop valve.

[0051] In an optional embodiment, if Figure 2 and Figure 3 As shown, the blowout prevention assembly 300 also includes: a rubber seal 330, which is arranged close to the top wellhead valve 310 and between the inner end surface of the top wellhead valve 310 and the end surface of the gas injection pipe unit at the upper end of the gas injection pipe 100, and is used to seal the top wellhead valve 310 and the gas injection pipe 100.

[0052] Exemplarily, the rubber seal 330 may be an inner V-shaped rubber seal ring, an inner U-shaped rubber seal ring, or an O-shaped rubber seal ring.

[0053] The drainage and gas production device for terminal natural gas wells of the present invention lowers a gas injection pipe into the gas production oil pipe by lifting the injection equipment. The gas injection pipe is connected in sequence by a plurality of gas injection pipe units without couplings, and the gas injection pipe units are connected by threads. A one-way valve is provided at the lower end of the gas injection pipe, and a wellhead valve is provided at the upper end of the gas injection pipe, which ensures the safety of the gas injection pipe lowering and gas injection and drainage operations. The lower end of the gas injection pipe directly reaches the natural gas well, and surfactants or gas injection are injected through the gas injection pipe, and the drainage annulus between the gas injection pipe and the gas production oil pipe is used for drainage, which meets the requirements of the bubble drainage operation of the terminal natural gas well and effectively improves the utilization rate of natural gas resources.

[0054] Embodiment 2

[0055] During the natural gas production process, a certain amount of water and mud and sand seep out with the natural gas, and gradually gather and settle at the bottom of the well. With the production of natural gas, the energy storage of the formation natural gas is gradually reduced, and the water column at the bottom of the well gradually rises. When the daily natural gas production is lower than a certain production capacity requirement, it is necessary to increase and release the energy storage of the natural gas through fracturing (energy storage is the pressure energy of the natural gas itself), so that the natural gas can spontaneously push the water column at the bottom of the well and bring it out of the ground. However, when the production is close to the end, after multiple fracturing and production increase, the energy storage of the natural gas gradually decreases. When the natural gas content in the natural gas layer to be produced is not much, even if the energy storage of the natural gas is increased by fracturing, it cannot meet the requirements of the drainage of the foaming drainage. However, there are still at least hundreds of thousands to tens of millions of cubic meters of natural gas resources left. Natural gas is a non-renewable energy source, which is undoubtedly a waste of resources. In view of this, the present embodiment provides a drainage and gas production method for terminal natural gas wells to improve the drainage capacity of the terminal wells and produce gas.

[0056] like Figure 5 As shown, the water drainage and gas production method for a terminal natural gas well of this embodiment includes:

[0057] S1: detecting the water level in the natural gas well by pressure gradient or ultrasonic wave, and obtaining a first length according to the water level in the natural gas well;

[0058] S2: After closing the valve at the bottom of the main path of the gas tree in sequence, opening the valves at the top and middle of the main path of the gas tree and opening the blowout preventer assembly, a plurality of gas injection pipe units are sequentially connected by lifting the injection equipment to form a gas injection pipe, and the gas injection pipe is synchronously lowered into the natural gas well until the total length of the gas injection pipe is greater than or equal to the first length and less than the depth of the natural gas well;

[0059] It can be understood that the first length is the distance between the water surface in the natural gas well and the top of the gas production tree. Whether it is gas injection or drainage, the gas injection pipe used needs to meet this length requirement, that is, the total length of the gas injection pipe is greater than or equal to the first length and less than the depth of the natural gas well. The gas injection pipe is formed by threading several gas injection pipe units to each other, which also improves the adaptability to this length requirement.

[0060] In an optional embodiment, S2 includes:

[0061] S2.1: Close the valve at the bottom of the main flow path of the gas tree in sequence, open the valves at the top and middle of the main flow path of the gas tree, and open the blowout preventer assembly;

[0062] S2.2: Install a bottom check valve on the lowest gas injection pipe unit, install a top wellhead valve on the highest gas injection pipe unit, keep the top wellhead valve in a closed state, connect the lower gas injection pipe unit and the upper gas injection pipe unit, and hang and lock them through the hanging assembly;

[0063] S2.3: First gradually open the valve at the bottom of the main bore of the gas tree, then gradually open the top wellhead valve to verify that the sealing performance of the bottom one-way valve is intact, then remove the top wellhead valve and install it on another gas injection pipe unit;

[0064] S2.4: Loosen the suspension assembly, and slowly lower the connected gas injection pipe unit into the natural gas well by lowering and lifting the gas injection pipe assembly. During the lowering process, observe the sealing performance of the sealing assembly to the gas injection pipe unit. If there is leakage, immediately close the lowering and lifting gas injection pipe assembly, and at the same time, lock the gas injection pipe by the suspension assembly and close the blowout prevention box assembly. Adjust the packing gland of the sealing assembly until the sealing performance of the sealing assembly is intact;

[0065] S2.5: Repeat S2.3 and S2.4 to connect several gas injection pipe units in sequence, keeping the top wellhead valve always installed on the upper gas injection pipe unit, until the total length of the gas injection pipe composed of the connected several gas injection pipe units is greater than or equal to the first length and less than the depth of the natural gas well.

[0066] It is worth noting that during the process of lowering the gas injection pipe, the top wellhead valve is always in a closed state. The combined effect of the bottom one-way valve and the top wellhead valve improves operational safety.

[0067] S3: Open the top wellhead valve of the gas injection pipe, inject the pressurized surfactant into the accumulated water in the natural gas well through the top wellhead valve from the gas injection pipe by applying external pressure, and then close the top wellhead valve;

[0068] It can be understood that with a certain pressure, the surfactant can directly open and pass through the bottom one-way valve.

[0069] S4: Open the top wellhead valve, and inject pressurized nitrogen or air into the natural gas well through the gas injection pipe or repeat several times until the water in the natural gas well is foamed, then close the top wellhead valve, open the valve on one side of the gas tree, and drain the foamed water through the drainage annulus between the gas injection pipe and the gas production oil pipe to complete the foaming and drainage operation;

[0070] It is understandable that in order to ensure the safety of the operation, the control of the valves of the gas tree and the gas injection pipe should meet the requirements of the operation sequence, that is, when lowering the pipe, the valve at the bottom of the main path of the gas tree should be closed to ensure blowout prevention, and the top wellhead valve should be opened only when injecting gas or injecting surfactants; similarly, the top wellhead valve should be closed immediately after injecting gas or injecting surfactants.

[0071] The principle is that when the surfactant is added to the water column at the bottom of the well, the water is finely foamed under the influence of the tension of the surfactant, making the mass lighter. Under normal circumstances, the fine foamed water column can be directly brought out of the ground by the natural gas with increased energy storage, which is called the foaming process. For the terminal wells, the energy storage of natural gas cannot even bring out the fine foamed water column, which is also the main problem affecting gas production. At this time, injecting a certain pressure of nitrogen or air into the well from the gas injection pipe is equivalent to increasing the energy of natural gas, so that the natural gas can lift and carry the water column at the bottom of the well to the ground to complete the foaming process. Achieve the purpose of natural gas extraction. In addition, the valves on both sides of the gas tree can be connected to the sewage treatment pipeline and the gas production pipeline respectively, and the sewage is transported to the sedimentation tank through the sewage treatment pipeline for recycling and treatment.

[0072] S5: After the water drainage operation is completed, open the valve on the other side of the gas tree to carry out gas production operation.

[0073] In an optional implementation, after S5, the step further includes:

[0074] S6: According to the water level in the natural gas well, assemble or disassemble several injection pipe units by lifting the injection equipment to extend or shorten the lowering length of the injection pipe; repeat S3 and S4 until the accumulated water in the natural gas well is discharged through the drainage annulus between the injection pipe and the gas production oil pipe. After the bubble drainage operation is completed, open the valve on the other side of the gas tree to achieve repeated gas production.

[0075] It is understandable that the bubble drainage operation is used to discharge the accumulated water in the terminal natural gas well, so that the pressure of the natural gas is greater than the water column at the bottom of the well. At this time, the normal extraction of natural gas can be achieved. However, there is a trade-off relationship between the pressure of natural gas and the accumulated water during the extraction process. Therefore, according to the natural gas reserves, the extraction of gas in the terminal natural gas well may also require up to 3 to 4 cycles of gas injection-drainage-gas extraction to be realized; sometimes in a bubble drainage operation of a natural gas well, it is even necessary to alternately cycle the steps of gas injection-drainage several times to complete a complete bubble drainage operation process. In addition, during the bubble drainage operation, it is also necessary to extend or shorten the length of the gas injection pipe according to the water level in the natural gas well to meet the requirements of the bubble drainage operation. It is not difficult to see the difficulty of the extraction of terminal natural gas wells. Through the drainage and gas extraction device and method used for terminal natural gas wells, the extraction of terminal natural gas that should have been abandoned has become possible.

[0076] In an optional implementation, after S5, the step further includes:

[0077] S7: After completing the gas production operation, the gas injection pipe is lifted by the lifting injection equipment and split into several gas injection pipe units. When the bottom one-way valve of the gas injection pipe unit at the lower end leaves the valve at the bottom end of the main path of the gas production tree, the bottom valve is immediately closed and the lifting injection equipment is removed.

[0078] It is worth noting that for different underground gas storage conditions, the treatment of drainage gas production devices is different. For terminal wells with natural gas reserves that still have multiple exploitations, the drainage gas production device can be retained and the gas injection pipe can be adaptively treated according to the water level in the natural gas well to achieve multiple exploitations, maximize resource utilization, and obtain significant economic and social benefits. For terminal wells that cannot be exploited again, the drainage gas production device can be removed after the foam drainage operation is completed and used for gas production in other natural gas wells. This setting can save equipment costs, improve equipment utilization, and realize the recycling of equipment.

[0079] In addition, in the production process, the detachable gas injection pipe and modular lifting injection equipment also have practical significance. After the bubble drainage and gas production operations, the gas injection pipe can be retained. When the bubble drainage operation is needed again, the gas injection pipe can be reused, thus saving labor costs. For the situation that only supports one-time mining, direct disassembly can also ensure the applicability of the drainage gas production device and drainage gas production method.

[0080] The drainage and gas production method for terminal natural gas wells of the present invention has a gas injection pipe whose length is adapted to the water level setting in the natural gas well, has a high degree of adaptability, is simple and convenient to operate, and has good safety, thus meeting the requirements for the foam drainage operation of terminal natural gas wells.

[0081] The drainage and gas production method for terminal natural gas wells of the present invention can, after lowering the gas injection pipe and achieving drainage and production, retain the gas injection pipe for multiple gas injections, drainage and step-by-step production in combination with the actual natural gas reserves and water level in the natural gas well; and in the case of one-time production completion, the gas injection pipe can also be recycled.

[0082] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant is intended to cover non-exclusive inclusion, so that the article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the article or device including the elements. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The orientation or position relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0083] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A drainage gas production device for a terminal natural gas well, which is arranged on a wellhead gas production device, and the wellhead gas production device comprises, from top to bottom: A gas production tree (1), a tubing head assembly (2) and a casing head assembly (3), characterized in that the water drainage gas production device comprises: The gas injection pipe (100) passes through the gas production tree (1), the tubing head assembly (2) and the casing head assembly (3) in sequence from top to bottom; the gas injection pipe (100) is coaxially arranged in the gas production oil pipe (10), and a drainage annulus is formed between the gas injection pipe (100) and the gas production oil pipe (10); the gas injection pipe (100) comprises: a plurality of gas injection pipe units, the plurality of gas injection pipe units are coaxially arranged in sequence and threadedly connected; A lifting injection device (200) is arranged on the gas tree (1) and connected to the gas injection pipe (100), and is used to assemble or disassemble the plurality of gas injection pipe units, and to lift or lower the gas injection pipe (100) as a whole; The blowout prevention assembly (300) comprises: a top wellhead valve (310) and a bottom one-way valve (320); the top wellhead valve (310) is arranged at the upper end of the gas injection pipe (100), and the bottom one-way valve (320) is arranged at the lower end of the gas injection pipe (100), both of which are used to prevent the natural gas in the natural gas well from spraying out from the gas injection pipe (100).

2. The drainage and gas production device for terminal natural gas wells according to claim 1, characterized in that: The lifting injection device (200) comprises: a lowering and lifting gas injection pipe assembly (210), a suspension assembly (220), a sealing assembly (230) and a blowout prevention box assembly (240); the lowering and lifting gas injection pipe assembly (210), the suspension assembly (220), the sealing assembly (230) and the blowout prevention box assembly (240) are arranged in sequence from top to bottom and are respectively connected to the gas injection pipe (100); The lowering and lifting gas injection pipe assembly (210) is used to assemble or disassemble the plurality of gas injection pipe units and to lift or lower the gas injection pipe (100) from the natural gas well; the hanging assembly (220) is used to hang the gas injection pipe (100); the sealing assembly (230) is used to seal the outside of the gas injection pipe (100); and the blowout prevention box assembly (240) is used to prevent the natural gas in the natural gas well from spraying out from the outside of the gas injection pipe (100).

3. The drainage and gas production device for terminal natural gas wells according to claim 1, characterized in that: The blowout prevention assembly (300) further comprises: a rubber seal (330), wherein the rubber seal (330) is arranged between the inner end surface of the top wellhead valve (310) and the end surface of the gas injection pipe unit at the upper end of the gas injection pipe (100), and is used for sealing the top wellhead valve (310) and the gas injection pipe (100).

4. The drainage and gas production device for terminal natural gas wells according to claim 3, characterized in that: The rubber sealing member (330) is an inner V-shaped rubber sealing ring, an inner U-shaped rubber sealing ring or an O-shaped rubber sealing ring.

5. The drainage and gas production device for terminal natural gas wells according to claim 1, characterized in that: The top wellhead valve (310) is a ball valve or a needle-type stop valve.

6. The drainage and gas production device for terminal natural gas wells according to claim 1, characterized in that: The size range of the gap of the drainage annulus is: 10 to 18 mm.

7. A method for water drainage and gas production in a terminal natural gas well, using the water drainage and gas production device for a terminal natural gas well as claimed in any one of claims 1 to 6, characterized in that: Drainage gas recovery methods include: S1: closing valves on both sides of the Christmas tree, detecting the water level in the natural gas well by pressure gradient or ultrasonic wave, and obtaining a first length according to the water level; S2: After closing the valve at the bottom of the main path of the gas tree, opening the valves at the top and middle of the main path of the gas tree and opening the blowout preventer assembly, a plurality of gas injection pipe units are sequentially connected by lifting the injection equipment to form a gas injection pipe, and the gas injection pipe is synchronously lowered into the natural gas well until the total length of the gas injection pipe is greater than or equal to the first length and less than the depth of the natural gas well; S3: opening the top wellhead valve of the gas injection pipe, injecting the pressurized surfactant through the top wellhead valve and the gas injection pipe into the accumulated water in the natural gas well by applying external pressure, and then closing the top wellhead valve; S4: Open the top wellhead valve, inject pressurized nitrogen or air into the natural gas well through the gas injection pipe or repeat several times until the water in the natural gas well is foamed, close the top wellhead valve, open the valve on one side of the gas tree, and discharge the foamed water through the drainage annulus between the gas injection pipe and the gas production oil pipe, completing the foaming and drainage operation; S5: After the water drainage operation is completed, the valve on the other side of the gas production tree is opened to carry out gas production operation.

8. The method for producing gas from water discharged from a terminal natural gas well according to claim 7, characterized in that: The S2 includes: S2.1: Close the valve at the bottom of the main path of the gas tree in sequence, open the valves at the top and middle of the main path of the gas tree, and open the blowout preventer assembly; S2.2: Install a bottom one-way valve on the lowest gas injection pipe unit, install a top wellhead valve on the highest gas injection pipe unit, keep the top wellhead valve in a closed state, connect the lower gas injection pipe unit and the upper gas injection pipe unit, and hang and lock them through a hanging assembly; S2.3: First gradually open the valve at the bottom end of the main path of the gas tree, then gradually open the top wellhead valve to verify that the sealing performance of the bottom one-way valve is intact, then remove the top wellhead valve and install it on another gas injection pipe unit; S2.4: Loosen the suspension assembly, and slowly lower the connected gas injection pipe unit into the natural gas well by lowering and lifting the gas injection pipe assembly. During the lowering process, observe the sealing performance of the sealing assembly to the gas injection pipe unit. If there is leakage, immediately close the lowering and lifting gas injection pipe assembly, and at the same time, lock the gas injection pipe by the suspension assembly and then close the blowout prevention box assembly, and adjust the packing gland of the sealing assembly until the sealing performance of the sealing assembly is intact; S2.5: Repeat S2.3 and S2.4 to connect several gas injection pipe units in sequence, keeping the top wellhead valve always installed on the gas injection pipe unit at the upper end, until the total length of the gas injection pipe composed of the connected several gas injection pipe units is greater than or equal to the first length and less than the depth of the natural gas well.

9. The method for producing gas from water discharged from a terminal natural gas well according to claim 7, characterized in that: The S5 also includes: S6: Assemble or disassemble several of the injection pipe units through the lifting injection equipment to extend or shorten the lowering length of the injection pipe, repeat S3 and S4 until the accumulated water in the natural gas well is discharged through the drainage annulus between the injection pipe and the gas production oil pipe. After the foam drainage operation is completed, open the valve on the other side of the gas production tree to achieve repeated gas production.

10. The method for producing gas from water discharged from a terminal natural gas well according to claim 8, characterized in that: The S5 also includes: S7: After the gas production operation is completed, the gas injection pipe is lifted by the lifting injection equipment and split into several gas injection pipe units. After the bottom one-way valve of the gas injection pipe unit at the lower end leaves the valve at the bottom end of the main path of the gas production tree, the valve at the bottom end is immediately closed and the lifting injection equipment is removed.

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