Wellhead casing pressure reducing and casing gas recycling device and using method thereof

Abstract

The invention relates to the technical field of wellhead casing gas recovery, in particular to a wellhead casing pressure reducing and casing gas recycling device and a using method thereof.The wellhead casing pressure reducing and casing gas recycling device comprises a gas collecting tank and a water seal tank, and the upper portion of the gas collecting tank is fixedly communicated with a casing gas conveying pipeline and a pressurizing pipeline; a pipeline pump is fixedly communicated between the lower portion of the gas collecting tank and the lower portion of the water-sealed tank, a liquid level sensor is fixedly installed on the lower portion of the water-sealed tank, an exhaust water injection valve is fixedly installed on the top of the water-sealed tank, and a pressure sensor is fixedly installed on the upper portion of the water-sealed tank. Valves are respectively connected in series with the inlet and outlet of the pipeline pump; and switching between a direct connection mode and a pressurization operation mode is carried out through a pressure threshold value. The system has the advantages of low cost, adaptability to all working conditions, automatic operation and zero-emission recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of wellhead casing gas recovery, and is a wellhead casing pressure reduction and casing gas recovery and utilization device and its usage method. Background Art

[0002] During the production process of oil wells, natural gas dissolved in crude oil will gradually precipitate and accumulate in the oil-casing annulus to form casing gas. As the casing pressure increases, the dynamic liquid level of the oil well is forced to drop, resulting in a reduction in the effective production pressure difference, a decrease in the pump efficiency of the deep-well pump, and even a gas locking effect. In severe cases, the oil well will completely stop production. To maintain normal production, it is necessary to regularly relieve the pressure of the casing gas. However, traditional pressure relief methods mostly use direct venting, which not only causes waste of natural gas resources but also releases greenhouse gases such as methane. Currently, the following five main casing gas recovery technologies are used in the industry, but they all have significant defects.

[0003] 1) Constant pressure gas release valve recovery technology: By setting a fixed pressure threshold, when the casing pressure exceeds the threshold, the gas is automatically released to the production pipeline through the constant pressure gas release valve. It is only applicable to oil wells where the casing pressure is higher than the pipeline network back pressure (about 30% of the total number of oil wells), and is ineffective for low-pressure casing gas wells. For example, the oil well casing gas pressurization recovery device disclosed in the patent application document with the publication number CN201963278U, and the oil production wellhead device and method for recovering casing gas disclosed in the patent application document with the publication number CN110778289A, both adopt such technology.

[0004] 2) Linkage type low-pressure air extraction pump technology: Utilize the reciprocating motion of the walking beam or polished rod of the pumping unit to drive the cylinder piston to compress the casing gas. The mechanical linkage structure requires the transformation of the four-link system of the pumping unit, and the installation cost increases by about 15% to 20%. Moreover, it changes the original mechanical balance and is prone to cause increased vibration of the pumping unit or even a "rollover" accident. In addition, its cylinder seals have poor tolerance to casing gas containing hydrogen sulfide and sediment, and need to be replaced frequently. For example, the casing pressure control device for a casing gas recovery pump disclosed in the patent application document with the publication number CN209621281U, and the oil well associated gas recovery device and associated gas recovery method disclosed in the patent application document with the publication number CN111472727A, both adopt such technology.

[0005] 3) Compressor unit pressurization recovery technology: Use a natural gas compressor to pressurize the casing gas and then transport it to the gathering pipeline network. The equipment such as natural gas compressors has high purchase costs, complex maintenance, and requires a supporting precision filtration system to remove impurities such as hydrogen sulfide and liquid hydrocarbons. The equipment has high energy consumption and poor economy for small gas volume wells (daily gas production < 500 m³). For example, the oilfield wellhead casing gas recovery device and recovery method disclosed in the patent application document with the publication number CN105114039A adopt such technology.

[0006] 4) Synchronous rotary compressor technology: The continuous pressurization of gas is achieved through a synchronous rotary compressor. In a low-temperature environment, the viscosity of the lubricating oil increases sharply, resulting in difficult startup and the need for an additional heating device, increasing energy consumption. It is sensitive to the liquid content of the gas. When the liquid hydrocarbon content > 5%, the risk of coking inside the compressor increases significantly. The equipment is bulky and has poor applicability to oil wells with limited space at the well site.

[0007] 5) Gas gathering pipeline network recovery technology: The casing gas of multiple wells is collected to the central processing station by laying pipelines. However, the laying cost per kilometer of the pipeline is high, and the economy is poor for remote well groups. During winter operation, the condensed water in the pipeline is prone to freezing and blocking. Summary of the Invention

[0008] The present invention provides a device for reducing the casing pressure at the wellhead and recovering and utilizing the casing gas and its usage method, which overcomes the above-mentioned deficiencies of the prior art and can effectively solve the problems of high equipment cost and poor environmental adaptability existing in the existing casing gas recovery technology.

[0009] One of the technical solutions of the present invention is achieved through the following measures: A device for reducing the casing pressure at the wellhead and recovering and utilizing the casing gas includes a gas collecting tank and a water seal tank. The upper part of the gas collecting tank is fixedly connected with a casing gas conveying pipeline and a pressurizing pipeline respectively. A pipeline pump is fixedly connected between the lower part of the gas collecting tank and the lower part of the water seal tank. The water seal tank is fixedly installed with a liquid level monitoring instrument and a pressure monitoring instrument. An exhaust and water injection valve is fixedly installed at the top of the water seal tank. Check valves are connected in series on both the casing gas conveying pipeline and the pressurizing pipeline. Valves are connected in series on both sides of the inlet and outlet of the pipeline pump.

[0010] The following is a further optimization or / and improvement of the above-mentioned technical solution of the invention: The above-mentioned device for reducing the casing pressure at the wellhead and recovering and utilizing the casing gas further includes an explosion-proof electric control cabinet. The explosion-proof electric control cabinet includes a controller, and the controller is a PLC controller or a control instrument; the liquid level monitoring instrument and the pressure monitoring instrument respectively adopt a liquid level sensor and a pressure sensor, and the control end of the pipeline pump, the liquid level sensor and the pressure sensor are all electrically connected to the PLC controller; or, the liquid level monitoring instrument and the pressure monitoring instrument adopt a differential pressure transmitter, and the control end of the pipeline pump and the differential pressure transmitter are electrically connected to the control instrument.

[0011] A communication interface is arranged at the lower part of the above-mentioned gas collecting tank. The valve on the left side of the pipeline pump is fixedly installed outside the communication interface, and an internal pipeline extending into the gas collecting tank is fixedly connected inside the communication interface. One end of the internal pipeline extending into the gas collecting tank inclines towards the bottom of the gas collecting tank.

[0012] Preferably, the angle at which one end of the internal pipeline extending into the gas collecting tank inclines towards the bottom of the gas collecting tank is 15 degrees to 60 degrees.

[0013] The outer sides of the above-mentioned gas collecting tank, water seal tank and booster pipeline are respectively provided with heat preservation layers, and electric heating tapes are wound on the inner sides of the heat preservation layers.

[0014] The bottoms of the above-mentioned gas collecting tank and water seal tank are both in a conical shape with a wider upper part and a narrower lower part.

[0015] The bottoms of the above-mentioned gas collecting tank and water seal tank are both fixedly connected with sewage discharge pipelines, and valves are connected in series on the sewage discharge pipelines.

[0016] On the casing gas transmission pipeline between the inlet side of the above-mentioned casing gas transmission pipeline and the check valve, a flow meter, a pressure monitoring instrument and a valve are fixedly installed; on the booster pipeline between the outlet side of the booster pipeline and the check valve, a flow meter, a pressure monitoring instrument and a valve are fixedly installed.

[0017] Between the lower part of the above-mentioned gas collecting tank and the outlet of the pipeline pump, a valve is connected in series through a flange; between the inlet of the pipeline pump and the lower part of the water seal tank, a valve is connected in series through a flange; or, between the lower part of the gas collecting tank and the outlet of the pipeline pump, they are fixedly connected through a connecting pipeline, between the inlet of the pipeline pump and the lower part of the water seal tank, they are fixedly connected through a connecting pipeline, and a valve is connected in series on the connecting pipeline.

[0018] The second technical solution of the present invention is realized through the following measures: A use method of a wellhead casing pressure reduction and casing gas recovery and utilization device, including a direct-through mode and a pressurization operation mode. When operating in the direct-through mode or the pressurization operation mode, the valves on both sides of the pipeline pump are in an always-open state; Inject clear water into the water seal tank, and stop injecting clear water after the liquid level reaches the liquid level injection value; Fix the connection between the inlet side of the casing gas transmission pipeline and the wellhead casing gate of the wellhead device, and fix the connection between the outlet side of the booster pipeline and the production pipeline; When the casing pressure is greater than the back pressure of the production pipeline, operate in the direct-through mode; Direct-through mode: The casing gas enters the upper part inside the gas collecting tank through the casing gas transmission pipeline, and then enters the production pipeline through the booster pipeline; When the casing pressure is not greater than the back pressure of the production pipeline, operate in the pressurization operation mode; Pressurization operation mode: After the casing gas enters the gas collecting tank, the casing gas pushes the clear water in the gas collecting tank to circulate to the water seal tank through the pipeline pump, and the liquid level in the water seal tank rises, prompting the pressure in the water seal tank to rise; The pressure sensor or differential pressure transmitter monitors the pressure in the water seal tank. When the pressure in the water seal tank is monitored to reach the pressure threshold, start the pipeline pump, pressurize and inject the clear water in the water seal tank into the gas collecting tank. Based on the liquid seal resistance, the casing gas in the space above the liquid level of the gas collecting tank is pressurized. After the casing gas is pressurized to be greater than the back pressure of the production pipeline, it is output through the booster pipeline; The liquid level sensor or differential pressure transmitter monitors the liquid level of the water seal tank in real time. When the liquid level of the water seal tank is lower than the liquid level threshold, the pipeline pump stops. The casing gas then pushes the clear water in the gas collection tank through the pipeline pump and circulates back to the water seal tank. When the pressure sensor or differential pressure transmitter monitors that the pressure in the water seal tank reaches the pressure threshold, the pipeline pump is restarted; In the boost operation mode, the pipeline pump runs intermittently.

[0019] The following is a further optimization and / or improvement of the second technical solution of the above invention: The usage method of the above wellhead casing pressure reduction and casing gas recovery and utilization device includes a direct-through mode and a boost operation mode. When operating in the direct-through mode or the boost operation mode, the valves on both sides of the pipeline pump are in the normally open state; Set the liquid level injection value, pressure threshold, and liquid level threshold of the water seal tank in the controller; Inject clear water into the water seal tank through the exhaust and water injection valve. After the liquid level reaches the liquid level injection value, stop injecting clear water; Fix the inlet side of the casing gas transmission pipeline to the wellhead casing gate of the wellhead device, and fix the outlet side of the boost pipeline to the production pipeline; When the casing pressure is greater than the back pressure of the production pipeline, operate in the direct-through mode; Direct-through mode: The casing gas enters the upper part of the gas collection tank through the casing gas transmission pipeline, and then enters the production pipeline through the boost pipeline; When the casing pressure is not greater than the back pressure of the production pipeline, operate in the boost operation mode; Boost operation mode: After the casing gas enters the gas collection tank, the casing gas pushes the clear water in the gas collection tank to circulate to the water seal tank through the pipeline pump. Based on the liquid seal resistance, the liquid level in the water seal tank rises, causing the pressure in the water seal tank to increase; The pressure sensor or differential pressure transmitter monitors the pressure in the water seal tank and sends the monitored pressure data to the controller. When it is monitored that the pressure in the water seal tank reaches the pressure threshold, the controller sends a start signal to the pipeline pump. The pipeline pump starts and pressurizes and injects the clear water in the water seal tank into the gas collection tank. Based on the liquid seal resistance, the casing gas in the upper part of the gas collection tank is forced to increase in pressure. After the casing gas is pressurized to be greater than the back pressure of the production pipeline, it is output to the production pipeline through the boost pipeline; The liquid level sensor or differential pressure transmitter monitors the liquid level of the water seal tank in real time and sends the monitored liquid level data to the controller. When the liquid level of the water seal tank is lower than the liquid level threshold, the controller sends a pump stop signal to the pipeline pump. The pipeline pump stops. The casing gas then pushes the clear water in the gas collection tank through the pipeline pump and circulates back to the water seal tank. When the pressure sensor or differential pressure transmitter monitors that the pressure in the water seal tank reaches the pressure threshold, the pipeline pump is restarted; In the boost operation mode, the pipeline pump runs intermittently.

[0020] When the wellhead casing pressure reduction and casing gas recovery and utilization device of the present invention is in use, the direct-through mode and the pressurization operation mode are switched through the pressure threshold.

[0021] The wellhead casing pressure reduction and casing gas recovery and utilization device of the present invention has the following advantages: 1) Low cost: Abandon the high-precision compressor unit, use hydraulic pressurization to replace mechanical compression, and the equipment investment is reduced by more than 60%. And the equipment has a small volume; 2) Full-condition adaptation: Isolate sulfur-containing and liquid-containing gases through a clear water medium to avoid corrosion of mechanical key components, and can adapt to an environmental temperature of -30°C to 50°C; 3) Automatic operation: Integrate a double-signal feedback system of liquid level and pressure to achieve unattended intelligent control; 4) Zero-emission recovery: Completely eliminate the casing gas venting and meet the environmental protection requirements; 5) Residual liquid recovery: The so-called residual liquid includes several liquids such as light hydrocarbons condensed into liquids carried in the casing gas, crude oil and water carried by the release of the casing gas, and condensed water of high-temperature steam. Light components such as light hydrocarbons or crude oil float on the liquid seal water surface, increasing the liquid seal height. In addition, when the casing pressure is greater than the back pressure of the production pipeline, the light components at the top of the liquid level in the gas collection tank are transported into the production pipeline along with the casing gas, causing the liquid level in the gas collection tank to drop. At the same time, the pressure in the space above the liquid level in the gas collection tank drops. Subsequently, when the casing pressure is greater than the back pressure of the production pipeline again, part of the light components at the top of the liquid level in the gas collection tank are transported into the production pipeline along with the casing gas. In this cyclic manner, components such as light components are continuously recovered, thereby achieving residual liquid recovery.

[0022] The wellhead casing pressure reduction and casing gas recovery and utilization device of the present invention is not only applicable to the oil extraction field, but also applicable to other application fields, such as the recovery of tank top gas in the oil and gas storage and transportation field, and the casing pressure reduction and casing gas recovery in the coalbed methane extraction field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attached Figure 1 is a process flow schematic diagram of the wellhead casing pressure reduction and casing gas recovery and utilization device of the present invention.

[0024] The codes in the drawings are respectively: 1 is a gas collection tank, 2 is a water seal tank, 3 is a casing gas transmission pipeline, 4 is a pressurization pipeline, 5 is a pipeline pump, 6 is a liquid level sensor, 7 is an exhaust and injection valve, 8 is a pressure sensor, 9 is an explosion-proof electric control cabinet, 10 is a sewage discharge pipeline, 11 is a production pipeline, 12 is a wellhead device, 13 is a check valve, and 14 is a valve. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solutions of the present invention and the actual situation.

[0026] In the present invention, for the convenience of description, the relative position relationship of each component is described according to the attached Figure 1 The layout is described in detail, such as the positional relationship of front, back, top, bottom, left, right, etc., which is based on the attached manual. Figure 1 The layout direction is determined and is only for the convenience of describing the present device and simplifying the description. It does not indicate or imply that the device or element must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention.

[0027] It should be noted that, unless otherwise clearly specified and limited, the terms "fixed installation", "series connection", etc. should be understood in a broad sense, for example, it can be fixedly connected or set, or detachably connected or set, or integrally connected or set, it can be directly connected, or indirectly connected through an intermediate medium, or it can be internal communication between two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The present invention will be further described below in conjunction with embodiments: Example 1: Figure 1 As shown, the wellhead casing pressure reduction and casing gas recovery and utilization device includes a gas collecting tank 1 and a water seal tank 2. The upper part of the gas collecting tank 1 is fixedly connected with a casing gas delivery pipeline 3 and a booster pipeline 4, and a pipeline pump 5 is fixedly connected between the lower part of the gas collecting tank 1 and the lower part of the water seal tank 2. The water seal tank 2 is fixedly installed with a liquid level monitoring instrument and a pressure monitoring instrument. An exhaust and water injection valve 7 is fixedly installed on the top of the water seal tank 2. Both the casing gas delivery pipeline 3 and the booster pipeline 4 are serially connected with a one-way valve 13, and valves 14 are serially connected on both sides of the inlet and outlet of the pipeline pump 5.

[0029] The casing gas delivery pipeline 3 and the wellhead casing gate of the wellhead device 12 can be connected through a flange or a thread.

[0030] The gas collecting tank 1, the water sealing tank 2 and the pipeline pump 5 therebetween form a U-shaped structure.

[0031] Embodiment 2: As an optimization of the above embodiment, Figure 1 As shown, the wellhead casing pressure reduction and casing gas recovery and utilization device also includes an explosion-proof electric control cabinet 9, which includes a controller, which is a PLC controller or a control instrument; the liquid level monitoring instrument and the pressure monitoring instrument respectively use a liquid level sensor 6 and a pressure sensor 8, and the control end of the pipeline pump 5, the liquid level sensor 6 and the pressure sensor 8 are all electrically connected to the PLC controller; or, the liquid level monitoring instrument and the pressure monitoring instrument use a differential pressure transmitter, and the control end of the pipeline pump 5, the differential pressure transmitter and the control instrument are electrically connected.

[0032] The controller can adopt an intelligent digital display controller with the model number AI-5013, and the supplier is Xiamen Yudian Automation Technology Co., Ltd.

[0033] The differential pressure transmitter can adopt a YD-1000 series diffused silicon differential pressure transmitter, and the supplier is Xiamen Yudian Automation Technology Co., Ltd. The differential pressure transmitter is used to measure the liquid level and pressure, and the differential pressure transmitter is used in combination with the controller.

[0034] The liquid level monitoring instrument is used to monitor the water level of the water seal tank 2.

[0035] The liquid level sensor 6 can adopt a float type liquid level sensor or an ultrasonic liquid level sensor, and other existing well-known liquid level sensors can also be used. The pipeline pump 5 can adopt an explosion-proof pipeline pump with a power of 2kW to 5.5kW, and the pipeline pump 5 is small in size.

[0036] When the liquid level monitoring instrument and the pressure monitoring instrument respectively adopt the liquid level sensor 6 and the pressure sensor 8, the liquid level sensor 6 is fixedly installed at the lower part of the water seal tank 2, and the pressure sensor 8 is fixedly installed at the top of the water seal tank 2.

[0037] Embodiment 3: As an optimization of the above embodiment, as required, the bottoms of the gas gathering tank 1 and the water seal tank 2 are both in a conical shape with a wider top and a narrower bottom.

[0038] The design of the conical shape with a wider top and a narrower bottom is convenient for collecting the sediment carried in the casing gas.

[0039] Embodiment 4: As an optimization of the above embodiment, as required, a connection interface is provided at the lower part of the gas gathering tank 1, and the valve 14 on the left side of the pipeline pump 5 is fixedly installed outside the connection interface, and an internal pipeline extending into the inside of the gas gathering tank 1 is fixedly connected inside the connection interface, and one end of the internal pipeline extending into the inside of the gas gathering tank 1 is inclined towards the bottom of the gas gathering tank 1.

[0040] The valve 14 on the left side of the pipeline pump 5 is fixedly installed outside the connection interface through a flange or a screw thread, and the internal pipeline is fixedly connected inside the connection interface through a flange or a screw thread or welding.

[0041] The inclined design of the internal pipeline can prevent sediment from entering the pipeline pump 5.

[0042] Embodiment 5: As an optimization of the above Embodiment 4, as required, the angle at which one end of the internal pipeline extending into the gas gathering tank 1 is inclined towards the bottom of the gas gathering tank 1 is 15 degrees to 60 degrees.

[0043] Embodiment 6: As an optimization of the above embodiment, as required, heat insulation layers are respectively provided on the outer sides of the gas gathering tank 1, the water seal tank 2 and the booster pipeline 4. Electric heating tapes are wound inside the heat insulation layers.

[0044] Adopt double anti-freezing measures of electric tracing band + thermal insulation layer to ensure continuous operation in an environment of -30°C and improve the low-temperature adaptability. The thermal insulation layer can use rock wool material or other existing well-known thermal insulation materials.

[0045] Embodiment 7: As an optimization of the above embodiment, as Figure 1 shown, sewage pipes 10 are fixedly connected to the bottoms of the gas collecting tank 1 and the water seal tank 2, and a valve 14 is connected in series on the sewage pipe 10.

[0046] The bottoms of the gas collecting tank 1 and the water seal tank 2 are designed in a conical shape with a wider top and a narrower bottom. Cooperating with the sewage pipe 10, sediment can be regularly discharged to avoid abrasion of the pipeline pump 5.

[0047] Embodiment 8: As an optimization of the above embodiment, as Figure 1 shown, a valve 14 is connected in series between the lower part of the gas collecting tank 1 and the outlet of the pipeline pump 5 through a flange, and a valve 14 is connected in series between the inlet of the pipeline pump 5 and the lower part of the water seal tank 2 through a flange; or, the lower part of the gas collecting tank 1 is fixedly connected to the outlet of the pipeline pump 5 through a connecting pipe, and the inlet of the pipeline pump 5 is fixedly connected to the lower part of the water seal tank 2 through a connecting pipe, and a valve 14 is connected in series on the connecting pipe.

[0048] The valve 14 can adopt a ball valve.

[0049] Embodiment 9: As an optimization of the above embodiment, as required, a flow meter, a pressure monitoring instrument and a valve 14 are fixedly installed on the casing gas transmission pipeline 3 between the inlet side of the casing gas transmission pipeline 3 and the check valve 13; a flow meter, a pressure monitoring instrument and a valve 14 are fixedly installed on the boosting pipeline 4 between the outlet side of the boosting pipeline 4 and the check valve 13.

[0050] The pressure monitoring instrument can adopt a pressure gauge or a pressure transmitter. The settings of the flow meter and the pressure monitoring instrument can monitor the flow rate and pressure of the casing gas transmission pipeline 3 and the boosting pipeline 4.

[0051] Embodiment 10: As Figure 1 shown, a usage method of a wellhead casing pressure reduction and casing gas recovery and utilization device includes a direct-through mode and a boosting operation mode. When operating the direct-through mode or the boosting operation mode, the valves 14 on both sides of the pipeline pump 5 are in an always-open state; Inject clean water into the water seal tank 2, and stop injecting clean water after the liquid level reaches the liquid level injection value; Fix the connection between the inlet side of the casing gas transmission pipeline 3 and the wellhead casing gate of the wellhead device 12, and fix the connection between the outlet side of the boosting pipeline 4 and the production pipeline 11; When the casing pressure is greater than the back pressure of the production pipeline 11, operate the direct-through mode; Direct flow mode: The casing gas enters the upper part of the gas collection tank 1 through the casing gas transmission pipeline 3, and then enters the production pipeline 11 through the pressurization pipeline 4; When the casing pressure is not greater than the back pressure of the production pipeline 11, the pressurization operation mode is run; Pressurization operation mode: After the casing gas enters the gas collection tank 1, the casing gas pushes the clear water in the gas collection tank 1 to circulate to the water seal tank 2 through the pipeline pump 5, and the liquid level in the water seal tank 2 rises, prompting the pressure in the water seal tank 2 to increase; The pressure sensor 8 or differential pressure transmitter monitors the pressure in the water seal tank 2. When the pressure in the water seal tank 2 reaches the pressure threshold, the pipeline pump 5 is started, and the clear water in the water seal tank 2 is pressurized and injected into the gas collection tank 1. Based on the liquid seal resistance, the casing gas in the space above the liquid level of the gas collection tank 1 is pressurized. After the casing gas is pressurized to be greater than the back pressure of the production pipeline 11, it is output through the pressurization pipeline 4; The liquid level sensor 6 or differential pressure transmitter monitors the liquid level of the water seal tank 2 in real time. When the liquid level of the water seal tank 2 is lower than the liquid level threshold, the pump is stopped, and the casing gas pushes the clear water in the gas collection tank 1 to circulate back to the water seal tank 2 through the pipeline pump 5 again. When the pressure sensor 8 or differential pressure transmitter monitors that the pressure in the water seal tank 2 reaches the pressure threshold, the pipeline pump 5 is restarted; In the pressurization operation mode, the pipeline pump 5 runs intermittently.

[0052] The valves 14 on both sides of the pipeline pump 5 are only closed when the pipeline pump 5 is under maintenance or sewage discharge.

[0053] Example 11: As Figure 1 shown, as an optimization of the above Example 10, the usage method of the wellhead casing pressure reduction and casing gas recovery and utilization device includes a direct flow mode and a pressurization operation mode. When running the direct flow mode or the pressurization operation mode, the valves 14 on both sides of the pipeline pump 5 are in an always-open state; Set the liquid level injection value, pressure threshold, and liquid level threshold of the water seal tank 2 in the controller; Inject clear water into the water seal tank 2 through the exhaust and injection valve 7. After the liquid level reaches the liquid level injection value (such as 60% liquid level), stop injecting clear water; Fix the inlet side of the casing gas transmission pipeline 3 to the wellhead casing gate of the wellhead device 12, and fix the outlet side of the pressurization pipeline 4 to the production pipeline 11; When the casing pressure is greater than the back pressure of the production pipeline 11, run the direct flow mode; Direct flow mode: The casing gas enters the upper part of the gas collection tank 1 through the casing gas transmission pipeline 3, and then enters the production pipeline 11 through the pressurization pipeline 4; When the casing pressure is not greater than the back pressure of the production pipeline 11, run the pressurization operation mode; Pressurization operation mode: After the casing gas enters the gas - collecting tank 1, the casing gas pushes the clear water in the gas - collecting tank 1 to circulate through the pipeline pump 5 to the water - seal tank 2. Based on the liquid - seal resistance, the liquid level in the water - seal tank 2 rises, prompting the pressure in the water - seal tank 2 to increase; The pressure sensor 8 or differential pressure transmitter monitors the pressure in the water - seal tank 2 and sends the monitored pressure data to the PLC controller or control instrument. When the pressure in the water - seal tank 2 reaches the pressure threshold (such as 0.1 MPa), the PLC controller or control instrument sends a start signal to the pipeline pump 5. The pipeline pump 5 starts, pressurizes the clear water in the water - seal tank 2 and injects it into the gas - collecting tank 1. Based on the liquid - seal resistance, the casing gas in the upper part of the gas - collecting tank 1 is forced to increase in pressure. After the casing gas is pressurized to be greater than the back - pressure of the production pipeline 11, it is output to the production pipeline 11 through the pressurizing pipeline 4; The liquid - level sensor 6 or differential pressure transmitter monitors the liquid level of the water - seal tank 2 in real - time and sends the monitored liquid - level data to the PLC controller or control instrument. When the liquid level of the water - seal tank 2 is lower than the liquid - level threshold (such as 10% of the liquid level), the PLC controller or control instrument sends a pump - stop signal to the pipeline pump 5. The pipeline pump 5 stops pumping, and the casing gas again pushes the clear water in the gas - collecting tank 1 to circulate back to the water - seal tank 2 through the pipeline pump 5. When the pressure sensor 8 or differential pressure transmitter monitors that the pressure in the water - seal tank 2 reaches the pressure threshold, the pipeline pump 5 is restarted; In the pressurizing operation mode, the pipeline pump 5 runs intermittently.

[0054] Example 12: Taking a low - production well in a certain oilfield in Daqing (the casing pressure is required to be controlled at 0.1 MPa, and the daily gas production is 30 m³ to 60 m³) as an example, the operation process of the well - head casing - pressure reduction and casing - gas recovery and utilization device is described as follows: 1) Installation and commissioning: Connect the casing - gas transmission pipeline 3 to the well - head casing gate of the well - head device 12, and connect the pressurizing pipeline 4 to the production pipeline 11; Inject water into the water - seal tank 2 to the liquid - level injection value (60% of the liquid level).

[0055] 2) Operating data: In the pressurizing operation mode, the pipeline pump 5 runs intermittently (operating 4 hours per day on average). After the pressure in the pressurizing pipeline 4 is greater than the back - pressure of the production pipeline (0.3 MPa), the casing gas is sent to the production pipeline 11 for recovery.

[0056] The above - mentioned technical features respectively constitute the embodiments of the present invention, which have strong adaptability and implementation effects. Non - essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. A device for reducing casing pressure at a wellhead and recovering casing gas, characterized in that: It includes an air collecting tank and a water seal tank. The upper part of the air collecting tank is fixedly connected with a casing gas delivery pipeline and a booster pipeline, and a pipeline pump is fixedly connected between the lower part of the air collecting tank and the lower part of the water seal tank. The water seal tank is fixedly installed with a liquid level monitoring instrument and a pressure monitoring instrument. An exhaust and water injection valve is fixedly installed on the top of the water seal tank. Both the casing gas delivery pipeline and the booster pipeline are connected in series with a one-way valve, and valves are connected in series on both sides of the inlet and outlet of the pipeline pump.

2. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 1, characterized in that: A connecting interface is provided at the lower part of the gas collecting tank, and the valve on the left side of the pipeline pump is fixedly installed on the outside of the connecting interface. An internal pipeline extending into the gas collecting tank is fixedly connected to the inside of the connecting interface, and one end of the internal pipeline extending into the gas collecting tank is inclined toward the bottom of the gas collecting tank.

3. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 2, characterized in that: One end of the internal pipe extending into the gas collecting tank is inclined at an angle of 15 to 60 degrees toward the bottom of the gas collecting tank; or / and, the wellhead casing pressure reduction and casing gas recovery and utilization device also includes an explosion-proof electric control cabinet, the explosion-proof electric control cabinet includes a controller, the controller is a PLC controller or a control instrument; the liquid level monitoring instrument and the pressure monitoring instrument respectively use a liquid level sensor and a pressure sensor, and the control end of the pipeline pump, the liquid level sensor and the pressure sensor are all electrically connected to the PLC controller; or, the liquid level monitoring instrument and the pressure monitoring instrument use a differential pressure transmitter, and the control end of the pipeline pump, the differential pressure transmitter and the controller are electrically connected.

4. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 1, 2 or 3, characterized in that: The outer sides of the gas collecting tank, the water sealing tank and the boosting pipeline are respectively provided with insulation layers, and the inner sides of the insulation layers are all wound with electric heating cables; or / and, the bottoms of the gas collecting tank and the water sealing tank are tapered with a wide top and a narrow bottom.

5. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 1, 2 or 3, characterized in that: The bottom of the gas collecting tank and the water seal tank are fixedly connected with a sewage pipe, and a valve is connected in series on the sewage pipe; or / and, a flow meter, a pressure monitoring instrument and a valve are fixedly installed on the casing gas delivery pipeline between the inlet side of the casing gas delivery pipeline and the one-way valve; or / and, a flow meter, a pressure monitoring instrument and a valve are fixedly installed on the boosting pipeline between the outlet side of the boosting pipeline and the one-way valve.

6. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 4, characterized in that: The bottom of the gas collecting tank and the bottom of the water seal tank are fixedly connected with a sewage pipe, and a valve is connected in series on the sewage pipe; or / and, a flow meter, a pressure monitoring instrument and a valve are fixedly installed on the casing gas delivery pipeline between the inlet side of the casing gas delivery pipeline and the one-way valve; or / and, a flow meter, a pressure monitoring instrument and a valve are fixedly installed on the boosting pipeline between the outlet side of the boosting pipeline and the one-way valve.

7. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 1, 2 or 3, characterized in that: A valve is connected in series between the lower part of the gas collecting tank and the outlet of the pipeline pump through a flange, and a valve is connected in series between the inlet of the pipeline pump and the lower part of the water seal tank through a flange; or, the lower part of the gas collecting tank and the outlet of the pipeline pump are fixedly connected through a connecting pipe, and the inlet of the pipeline pump and the lower part of the water seal tank are fixedly connected through a connecting pipe, and a valve is connected in series on the connecting pipe.

8. The device for reducing casing pressure at the wellhead and recovering casing gas according to claim 6, characterized in that: A valve is connected in series between the lower part of the gas collecting tank and the outlet of the pipeline pump through a flange, and a valve is connected in series between the inlet of the pipeline pump and the lower part of the water seal tank through a flange; or, the lower part of the gas collecting tank and the outlet of the pipeline pump are fixedly connected through a connecting pipe, and the inlet of the pipeline pump and the lower part of the water seal tank are fixedly connected through a connecting pipe, and a valve is connected in series on the connecting pipe.

9. A method for using the wellhead casing pressure reduction and casing gas recovery device according to any one of claims 1 to 8, characterized in that: Including straight-through mode and booster operation mode. When running in straight-through mode or booster operation mode, the valves on the left and right sides of the pipeline pump are in the normally open state; Inject clean water into the water seal tank. When the liquid level reaches the liquid level injection value, stop injecting clean water; The inlet side of the casing gas delivery pipeline is fixedly connected to the wellhead casing gate of the wellhead device, and the outlet side of the booster pipeline is fixedly connected to the production pipeline; When the casing pressure is greater than the back pressure of the production pipeline, the straight-through mode is operated; Straight-through mode: Casing gas enters the upper part of the gas collecting tank through the casing gas transmission pipeline, and then enters the production pipeline through the booster pipeline; When the casing pressure is not greater than the back pressure of the production pipeline, the boost operation mode is operated; Boost operation mode: After the casing gas enters the gas collecting tank, the casing gas pushes the clean water in the gas collecting tank to circulate to the water seal tank through the pipeline pump, and the liquid level in the water seal tank rises, causing the pressure in the water seal tank to rise; The pressure sensor or differential pressure transmitter monitors the pressure in the water seal tank. When the pressure in the water seal tank reaches the pressure threshold, the pipeline pump is started to pressurize the clean water in the water seal tank and inject it into the gas collecting tank. Based on the liquid seal resistance, the casing gas in the space above the liquid level of the gas collecting tank is pressurized. After the casing gas is pressurized to a pressure greater than the back pressure of the production pipeline, it is output through the booster pipeline. The liquid level sensor or differential pressure transmitter monitors the liquid level of the water seal tank in real time. When the liquid level of the water seal tank is lower than the liquid level threshold, the pump is stopped, and the casing gas pushes the clean water in the gas collecting tank to circulate back to the water seal tank through the pipeline pump. When the pressure sensor or differential pressure transmitter monitors that the pressure in the water seal tank reaches the pressure threshold, the pipeline pump is restarted; In the boost operation mode, the pipeline pump runs intermittently.

10. The method of use according to claim 9, characterized in that: Including straight-through mode and booster operation mode. When running in straight-through mode or booster operation mode, the valves on the left and right sides of the pipeline pump are in the normally open state; Set the liquid level injection value, pressure threshold and liquid level threshold of the water seal tank in the controller; Inject clean water into the water seal tank through the exhaust water injection valve. When the liquid level reaches the liquid level injection value, stop injecting clean water; The inlet side of the casing gas delivery pipeline is fixedly connected to the wellhead casing gate of the wellhead device, and the outlet side of the booster pipeline is fixedly connected to the production pipeline; When the casing pressure is greater than the back pressure of the production pipeline, the straight-through mode is operated; Straight-through mode: Casing gas enters the upper part of the gas collecting tank through the casing gas transmission pipeline, and then enters the production pipeline through the booster pipeline; When the casing pressure is not greater than the back pressure of the production pipeline, the boost operation mode is operated; Boost operation mode: After the casing gas enters the gas collecting tank, the casing gas pushes the clean water in the gas collecting tank to circulate to the water seal tank through the pipeline pump. Due to the liquid seal resistance, the liquid level in the water seal tank rises, causing the pressure in the water seal tank to rise; The pressure sensor or differential pressure transmitter monitors the pressure in the water seal tank and sends the monitored pressure data to the controller. When the pressure in the water seal tank reaches the pressure threshold, the controller sends a start signal to the pipeline pump, and the pipeline pump starts to pressurize the clean water in the water seal tank and inject it into the gas collecting tank. Based on the liquid seal resistance, the casing gas on the upper part of the gas collecting tank is forced to be pressurized. After the casing gas is pressurized to a pressure greater than the back pressure of the production pipeline, it is output to the production pipeline through the booster pipeline; The liquid level sensor or differential pressure transmitter monitors the liquid level of the water seal tank in real time and sends the monitored liquid level data to the controller. When the liquid level of the water seal tank is lower than the liquid level threshold, the controller sends a pump stop signal to the pipeline pump, the pipeline pump stops, and the casing gas pushes the clean water in the gas collection tank to circulate back to the water seal tank through the pipeline pump. When the pressure sensor or differential pressure transmitter detects that the pressure in the water seal tank reaches the pressure threshold, the pipeline pump is restarted; In the boost operation mode, the pipeline pump runs intermittently.

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