阅读说明：本技术 一种多相压缩实现套管气混输回收的系统和方法 (System and method for realizing mixed transportation and recovery of sleeve gas by multi-phase compression ) 是由 廖文勇 于 2019-07-19 设计创作，主要内容包括：本发明公开一种多相压缩实现套管气混输回收的系统和方法,特别涉及石油生产中套管气的回收和带液压缩、以及利用现有输油管线进行混输的方法。系统由工艺管线、阀门、过滤设备、压缩机、液压驱动系统、冷却系统、放空系统和就地控制柜组成。其实现方法为：当套管气压力低于油管线输送压力且高于套压的最低设定值时,只需要对套管气进行粉尘和固体颗粒杂质过滤,而不需对其进行气液分离,过滤后的套管气由压缩机增压后进入输油管线混输；当套管气压力高于油管线输送压力时,套管气通过旁路管线直接进入输油管线混输；系统运行由就地控制柜自动控制。本发明能实现套管气完全无排放回收,并自动保持井筒内适当的套压值,进而保持井筒内动液面在一个合理的高度范围,在此高度范围内,抽油泵维持在较高泵效水平稳定运行,从而稳定和提高原油产量。(The invention discloses a system and a method for realizing mixed transportation and recovery of casing gas by multiphase compression, and particularly relates to a method for recovering the casing gas in petroleum production, compressing the casing gas with liquid and carrying out mixed transportation by using the conventional oil pipeline. The system consists of a process pipeline, a valve, filtering equipment, a compressor, a hydraulic driving system, a cooling system, a venting system and an on-site control cabinet. The realization method comprises the following steps: when the pressure of the casing gas is lower than the conveying pressure of the oil pipeline and higher than the lowest set value of the casing pressure, only dust and solid particle impurities are required to be filtered, gas-liquid separation is not required to be carried out on the casing gas, and the filtered casing gas enters the oil pipeline for mixed transportation after being pressurized by a compressor; when the pressure of the casing gas is higher than the conveying pressure of the oil pipeline, the casing gas directly enters the oil pipeline for mixed conveying through the bypass pipeline; the system operation is automatically controlled by the local control cabinet. The invention can realize the complete non-discharge recovery of the casing gas, automatically keep the proper casing pressure value in the shaft, further keep the working fluid level in the shaft in a reasonable height range, and in the height range, the oil well pump can be stably operated at a higher pump efficiency level, thereby stabilizing and improving the yield of crude oil.)

1. A system and a method for realizing mixed transportation and recovery of casing gas by multiphase compression are characterized in that: the device comprises a sleeve gas inlet (A), a sleeve gas outlet (B), a vent hole (C), a main fluid pipeline (L1), an inlet hand valve (01), an outlet hand valve (12), a first three-way reversing valve (03), an outlet electric valve (11), a purging valve (02), a bypass one-way valve (04), an outlet one-way valve (09), a filter (20), a second three-way reversing valve (05), a pre-cooler (21), an outlet cooler (26), a compressor (23), a hydraulic drive system (22), an air inlet valve (24), an exhaust valve (25), a vent safety valve (07, 08), a manual vent valve (06, 10), an on-site control instrument (32, 33,34, 35), an on-site control cabinet (20), a bypass pipeline (L2) and a vent pipe (L3); the sleeve gas inlet (A) is connected with an inlet hand valve (01), the downstream of the inlet hand valve (01) is sequentially connected with a first three-way reversing valve (03) and a filter (20), the outlet of the filter (20) is connected with a second three-way reversing valve (05), the outlet of the second three-way reversing valve (05) is connected to a compressor (23), the outlet of the compressor (23) is connected to an outlet cooler (26), an outlet one-way valve (09) is arranged on the downstream of the outlet cooler (26), the outlet one-way valve (09) is connected to an outlet electric valve (11), and the downstream of the outlet electric valve (11) is sequentially connected with an outlet hand valve (12) and a sleeve gas outlet (B; one path of outlet of the second three-way reversing valve (05) is connected with the pre-cooler (21), and the outlet of the pre-cooler (21) is converged into a main pipeline (L1) in front of the compressor (23); a bypass pipeline (L2) is led out from the bypass outlet of the first three-way reversing valve (03), the bypass pipeline (L2) is converged between the outlet of the outlet check valve (09) and the inlet of the outlet electric valve (11), and a bypass check valve (04) is installed on the bypass pipeline (L2); and the main fluid pipeline (L1) is provided with a venting safety valve (07, 08) and a manual venting valve (06, 10), and the outlets of the venting safety valve (07, 08) and the manual venting valve (06, 10) are connected to a venting header (L3).

2. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by: the system does not need to carry out gas-liquid separation on the incoming gas.

3. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by: the local control cabinet 20 is provided with a PLC control module, and the system adopts the PLC control module to automatically control and operate.

4. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by: the compressor (23) is a positive displacement compressor.

5. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by: neither the system nor the compressor (23) need be unloaded when the system is not in operation.

6. The compressor of claim 4, further characterized by: the compressor cylinder is lubricated without oil, and the compressor is not provided with a lubricating oil system.

7. The compressor of claim 4, further characterized by: the air inlet valve (24) and the air outlet valve (25) of the compressor adopt a plate-free air valve structure and a linear sealing mode.

8. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by comprising the steps of: when the pressure of the casing gas is lower than the conveying pressure of the oil pipe, the compressor (23) is started, the casing gas enters the compressor (23) from the fluid main pipeline (L1) to be compressed by gas-liquid mixing, and the compressed casing gas is cooled to the required temperature by the outlet gas cooler (26) and then enters the downstream oil conveying pipeline to be mixed and conveyed; when the pressure of the casing gas is higher than the pressure of the oil pipeline, the first three-way reversing valve (03) opens the bypass, the casing gas directly enters the downstream oil pipeline through the bypass pipeline (L2) for mixed transportation, and the compressor (23) cannot be started at the moment.

9. The system and method for achieving casing gas transport recovery by multiphase compression according to claim 1, further characterized by: a pre-cooler (21) is arranged in front of the compressor (23), and is automatically started to cool the incoming air when the incoming air temperature exceeds the set compressor inlet alarm temperature.

Technical Field

The invention relates to an upstream mining and production technical link in the field of petroleum and natural gas production, in particular to a system and a method for extracting and compressing casing gas in petroleum production and carrying out mixed transportation and recovery of the casing gas by utilizing the existing oil pipeline.

Background

In oil production, the pressure at the bottom of the well must be less than the formation pressure in order for oil to flow into the well. When the bottom hole pressure is reduced to the bubble point pressure, associated gas (mainly natural gas) in crude oil is gradually separated out, a part of the natural gas and oil flow enter a pump cavity of the oil well pump to generate gas invasion, meanwhile, the pump efficiency is reduced, and air lock is caused when the situation is heavier, so that the oil well pump cannot work normally; another portion of the evolved gas "collects" between the tubing and the casing, forming casing gas. The large accumulation of the casing gas can cause the pressure (casing pressure) of the casing to rise, the working fluid level of the oil production to fall, the production pressure difference to decrease and the yield of crude oil to decrease.

Casing gas is released and recovered purposefully, and casing pressure is reduced, so that natural gas can be prevented from entering an oil well pump in a gaseous state; on the other hand, the casing pressure reduced by releasing the casing gas can keep the working fluid level of the oil extraction at a proper height, form reasonable pump submergence, ensure the pump efficiency and stabilize the crude oil yield.

From another perspective, reducing casing gas pressure means reducing the back pressure against the formation, which is beneficial for increasing oil production.

The influence of casing pressure on the pressure of an oil well is described in detail in the text of oil well casing gas recovery potential and technical application of Zhujianhua and the like (Zhujianhua and the like, oil well casing gas recovery potential and technical application [ J ]. petroleum and petrochemical energy conservation, volume 8, phase 11: 11-14), and in the production of an oil field, because the gas quantity of associated gas produced by the oil well is small, the recovery is not enough to form a certain economic benefit, or because of geographical factors and construction investment, a separate gas transmission pipeline is not constructed, most oil fields adopt a method of emptying and burning to treat casing gas. The treatment mode not only causes serious pollution to the natural environment, but also causes great waste of natural gas resources.

The main component of the casing gas is methane, and the casing gas also contains some hydrocarbon substances with longer molecular chains, moisture and other impurities. Among them, methane has a greenhouse effect (GWP value) 21 times that of carbon dioxide (qin da river. greenhouse gas and greenhouse effect [ M ] meteorological publisher, 2009: 115-.

Because the requirements of energy conservation, emission reduction and environmental protection are more and more strict, the emptying or the combustion is also more and more strictly limited. In recent years, the process technology for treating and recycling casing gas has been actively explored in various large oil fields.

For producing pumping wells, the pressure in the return main is called the back pressure. In the early stage of oil field exploitation, when the casing pressure of an oil well with high ground pressure and abundant associated gas resources is higher than the back pressure, a pressure-building recovery process or a constant-pressure recovery process is generally adopted to recover casing gas. The two processes do not discharge waste gas, and the casing gas directly enters the oil pipeline for mixed transportation, thereby achieving good effect in some oil fields. (Zhujianhua, etc. oil well casing gas recovery potential and technical application [ J ]. petroleum and petrochemical energy conservation, No. 8, No. 11, 11-14, Caocangmu, etc. oilfield associated gas comprehensive utilization and analysis [ J ]. petroleum and natural gas chemical industry, No. 44, No.2, 60-64).

The constant pressure valve recovery process is suitable for oil wells with high oil-gas ratio, large gas amount and normal pressure submergence degree of more than 150 m. On the other hand, the constant pressure or suppressed pressure recovery process can increase casing pressure, which is not beneficial to improving the yield of the oil well.

The pressure of casing gas of most oil wells is lower than the back pressure, so that the guide pipe gas needs to be pressurized before entering an oil pipe for mixed transportation, technicians develop mixed transportation technologies such as a beam-linkage low-pressure air suction cylinder and a synchronous rotation oil-gas mixed transportation compressor correspondingly (in spring, Changqing oil field oil well casing gas recovery process technology research [ J ] scientific and technical information [ 2012 NO. 24: 64-66 ]), and the universality of application and popularization is limited due to various reasons such as process structure, maintenance difficulty, pressure adaptation range, high-pressure operation stability and production adaptability.

Along with the production of oil fields, the oil field production generally faces the specific problems of reduced crude oil yield, quicker attenuation of the production speed of associated gas of the oil field, increased liquid production amount, insufficient pressure of casing gas lower than the back pressure to directly enter an oil pipeline, difficulty in on-site recovery treatment or utilization of the casing gas and the like. The special gas collection pipeline laying mode cannot adapt to the characteristic of low-permeability reservoir capacity construction, the later-stage yield adjustment is not convenient, the project cost is high, and the later-stage return is gradually exhausted.

If the existing oil pipeline can be effectively utilized, the pressurizing mixed transportation process is adopted to recover the casing gas and the crude oil are mixed and transported to the downstream for centralized treatment, the optimization of the collecting and transporting system and the full recovery and utilization of the casing gas are realized, and the method is one of the most economical and feasible recovery methods. The low-cost recovery and mixed transportation technology of the associated gas of the oil field is a core technology for realizing economic and efficient development, full utilization of resources, energy conservation and environmental protection of the low-permeability oil field in China at present.

The key problem is that the casing gas often carries a large amount of liquid, hydrocarbons, water and other impurities are contained in the liquid, the liquid carrying amount of a plurality of well heads exceeds more than 10%, when a constant pressure recovery or pressure build-up recovery process is not suitable, the common technical route is that the casing gas is firstly subjected to gas-liquid separation, the separated gas is independently compressed and then is mixed with the liquid to enter an oil pipe for conveying, the complexity of the process is increased, and a lot of workload and equipment investment are increased in production.

In the mixed transportation technology proposed by CN102588737B, the gas transmission pump is only suitable for low-pressure transportation, and is not suitable for transportation of gas with liquid and compression at higher pressure, and this method is not suitable for the case where the sleeve carries liquid or the back pressure is higher; the jetting and leading booster-type casing gas recovery device disclosed by CN104100238B is simple in structure and has a certain recovery effect, but the sleeve pressure reduction capability is limited, so that the device is only suitable for oil wells with high wellhead pressure (more than 1.0 MPa), and has limitation on the application of low-pressure wells; the device for recovering associated gas of a cluster well group, which is described in CN104405343B, drives a piston to compress by utilizing the reciprocating motion of a walking beam of a pumping unit, does not need extra power, but needs to perform gas-liquid separation on the associated gas, and cannot compress the associated gas with liquid, and is only suitable for the cluster well group for oil extraction of the pumping unit, and is not suitable for a well site for oil extraction of an oil-submerged pump, and the exhaust pressure can only reach 0.6MPa, and cannot realize mixed transportation for the well site with higher back pressure, and is limited by the reciprocating speed of the walking beam, so that the capacity of recovering gas and reducing casing pressure is limited; the method adopted by the sleeve gas recovery device of CN101915074B is to introduce all sleeve gas and part or all crude oil into a synchronous rotary compressor for compression and transportation, the sleeve gas does not need to be subjected to gas-liquid separation, and the sleeve gas is the device closest to sleeve gas-liquid mixed transportation at present, and has the disadvantages of large maintenance amount of the synchronous rotary oil-gas mixed transportation device, high belt breakage frequency, long maintenance period and insufficient high-pressure operation stability, and the synchronous rotary compressor is not suitable for simply compressing the sleeve gas with low liquid content; CN109826594A discloses a sleeve gas collection device and a use method, wherein a mixed transportation pump is adopted for oil-gas mixed transportation, the device is characterized in that sleeve gas can be recovered in a sealed manner, but when the sleeve pressure is high, an oil well pump is required to stop working, then the sleeve pressure is further released through the device, and the limitation is that the device has insufficient adaptability to various pressure working conditions and field production; the oilfield associated gas pressurization mixed transportation device and the recovery method thereof described in CN102444783B propose two different casing gas recovery routes, the compressor is essentially a screw mixed transportation pump, the screw pump can be well adapted to gas-liquid mixed transportation at the same time, but the high temperature resistance is weak, sufficient crude oil needs to be additionally introduced for spray cooling and keeping a certain liquid filling degree in the pump, when the upstream working condition is unstable, dry grinding is easily caused, the stator is easily damaged, and the maintenance cost is high.

To sum up, the existing casing gas recovery technology has various limitations: the constant pressure or pressure-building recovery technology is simple in process, but is not suitable for most oil wells with lower casing pressure due to the limitation of oil return pressure, and the constant pressure release or pressure-building release process conversely increases the casing pressure and reduces the oil well yield; the synchronous rotary compressor mixed transportation technology or the screw pump mixed transportation technology has the dual characteristics of a pump and a compressor, the suction pressure of the pump is low, the viscosity of the liquid which can be transported is wide, but the pump efficiency is rapidly reduced when the gas content is high (the GVF exceeds more than 80 percent), the pump is easy to damage, the maintenance cost is higher, the field maintenance is difficult, the pump is suitable for being used as a mixed transportation pump in the process flow, and the pump is not suitable for being used for recovering associated gas only; the common technology of recovering the associated gas by the gas compressor needs to carry out gas-liquid separation on the incoming gas, the separated gas can be utilized on the spot after being compressed, or the gas and the separated liquid are mixed again and enter an oil pipe for mixed transportation, the method has larger equipment investment, needs to increase the gas-liquid separation process flow, and has no economic value when the amount of the associated gas is small; other recovery methods have insufficient adaptability for large-area popularization and application due to the limitation of processes or technical routes.

Disclosure of Invention

Aiming at the defects or limitations of the prior art and process, the invention provides a system and a method for realizing mixed transportation and recovery of casing gas by multiphase compression, which do not need gas-liquid separation treatment on the casing gas and have wide adaptability to different casing gas pressures, different liquid carrying amounts and different oil pipe conveying pressures.

In order to realize the purpose, the technical scheme adopted by the invention is as follows:

a system and a method for realizing mixed transportation and recovery of casing gas by multiphase compression are composed of a casing gas inlet A, a casing gas outlet B, a vent C, a main fluid pipeline L1, an inlet hand valve 01, an outlet hand valve 12, a first three-way reversing valve 03, an outlet electric valve 11, a purge valve 02, a bypass one-way valve 04, an outlet one-way valve 09, a filter 20, a second three-way reversing valve 05, a pre-cooler 21, an outlet cooler 26, a compressor 23, a hydraulic drive system 22, an air inlet valve 24, an exhaust valve 25, a vent safety valve 07, a filter 08, a manual vent valve 06, a manual vent valve 10, an on-site control instrument 32,33,34,35, an on-site control cabinet 20, a bypass pipeline L2 and a vent collecting pipe L3; the sleeve gas inlet A is connected with an inlet hand valve 01, the downstream of the inlet hand valve 01 is sequentially connected with a first three-way reversing valve 03 and a filter 20, the outlet of the filter 20 is connected with a second three-way reversing valve 05, the outlet of the second three-way reversing valve 05 is connected with a compressor 23, the outlet of the compressor 23 is connected with an outlet cooler 26, an outlet one-way valve 09 is arranged on the downstream of the outlet cooler 26, the outlet one-way valve 09 is connected with an outlet electric valve 11, and the downstream of the outlet electric valve 11 is sequentially connected with an outlet hand valve 12 and a sleeve gas outlet B; one outlet of the second three-way reversing valve 05 is connected with the pre-cooler 21, and the outlet of the pre-cooler 21 is converged into a main pipeline L1 in front of the compressor 23; a bypass line L2 leads out from the bypass outlet of the first three-way reversing valve 03, the bypass line L2 is converged between the outlet of the outlet check valve 09 and the inlet of the outlet electric valve 11, and a bypass check valve 04 is installed on the bypass line L2; and the main fluid pipeline L1 is provided with emptying safety valves 07 and 08 and manual emptying valves 06 and 10, and the outlets of the emptying safety valves 07 and 08 and the manual emptying valves 06 and 10 are connected to an emptying header L3.

The invention realizes the multiphase compression of the casing gas and the mixed transportation of the casing gas entering the oil pipeline by the following technical scheme:

the first scheme is as follows: when the pressure of the upstream casing gas is lower than a set value, the casing gas flows away from a main pipeline L1, dust impurities in the casing gas are filtered by a filter 20 before entering a compressor, the casing gas enters the compressor 23 for multiphase compression, and the compressed casing gas is cooled to a required temperature by an outlet gas cooler 26 and then enters a downstream oil pipeline for mixed transportation;

scheme II: when the pressure of the upstream casing is higher than a set value, the bypass of the first three-way reversing valve 03 is automatically opened, the casing gas directly enters the oil pipeline through the outlet electric valve 11 without entering the main fluid pipeline L1 or the bypass pipeline L2, and the compressor 23 cannot be started at this time.

The technical scheme of the invention is that the compressor 23 is different from a common reciprocating compressor in that a gas inlet valve and a gas outlet valve of the compressor adopt a plate-free gas valve structure and a linear sealing form so as to realize simultaneous circulation of gas phase and liquid phase, and liquid impact phenomenon cannot occur in a cylinder of the compressor.

The further technical scheme of the invention is that the linear velocity of the motion of the piston of the compressor 23 is far lower than that of a common reciprocating compressor, the heat generated by the friction between the piston and the cylinder is small, and the liquid carried in the sleeve gas has a lubricating effect, so that the cylinder of the compressor does not need to be provided with an independent lubricating system.

The technical scheme of the invention is that before the casing gas enters the compressor, only the dust filter 20 is arranged to filter out dust and solid particles in the incoming gas, the purpose is to protect the cylinder, the filter can be a conical filter or a basket filter, the filter core is generally made of a stainless steel filter screen, and liquid and gas can smoothly pass through the filter.

The further technical scheme of the invention is that in order to realize the wide adaptability of the compressor 23 to different air inlet pressures and exhaust pressures, the piston of the compressor is driven by a hydraulic system, the hydraulic system can automatically adapt to and adjust the air inlet pressure and the exhaust pressure and can provide enough hydraulic pressure, and the mixed transportation compressor of the system can adapt to the working condition of the compressor as long as the inlet and outlet pressure of the sleeve air is within the working pressure range set by the compressor and the design pressure of the air cylinder meets the relevant standard of the positive displacement compressor.

The technical scheme of the invention is that the compressor can be loaded and unloaded at any time due to the characteristic that the hydraulic driving system is controlled by the action of the hydraulic element, and when the system does not work, the system and the compressor do not need to be unloaded, so that the compressor can be quickly started after being stopped, and the problem that the common reciprocating compressor needs to be unloaded after being stopped is solved.

The further technical scheme of the invention is that in order to adapt to different sleeve gas air inflow, air inflow pressure and air exhaust pressure, one or more matched cylinders can be adopted, and the compression stage number can be single-stage compression or multi-stage compression.

The further technical scheme of the invention is that the local control cabinet 20 is provided with a PLC control module which can automatically open or close the first three-way reversing valve 03, the second three-way reversing valve 05, the pre-cooler 21 and the compressor 23 according to the inlet pressure and the temperature of the casing gas and the back pressure of the oil pipeline, and the casing gas is pressurized to the required pressure and then enters the oil pipeline for mixed transportation.

The invention further adopts the technical scheme that manual shut-off valves 01 and 12 are arranged at the inlet and the outlet of the system, and manual emptying valves 06 and 10 are arranged on the system pipelines and used for cutting off the connection between the system and the upstream and downstream and emptying dangerous gas in the system when the system is in fault or overhauled; a purge valve 02 is provided at the system inlet for the replacement of hazardous gases in the system before the system is restarted.

The invention further adopts the technical scheme that in order to ensure safety, safety valves 07 and 08 are arranged on a system pipeline and are connected to a vent manifold L3, and when the pressure in the system exceeds the set safety pressure, the safety valves are automatically opened to release the pressure and vent the system.

Compared with the prior art, the invention has the advantages that:

1. the sleeve gas-liquid compression can be met, gas-liquid separation is not needed, and the sleeve gas is completely recovered without emission; 2. the adaptive sleeve gas inlet range is wide, and the sleeve gas inlet can also be used for negative pressure extraction; 3. the exhaust pressure is high, the transmission pressure of most oil pipelines can be met, and the casing gas and the crude oil are mixed and transmitted to downstream for centralized processing; 4. the compressor automatically matches proper inlet and outlet pressure, sleeve pressure is reduced and controlled, pump efficiency is improved, and crude oil yield is increased; 5. the system has simple and reliable process, safety, full automatic operation, unattended operation, convenient field maintenance and less investment.

Drawings

The invention is further illustrated with reference to the accompanying drawings:

FIG. 1 is a schematic diagram of the system of the present invention,

wherein: the system comprises a sleeve A gas inlet, a sleeve B gas outlet, a vent outlet C, a main fluid pipeline L1, an inlet hand valve 01, an outlet hand valve 12, a first three-way reversing valve 03, an outlet electric valve 11, a purging valve 02, a bypass check valve 04, an outlet check valve 09, a filter 20, a second three-way reversing valve 05, a pre-cooler 21, an outlet cooler 26, a compressor 23, a hydraulic driving system 22, an inlet valve 24, an exhaust valve 25, a vent valve 07, a vent safety valve 08, a manual vent valve 06, a manual vent valve 10, a manual vent valve 32,33,34,35, an on-site control instrument, a 20 on-site control cabinet, a bypass pipeline L2 and a vent manifold L3.

Detailed Description

The present invention will be further described with reference to the accompanying drawings in order to more clearly illustrate the objects, technical means employed, embodiments and advantages of the present invention.

The first embodiment is as follows:

the start-up of the compressor 23 requires two conditions to be satisfied: the air pressure of the inlet sleeve of the compressor is lower than the conveying pressure of the oil pipe and higher than the lowest set value of the sleeve pressure, and if one of the air pressures is not met, the compressor does not work; the compressor inlet casing gas pressure signal is taken from the pressure transmitter 33, the oil pipeline transmits the pressure signal to the pressure transmitter 34; the PLC module of the local control cabinet automatically compares the air pressure signal value of the inlet casing of the compressor with the conveying pressure signal of the oil pipeline, when the starting conditions are met, the PLC module sends out an instruction, the compressor is started to work, the casing air flows out of the main pipeline L1 and enters the filter 20 to filter out dust impurities in the casing air, but liquid in the casing air cannot be filtered, the filtering precision is generally set to be 5-10 mu m, the filtered casing air enters the compressor 23 to be compressed, the casing air is pressurized to be higher than the pressure of the oil pipeline, and the compressed casing air sequentially passes through the outlet cooler 26, the outlet check valve 09, the outlet electric valve 11 and the outlet hand valve 12 and enters the oil pipeline for mixed conveying.

In the process flow described in the first embodiment, the temperature signal of the inlet casing gas is transmitted to the local control cabinet 20 by the local meter 33, when the casing gas temperature exceeds the upper limit of the inlet temperature set by the compressor, the PLC control module sends out a command to sequentially start the pre-cooler 21, open the second three-way reversing valve 05, start the compressor 23, and the casing gas bypasses the second three-way reversing valve 05 to enter the pre-cooler 21 for cooling, and then is converged into the main fluid line L1 to enter the compressor 23 for pressurization.

Embodiment two:

when the control cabinet detects that the pressure value of the casing gas at the inlet of the compressor is higher than the conveying pressure of the oil pipeline, the compressor 23 does not meet the starting condition at the moment, the compressor cannot work, the PLC module sends an instruction, the bypass is opened by the first three-way reversing valve 03, the casing gas does not flow through the main fluid pipeline L1, directly flows through the bypass pipeline L2, and enters the oil pipeline for mixed conveying through the electric outlet valve 11.

When the system actually operates, the two implementation schemes are automatically switched and mutually supplemented to form a complete method for realizing the mixed transportation of the casing gas by using the oil pipeline by the system.

The best parameters set by the above embodiment are: the air inlet pressure range of the compressor is 0-1.0 MPa, the highest exhaust pressure is 5.0MPa, the double-cylinder two-stage compression is realized, and the amount of liquid carried by the sleeve is allowed to exceed 10%. The parameter can completely meet the working conditions of most well sites and has wide adaptability.

Particularly, after the oil-gas mixture transportation and recovery casing gas system is put into operation, the casing gas pressure in the shaft can be reduced to a proper range, so that the working fluid level in the shaft is kept at a reasonable height (range), and in the range, the pumping efficiency of an oil well pump is maintained at a high level to stably operate, so that the crude oil yield is stabilized and improved.

While the foregoing is directed to the preferred embodiment of the present invention, it will be appreciated by those skilled in the art that the present invention is not limited by the foregoing embodiment, but is intended to be illustrative only of the principles and methods of the invention, and that other arrangements, modifications and variations can be devised without departing from the spirit and scope of the invention.