Waste shale gas well recovery device and working principle thereof

Abstract

The invention discloses a waste shale gas well re-mining device and a working principle thereof, and belongs to the technical field of waste well re-mining in the later period of unconventional shale gas reservoir development. One end of a gas injection pipeline is arranged outside a shaft and is sequentially connected with a compressor, a gas injection valve and a pressure gauge; the other end of the gas injection pipeline extends into the shaft; one end of the gas production pipeline is arranged outside the shaft and is connected with a gas production valve; the other end of the gas production pipeline extends into the shaft; according to the working principle of the waste shale gas well recovery device, a gas injection mode is selected; a CO2 gas injection, pressurization, permeation enhancement and deblocking stage; a well closing pressurization and CO2 gas high-pressure replacement stage; a mixed gas extraction and separation stage; and a CO2 gas circulation injection stage. According to the method, the problems of pressurization, permeation enhancement and deblocking of the shale gas waste well and desorption of the adsorbed gas under the high-pressure condition are solved, and the purpose of re-mining of the waste well is finally achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of recovery technology of abandoned wells in the late stage of unconventional shale gas reservoir development, and in particular to a recovery device for an abandoned shale gas well and a working principle thereof. Background Art

[0002] Shale gas reservoir is a special unconventional natural gas reservoir with poor reservoir properties. It is an ultra-low porosity and permeability gas reservoir, mostly distributed in the syncline area of ​​oil and gas basins. The gas reservoir closure type is mostly pressure closure. The gas reservoir pressure is mainly provided by the abnormal pressure inside the gas reservoir and the elastic energy of the formation, and there is no edge and bottom water to provide energy supply.

[0003] The initial production of gas reservoirs is high, but the production and formation pressure decrease very rapidly, reaching the abandonment pressure point in a short period of time, resulting in a low recovery rate of shale gas reservoirs, generally only about 20-30%. The main reason for this phenomenon is that during the rapid decline of abnormal pressure in the gas reservoir, the porosity and permeability of the shale gas reservoir will also decrease sharply, resulting in a large amount of shale gas being sealed in the original formation and unable to be extracted, and being abandoned prematurely.

[0004] As shale gas development progresses, a large number of shale gas wells will face abandonment in the next 3-5 years, and research on the recovery of abandoned wells is imminent.

[0005] In order to extend the abandonment time of shale gas and improve the recovery rate of shale gas, relevant personnel have started relevant research work, and the measures currently taken are mainly repeated fracturing. Repeated fracturing is to implement re-hole fracturing between the first fracturing stages when the production pressure and gas production of shale gas wells have dropped to a lower value after a certain period of development, in order to recover the shale gas remaining in the formation that was not affected by the first fracturing and replenish the formation with energy, so as to achieve the purpose of improving the recovery rate of shale gas.

[0006] However, shale gas repeated fracturing still mostly uses the same hydraulic fracturing as the primary fracturing. Analysis shows that due to the special geological characteristics of shale gas, repeated fracturing has the problems of high cost and poor benefits. Since shale gas reservoirs are usually overpressure gas reservoirs, shale gas is enriched in the pressure trap formed by abnormal pressure. When natural depletion is used for exploitation, the gas reservoir capacity (abnormal pressure) disappears quickly, and the micro-cracks in the formation also close quickly, and a large amount of shale gas in the tiny pores in the matrix shale is trapped in them. Therefore, when repeated fracturing is carried out, the following problems will arise:

[0007] (1) Artificial fracturing can only produce a small number of large-scale fractures, and still cannot effectively connect the micro-fractures in the matrix. The formation pressure under abandoned shale gas wells has dropped to a very low level, and the permeability has also dropped significantly. Simply repeating fracturing has little effect on increasing the pressure of the matrix rock.

[0008] (2) During hydraulic fracturing, a large amount of water (fracturing fluid) is injected into the formation. However, this water is difficult to inject into the matrix rock blocks of the formation. Instead, it exists more in the cracks (including artificial cracks and natural cracks). This results in the water in the cracks surrounding the matrix rock blocks (including the shale gas therein). At the same time, since the fracturing fluid pressure in the cracks is greater than the pore pressure of the matrix blocks, a "water-sealed gas" situation is easily formed, making the shale gas remaining in the matrix blocks more difficult to extract.

[0009] Therefore, it is necessary to provide an abandoned shale gas well recovery device and its working principle. Summary of the invention

[0010] The purpose of the present invention is to provide an abandoned shale gas well recovery device and its working principle to solve the following problems:

[0011] (1) Issues of increasing formation pressure

[0012] The main reason for the abandonment of shale gas wells is that the formation pressure, especially the matrix rock pressure, is too low. The residual shale gas in the formation cannot overcome the water column pressure in the wellbore and is difficult to be produced, resulting in a large amount (70-80%) of geological reserves being wasted. Although repeated fracturing can replenish some energy for the formation, this energy is mainly concentrated in the cracks. The pore pressure in the cracks may be effectively increased, while the pore pressure in the matrix rock is difficult to increase.

[0013] (2) The problem of “water-sealed gas” in the formation

[0014] Since the pore pressure in the fractures is greater than the pore pressure in the matrix rock, the residual shale gas in the matrix rock is pressure-sealed. How to release the water's seal on the gas is also a key issue in the revival of abandoned shale gas wells.

[0015] (3) Desorption of adsorbed gas in organic pores of shale reservoirs under high pressure

[0016] There is a large amount of adsorbed gas on the surface of shale organic matter. Although part of the adsorbed gas has been desorbed as the formation pressure decreases during the first production, most of the adsorbed gas still remains on the surface of the organic matter. The adsorption characteristic of organic matter is that the adsorption amount is positively correlated with the pressure. The greater the pressure, the greater the adsorption amount. This will conflict with the previous concept of pressurized gas production. Therefore, how to achieve desorption of adsorbed gas during the pressurization process will be another key issue.

[0017] In order to achieve the above object, the present invention adopts the following technical solutions:

[0018] An abandoned shale gas well recovery device, comprising:

[0019] A gas injection pipeline, one end of which is arranged outside the wellbore and is sequentially connected to a compressor, a gas injection valve and a pressure gauge; the other end of which extends to a predetermined distance inside the wellbore;

[0020] A gas production pipeline, one end of which is arranged outside the wellbore and connected to a gas production valve; the other end of the gas production pipeline extends to a predetermined distance inside the wellbore; the gas production pipeline and the gas injection pipeline do not interfere with each other.

[0021] Furthermore, it also includes:

[0022] A bridge plug is arranged at a predetermined position in the wellbore and divides the wellbore into two separate wellbores that are not connected to each other;

[0023] The end of the gas injection pipeline located in the wellbore reaches the predetermined position after passing through the bridge plug;

[0024] One end of the gas production pipeline located in the wellbore passes through the bridge plug and extends to the bottom of the wellbore.

[0025] The working principle of the abandoned shale gas well recovery device as described above includes:

[0026] S1, select gas injection method

[0027] S2, CO2 gas injection and pressurization, permeation and unsealing stage

[0028] After the CO2 gas is continuously injected, the pressure inside the gas chamber gradually increases, and a part of the CO2 gas (or mixed gas) is pressed into the formation, and the formation pressure also increases accordingly; at the same time, as the pore pressure of the matrix rock increases, the permeability of the matrix rock gradually increases, and the "water-sealed gas" phenomenon will be broken, thereby achieving the triple goals of pressurization, permeability enhancement, and unsealing;

[0029] S3, well pressurization and CO2 gas high pressure replacement stage

[0030] After CO2 gas is injected, in order to allow the injected CO2 gas to be fully mixed and replaced with the methane gas in the formation, a certain period of well sealing is required; the mixing is mainly carried out between the free gas and the CO2 gas, and the replacement is mainly carried out between the adsorbed gas and the CO2 gas; during the well sealing period, the gas composition and pressure in the gas chamber need to be continuously monitored, and the well sealing ends when the methane composition in the gas chamber no longer continues to increase;

[0031] S4, mixed gas extraction and separation stage

[0032] After the well is sealed, the mixed gas formed by methane gas and CO2 gas in the formation is produced with reasonable production allocation; after the mixed gas is produced, it is strictly separated, the methane gas enters the gathering and transportation pipeline network, and the separated CO2 gas is recovered for the next injection cycle;

[0033] S5, CO2 gas cycle injection stage

[0034] After a period of production, when the formation pressure drops to a predetermined value, gas production is stopped and steps S2-S4 are repeated until the methane content of the mixed gas in the formation is lower than the secondary abandonment value, thus completing the recovery of the abandoned shale gas well.

[0035] Furthermore, the gas injection method selected in step S1 includes:

[0036] A. If the well type is an up-dip well, a single tubing gas injection and production method is used;

[0037] B. If the well type is a down-dip well, the double-tubing gas injection and production method is adopted.

[0038] Furthermore, the single oil pipe gas injection and production method is specifically as follows:

[0039] The end of the gas injection pipeline is extended to above the gas-water interface. When high-pressure CO2 gas is injected through the gas injection pipeline, the gas chamber pressure gradually increases. When the gas chamber pressure is greater than the formation pressure, the mixed gas of CO2 and methane in the gas chamber begins to be injected back into the formation. After the gas injection is completed, the gas production pipeline is used for gas production.

[0040] Furthermore, the double oil pipe gas injection and production method is specifically as follows:

[0041] A bridge plug is lowered into the target layer, the gas injection pipeline is lowered to the bottom interface of the bridge plug, and the gas production pipeline is lowered to the bottom of the well; with the gas production valve open, CO2 gas is injected, and the water under the bridge plug is discharged from the wellbore. After all the water is discharged, the gas production valve is closed and pressurized gas injection is started; after the gas injection is completed, gas is produced using the gas production pipeline.

[0042] Furthermore, the high-pressure gas replacement in step S1 refers to using a gas with stronger adsorption to replace the adsorbed methane in the shale reservoir from the surface of the organic matter, so that the original adsorbed methane is converted into a free state and enters the pores, and the original free state strongly adsorbed gas is converted into an adsorbed state and adsorbed by the organic matter; the adsorption of CO2 gas in organic matter is much greater than that of methane gas, and its adsorption is proportional to the pressure. As the pressure increases, the adsorption amount increases; therefore, when CO2 gas is injected, the adsorbed methane in the shale will be replaced by the CO2 gas with stronger adsorption to form free gas, thereby achieving the purpose of desorption of the adsorbed gas in the high-pressure state.

[0043] The present invention has the following beneficial effects:

[0044] 1. The gas pressure injection method of the present invention can effectively increase the formation pressure, improve the reservoir seepage properties, and break through the "water-sealed gas" constraint of the shale reservoir. In addition, the injected gas continuously replaces the shale gas, especially the adsorbed gas, so the formation energy of the abandoned shale gas well is effectively supplemented, the reservoir permeability is gradually improved, and the free part of shale gas is also continuously increased. Therefore, with the continuous injection of gas, the shale gas remaining in the formation after one mining can be effectively extracted.

[0045] 2. The present invention can effectively revive most abandoned shale gas wells and greatly improve the recovery rate of shale. Theoretically, 100% of the shale gas in the formation can be recovered. However, as external gas is continuously injected and replaced, the recovery rate will continue to decrease with the decrease of methane gas content in the shale reservoir, and the recovery cost will continue to increase. Based on economic benefits, the second abandonment can be re-established with shale gas content as the abandonment indicator. Nevertheless, the present invention can at least increase the current recovery rate of 20-30% to more than 50%, greatly improving the production efficiency of shale gas wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of the principle of multiple mining provided by the present invention;

[0047] Figure 2 A schematic diagram of the principle of gas injection and recovery in an up-dip well provided by the present invention;

[0048] Figure 3 A schematic diagram of the principle of gas injection and recovery in a down-dip well provided by the present invention;

[0049] Figure 4 This is a schematic diagram of the relationship between the organic methane and CO2 adsorption capacity and pressure provided by the present invention. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0051] The present invention specifically relates to a technology for filling abandoned shale gas development wells with gas to supplement formation energy, improve shale reservoir permeability, achieve abandoned well revival, and ultimately improve shale gas recovery rate.

[0052] like Figure 2 , Figure 3 As shown, the present application provides an abandoned shale gas well recovery device, including: a gas injection pipeline, one end of which is arranged outside the wellbore and is connected to a compressor, a gas injection valve and a pressure gauge in sequence; the other end of the gas injection pipeline extends to a predetermined distance inside the wellbore.

[0053] A gas production pipeline, one end of which is arranged outside the wellbore and is connected to a gas production valve; the other end of the gas production pipeline extends to a predetermined distance inside the wellbore; the gas production pipeline and the gas injection pipeline do not interfere with each other.

[0054] It also includes a bridge plug, which is arranged at a predetermined position in the wellbore and divides the wellbore into two unconnected sub-wellbores; one end of the gas injection pipeline located in the wellbore passes through the bridge plug and reaches the predetermined position; one end of the gas production pipeline located in the wellbore passes through the bridge plug and extends to the bottom of the wellbore.

[0055] The object of the present invention is to realize the technology of pressurizing, increasing permeability and unsealing abandoned shale gas wells by injecting gas into the formation.

[0056] like Figure 1 As shown, this embodiment provides a working principle of an abandoned shale gas well recovery device, including:

[0057] S1, select the gas injection method;

[0058] Shale gas development usually adopts horizontal well groups for exploitation. There are two types of wells: up-dip wells and down-dip wells. Due to the different inclination directions of the wellbore trajectories, the gas injection methods and processes will be very different.

[0059] A. If the well type is an upward-inclined well, a single-tube gas injection and gas production method is adopted. This type of well type does not require a separate gas production pipeline. It only needs to install a gas production valve at the wellhead (such as Figure 2 ).

[0060] The working principle of the single-tubing gas injection and production technology is as follows: Since the altitude of the bottom of the well is higher than the altitude of point A (the starting point of the horizontal section), a portion of methane gas will remain between point A and the bottom of the well after the up-dip well is abandoned, and it will be sealed in the wellbore by water to form an air chamber. During the gas injection process, it is only necessary to lower the gas injection pipeline above the gas-water interface to implement gas injection. After the gas injection pipeline injects high-pressure CO2 gas, the pressure in the gas chamber gradually increases. When it is greater than the formation pressure, the mixed gas of CO2 and methane in the gas chamber begins to be injected back into the formation. After the gas injection is completed, the gas injection pipeline is used for gas production.

[0061] B. If the well type is a down-dip well, the double-tubing gas injection and gas production method is adopted (such as Figure 3 ).

[0062] The working principle of the double-tubing gas injection and production technology is as follows: the situation of the down-dip well is more complicated than that of the up-dip well. Since the wellbore is completely filled with water and there is no natural gas chamber, an artificial gas chamber must be built in the initial stage of gas injection, that is, a bridge plug is lowered into the target layer (near point A) to separate the wellbore below point A from the above, and then the gas injection pipeline is lowered to the bottom interface of the bridge plug and the gas production pipeline is lowered to the bottom of the well. When the gas production valve is open, CO2 gas is injected. Due to the buoyancy, the water under the bridge plug is discharged from the wellbore. After all the water is discharged, the artificial gas chamber is built, the gas production valve is closed, and pressurized gas injection begins. After the gas injection is completed, gas is produced using the gas production pipeline.

[0063] S2, CO2 gas injection and pressurization, permeation and unsealing stage;

[0064] After the CO2 gas is continuously injected, the pressure inside the gas chamber gradually increases, and a part of the CO2 gas (or mixed gas) is pressed into the formation, and the formation pressure also increases accordingly.

[0065] ΔP=P-P0 (1)

[0066] P0 is the residual pressure of the formation after one development, P is the real-time formation pressure during pressurized gas injection, and ΔP is the increase in formation pressure.

[0067] When ΔP reaches the preset pressure, stop gas injection.

[0068] Since water injection into shale gas wells cannot achieve the purpose of pressurizing the matrix rock blocks, but will increase the degree of "water-sealed gas" in the formation, the present invention adopts a method of gas injection pressurization. Because the diameter of gas molecules is much smaller than the diameter of water molecules, and the wetting angle of gas on the rock surface (especially rocks with high clay content) is much larger than the wetting angle of water, its wettability is smaller, it is easy to break through the water surround and penetrate into the low-pressure matrix rock blocks surrounded by water, thereby increasing the pore pressure of the matrix rock blocks, achieving pressurization of the formation (especially pressurization of the matrix rock blocks), and at the same time, with the increase of the pore pressure of the matrix rock blocks, the permeability of the matrix rock blocks gradually increases, and the "water-sealed gas" phenomenon will be broken, thereby achieving the triple purposes of pressurization, permeability increase, and unsealing.

[0069] S3, the stage of well pressurization and CO2 gas high-pressure replacement;

[0070] According to the Langmuir curve, the amount of adsorbed gas is greater under high pressure, that is, the adsorption capacity of organic matter is stronger under high pressure. Therefore, the higher the pressure, the more difficult it is to desorb the adsorbed gas. In order to solve the problem of desorption of adsorbed gas in the gas injection and pressurization link, CO2 gas high-pressure replacement technology was adopted.

[0071] Gas high-pressure replacement refers to the use of more strongly adsorbent gas to displace adsorbed methane from the surface of organic matter in shale reservoirs, so that the original adsorbed methane is converted into a free state and enters the pores, while the original free state of highly adsorbent gas is converted into an adsorbed state and adsorbed by organic matter.

[0072] like Figure 4 As shown in the figure, CO2 gas has a much greater adsorption capacity in organic matter than methane gas, and its adsorption capacity is proportional to pressure. As the pressure increases, the adsorption amount increases. Therefore, when CO2 is injected, the adsorbed methane in the shale will be replaced by the more adsorbed CO2 to form free gas, thereby achieving the purpose of desorption of adsorbed gas in a high-pressure state.

[0073] After the CO2 gas is injected, it is impossible to completely mix or replace it with the residual gas in the formation immediately. It takes a certain period of time to seal the well. The purpose is to allow the injected CO2 gas to fully mix and replace the methane gas in the formation. The mixing is mainly between the free gas and the CO2 gas, and the replacement is mainly between the adsorbed gas and the CO2 gas. During the sealing period, it is necessary to continuously monitor the gas composition and pressure in the gas chamber. When the methane component in the gas chamber no longer continues to increase, the sealing can be ended.

[0074] S4, mixed gas extraction and separation stage;

[0075] After the well is sealed, the mixed gas formed by methane and CO2 in the formation is produced with reasonable production allocation. After the mixed gas is produced, it is strictly separated, the methane gas enters the gathering and transportation pipeline network, and the separated CO2 gas is recovered for the next injection cycle.

[0076] S5, CO2 gas cycle injection stage

[0077] After a period of exploitation, when the formation pressure drops to a predetermined value, gas extraction is stopped and secondary injection is carried out, repeating the above-mentioned "injection-extraction-injection-extraction" cycle until the methane content of the mixed gas in the formation is lower than the secondary abandonment value, thus completing the recovery of the abandoned shale gas well.

[0078] The core of the present invention is to increase the formation pressure of abandoned shale gas reservoirs and provide energy supplement to the gas reservoirs so that more shale gas can be produced. The necessary condition is to have the technology of formation pressurization, especially to pressurize the matrix rock blocks and be able to release the "water-sealed gas". The basic element is that after the gas reservoir reaches the abandonment pressure, the wellbore must remain in good condition to achieve the purpose of formation pressurization.

[0079] The present invention solves the problems of pressurization, permeability enhancement, unsealing of abandoned shale gas wells and desorption of adsorbed gas under high pressure conditions through the implementation of the above-mentioned technologies, and ultimately achieves the purpose of re-production of abandoned wells.

[0080] The gas pressure injection method of the present invention can effectively increase the formation pressure, improve the reservoir seepage properties, and break through the "water-sealed gas" constraint of the shale reservoir. In addition, the injected gas continuously replaces the shale gas, especially the adsorbed gas, so the formation energy of the abandoned shale gas well is effectively supplemented, the reservoir permeability is gradually improved, and the free part of shale gas is also continuously increased. Therefore, with the continuous injection of gas, the shale gas remaining in the formation after one mining can be effectively extracted.

[0081] The present invention can effectively revive most abandoned shale gas wells and improve the recovery rate of shale. Theoretically, 100% of the shale gas in the formation can be recovered. However, as external gas is continuously injected and replaced, the recovery rate will continue to decrease with the decrease of methane gas content in the shale reservoir, and the recovery cost will continue to increase. Based on economic benefits, the second abandonment can be re-established with shale gas content as the abandonment indicator. Nevertheless, the present invention can at least increase the current recovery rate of 20-30% to more than 50%, greatly improving the production efficiency of shale gas wells.

[0082] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A device for recovering abandoned shale gas wells, characterized in that: include: A gas injection pipeline, one end of which is arranged outside the wellbore and is sequentially connected to a compressor, a gas injection valve and a pressure gauge; the other end of which extends to a predetermined distance inside the wellbore; A gas production pipeline, one end of which is arranged outside the wellbore and connected to a gas production valve; the other end of the gas production pipeline extends to a predetermined distance inside the wellbore; the gas production pipeline and the gas injection pipeline do not interfere with each other.

2. The abandoned shale gas well recovery device according to claim 1, characterized in that: Also includes: A bridge plug is arranged at a predetermined position in the wellbore and divides the wellbore into two separate wellbores that are not connected to each other; The end of the gas injection pipeline located in the wellbore reaches the predetermined position after passing through the bridge plug; One end of the gas production pipeline located in the wellbore passes through the bridge plug and extends to the bottom of the wellbore.

3. A working principle of the abandoned shale gas well recovery device according to any one of claims 1 to 2, characterized in that: include: S1, select gas injection method S2, CO2 gas injection and pressurization, permeation and unsealing stage After the CO2 gas is continuously injected, the pressure inside the gas chamber gradually increases, and a part of the CO2 gas (or mixed gas) is pressed into the formation, and the formation pressure also increases accordingly; at the same time, as the pore pressure of the matrix rock increases, the permeability of the matrix rock gradually increases, and the "water-sealed gas" phenomenon will be broken, thereby achieving the triple goals of pressurization, permeability enhancement, and unsealing; S3, well pressurization and CO2 gas high pressure replacement stage After CO2 gas is injected, in order to allow the injected CO2 gas to be fully mixed and replaced with the methane gas in the formation, a certain period of well sealing is required; the mixing is mainly carried out between the free gas and the CO2 gas, and the replacement is mainly carried out between the adsorbed gas and the CO2 gas; during the well sealing period, the gas composition and pressure in the gas chamber need to be continuously monitored, and the well sealing ends when the methane composition in the gas chamber no longer continues to increase; S4, mixed gas extraction and separation stage After the well is sealed, the mixed gas formed by methane gas and CO2 gas in the formation is produced with reasonable production allocation; after the mixed gas is produced, it is strictly separated, the methane gas enters the gathering and transportation pipeline network, and the separated CO2 gas is recovered for the next injection cycle; S5, CO2 gas cycle injection stage After a period of exploitation, when the formation pressure drops to a predetermined value, gas production is stopped and steps S2-S4 are repeated until the methane content of the mixed gas in the formation is lower than the secondary abandonment value, thus completing the recovery of the abandoned shale gas well.

4. The working principle of the abandoned shale gas well recovery device according to claim 3 is characterized in that: The gas injection method selected in step S1 includes: A. If the well type is an up-dip well, a single tubing gas injection and production method is used; B. If the well type is a down-dip well, the double-tubing gas injection and production method is adopted.

5. The working principle of the abandoned shale gas well recovery device according to claim 4 is characterized in that: The single oil pipe gas injection and production method is specifically as follows: The end of the gas injection pipeline is extended to above the gas-water interface. When high-pressure CO2 gas is injected through the gas injection pipeline, the gas chamber pressure gradually increases. When the gas chamber pressure is greater than the formation pressure, the mixed gas of CO2 and methane in the gas chamber begins to be injected back into the formation. After the gas injection is completed, the gas production pipeline is used for gas production.

6. The working principle of the abandoned shale gas well recovery device according to claim 4 is characterized in that: The double oil pipe gas injection and production method is specifically as follows: A bridge plug is lowered into the target layer, the gas injection pipeline is lowered to the bottom interface of the bridge plug, and the gas production pipeline is lowered to the bottom of the well; with the gas production valve open, CO2 gas is injected, and the water under the bridge plug is discharged from the wellbore. After all the water is discharged, the gas production valve is closed and pressurized gas injection is started; after the gas injection is completed, gas is produced using the gas production pipeline.

7. The working principle of the abandoned shale gas well recovery device according to claim 3 is characterized in that: The high-pressure gas replacement in step S1 refers to using a gas with stronger adsorption to replace the adsorbed methane in the shale reservoir from the surface of the organic matter, so that the original adsorbed methane is converted into a free state and enters the pores, and the original free state strongly adsorbed gas is converted into an adsorbed state and adsorbed by the organic matter; the adsorption of CO2 gas in organic matter is much greater than that of methane gas, and its adsorption is proportional to the pressure. As the pressure increases, the adsorption amount increases; therefore, when CO2 gas is injected, the adsorbed methane in the shale will be replaced by the CO2 gas with stronger adsorption to form free gas, thereby achieving the purpose of desorption of the adsorbed gas in the high-pressure state.

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