Test system and method for simulating salt cavern reservoir gas variable-speed injection and production

Abstract

The invention discloses a test system and method for simulating salt cavern reservoir gas variable-speed injection and production, and the system comprises a formation pressure simulation system which is used for applying axial pressure and confining pressure to a rock core. The gas injection and exhaust system is used for performing variable-speed gas injection and variable-pressure exhaust on the interior of the rock core; the controller is used for controlling the formation pressure simulation system and the gas injection and exhaust system; and the flaw detection sensor is used for detecting the damage of the rock core. The formation pressure simulation system can simulate the ground stress relation of different areas of the salt cavern reservoir, and the gas injection and exhaust system can conveniently regulate and control the gas inlet and exhaust rate and pressure change in the rock core, so that the actual working condition of the salt cavern gas storage can be reflected more truly, and a more accurate salt cavern surrounding rock gas-solid coupling damage rule can be obtained.

Description

Technical Field

[0001] The invention relates to the technical fields of salt cavern energy storage, rock fluid-solid coupling and rock damage mechanics, and in particular to an experimental system and method for simulating gas injection and production in a salt cavern reservoir. Background Art

[0002] Salt caverns are good gas storage reservoirs that can be used to store hydrogen, compressed air, natural gas, etc. Salt cavern energy storage is an important part of the national strategic energy reserve. During the operation of salt cavern storage, under the combined effect of gas pressure in the cavity and formation stress, the surrounding rock and wellbore of the salt cavern will be subjected to higher deviatoric stress, and the influence of high pore pressure will be coupled at the same time. The gas injection and production rate in the salt cavern will continuously change with actual demand. Under the coupling effect of different gas pressure change rates and formation stress, the deviatoric stress loading and unloading rate borne by the surrounding rock is also continuously changing. Since rocks have significant rate effects (especially soft rocks such as salt rock with extremely strong plastic deformation ability), evaluating the influence of periodic gas pressure variable injection and production on the evolution law of rock damage under gas-solid coupling conditions has important reference value for salt cavern stability analysis.

[0003] The gas-solid test methods used in the existing technology mostly apply a surface gas pressure to the core, such as the commonly used MTS, GCTS and other test systems, but these test systems cannot directly simulate the process of large-scale flow contact between high-pressure gas and surrounding rock, but realize the gas-solid coupling of core pore pressure and external stress through the pore seepage of the rock. During the injection and production process of salt cavern reservoirs, high-pressure gas contacts the wall of the open hole section of the wellbore, the surrounding rock and other areas at a high flow rate, and the pressure change rate of the contact gas changes continuously. The existing test system cannot accurately simulate the actual working conditions of salt cavern reservoirs. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an experimental system and method for simulating variable-speed injection and production of gas in a salt cavern reservoir, so as to solve the technical problem of studying the gas-solid coupling damage law of the salt cavern surrounding rock during the variable-speed injection and production process of the salt cavern reservoir when the injection and production gas rate and the gas pressure change rate are changed.

[0005] The present invention includes a formation pressure simulation system for applying axial pressure and confining pressure to the core, a gas injection and discharge system for variable speed gas injection and variable pressure exhaust inside the core, a controller for controlling the formation pressure simulation system and the gas injection and discharge system, and a flaw detection sensor for detecting core damage.

[0006] Furthermore, the formation pressure simulation system includes a bracket, a confining pressure container arranged on the bracket, a lower pressure head arranged at the bottom of the inner cavity of the confining pressure container, an upper pressure head slidingly sealed with the top of the confining pressure container, an electric cylinder arranged on the bracket for applying axial pressure to the upper pressure head, an axial pressure sensor arranged between the upper pressure head and the electric cylinder, a booster pump for filling pressure oil into the confining pressure container, and an oil pressure sensor for detecting the oil pressure in the confining pressure container, the signal output ends of the axial pressure sensor and the oil pressure sensor are connected to the signal input end of the controller, the control signal input ends of the electric cylinder and the booster pump are connected to the signal output end of the controller, and the upper pressure head is provided with a gas flow channel connected to the gas channel in the core.

[0007] Furthermore, the gas injection and exhaust system includes a gas source, a gas injection flow control unit for controlling the gas source to inject gas into the gas channel in the core at a variable speed, and an exhaust pressure control unit for controlling the variable speed exhaust of gas in the core.

[0008] Further, the gas injection flow control unit includes an air inlet joint connected to the gas flow channel on the upper pressure head, an air inlet pipe connecting the gas source and the air inlet joint, a pressure reducing valve arranged on the air inlet pipe, an air injection electric flow control valve and a flow sensor for detecting the core air inlet flow;

[0009] The exhaust pressure regulating unit comprises an exhaust joint, an exhaust pipe connected to the exhaust joint, an exhaust electric flow regulating valve arranged on the exhaust pipe, an electric back pressure valve and a pressure sensor for detecting the exhaust pressure of the core; the exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole connecting the internal air passage of the core and the exhaust joint; or the exhaust joint is arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air intake pipe extending into the internal air passage of the core along the gas passage on the upper pressure head;

[0010] The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the gas injection electric flow regulating valve, the exhaust electric flow regulating valve and the electric back pressure valve are connected to the control signal output end of the controller.

[0011] Further, the gas injection flow control unit includes an air inlet joint connected to the gas flow channel on the upper pressure head, an air inlet pipe connecting the gas source and the air inlet joint, a pressure reducing valve arranged on the air inlet pipe, and a plurality of groups of flow control components connected in parallel between the pressure reducing valve and the air inlet joint, each group of flow control components includes a solenoid valve, a manual flow control valve and a flow sensor connected in series on the air inlet pipe, and the valve opening of the manual flow control valve of each group of flow control components is different;

[0012] The exhaust pressure regulating unit comprises an exhaust joint, an exhaust pipe connected to the exhaust joint and several groups of pressure regulating components arranged in parallel, wherein the exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole connecting the internal airway of the core and the exhaust joint; or the exhaust joint is arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air intake pipe extending into the internal airway of the core along the gas channel of the upper pressure head; each group of pressure regulating components comprises an exhaust electric force regulating valve, a manual back pressure valve and a pressure sensor connected in series on the exhaust pipe; the valve opening of the manual back pressure valve of each group of pressure regulating components is different;

[0013] The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the solenoid valve and the exhaust electric force regulating valve are connected to the control signal output end of the controller.

[0014] Furthermore, the flaw detection sensor is an acoustic emission sensor arranged on the upper pressure head and / or the lower pressure head.

[0015] Furthermore, the test system for simulating variable-speed injection and production of gas in a salt cavern reservoir further includes end sealing gaskets arranged at both ends of the core specimen to prevent confining pressure oil from entering the core specimen from the ends.

[0016] The present invention also discloses a test method for a test system for simulating variable-speed injection and production of gas in a salt cavern reservoir, which comprises the following steps:

[0017] 1) Wrapping an oil barrier layer on the outer surface of the core specimen with an axial air channel;

[0018] 2) placing the core specimen wrapped with the oil barrier layer into a formation pressure simulation system, and applying axial pressure and confining pressure to the core specimen to set values ​​through the formation pressure simulation system;

[0019] 3) Control the gas injection and discharge system to inject gas into the axial gas channel of the core specimen, and the gas injection flow rate varies according to the set rule to simulate different gas injection rates; while injecting gas or after the gas injection stops, control the gas injection and discharge system to discharge the gas in the axial gas channel of the core specimen to the outside, and change the gas pressure in the axial gas channel according to the set rule to simulate different gas production rates; during the test, the internal damage of the rock is detected by the flaw detection sensor, and the test is terminated after the set test time is reached.

[0020] Beneficial effects of the present invention:

[0021] 1. The test system and method for simulating variable-speed gas injection and production in salt cavern reservoirs of the present invention can realize both long-term creep tests of core specimens under constant external pressure and fatigue tests of core specimens under constant external pressure and changes in internal gas injection and exhaust rates.

[0022] 2. The test system and method for simulating variable-speed injection and production of gas in a salt cavern reservoir of the present invention, wherein the formation pressure simulation system can simulate the geostress relationship of different locations in the salt cavern reservoir, and the gas injection and exhaust system can conveniently regulate the injection and exhaust rate inside the core. The change of the rate inside the core also causes the change of the pressure change rate inside the test piece, thereby being able to more realistically reflect the actual working conditions of the salt cavern gas storage reservoir, and the influence of the gas flow impact and the gas pressure loading and unloading rate on the rock, thereby being able to obtain a more accurate gas-solid coupling damage law of the salt cavern surrounding rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the first implementation structure of the experimental system for simulating variable-speed injection and production of gas in a salt cavern storage.

[0024] Figure 2 A schematic diagram of the second implementation structure of the experimental system for simulating variable-speed injection and production of gas in a salt cavern storage. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] Embodiment 1: Figure 1 As shown, the test system for simulating variable-speed gas injection and production in a salt cavern reservoir in this embodiment includes a formation pressure simulation system for applying axial pressure and confining pressure to the core, a gas injection and discharge system for variable-speed gas injection and variable-pressure exhaust inside the core, a controller 1 for controlling the formation pressure simulation system and the gas injection and discharge system, and a flaw detection sensor 2 for detecting core damage.

[0027] In this embodiment, the formation pressure simulation system includes a bracket 3, a confining pressure container 4 arranged on the bracket, a lower pressure head 5 arranged at the bottom of the inner cavity of the confining pressure container, an upper pressure head 6 slidingly sealed with the top of the confining pressure container, an electric cylinder 7 arranged on the bracket for applying axial pressure to the upper pressure head, an axial pressure sensor 8 arranged between the upper pressure head and the electric cylinder, a booster pump 9 for filling pressure oil into the confining pressure container, and an oil pressure sensor 10 for detecting the oil pressure in the confining pressure container, the signal output ends of the axial pressure sensor and the oil pressure sensor are connected to the signal input end of the controller, the control signal input ends of the electric cylinder and the booster pump are connected to the signal output end of the controller, and the upper pressure head is provided with a gas flow channel 11 connected to the gas channel in the core.

[0028] In this embodiment, the gas injection and exhaust system includes a gas source 12, a gas injection flow control unit for controlling the gas source to inject gas into the gas channel in the core at a variable speed, and an exhaust pressure control unit for controlling the variable speed exhaust of gas in the core.

[0029] In this embodiment, the gas injection flow control unit includes an air intake joint 13 connected to the gas flow channel on the upper pressure head, an air intake pipe 14 connecting the gas source and the air intake joint, a pressure reducing valve 15 arranged on the air intake pipe, an air injection electric flow regulating valve 16 and a flow sensor 17 for detecting the core air intake flow rate.

[0030] The exhaust pressure control unit includes an exhaust joint 18, an exhaust pipe 19 connected to the exhaust joint, an exhaust electric flow regulating valve 20 arranged on the exhaust pipe, an electric back pressure valve 21 and a pressure sensor 22 for detecting the exhaust pressure of the core. The exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole 23 connecting the internal gas channel of the core and the exhaust joint; this structure is suitable for the core specimen in which the gas channel 24 in the core axially penetrates the core, and the core specimen in which the gas channel completely penetrates can simulate the open hole section of the injection and production well. Of course, in different embodiments, the exhaust joint 18 can also be arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air intake pipe 25 extending into the internal gas channel 24 of the core along the gas channel on the upper pressure head. This structure is suitable for the core specimen in which the gas channel 24 in the core axially penetrates half of the core, and the gas channel penetrates half of the rock specimen to simulate the salt cavern storage cavity. In specific implementation, the core specimens of the two structures can be tested simultaneously or separately.

[0031] The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the gas injection electric flow regulating valve, the exhaust electric flow regulating valve and the electric back pressure valve are connected to the control signal output end of the controller.

[0032] The test method of the test system for simulating variable-speed injection and production of gas in a salt cavern reservoir in this embodiment includes the following steps:

[0033] 1) An oil-isolating layer 26 is wrapped on the outer surface of the core specimen with the axial air channel, and the oil-isolating layer is used to prevent the confining pressure oil from entering the specimen.

[0034] 2) Place the core specimen wrapped with the oil barrier layer into the formation pressure simulation system, and apply axial pressure and confining pressure to the core specimen to the set value through the formation pressure simulation system. In the specific implementation, the controller 1 controls the electric cylinder 7 to push the upper pressure head 6 to apply axial pressure to the core specimen. When the axial pressure sensor 8 detects that the axial pressure reaches the set value, the controller controls the electric cylinder 7 to stop working; the controller 1 controls the booster pump 9 to add pressure oil into the confining pressure container. When the oil pressure sensor 10 detects that the oil pressure reaches the set value, the booster pump is controlled to stop working; in the specific implementation, a check valve or an electric gate valve is provided on the outlet pipeline of the booster pump to prevent the pressure oil in the confining pressure container from flowing back.

[0035] 3) Control the gas injection and discharge system to inject gas into the axial gas channel of the core specimen, and the gas injection flow rate varies according to the set rule to simulate different gas injection rates; while injecting gas or after the gas injection stops, control the gas injection and discharge system to discharge the gas in the axial gas channel of the core specimen to the outside, and change the gas pressure in the axial gas channel according to the set rule to simulate different gas production rates; during the test, the internal damage of the rock is detected by the flaw detection sensor, and the test is terminated after the set test time is reached.

[0036] Specifically, during the gas injection process, the exhaust pressure of the gas source is reduced by the pressure reducing valve 15 to ensure the stability and safety of the pressure on the gas inlet side of the core specimen; the controller 1 controls the gas injection electric flow regulating valve 16 to change the gas injection flow rate as needed, thereby simulating different gas injection rates of the salt cavern gas storage reservoir, and the flow sensor 17 detects the core gas inlet flow rate to implement feedback adjustment of the opening of the gas injection electric flow regulating valve 16 to ensure that the gas injection flow rate can stably track the changing set gas injection flow rate.

[0037] Specifically, during the exhaust process, the electric back pressure valve 21 is adjusted by the controller 1 to set the target exhaust pressure. When the air pressure in the core gas channel drops to the set target exhaust pressure, the core gas channel will no longer exhaust. In this way, different target exhaust pressures can be flexibly set according to actual conditions, which can better meet the experimental needs. The controller controls the exhaust electric flow control valve 20 to change the exhaust flow rate as needed, thereby simulating different gas production rates of the salt cavern gas storage. The air pressure of the core gas channel is detected by the pressure sensor 22. The opening of the exhaust electric flow control valve 20 can be adjusted according to the air pressure change to ensure that the air pressure in the core specimen stably tracks the changing set air pressure.

[0038] Embodiment 2: Figure 2 As shown, the difference between the experimental system for simulating variable speed injection and production of gas in salt cavern storage in this embodiment and the first embodiment lies in the difference between the gas injection flow control unit and the exhaust pressure control unit. In this embodiment, the gas injection flow control unit includes an intake joint 13 connected to the gas flow channel on the upper pressure head, an intake pipe 14 connecting the gas source 12 and the intake joint 13, a pressure reducing valve 15 arranged on the intake pipe, and several groups of flow control components connected in parallel between the pressure reducing valve and the intake joint, each group of flow control components includes a solenoid valve 27, a manual flow control valve 28 and a flow sensor 29 connected in series on the intake pipe, and the valve opening of the manual flow control valve of each group of flow control components is different. The opening of the manual flow control valve 28 is adjusted to different sizes in advance, and then by selecting and controlling different solenoid valves 27 to be turned on during gas injection, it is possible to inject gas into the core specimen at different flow rates to achieve the purpose of changing the gas injection rate.

[0039] The exhaust pressure control unit includes an exhaust joint 18, an exhaust pipe 19 connected to the exhaust joint, and several groups of pressure control components arranged in parallel. The exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole 23 connecting the internal gas passage 24 of the core and the exhaust joint. Or the exhaust joint is arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air suction pipe extending into the internal gas passage of the core along the gas passage on the upper pressure head. Each group of pressure control components includes an exhaust electric force regulating valve 30, a manual back pressure valve 31 and a pressure sensor 32 connected in series on the exhaust pipe; the valve opening of the manual back pressure valve of each group of pressure control components is different. The opening pressure of the manual back pressure valve 31 is adjusted in advance, and then when exhausting, by selecting the corresponding exhaust electric force regulating valve 30 conduction and the valve conduction opening, it is possible to achieve exhaust with different flow directions to achieve the purpose of changing the exhaust rate, and in the exhaust process, the opening of the exhaust electric force regulating valve 30 is controlled by the air pressure feedback of the pressure sensor 32, so that the air pressure in the internal gas passage 24 of the core can stably track the changing set air pressure.

[0040] The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the solenoid valve and the exhaust electric force regulating valve are connected to the control signal output end of the controller.

[0041] In the above two embodiments, the flaw detection sensor is an acoustic emission sensor arranged on the upper pressure head and / or the lower pressure head. By scanning the core specimen with the acoustic emission sensor, crack propagation data in the core can be obtained, and then the crack propagation law can be studied.

[0042] As an improvement of the above two embodiments, the test system for simulating variable speed injection and production of gas in a salt cavern reservoir further includes end sealing gaskets 33 arranged at both ends of the core specimen to prevent the confining pressure oil from entering the core specimen from the ends. By arranging sealing gaskets at the ends of the core specimen, it is possible to better prevent the confining pressure oil from entering the core specimen.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A test system for simulating variable-speed injection and production of gas in a salt cavern reservoir, including a formation pressure simulation system for applying axial pressure and confining pressure to a core, characterized in that: It also includes a gas injection and discharge system for variable-speed gas injection and variable-pressure gas exhaust inside the core, a formation pressure simulation system and a controller for the gas injection and discharge system, and a flaw detection sensor for detecting core damage.

2. The test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 1, characterized in that: The formation pressure simulation system includes a bracket, a confining pressure container arranged on the bracket, a lower pressure head arranged at the bottom of the inner cavity of the confining pressure container, an upper pressure head slidingly sealed with the top of the confining pressure container, an electric cylinder arranged on the bracket for applying axial pressure to the upper pressure head, an axial pressure sensor arranged between the upper pressure head and the electric cylinder, a booster pump for filling pressure oil into the confining pressure container, and an oil pressure sensor for detecting the oil pressure in the confining pressure container, the signal output ends of the axial pressure sensor and the oil pressure sensor are connected to the signal input end of the controller, the control signal input ends of the electric cylinder and the booster pump are connected to the signal output end of the controller, and the upper pressure head is provided with a gas flow channel connected to the gas channel in the core.

3. The test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 2 is characterized in that: The gas injection and exhaust system comprises a gas source, a gas injection flow control unit for controlling the gas source to inject gas into the gas channel in the rock core at a variable speed, and an exhaust pressure control unit for controlling the variable speed exhaust of gas in the rock core.

4. The test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 3 is characterized in that: The gas injection flow control unit includes an air inlet joint connected to the gas flow channel on the upper pressure head, an air inlet pipe connecting the gas source and the air inlet joint, a pressure reducing valve arranged on the air inlet pipe, an electric air injection flow control valve and a flow sensor for detecting the core air inlet flow; The exhaust pressure regulating unit comprises an exhaust joint, an exhaust pipe connected to the exhaust joint, an exhaust electric flow regulating valve arranged on the exhaust pipe, an electric back pressure valve and a pressure sensor for detecting the exhaust pressure of the core; the exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole connecting the internal air passage of the core and the exhaust joint; or the exhaust joint is arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air intake pipe extending into the internal air passage of the core along the gas passage on the upper pressure head; The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the gas injection electric flow regulating valve, the exhaust electric flow regulating valve and the electric back pressure valve are connected to the control signal output end of the controller.

5. The test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 3 is characterized in that: The gas injection flow control unit includes an intake joint connected to the gas flow channel on the upper pressure head, an intake pipe connecting the gas source and the intake joint, a pressure reducing valve arranged on the intake pipe, and a plurality of groups of flow control components connected in parallel between the pressure reducing valve and the intake joint, each group of flow control components includes a solenoid valve, a manual flow control valve and a flow sensor connected in series on the intake pipe, and the valve opening of the manual flow control valve of each group of flow control components is different; The exhaust pressure regulating unit comprises an exhaust joint, an exhaust pipe connected to the exhaust joint and several groups of pressure regulating components arranged in parallel, wherein the exhaust joint is arranged on the bottom of the container, and the lower pressure head is provided with an axial hole connecting the internal airway of the core and the exhaust joint; or the exhaust joint is arranged on the upper pressure head, and the air inlet end of the exhaust joint is provided with an air intake pipe extending into the internal airway of the core along the gas channel of the upper pressure head; each group of pressure regulating components comprises an exhaust electric force regulating valve, a manual back pressure valve and a pressure sensor connected in series on the exhaust pipe; the valve opening of the manual back pressure valve of each group of pressure regulating components is different; The signal output ends of the flow sensor and the pressure sensor are connected to the signal input end of the controller, and the control signal input ends of the solenoid valve and the exhaust electric force regulating valve are connected to the control signal output end of the controller.

6. The test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 1, characterized in that: The flaw detection sensor is an acoustic emission sensor arranged on the upper pressure head and / or the lower pressure head.

7. The test system for simulating variable-speed injection and production of gas in a salt cavern storage according to claim 1, characterized in that: It also includes end sealing gaskets which are arranged at both ends of the core specimen to prevent the confining pressure oil from entering the core specimen from the ends.

8. The test method of the test system for simulating variable-speed injection and production of gas in salt cavern storage according to claim 1, characterized in that: The following steps are involved: 1) Wrapping an oil barrier layer on the outer surface of the core specimen with an axial air channel; 2) placing the core specimen wrapped with the oil barrier layer into a formation pressure simulation system, and applying axial pressure and confining pressure to the core specimen to set values ​​through the formation pressure simulation system; 3) Control the gas injection and discharge system to inject gas into the axial gas channel of the core specimen, and the gas injection flow rate varies according to the set rule to simulate different gas injection rates; while injecting gas or after the gas injection stops, control the gas injection and discharge system to discharge the gas in the axial gas channel of the core specimen to the outside, and change the gas pressure in the axial gas channel according to the set rule to simulate different gas production rates; during the test, the internal damage of the rock is detected by the flaw detection sensor, and the test is terminated after the set test time is reached.

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