Salt cavern brine circulation crack repairing system and repairing method

Abstract

The salt cavern brine circulation crack repairing system comprises a brine injection pipe, a brine outlet channel, an earth surface brine circulation device and an earth surface brine pump system, the brine injection pipe and the brine outlet channel are located in a salt cavern shaft, and the brine injection pipe is located on the center line of the space of the salt cavern shaft; the brine outlet channel is an annular space defined by a salt cavern shaft and a brine injection pipe, the brine injection pipe is connected with the earth surface brine pump system, the brine outlet channel is connected with the earth surface brine circulating device, the earth surface brine circulating device is connected with the earth surface brine pump system, brine is injected into a salt cavern through the brine injection pipe, and the brine is injected into the salt cavern through the brine injection pipe. Brine flows back to the earth surface brine circulating device through the brine outlet channel and then is circularly injected into the salt cavern through the earth surface brine pump system; through the brine positive circulation system in the shaft and in combination with the salt crystallization effect driven by the temperature difference, the damage and leakage problems of the second interface position of the salt cavern injection and production pipe are efficiently repaired, and the hidden danger of gas leakage is eliminated.

Description

Technical Field

[0001] The present application relates to the field of salt cavern energy storage technology, and in particular to a salt cavern brine circulation fissure repair system and repair method. Background Art

[0002] At present, underground salt caverns are widely used to store gas media, such as natural gas, compressed air and hydrogen. Salt caverns are ideal gas storage spaces due to the high sealing properties of the surrounding salt rock layers. However, in the actual energy storage process of salt caverns, a large number of cracks will be generated at the interface between the injection and production pipe and the salt rock (i.e., the second interface) and the surrounding salt rock positions due to insufficient consolidation, mechanical disturbance and other factors, potentially threatening the sealing properties of the reservoir.

[0003] Most existing repair technologies rely on static self-healing mechanisms, which are performed by injecting saturated brine to soak the cracks and using the self-healing ability of salt rock in a saturated brine environment for repair. The specific operation is to soak the damaged salt cavern in saturated brine in order to repair the cracks through the self-healing effect of salt rock. This method mainly relies on capillary action, with brine penetrating into the cracks to provide the liquid brine environment required for recrystallization and diffusion mass transfer, the two self-healing mechanisms of salt rock, thereby achieving the effect of crack repair. This process does not require complex equipment and is mainly composed of conventional injection and production systems. Although the saturated brine immersion repair method can restore the sealing of salt caverns to a certain extent, its effect is limited and there are many defects:

[0004] 1. Long repair time: Existing technologies rely on the natural diffusion and migration of salt and the self-healing process, which is a relatively slow process and usually takes several months to significantly improve the sealing of the damaged location or even the entire salt cavern. This will take too much time for engineering scenarios that require rapid restoration of reservoir sealing performance, and is obviously not efficient enough.

[0005] 2. Limited repair ability: When the crack opening is large or the crack structure is complex, it is difficult to effectively repair it by the natural penetration-crystallization of saturated brine alone. In this case, the self-healing ability is obviously insufficient, and it is difficult for brine to completely fill and repair the cracks, especially in areas with deep cracks or complex structures.

[0006] Through the above analysis, it can be seen that the current technology has many deficiencies in terms of repair speed and repair capacity. The present application provides a salt cavern brine circulation fissure repair system and repair method, aiming to solve the defects of the above-mentioned prior art. Summary of the invention

[0007] In order to solve the above problems, the present application provides a salt cavern brine circulation fissure repair system and repair method, so as to quickly and specifically solve the hidden danger of gas leakage caused by rock damage at the interface between the salt cavern injection and production wellbore and the salt rock (i.e., the second interface). The technical solution is as follows:

[0008] A first aspect of the present application provides a salt cavern brine circulation fissure repair system, comprising a brine injection pipe, a brine outlet channel, a surface brine circulation device and a surface brine pump system, wherein the brine injection pipe and the brine outlet channel are located in a salt cavern wellbore, and the brine injection pipe is located on the center line of the salt cavern wellbore space, the brine outlet channel is an annular space surrounded by the salt cavern wellbore and the brine injection pipe, the brine injection pipe is connected to the surface brine pump system, the brine outlet channel is connected to the surface brine circulation device, the surface brine circulation device is connected to the surface brine pump system, brine is injected into the salt cavern through the brine injection pipe, the brine flows back to the surface brine circulation device through the brine outlet channel, and then is circulated and injected into the salt cavern through the surface brine pump system.

[0009] For example, in the salt cavern brine circulation fracture repair system provided in one embodiment, the brine injection pipe extends deep into the cavity area at the bottom of the salt cavern.

[0010] For example, in the salt cavern brine circulation fissure repair system provided in one embodiment, a filtering and salt replenishing device is provided in the surface brine circulation device to ensure that the brine flowing back into the surface brine circulation device through the brine outlet channel is in a saturated state.

[0011] For example, in the salt cavern brine circulation fracture repair system provided in one embodiment, the surface brine pump system includes a flow control device to control the brine injection flow rate, thereby controlling the brine circulation rate in the salt cavern.

[0012] For example, in the salt cavern brine circulation fissure repair system provided in one embodiment, a heating device is also included. The heating device is arranged at the water inlet of the brine injection pipe, or the heating device is arranged on the periphery of the surface brine circulation device to heat the brine, thereby maintaining the temperature difference of the brine at the bottom and the top of the cavity during the brine circulation process.

[0013] The second aspect of the present application provides a salt cavern brine circulation fissure repair method, which uses the above-mentioned salt cavern brine circulation fissure repair system for repair, comprising the following steps:

[0014] S1 closes the wellbore and fills the salt cavern with saturated brine;

[0015] S2 inserts the brine injection pipe into the wellbore and goes deep into the cavity area at the bottom of the salt cavern. Through the surface brine pump system, saturated brine is slowly and continuously injected into the wellbore to push the bottom brine up to the cavity top position, so that heat exchange occurs between the brine at the cavity bottom and the cavity top;

[0016] S3 continuously circulates brine through the surface brine circulation device and the surface brine pump system. The high-temperature saturated brine at the bottom is cooled and converted into a supersaturated state at the top of the cavity close to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern. Driven by the interfacial potential energy, the supersaturated brine undergoes salt crystallization at the second interface position where the surrounding rock cracks and damage are detached, so as to gradually fill the cracks at the interface and repair the damage.

[0017] For example, in the salt cavern brine circulation fissure repair method provided in one embodiment, in S1, saturated brine is filled into the salt cavern, and the salt cavern is left to stand for a period of time to ensure that the liquid inside the salt cavern reaches a fully saturated state and a thermally stable state, and saturated brine is injected through the brine injection pipe after the state stabilizes.

[0018] For example, in the salt cavern brine circulation fissure repair method provided in one embodiment, in S2, the flow rate of the brine is controlled to ensure sufficient heat exchange between the brine and the formation, thereby maintaining the brine temperature difference between the top and bottom of the cavity between 1-3°C.

[0019] For example, in the salt cavern brine circulation fissure repair method provided in one embodiment, in S3, the brine in the salt cavern flows in a positive circulation so that the brine circulates to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern, to form turbulence.

[0020] The beneficial effects of a salt cavern brine circulation fissure repair system and repair method provided in some embodiments of the present application are as follows: the present application can improve the repair speed, enhance the repair capacity, and introduce active repair power to effectively deal with the serious damage at the second interface position of the salt cavern injection and production wellbore and the risk of leakage caused by large fissures. Compared with the prior art, the present application has the following significant advantages:

[0021] 1. Improved repair efficiency: Traditional methods use static immersion to achieve self-healing of salt rock, which takes a long time and has limited effect on the repair of complex fracture networks with severe damage. This application uses a continuous saturated brine positive circulation system, with the help of temperature difference, the law of change of solubility of soluble salt with temperature and flow field conditions, to significantly accelerate the healing speed of salt rock fractures, especially for large-opening fractures.

[0022] 2. Simple and economical process: This application does not require complex wellbore structure modification or the introduction of new equipment. The repair work can be completed by relying only on the existing wellbore brine, pipe string and surface brine circulation system. The positive circulation of brine can achieve flow field driven fracture repair, avoiding high cost investment and having good economic efficiency.

[0023] 3. Efficient self-healing mechanism: This application uses the temperature difference between the top and bottom of the salt cavern to make the brine flow through the junction of the wellbore and the salt cavern, which is also the necking position of the salt cavern, from a saturated state to an oversaturated state, forming salt crystals. This crystallization process effectively promotes the self-healing mechanism of salt rock in the damaged area and improves the repair efficiency.

[0024] 4. Environmental friendliness: Since this application only uses the existing brine in the salt cavern, there is no need to discharge a large amount of brine, and no external chemical reagents or complex mechanical equipment are introduced, it has little impact on the environment and meets the requirements of green and sustainable development.

[0025] In general, this application not only improves the speed and effect of salt cavern repair, but also achieves rapid repair of damaged cracks at the second interface of the salt cavern wellbore through a simple and economical technical path, while being highly environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a schematic diagram of the structure of the salt cave brine circulation fissure repair system of the present application. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] The following are the main problems in the repair technology of the interface between the existing salt cave injection and production pipe and the salt rock (i.e. the second interface):

[0031] 1. Slow repair speed. In the existing technology, saturated brine is used to naturally soak the cracks to repair the salt cavern interface, but due to the lack of driving force, the repair process usually takes several months and it is difficult to quickly restore the sealing performance of the salt cavern. This technology lags behind the actual industrial application needs and cannot prevent possible gas leakage in time.

[0032] 2. Limited repair ability. When the second interface of the salt cavern injection and production wellbore is severely damaged, especially when the crack opening is large, the repair effect of the existing method is significantly reduced, and the crack cannot be effectively closed in a short period of time. Especially in the face of complex rock damage and large crack structures, this repair method shows great limitations and it is difficult to ensure the long-term airtightness of the salt cavern.

[0033] The present application provides a salt cavern brine circulation fissure repair system and repair method, so as to achieve a rapid and targeted solution to the hidden danger of gas leakage caused by rock damage at the interface between the salt cavern injection and production pipe string and the salt rock (i.e., the second interface).

[0034] The first aspect of the present application provides a salt cave brine circulation fissure repair system, such as Figure 1As shown, it includes a brine injection pipe 2, a brine outlet channel 1, a surface brine circulation device 3 and a surface brine pump system 9, the brine injection pipe 2 and the brine outlet channel 1 are located in the salt cavern shaft 4, and the brine injection pipe 2 is located on the center line of the salt cavern shaft 4 space, the brine outlet channel 1 is an annular space surrounded by the salt cavern shaft 4 and the brine injection pipe, the brine injection pipe 2 is connected to the surface brine pump system 9, the brine outlet channel 1 is connected to the surface brine circulation device 3, the surface brine circulation device 3 is connected to the surface brine pump system 9, brine is injected into the salt cavern 7 through the brine injection pipe 2, the brine flows back to the surface brine circulation device 3 through the brine outlet channel 1, and then circulated and injected into the salt cavern 7 through the surface brine pump system 9.

[0035] Among them, the surface brine circulation device 3 and the surface brine pump system 9 are arranged on the ground, the salt cavern 7 is located in the underground salt rock formation 5, the wellbore 4 is connected to the cavity, and its internal space is the key channel for the positive circulation of brine. The connection between the bottom of the wellbore 4 and the salt cavern 7 is the casing shoe 6. The area near the wellbore 4 and the casing shoe 6 is the geometric distortion area of ​​the salt cavern, and it is also a weak sealing area, which is prone to cracks.

[0036] For example, in the salt cave brine circulation fracture repair system provided in one embodiment, Figure 1 As shown, the bottom end 8 of the brine injection pipe 2 extends deep into the cavity area at the bottom of the salt cavern 7.

[0037] According to the above embodiment, the brine injection pipe 2 is inserted into the wellbore 4, and the bottom end 8 is as deep as possible into the bottom of the salt cavern, and its main function is to provide a channel for injecting saturated brine during the positive circulation of brine.

[0038] For example, in the salt cavern brine circulation fissure repair system provided in one embodiment, a filtering and salt replenishing device is provided in the surface brine circulation device 3 to ensure that the brine flowing back into the surface brine circulation device 3 through the brine outlet channel 1 is in a saturated state.

[0039] According to the above embodiment, the surface brine circulation device 3 is used to recollect the brine returned from the wellbore 4 and recycle it through filtering, salt replenishment and reinjection processes to ensure that the brine is always saturated during the circulation process.

[0040] For example, in the salt cavern brine circulation fracture repair system provided in one embodiment, the surface brine pump system 9 includes a flow control device to control the brine injection flow rate, thereby controlling the brine circulation rate in the salt cavern.

[0041] According to the above embodiment, the surface brine pump system 9 is installed on the surface and is responsible for re-injecting the collected brine into the salt cavity and performing positive circulation through the brine injection pipe 2. The surface brine pump system 9 needs to maintain a constant and slow flow rate to ensure the stability of the repair process.

[0042] Under special conditions, such as larger cavities or more complex formation environments, the flow rate and temperature difference of the brine positive circulation may not achieve the ideal effect. For example, in the salt cavern brine circulation fracture repair system provided in one embodiment, a heating device is also included. The heating device is arranged at the water inlet of the brine injection pipe, or the heating device is arranged on the periphery of the surface brine circulation device to heat the brine and increase the temperature difference of the brine at the bottom and the top of the cavity during the brine circulation process, thereby accelerating the formation of an oversaturated state and further promoting repair.

[0043] Focusing on the self-healing repair of the second interface position of the salt cavern injection and production wellbore / pipe string, the second aspect of the present application provides a salt cavern brine circulation fissure repair method, which accelerates the healing of the fissures through a brine positive circulation system. The core technology is to use the temperature difference and flow field effect to drive the salt in the brine to recrystallize at the damaged interface, thereby realizing the rapid repair of the damaged fissure position. When the salt cavern brine circulation fissure repair system of the present application is used for repair, the specific repair method is as follows:

[0044] S1. Close the wellbore, fill the salt cave with saturated brine, and let it stand for a while to ensure that the liquid inside the salt cave reaches a fully saturated state and thermally stable state;

[0045] S2 After the state is stable, the brine injection pipe is inserted into the wellbore and penetrated into the cavity area at the bottom of the salt cavern. Saturated brine is slowly and continuously injected into the wellbore through the surface brine pump system to push the brine with higher temperature at the bottom to the top of the cavity. When the brine flows through the damaged position, heat exchange occurs with the formation with lower temperature, and the temperature is reduced;

[0046] S3 continuously circulates brine through the surface brine circulation device and the surface brine pump system. The high-temperature saturated brine at the bottom is cooled and converted into a supersaturated state at the top of the cavity close to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern. Driven by the interfacial potential energy, the supersaturated brine undergoes salt crystallization at the second interface position where the surrounding rock cracks and damage are detached, so as to gradually fill the cracks at the interface and repair the damage.

[0047] The salt cavern brine circulating fissure repair method of the present application has a geothermal gradient difference of 1-3°C between the bottom and top of the salt cavern, and the solubility of the solute with sodium chloride as the main component in the salt cavern brine increases monotonically with temperature. Therefore, the saturated brine with a higher temperature at the bottom will be cooled and converted to a supersaturated state at the connection between the wellbore at the top of the cavity and the salt cavern, which is also the necking position of the salt cavern. Driven by the interfacial potential energy, the supersaturated brine undergoes salt crystallization at the second interface position where the rock fissures and damage are detached to repair the damage. The crystallization process is driven by the following two mechanisms:

[0048] 1. Turbulence effect: Due to the necking at the wellbore 4 position, the brine will form turbulence when circulating here, which increases the free energy of salt ions and promotes the formation of salt crystals.

[0049] 2. Reduction of interfacial energy: The rough geometric characteristics of cracks and interfacial damage sites provide an ideal crystallization bed for salt ions, where the energy barrier required for crystallization is reduced, promoting rapid crystallization.

[0050] Through the surface brine circulation device 3 and the surface brine pump system 9, the positive circulation of brine continues, and the repair process is gradually advanced. As the brine continues to crystallize during the circulation process, the cracks at the interface are gradually filled, and the crack opening is gradually reduced, thereby restoring the sealing of the second interface position of the injection and production wellbore.

[0051] To ensure the mechanical stability of the crystal healing structure, for example, in the salt cavern brine circulation fissure repair method provided in one embodiment, in S3, the brine in the salt cavern flows in a positive circulation so that the brine circulates to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern, to form turbulence.

[0052] Among them, the circulation rate should be controlled at a low level to avoid the damage of the recrystallization structure to the excessive turbulent field. The circulation flow control needs to control the flow rate of the brine according to the specific damage situation in the wellbore. First, the crystallization reaction in the repair process can be fully carried out to maintain the mechanical stability of the recrystallization structure. Second, it is to ensure that the brine in the cavity has sufficient heat exchange with the formation at the depth, and to ensure that the temperature difference of the brine at the bottom and top of the cavity is maintained within the ideal range of 1-3°C to ensure the repair efficiency.

[0053] The brine is mainly composed of sodium chloride, with a small amount of other soluble salts such as sodium sulfate and sodium carbonate. All crystallized materials are natural salt solution components, and no external chemical reagents are required. In addition, the positive circulation system can be replaced with more suitable pump devices or pipeline materials according to different salt cave conditions to avoid pipeline corrosion.

[0054] The salt cavern brine circulation fissure repair method of the present application adopts a self-healing mechanism driven by a positive circulation salt water system. By designing a positive circulation saturated brine flow system, the temperature gradient difference and the solubility characteristics of the salt solution are used to promote the spontaneous crystallization of salt at the damaged interface. This method significantly improves the healing speed of the connection between the wellbore and the salt cavern, and also the surrounding rock and the second interface at the necking position of the salt cavern. In particular, the sealing performance of this location is enhanced through recrystallization, which solves the problem of the traditional static immersion method with long repair time and limited repair effect.

[0055] The supersaturated state is induced by the temperature difference of the formation to promote crystallization. The supersaturated salt solution formed by the temperature difference inside the salt cavity is used to make the brine crystallize due to cooling when it circulates to the position near the interface at the top of the cavity. This supersaturation effect driven by the temperature difference effectively promotes the crystallization process of salt ions, especially generating stable recrystallization structures at the geometric neck of the salt cavity and the interface damage, which improves the efficiency of repairing severe damage.

[0056] The turbulence and damage morphology at the geometric distortion are used to enhance crystallization. In the target repair area, that is, the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern, the local turbulence caused by the geometric distortion increases the kinetic energy of the salt ions and further promotes the crystallization process of the salt. In addition, the reduction in free energy at the interface damage provides an ideal crystal bed for crystallization, promoting the local crystallization healing process.

[0057] In summary, the present application realizes efficient repair of damage and leakage problems at the second interface of the salt cavern injection and production wellbore / tubing string through a brine positive circulation system in the wellbore, combined with the salt crystallization effect driven by temperature difference, and has the advantages of simple technology, economic feasibility, and rapid repair.

[0058] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the specification and implementation modes, and it can be fully applicable to various fields suitable for the present application. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A salt cave brine circulation fissure repair system, characterized in that: It includes a brine injection pipe, a brine outlet channel, a surface brine circulation device and a surface brine pump system. The brine injection pipe and the brine outlet channel are located in the salt cavern wellbore, and the brine injection pipe is located on the center line of the salt cavern wellbore space. The brine outlet channel is an annular space surrounded by the salt cavern wellbore and the brine injection pipe. The brine injection pipe is connected to the surface brine pump system, the brine outlet channel is connected to the surface brine circulation device, and the surface brine circulation device is connected to the surface brine pump system. Brine is injected into the salt cavern through the brine injection pipe, and the brine flows back to the surface brine circulation device through the brine outlet channel, and then circulated into the salt cavern through the surface brine pump system.

2. The salt cave brine circulation fissure repair system according to claim 1 is characterized in that: The brine injection pipe extends deep into the cavity area at the bottom of the salt cavern.

3. The salt cave brine circulation fissure repair system according to claim 1 is characterized in that: A filtering and salt replenishing device is provided in the surface brine circulation device to ensure that the brine flowing back into the surface brine circulation device through the brine outlet channel is in a saturated state.

4. The salt cave brine circulation fissure repair system according to claim 1 is characterized in that: The surface brine pump system includes a flow control device to control the brine injection flow rate, thereby controlling the brine circulation rate in the salt cavern.

5. The salt cave brine circulation fissure repair system according to claim 1 is characterized in that: It also includes a heating device, which is arranged at the water inlet of the brine injection pipe, or the heating device is arranged at the periphery of the surface brine circulation device to heat the brine, thereby maintaining the temperature difference of the brine at the bottom and the top of the cavity during the brine circulation process.

6. A method for repairing cracks in brine circulation in salt caverns, characterized in that: The salt cave brine circulation fissure repair system according to any one of claims 1 to 5 is used for repair, comprising the following steps: S1 closes the wellbore and fills the salt cavern with saturated brine; S2 inserts the brine injection pipe into the wellbore and goes deep into the cavity area at the bottom of the salt cavern. Through the surface brine pump system, saturated brine is slowly and continuously injected into the wellbore to push the bottom brine up to the cavity top position, so that heat exchange occurs between the brine at the cavity bottom and the cavity top; S3 continuously circulates brine through the surface brine circulation device and the surface brine pump system. The high-temperature saturated brine at the bottom is cooled and converted into a supersaturated state at the top of the cavity close to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern. Driven by the interfacial potential energy, the supersaturated brine undergoes salt crystallization at the second interface position where the surrounding rock cracks and damage are detached, so as to gradually fill the cracks at the interface and repair the damage.

7. The method for repairing brine circulation cracks in salt caverns according to claim 6, characterized in that: In S1, the salt cavern is filled with saturated brine, and the salt cavern is left to stand for a period of time to ensure that the liquid inside the salt cavern reaches a fully saturated state and a thermally stable state, and saturated brine is then injected through the brine injection pipe after the state is stabilized.

8. The method for repairing brine circulation cracks in salt caverns according to claim 6, characterized in that: In S2, the flow rate of the brine is controlled to ensure sufficient heat exchange between the brine and the formation, thereby maintaining the temperature difference of the brine between the top and bottom of the cavity between 1-3°C.

9. The method for repairing brine circulation cracks in salt caverns according to claim 6, characterized in that: In S3, the brine in the salt cavern flows in a positive cycle, so that the brine circulates to the connection between the wellbore and the salt cavern, which is also the necking position of the salt cavern, to form turbulence.

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