A method for sealing cracks in interlayers of a salt cavern storage cavity

Abstract

The present invention belongs to the field of oil and gas storage and transportation, and specifically relates to a method for plugging interlayer cracks in the cavity of a salt cavern storage. The present invention adjusts the gas-liquid interface to be lower than the depth of the interlayer cracks by injecting gas or brine, injects a low-density plugging agent at the gas-liquid interface, and uses a two-way pressurization method to allow the plugging agent to seep into the crack channel and form consolidation with the formation, thereby achieving the plugging of the interlayer cracks. The present invention uses a two-way pressurization method to make the plugging agent evenly stressed up and down, and can only flow laterally along the cavity under pressure, so that the plugging agent can accurately seep into the crack channel and form consolidation with the formation. The present invention establishes an effective method for plugging interlayer cracks inside a salt cavern cavity for the first time, solves the problem of cavity interlayer leakage, and provides an effective solution to the risks of interlayer leakage and the like in the long-term production and operation of the salt cavern cavity.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas storage and transportation, and relates specifically to a method for plugging interlayer cracks in a salt cavern storage cavity. Background Art

[0002] As a mine cave formed after the mining of underground salt layers, salt caverns are characterized by large volume, good sealing and high stability. They are ideal places for storing energy such as natural gas, crude oil and compressed air energy storage. The good physical properties of salt make salt caverns stable for a long time and completely airtight. Although salt cavern reservoirs have obvious advantages in energy storage, the sealing safety of energy reservoirs has encountered huge challenges. Under long-cycle / high-frequency injection and production cycle operation conditions, cracks are formed in the cavity interlayer under the action of stress damage. If the interlayer cracks are connected to the faults or stratigraphic unconformity zones near the salt cavern, the risk of leakage in the salt cavern cavity is increased. Some old cavities cannot be effectively utilized due to poor sealing and high permeability cracks in the cavity interlayer. During the operation of foreign salt cavern gas storage, gas leaked along the cracks and connected with the faults outside the storage area, and natural gas escaped to the ground several kilometers away, causing serious safety accidents. If the cavity of salt cavern compressed air energy storage leaks, the energy storage efficiency will be reduced, and in severe cases, the project will be shut down. Strengthening the sealing evaluation and repair of salt caverns under construction and in service is the core issue to ensure the safe operation of the caverns.

[0003] Domestic scholars have conducted relevant research on the evaluation of the sealing performance of salt cavern cavities, and carried out a large number of numerical simulations and indoor physical experimental studies on the permeability and mechanical damage mechanism of salt cavern interlayers. According to the location of the interlayer in the gas storage reservoir, it can be divided into wellbore and open hole section (neck section) interlayers and intracavity interlayers. Due to the concealment and uncontrollability of deep interlayers, the most reasonable and effective means to prevent and deal with interlayer leakage are interlayer grouting and sealing testing. At present, grouting and plugging technology has achieved successful plugging of leaking interlayers in wellbore and open hole sections, with good results. However, due to the huge difference between the inside of the salt cavern cavity and the wellbore, there is still no effective plugging means and method for plugging leakage of interlayers in the salt cavern cavity. Summary of the invention

[0004] In view of the leakage of interlayer in the salt cavern cavity, the present invention provides a method for sealing the cracks of the interlayer in the salt cavern storage cavity.

[0005] The present invention is applicable to the final stage of water injection into the dissolution cavity or the period when the existing old cavity is filled with brine.

[0006] The present invention adjusts the gas-liquid interface to be lower than the position of the interlayer crack, injects a low-density plugging agent at the gas-liquid interface, and uses a two-way pressurization method to allow the plugging agent to seep into the crack channel and form consolidation with the formation, thereby achieving interlayer crack plugging.

[0007] The specific steps are:

[0008] (1) Adjust the depth of the gas-liquid interface

[0009] After the cavity is made, the intermediate pipe string and the central pipe string are lowered into the wellbore to perform gas injection and brine expulsion or brine injection and exhaust operations. At the same time, the optical fiber monitoring equipment is lowered to monitor the depth of the gas-liquid interface in real time. Through gas injection and brine expulsion or brine injection and exhaust operations, the gas-liquid interface is made lower than the position of the interlayer cracks.

[0010] Preferably, the monitoring accuracy of the gas-liquid interface is not less than 0.02 m; the gas-liquid interface is 0.05-0.10 m below the position of the cavity interlayer crack.

[0011] (2) Calculation of plugging agent dosage

[0012] According to the depth and height of the interlayer cracks, the cross-sectional area of ​​the cavity in the layer section is measured by sonar cavity measurement to calculate the amount of plugging agent;

[0013] In this process, the plugging agent can be an oil-based plugging agent commonly used in the art, which has a lower density than brine, is insoluble in brine, has high salt resistance, and has strong consolidation. The plugging agent can not only chemically react with the mineral components in the cracks to generate crystals and continuously grow to fill the pores inside the cracks, but also be suspended on the surface of the brine. Those skilled in the art can prepare or purchase a suitable plugging agent based on the interlayer mineral components and brine parameters, combined with common knowledge in the art.

[0014] (3) Injection of plugging agent into the salt cavern cavity and thickness detection

[0015] Adjust the central pipe string to the depth of the brine interface and inject the calculated amount of plugging agent into the salt cavern cavity; after the injection is completed, test the thickness of the plugging agent to ensure that the thickness of the plugging agent can cover the crack position;

[0016] During this process, the central pipe column is adjusted to the depth of the brine interface to avoid the injected plugging agent from contacting and mixing with the brine and the cavity wall, which would cause the quality of the plugging agent to decrease; preferably, the thickness of the plugging agent on the brine surface is 0.05~0.15m higher than the crack position.

[0017] (4) Pressurizing the salt cavern cavity to squeeze the plugging agent into the interlayer cracks

[0018] Gas is injected into the cavity through the annulus between the intermediate pipe string and the central pipe string, and brine is injected into the cavity through the central pipe string. The bidirectional pressurization causes the plugging agent to be squeezed into the interlayer cracks under pressure. During this process, the gas space pressure and brine space pressure around the plugging agent in the cavity are monitored in real time; the plugging agent thickness is monitored in real time; the plugging agent thickness is 0.05~0.15m higher than the crack position.

[0019] During the two-way pressurization process, the cavity pressure is monitored in real time. The maximum cavity pressure shall not exceed 85% of the formation fracture pressure. The gas space pressure around the plugging agent in the cavity is consistent with the brine space pressure. The plugging agent thickness is monitored in real time to prevent the plugging agent thickness from being lower than the fracture height, and the gas in the cavity from entering the fracture and causing the plugging operation to fail.

[0020] (5) Salt cavern air tightness test

[0021] After the plugging agent is injected into the interlayer cracks, the plugging agent and the mineral are fully cemented according to the consolidation time of the plugging agent and the interlayer components, and gas is injected to expel brine, so that the gas-liquid interface is lower than the position of the interlayer cracks, and the cavity gas tightness test is carried out;

[0022] If the cavity air tightness does not meet the relevant requirements, repeat the above steps (3)-(4) until the cavity air tightness test passes.

[0023] (6) Adjust the depth of the lower end of the center pipe string to discharge the remaining plugging agent in the salt cavern cavity back to the ground to complete the plugging operation.

[0024] When the cavity meets the requirements of airtightness detection, adjust the lower end of the central column in the cavity to the depth of the plugging agent interface, and discharge the plugging agent in the cavity to the ground. After the plugging agent is discharged to the ground, it can be reused to reduce resource waste.

[0025] In order to ensure the safety and reliability of subsequent production operations of the cavity, monitoring wells can be encrypted around the crack plugging cavity to carry out safety monitoring of the cavity.

[0026] Compared with the prior art, the present invention provides a method for plugging interlayer cracks inside a salt cavern cavity, adjusts the gas-liquid interface to be lower than the interlayer crack position, injects a low-density plugging agent at the gas-liquid interface, and adopts a two-way pressurization method to make the plugging agent evenly stressed up and down, and can only flow laterally along the cavity under pressure, so that the plugging agent can accurately seep into the crack channel and form consolidation with the formation. The present invention establishes an effective plugging method for interlayer cracks inside a salt cavern cavity for the first time, solves the problem of cavity interlayer leakage, and provides an effective solution to the risk of interlayer leakage in the long-term production and operation of the salt cavern cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A step diagram of a method for plugging interlayer cracks in a salt cavern storage cavity;

[0028] Figure 2 Schematic diagram of the flow of plugging agent into the cavity;

[0029] Figure 3 This is a schematic diagram of sealing interlayer cracks in the salt cavern storage cavity;

[0030] Figure 4This is an enlarged schematic diagram of the flow of plugging agents in cavities and cracks;

[0031] In the figure, 1 is the gas injection (exhaust) port, 2 is the brine injection (exhaust) port, 3 is the intermediate pipe string, 4 is the center pipe string, 5 is the gas in the cavity, 6 is the interlayer, 7 is the plugging agent, 8 is the interlayer crack, 9 is the brine in the cavity, 10 is the plugging agent injection (discharge) port, 11 is the production casing, 12 is the plugging agent squeezed into the crack, and 13 is the wall of the salt cavern cavity. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0033] The present invention proposes a method for sealing cracks in the interlayer of a salt cavern storage cavity, which achieves effective sealing of leakage inside the salt cavern cavity and provides an effective disposal measure for the risk of interlayer leakage in the long-term operation of the salt cavern gas storage cavity.

[0034] A method for sealing cracks in an interlayer of a salt cavern storage cavity comprises the following steps:

[0035] Example 1: Taking a salt cavity with interlayer leakage as an example, the effectiveness of the technical method is further illustrated, and the implementation of the present invention is described as follows:

[0036] S100: There are four interlayers in the P1 cavity layer of a salt mine, with an interlayer thickness of 1-3m. Through the salt cavern cavity sealing test, it was found that the gas-liquid interface in the cavity dropped by a total of about 0.12m in 25 days. At the same time, the gas sealing test of the cavity shaft found that there was no leakage problem. The tracer test found that the leakage point was located in the interlayer crack in the middle and upper part of the cavity. The horizontal width of the crack was about 0.55m and the vertical height was 0.05m.

[0037] Table 1 P1 salt cavern parameters

[0038] .

[0039] The storage capacity parameters of the P1 salt cavity in the reservoir construction area are as follows:

[0040] Table 2 Salt cavern storage capacity parameters

[0041] .

[0042] The depth of the P1 salt cavity in the reservoir construction area is as follows:

[0043] Table 3 Salt cavern cavity parameters

[0044] .

[0045] S200: Inject gas to remove brine and adjust the depth of the gas-liquid interface. After the P1 salt cavity is completed, the brine interface is higher than the crack depth, and the intermediate pipe string and the central pipe string are lowered to perform gas injection and brine removal operations; at the same time, the fiber optic monitoring equipment is lowered to monitor the depth of the gas-liquid interface in real time; the crack depth is 1681.6~1681.8m, and the depth of the intermediate pipe string and the central pipe string is adjusted to make the height of the gas-liquid interface lower than the depth of the interlayer crack position. Among them, the monitoring accuracy of the gas-liquid interface should not be less than 0.02m, and the gas-liquid interface is 0.05~0.10m lower than the position of the cavity interlayer crack, and the depth of the gas-liquid interface is adjusted to 1681.9m.

[0046] S300: Calculation of plugging agent dosage. According to the stratum depth and fracture height of the interlayer fracture, the cavity cross-sectional area of ​​the layer section is measured by sonar cavity measurement, and the plugging agent thickness is preset according to the longitudinal height of the fracture. The plugging agent dosage is calculated to be 1452m 3 .

[0047] The plugging agent is formulated according to the mineral components of the target salt layer interlayer core and the parameters of the brine. In parts by weight, the raw materials of the plugging agent are: 0.7 parts of silicon nanoparticles, 1.5 parts of polyacrylic acid, 1 part of cement-based permeable crystallization waterproof material, 7 parts of diesel, and 0.3 parts of viscosity reducer. The plugging agent is an oil-based plugging agent, which is insoluble in brine, has a lower density than water, and has high salt resistance. It reacts chemically with the interlayer mineral components, and the generated crystals continue to grow and fill the pores inside the cracks; it is easy to form high-strength bonding with the interlayer mineral components and can withstand high pressure for a long time.

[0048] S400: Injection of plugging agent into the cavity and thickness detection. According to the calculated plugging agent dosage, the central pipe column is adjusted to the brine interface depth of 1682m, and the plugging agent is injected into the salt cavern cavity; after the injection, the plugging agent layer thickness is tested. The thickness of the plugging agent suspended at the brine interface is 0.40m, and the plugging agent thickness can cover the height of the crack position.

[0049] S500: By injecting gas into the cavity through the annulus of the intermediate pipe string and the central pipe string, and by injecting brine back into the cavity through the central pipe string, the plugging agent is squeezed into the interlayer cracks along the wall of the salt cavern cavity under the action of pressure, and the plugging agent reacts physically and chemically with the mineral components in the cracks to form consolidation for plugging. In this process, the gas space pressure and brine space pressure around the plugging agent in the cavity are monitored in real time to keep them consistent. By injecting gas and water in both directions and smoothly increasing pressure, the plugging agent between the gas and brine is pressurized into the interlayer crack channel; the thickness of the plugging agent is monitored in real time to prevent the plugging agent thickness from being lower than the crack height, and the gas in the cavity from entering the cracks and causing the plugging operation to fail. During the pressurization process, the cavity pressure should be monitored in real time, and the maximum cavity pressure should not exceed 85% of the formation fracture pressure.

[0050] S600: Salt cavern cavity air tightness test. The plugging agent is injected into the interlayer cracks. According to the consolidation time of the plugging agent and the interlayer components, the plugging agent and the minerals are fully cemented after stabilization for 20 days. Gas is injected to expel brine, so that the gas-liquid interface is lower than the depth of the interlayer cracks. The gas tightness test string is lowered into the wellbore to carry out the cavity gas tightness test. The change in the depth of the gas-water interface in the wellbore is less than 1m within the 24-hour test time, and the gas tightness test is completed.

[0051] S700: After the cavity meets the requirements of air-tightness detection, adjust the lower end of the central pipe column to the depth of the plugging agent interface, and inject gas to discharge the plugging agent in the cavity to the ground, and at the same time drain the brine in the cavity to complete the cavity crack plugging operation. In order to ensure the safety and reliability of the subsequent production and operation of the cavity, the monitoring wells can be encrypted around the crack plugging cavity to monitor the cavity for long-term safety.

[0052] Taking this implementation as an example, the leakage plugging and reuse of interlayers in newly built and abandoned salt caverns with poor sealing performance is realized, which is conducive to further improving the resource utilization rate of salt rock. In view of the risks of interlayer leakage in the long-term production and operation of salt caverns, an effective solution is provided, which has good practicality and application value.

[0053] Personnel in the technical field can easily make various changes and modifications based on the text description, drawings and claims provided by the present invention without departing from the concept and scope of the present invention defined by the claims. Any modification or equivalent change made to the above embodiments based on the technical concept and essence of the present invention shall fall within the scope of protection defined by the claims of the present invention.

[0054] 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 method for plugging interlayer cracks in a salt cavern storage cavity, characterized in that: Adjust the gas-liquid interface to be lower than the interlayer fracture position, inject low-density plugging agent at the gas-liquid interface, and use a two-way pressurization method to make the plugging agent seep into the fracture channel and consolidate with the formation. The specific steps are: (1) Adjust the depth of the gas-liquid interface After the cavity is made, the intermediate pipe string and the central pipe string are lowered into the wellbore to perform gas injection and brine expulsion or brine injection and exhaust operations. At the same time, the optical fiber monitoring equipment is lowered to monitor the depth of the gas-liquid interface in real time. Through gas injection and brine expulsion or brine injection and exhaust operations, the gas-liquid interface is made lower than the position of the interlayer cracks. (2) Calculation of plugging agent dosage According to the depth and height of the interlayer cracks, the cross-sectional area of ​​the cavity in the layer section is measured by sonar cavity measurement to calculate the amount of plugging agent; (3) Injection of plugging agent into the salt cavern cavity and thickness detection Adjust the central pipe string to the depth of the brine interface and inject the plugging agent into the salt cavern cavity; after the injection is completed, test the thickness of the plugging agent to ensure that the thickness of the plugging agent can cover the crack position; (4) Pressurizing the salt cavern cavity to squeeze the plugging agent into the interlayer cracks Inject gas into the cavity through the annulus between the intermediate and central tubulars, and inject brine into the cavity through the central tubular. The bidirectional pressurization allows the plugging agent to be squeezed into the interlayer cracks under pressure. During this process, the gas space pressure and brine space pressure around the plugging agent in the cavity are monitored in real time; the plugging agent thickness is monitored in real time. (5) Salt cavern air tightness test After the plugging agent is injected into the interlayer cracks and the plugging agent is fully cemented with the minerals, gas is injected to expel the brine so that the gas-liquid interface is lower than the position of the interlayer cracks, and the cavity gas tightness test is carried out; (6) Adjust the depth of the lower end of the center pipe string to discharge the remaining plugging agent in the salt cavern cavity back to the ground to complete the plugging operation.

2. A method for plugging interlayer cracks in a salt cavern storage cavity according to claim 1, characterized in that: The monitoring accuracy of the gas-liquid interface in step (1) is not less than 0.02 m; the gas-liquid interface is 0.05-0.10 m below the position of the cavity interlayer crack.

3. A method for sealing interlayer cracks in a salt cavern storage cavity according to claim 1, characterized in that: The plugging agent in step (2) is a plugging agent having a density lower than that of brine and being insoluble in brine.

4. A method for sealing interlayer cracks in a salt cavern storage cavity according to claim 1, characterized in that: The thickness of the plugging agent is 0.05~0.15m higher than the crack position.

5. The method for sealing interlayer cracks in a salt cavern storage cavity according to claim 1, characterized in that: During the bidirectional pressurization process in step (4), the cavity internal pressure is monitored in real time, and the maximum cavity internal pressure shall not exceed 85% of the formation fracture pressure.

6. A method for sealing interlayer cracks in a salt cavern storage cavity according to claim 1, characterized in that: In step (4), during the bidirectional pressurization process, the pressure of the gas space around the plugging agent in the cavity is consistent with the pressure of the brine space.

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