A method of slotting a salt cavern reservoir

Abstract

The present application relates to a salt cavern storage slot expansion method, belonging to the technical field of salt rock stratum halogen mining and cavity building. The salt cavern storage slot expansion method prevents the injected clean water liquid level from rising too fast, thereby causing the formation of a small size sharp cone bottom slot during slot building, through reciprocating regulation of the gas-liquid interface and combined positive circulation and reverse circulation operation. Through reciprocating regulation of the gas-liquid interface, saturated brine inside the storage slot bottom slot can be discharged in time, and multiple side wall dissolution of the storage slot bottom slot can be achieved. Through reverse circulation operation, the purpose of expanding the horizontal size of the storage slot bottom slot can be achieved. After completing the positive circulation slot expansion and cavity building of the storage slot bottom slot, combined effective control of the gas-liquid interface and reverse circulation secondary slot expansion and cavity building are adopted, realizing a substantial expansion of the horizontal size. The final effect is to expand the size of the storage slot bottom slot, reduce the side dissolution angle of the storage slot bottom slot, thereby substantially increasing the volume of the storage slot bottom slot, and improving the economic benefits of the salt cavern water solution cavity building.

Description

Technical Field

[0001] This invention relates to a method for expanding salt cavern storage, belonging to the field of brine extraction and cavity construction technology in salt rock strata. Background Technology

[0002] During the conventional oil-pad method for cavity construction and trenching, due to the small wellbore size, fresh water from the inner tubing of the cavity rises rapidly along the annulus between the open hole and the inner tubing. Because the annulus channel is narrow during trenching, the rapid rise of fresh water results in short contact time with the salt rock on the cavity sidewalls, leading to insufficient salt rock dissolution. As the oil-pad interface gradually rises, the brine in the lower part of the cavity quickly becomes saturated, and the salt rock stops dissolving. The size of the lower part of the cavity then stabilizes and stops expanding, ultimately resulting in very little salt rock dissolution in the lower cavity during trenching. The bottom of the cavity often forms a sharp cone shape. The height of the cone-shaped cavity bottom is at least 5-10 meters, meaning that the salt rock within the cone area is unusable, resulting in a significant waste of salt rock resources. Furthermore, due to the presence of the conical bottom of the cavity during the construction phase, sediment accumulates rapidly at the conical point, resulting in a large lateral dissolution angle (37-50°) in the subsequent cavity and making it difficult for the interlayer above the conical point to collapse. The sediment accumulation forms an inverted cone shape (making it difficult to drain the brine below the cone tip during subsequent aeration and brine discharge). Under these combined effects, the salt layer resources at the bottom of the cavity are wasted, and the excessively large lateral dissolution angle at the bottom of the cavity leads to a reduction in cavity volume, which may cause inverted cone-shaped sediment accumulation, preventing the subsequent discharge of residual brine. Summary of the Invention

[0003] The purpose of this invention is to provide a method for expanding salt cavern storage, which can solve the problems of wasting salt resources due to the inverted conical cavity bottom and the excessively large dissolution angle of the bottom trench resulting in an insufficient volume of the bottom trench during the current construction of trenches in salt rock formations.

[0004] To achieve the above objectives, the technical solution adopted by the salt cavern storage expansion method of the present invention is as follows:

[0005] A method for expanding a salt cavern storage tank employs an aeration and brine discharge device. The device includes a central pipe, an intermediate pipe, and an outer cavity-forming pipe. The central pipe is used to inject clean water into the bottom tank of the storage tank or to collect brine from the bottom tank. An annular space is formed between the central pipe and the intermediate pipe to collect brine from the bottom tank or inject clean water. An aeration channel is formed between the outer cavity-forming pipe and the intermediate pipe. The soluble content of the salt layer within the salt cavern storage tank is not less than 85%. The method for expanding the salt cavern storage tank includes the following steps:

[0006] (1) Inject gas into the bottom tank of the storage tank through the gas injection channel between the outer tube and the middle tube until the gas-liquid interface in the bottom tank of the storage tank is located at a position not less than 3m above the lower end of the middle tube.

[0007] (2) Then, clean water is continuously injected from the central pipe into the bottom tank of the storage tank at a discharge rate of 10~20m³ / h to dissolve the side wall of the bottom tank of the storage tank; when the gas-liquid interface rises, the rising speed is reduced by injecting gas.

[0008] (3) When the gas-liquid interface rises to the top plate of the bottom tank of the storage tank, gas is continuously injected to make the gas-liquid interface move down continuously, and the brine inside the bottom tank of the storage tank is discharged through the central pipe and the intermediate pipe until the gas-liquid interface is lowered to a position not less than 3m above the opening of the intermediate pipe.

[0009] (4) Repeat steps (2) to (3) until the radius of the top plate of the storage tank bottom is not less than 3m;

[0010] (5) Continuously inject clean water into the bottom tank of the storage tank from the annulus between the central pipe and the intermediate pipe at a discharge rate of 10~20m³ / h to dissolve the side wall of the bottom tank of the storage tank. At the same time, adjust the discharge rate of clean water according to the concentration of brine discharged from the central pipe. When the gas-liquid interface rises, reduce the rising speed by injecting gas.

[0011] (6) When the gas-liquid interface rises to the top plate of the bottom tank of the storage tank, gas is continuously injected to make the gas-liquid interface move down continuously, and the brine inside the bottom tank of the storage tank is discharged through the central pipe and the intermediate pipe until the gas-liquid interface is lowered to a position not less than 3m above the opening of the intermediate pipe.

[0012] (7) Repeat steps (5) to (6) until the radius of the top plate of the storage tank reaches 5 to 10 m;

[0013] (8) Continuously inject clean water into the bottom tank of the storage tank from the central pipe and intermediate pipe annulus at a discharge rate of 50~55m³ / h to dissolve the side wall of the bottom tank until the gas-liquid interface rises to the top plate of the bottom tank; then gradually increase the discharge rate of clean water. When the gas-liquid interface rises, reduce the gas-liquid interface to the top plate of the bottom tank by injecting gas until the radius of the top plate of the bottom tank reaches the design value.

[0014] The salt cavern expansion method of this invention effectively expands the size of the storage tank during the construction phase by repeatedly controlling the gas-liquid interface and combining forward and reverse circulation. This prevents the injected clear water level from rising too quickly, which could lead to the formation of a small, pointed conical bottom tank during the construction phase. The repeated control of the gas-liquid interface allows for timely discharge of saturated brine from the storage tank bottom and enables multiple dissolutions of the tank sidewalls, thereby increasing the tank bottom size. Reverse circulation ensures the expansion of the tank bottom's lateral dimensions. After completing the forward circulation expansion of the storage tank bottom, effective control of the gas-liquid interface and a secondary reverse circulation expansion further enhance the lateral expansion. The ultimate effect is to increase the size of the storage tank bottom, reduce the lateral dissolution angle, and significantly increase the volume of the storage tank bottom, thereby improving the economic efficiency of salt cavern water-soluble cavity construction.

[0015] It is understood that, in this invention, the gas-liquid interface rising to the top plate of the storage tank bottom refers to the position where the gas-liquid interface rises to the bottom of the top plate of the storage tank bottom.

[0016] Preferably, in the salt cavern expansion method, the distance between the lower end of the intermediate pipe and the lower end of the central pipe is controlled to be no less than 5m. Maintaining a distance of no less than 5m between the two pipes ensures a sufficient distance between their openings, preventing brine from the central pipe from directly entering the intermediate pipe and thus achieving the desired effect of dissolving the salt rock.

[0017] Preferably, in step (2), the discharge rate of the injected water is adjusted according to the concentration of the brine collected from the bottom tank of the storage tank. If the concentration of the discharged brine is greater than 150 g / L, the discharge rate is increased, but the increased discharge rate is not greater than 20 m³ / h.

[0018] Preferably, in step (2), the reduction of the rising speed by injecting gas is achieved by replenishing gas every 0.4~0.6m when the gas-liquid interface rises, so that the gas-liquid interface falls by 0.1~0.3m. For example, in step (2), the reduction of the rising speed by injecting gas is achieved by replenishing gas every 0.5m when the gas-liquid interface rises, so that the gas-liquid interface falls by 0.3m.

[0019] Preferably, in step (5), the principle for adjusting the discharge rate of the injected clean water according to the concentration of the brine discharged from the central pipe is as follows: when the concentration of the brine is 150~180g / L, the discharge rate of the clean water is 25~30m³ / h; when the concentration of the brine is 180~200g / L, the discharge rate of the clean water is 30~35m³ / h; when the concentration of the brine is 200~220g / L, the discharge rate of the clean water is 35~40m³ / h; when the concentration of the brine is 220~240g / L, the discharge rate of the clean water is 40~45m³ / h; when the concentration of the brine is greater than 240g / L, the discharge rate of the clean water is 45~50m³ / h.

[0020] Preferably, in step (5), the rising speed is reduced by injecting gas by the following method: gas is added every 0.4~0.6m when the gas-liquid interface rises so that the gas-liquid interface falls by 0.1~0.3m.

[0021] Preferably, in step (8), the method for gradually increasing the injection rate of clean water is as follows: when the concentration of brine discharged from the central pipe is 200~220g / L, the injection rate is 55~60m³ / h; when the concentration of brine discharged from the central pipe is 220~240g / L, the injection rate is 60~65m³ / h; when the concentration of brine discharged from the central pipe is 240~260g / L, the injection rate is 65~70m³ / h; when the concentration of brine discharged from the central pipe is 260~280g / L, the injection rate is 70~75m³ / h; when the concentration of brine discharged from the central pipe is not less than 280g / L, the injection rate is 75~80m³ / h.

[0022] Preferably, in step (6), the position of the gas-liquid interface is determined based on the accumulation of sediment. When there is a lot of sediment accumulation, which makes it necessary to raise the position of the middle pipe opening on site, the gas-liquid interface can be pressed down to a position not less than 5m above the lower end of the middle pipe opening by injecting air. When there is little sediment accumulation and there is no need to move the position of the middle pipe opening on site, the gas-liquid interface should be controlled at a position not less than 3m above the lower end of the middle pipe opening.

[0023] In this invention, the positive circulation expansion tank is performed first, followed by the initial and secondary reverse circulation expansion tanks. This avoids initial blockage of the tubing and fully utilizes the advantages of high dissolution efficiency and large cavity size in the later reverse circulation cavity. If the reverse circulation expansion tank is performed first, followed by the positive circulation expansion tank, the central tube is likely to be blocked from the beginning, and it will be difficult to obtain a high concentration of brine in the later stages.

[0024] A schematic diagram of the salt cavern storage expansion method of the present invention is shown below. Figure 1As shown, the air cushion water-soluble expansion tank device includes a central pipe 1, an intermediate pipe 2, and a cavity-forming outer pipe 3. First, positive circulation expansion tank formation (steps 1-4) is performed. Gas is injected into the storage tank bottom (at this time, the storage tank bottom is the initial naked eye 8, and the storage tank bottom boundary is the initial naked eye boundary 9) to form an air cushion 5. The gas-liquid interface 4 is located at least 3m above the lower end of the intermediate pipe 6. Then, clean water 11 is injected through the lower end of the central pipe 10. During the positive circulation expansion tank formation process, brine 7 is discharged. After one round of positive circulation expansion tank formation, the storage tank bottom 12 and the transverse boundary 13 of the storage tank bottom are obtained. After the cycle is completed, the bottom tank 14 and the transverse boundary 15 of the bottom tank at the end of the positive cycle are obtained. Then, the initial reverse cycle is performed to expand the tank and create a cavity. Clear water 16 is injected into the cavity through the annulus between the central pipe 1 and the intermediate pipe 2. Brine 17 is discharged from the central pipe 1. After a certain round of reverse cycle, the bottom tank 18 and the transverse boundary 19 of the bottom tank after reverse cycle are obtained. After the initial reverse cycle is completed, the bottom tank 20 and the transverse boundary 21 of the bottom tank after the initial reverse cycle are formed. The radius of the top plate 25 of the bottom tank increases continuously during the expansion and cavity creation process, but the height remains unchanged.

[0025] The specific process of positive circulation expansion and cavity creation is as follows: Figure 2 As shown, gas is first injected to form an air cushion 5-1, and then water 22-1 is injected through the central pipe 1. As the water rises, it dissolves the salt rock to form brine. During this process, the gas-liquid interface 4-1 is controlled. Then, the positive circulation expansion and cavity-building process is repeated continuously. Gas is first injected to form an air cushion 5-2, and then water 22-2 is injected through the central pipe 1. As the water rises, it dissolves the salt rock to form brine. During this process, the gas-liquid interface 4-2 is controlled. The radius of the top plate 25 of the bottom tank of the storage tank increases continuously during the expansion and cavity-building process, but the height remains unchanged.

[0026] The specific process for the initial reverse circulation expansion and cavity creation is as follows: Figure 3 As shown, gas is first injected to form an air cushion 5-3. Then, clean water 22-3 is injected into the bottom tank of the storage tank through the annulus between the central pipe 1 and the intermediate pipe 2. As the clean water descends, it dissolves the salt rock to form brine. During this process, the gas-liquid interface 4-3 is controlled. Then, the reverse circulation tank expansion and cavity-building process is repeated continuously. Gas is first injected to form an air cushion 5-4. Then, clean water 22-4 is injected into the bottom tank of the storage tank through the annulus between the central pipe 1 and the intermediate pipe 2. As the clean water descends, it dissolves the salt rock to form brine. During this process, the gas-liquid interface 4-4 is controlled. The radius of the top plate 25 of the bottom tank of the storage tank increases continuously during the tank expansion and cavity-building process, but the height remains unchanged.

[0027] A schematic diagram of the bottom tank boundary expansion method in the salt cavern storage expansion method of the present invention is shown below. Figure 4As shown, the central axis 29 of the reservoir bottom trench of the cavity remains unchanged during the expansion of the cavity. The gas-liquid interface position 5-5 changes continuously during the expansion process. The bottom trench boundary before trench expansion is the open hole wellbore boundary 21. The bottom trench boundary after the second reverse circulation trench expansion is the bottom trench boundary 23 at the end of the second reverse circulation trench expansion. The side dissolution angle is the bottom trench side dissolution angle 24 at the end of the second reverse circulation trench expansion. The radius of the top plate 25 of the reservoir bottom trench increases continuously during the trench expansion process, but the height remains unchanged.

[0028] A comparative schematic diagram of the bottom trench profile obtained by the salt cavern storage expansion method of the present invention and the bottom trench profile obtained by the oil pad method for cavity construction is shown below. Figure 5 As shown, the central axis 29 of the storage tank bottom obtained by the two methods is the same. The boundary of the storage tank bottom obtained by the present invention is the final boundary 23 of the bottom tank during the construction period, which is more open than the boundary of the storage tank bottom obtained by the oil pad method (final boundary 26 of the bottom tank during the construction period of the oil pad method). Compared with the traditional method, the volume of the storage tank bottom obtained by the present invention is larger, with the increase being the newly added volume portion 27. Furthermore, the lateral dissolution angle (final lateral dissolution angle 24) of the storage tank bottom obtained by the present invention is significantly smaller than the lateral dissolution angle of the storage tank bottom obtained by the oil pad method (final lateral dissolution angle 28 during the construction period of the oil pad method). Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process for expanding the salt cavern storage tank according to the present invention; wherein, Figure 1 (a) is a schematic diagram of the wellbore and air cushion positions during the initial stage of positive circulation; Figure 1 (b) is a schematic diagram of the bottom tank shape at the end of a certain positive cycle; Figure 1 (c) is a schematic diagram of the bottom tank shape at the end of all positive cycles; Figure 1 (d) is a schematic diagram of the shape of the storage tank bottom and the position of the air cushion at the beginning of a certain cycle in the initial reverse circulation expansion and cavity building process; Figure 1 (e) is a schematic diagram of the bottom tank morphology at the end of the initial reverse circulation expansion and cavity creation; the reference numerals are as follows: 1-Central pipe; 2-Intermediate pipe; 3-Outer pipe for cavity creation; 4-Gas-liquid interface; 5-Air cushion; 6-Lower end of intermediate pipe; 7-Brine; 8-Initial naked eye; 9-Initial naked eye boundary; 10-Lower end of central pipe; 11-Clear water; 12-Bottom tank of the storage tank; 13-Transverse boundary of the bottom tank of the storage tank; 14-Bottom tank of the storage tank at the end of the forward circulation; 15-Transverse boundary of the bottom tank of the storage tank at the end of the forward circulation; 16-Clear water; 17-Brine; 18-Bottom tank of the storage tank after reverse circulation; 19-Transverse boundary of the bottom tank of the storage tank after reverse circulation; 20-Bottom tank of the storage tank after the initial reverse circulation; 21-Transverse boundary of the bottom tank of the storage tank after the initial reverse circulation; 25-Top plate of the bottom tank of the storage tank;

[0030] Figure 2 This is a schematic diagram of positive circulation expansion cavity creation; where, Figure 2(a) is a schematic diagram of the gas-liquid interface position at the start of the positive cycle; Figure 2 (b) is a schematic diagram of the gas-liquid interface rising during a certain positive cycle process; Figure 2 (c) is a schematic diagram of the shape of the bottom tank and the position of the gas-liquid interface at the end of the entire positive cycle; the attached diagram is labeled as follows: 4-1-Gas-liquid interface; 5-1-Air cushion; 4-2-Gas-liquid interface; 5-2-Air cushion; 22-1-Clear water; 22-2-Clear water; 25-Top plate of the bottom tank;

[0031] Figure 3 This is a schematic diagram of the initial reverse circulation expansion cavity creation; where, Figure 3 The first image in the middle is a schematic diagram of the air cushion position during the initial reverse circulation expansion and cavity creation; Figure 3 The second image is a schematic diagram of the gas-liquid interface rising during a certain round of reverse circulation; Figure 3 The third figure in the middle is a schematic diagram of the reservoir shape and gas-liquid interface position at the end of the initial reverse circulation expansion tank construction; the attached figures are labeled as follows: 4-3-Gas-liquid interface; 5-3-Air cushion; 4-4-Gas-liquid interface; 5-4-Air cushion; 22-3-Clear water; 22-4-Clear water; 25-Top plate of the reservoir bottom tank;

[0032] Figure 4 This is a schematic diagram of the bottom trench boundary expansion in the salt cavern storage expansion method of the present invention; wherein, the reference numerals are as follows: 5-5-position of gas-liquid interface; 21-bore boundary of open hole section; 23-bottom trench boundary at the end of the second reverse circulation expansion and cavity creation; 24-side dissolution angle of bottom trench at the end of the second reverse circulation expansion and cavity creation; 25-top plate of bottom trench of storage tank; 29-central axis of bottom trench of storage tank;

[0033] Figure 5 This is a comparative schematic diagram of the bottom tank outline obtained by the salt cavern storage expansion method of the present invention and the bottom tank outline obtained by the oil pad method for cavity construction; wherein, the reference numerals are as follows: 23-final bottom tank boundary during the construction period; 24-final lateral dissolution angle; 26-final bottom tank boundary during the construction period of the oil pad method; 27-newly added volume portion; 28-final lateral dissolution angle during the construction period of the oil pad method; 29-central axis of the storage bottom tank. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] Example 1

[0036] Taking a salt cavern storage facility as an example, the soluble content of the salt layer in the storage facility is not less than 85%. The estimated dissolution angle of the bottom tank after the expansion is about 35°. The designed radius of the top plate of the bottom tank after the expansion is 30m. The salt cavern storage facility expansion method in this embodiment specifically includes the following steps:

[0037] During the expansion process, the distance between the lower end of the intermediate pipe and the lower end of the central pipe should be more than 5m, and the distance between the bottom of the storage tank and the horizontal line of the upper boundary of the tank should be 25m.

[0038] S1, Positive circulation groove expansion and cavity creation

[0039] (1) First, inject clean water into the bottom tank (wellbore) through the central pipe to fill the bottom tank with liquid. Then, inject gas into the bottom tank through the outer pipe and the middle pipe to form an air cushion in the bottom tank. When the gas-liquid interface is 4m above the lower end of the middle pipe, stop injecting gas. During this process, some liquid will overflow through the annulus between the central pipe and the middle pipe.

[0040] (2) Using a small flow rate (around 15 m³ / h), clean water is continuously injected into the bottom tank of the reservoir from the central pipe. Since the density of clean water is less than that of brine in the bottom tank, the clean water slowly rises. During the rising process, it continuously dissolves the salt rock on the side wall of the bottom tank. As clean water is continuously injected, brine also continuously overflows and is discharged through the annulus of the central pipe and intermediate pipe. This process is the positive circulation salt dissolution cavity creation process. During the positive circulation salt dissolution cavity creation process, the gas-liquid interface monitor arranged on the outside of the intermediate pipe is used to monitor the dynamic changes in the position of the gas-liquid interface. If the position of the gas-liquid interface rises, it indicates that gas needs to be added. If the position of the gas-liquid interface falls, it indicates that the pressure at the wellhead of the water injection pipe may be insufficient. At the same time, the pressure at the wellhead is monitored by the gas-liquid interface monitor arranged on the outside of the intermediate pipe. The concentration meter is used to test the concentration change of the discharged brine; if the concentration of the discharged brine is greater than 150 g / L, the discharge rate is increased slowly, but not exceeding 20 m³ / h; if the concentration of the discharged brine does not increase and is still less than 150 g / L, the water injection discharge rate remains unchanged; as the expansion and cavity-building process continues, the radius of the top plate of the storage tank bottom increases, while the thickness of the air cushion decreases, causing the gas-liquid interface to rise continuously. Based on the dynamic monitoring results of the gas-liquid interface position, air is automatically replenished every 0.5 m rise of the gas-liquid interface to make the gas-liquid interface drop by 0.3 m (ensuring that the air cushion thickness is not less than 0.3 m), until the gas-liquid interface rises to the upper set position (the top plate of the storage tank bottom).

[0041] (3) When the gas-liquid interface rises to the upper set position (top plate of the storage tank bottom), gas is continuously injected to make the gas-liquid interface move down continuously, and the brine inside the storage tank bottom is gradually discharged through the central pipe and the intermediate pipe until the gas-liquid interface is lowered to a position 4m above the opening of the intermediate pipe.

[0042] (4) Repeat steps (2) to (3) at least 3 times. When the calculated top plate radius of the storage tank bottom is not less than 3m, the repeated operation ends. The top plate radius of the storage tank bottom is determined by sonar cavity measurement or salt sampling back-calculation method. In this embodiment, when steps (2) to (3) are repeated 4 times, the calculated top plate radius of the storage tank bottom is 3.5m, and the repeated operation ends.

[0043] S2, Initial Reverse Circulation Expansion and Cavity Formation

[0044] After the positive circulation expansion and cavity construction is completed, the top plate radius of the bottom tank of the storage tank has reached the predetermined size (≥3~5m), and during the dissolution process, the bottom tank of the storage tank will present an inverted trapezoidal shape with a larger upper part and a smaller lower part in the longitudinal section; at this time, the water injection mode is adjusted from positive circulation to reverse circulation (i.e., water is injected through the annular space of the central pipe and the intermediate pipe, and brine is discharged through the central pipe).

[0045] (1) Based on the increase in brine concentration at the wellhead, the discharge rate of the injected clean water is gradually increased from the discharge rate (15 m³ / h) used in the positive circulation expansion and cavity creation to 20~50 m³ / h. As clean water is continuously injected, brine is also continuously overflowed and discharged through the central pipe. If it is difficult to discharge brine through the central pipe, backwashing or raising the position of the central pipe opening can be adopted to ensure smooth reverse circulation. By increasing the discharge rate of clean water, the dissolution efficiency can be improved and the cavity creation rate can be accelerated.

[0046] The principle for increasing the injection rate of clean water based on the rise in brine concentration at the wellhead is as follows:

[0047] When the brine concentration at the wellhead is 150~180g / L, the discharge rate of clean water is 25~30m³ / h; when the brine concentration at the wellhead is 180~200g / L, the discharge rate of clean water is 30~35m³ / h; when the brine concentration at the wellhead is 200~220g / L, the discharge rate of clean water is 35~40m³ / h; when the brine concentration at the wellhead is 220~240g / L, the discharge rate of clean water is 40~45m³ / h; and when the brine concentration at the wellhead is greater than 240g / L, the discharge rate of clean water is 45~50m³ / h.

[0048] (2) During the reverse circulation expansion tank process, the rise of the gas-liquid interface is monitored in real time. For every 0.5m rise of the gas-liquid interface, a supplementary gas injection is performed to make the gas-liquid interface drop by 0.3m (to ensure that the thickness of the air cushion is not less than 0.3m).

[0049] (3) When the gas-liquid interface rises to the upper set position (top plate of the storage tank bottom), the gas-liquid interface is continuously moved down by injecting air, the brine is discharged through the central pipe, and the gas-liquid interface is pressed down to a position 4m above the lower end of the middle pipe (depending on the sludge accumulation); when there is a lot of sludge accumulation, it is necessary to raise the position of the middle pipe opening on site, the gas-liquid interface can be pressed down to a position 5m above the lower end of the middle pipe opening by injecting air; when there is little sludge accumulation, it is not necessary to move the position of the middle pipe opening on site, the gas-liquid interface should be controlled at a position 4m above the lower end of the middle pipe opening.

[0050] (4) Repeat steps (1) to (3) at least 3 times, and combine the gas-liquid interface monitoring and brine data calculation, and use the calculated top plate radius of the storage tank bottom to reach 5 to 10 m as the stop mark for the first reverse circulation tank expansion cavity creation; in this embodiment, when steps (1) to (3) are repeated 4 times, the calculated top plate radius of the storage tank bottom reaches 7 m, and the first reverse circulation tank expansion cavity creation ends.

[0051] S3, reverse circulation expansion and cavity creation again

[0052] After the initial reverse circulation expansion and cavity construction, the radius of the top plate of the storage tank bottom is no less than 5m. To further expand the lateral dimensions of the storage tank bottom, clean water is injected into the tank bottom at a rate of 50m³ / h through the annular space between the central and intermediate pipes. When the gas-liquid interface rises to the upper set position (top plate of the storage tank bottom), the water injection rate is gradually increased to 50-80m³ / h. Simultaneously, the rise of the gas-liquid interface is monitored in real time. For every 5cm the gas-liquid interface rises, supplementary gas injection is performed to lower the gas-liquid interface to the upper set position (top plate of the storage tank bottom), until all tank construction is completed (top plate of the storage tank bottom). (Radius 30~35m); the method for gradually increasing the water injection rate to 50~80m³ / h is as follows: when the brine concentration is 200~220g / L, the water injection rate is 55~60m³ / h; when the brine concentration is 220~240g / L, the water injection rate is 60~65m³ / h; when the brine concentration is 240~260g / L, the water injection rate is 65~70m³ / h; when the brine concentration is 260~280g / L, the water injection rate is 70~75m³ / h; and when the brine concentration is not less than 280g / L, the water injection rate is 75~80m³ / h.

Claims

1. A method for expanding a salt cavern storage tank, characterized in that, An aeration and brine discharge device is employed, comprising a central pipe, an intermediate pipe, and an outer cavity-forming pipe. The central pipe is used to inject clean water into the bottom tank of the storage pit or to collect brine from the bottom tank. The central pipe and the intermediate pipe form an annular space for collecting brine from the bottom tank or injecting clean water into the bottom tank. An aeration channel is formed between the outer cavity-forming pipe and the intermediate pipe. The soluble content of the salt layer in the salt cavern storage pit is not less than 85%. The method for expanding the salt cavern storage pit includes the following steps: (1) Inject gas into the bottom tank of the storage tank through the gas injection channel between the outer tube and the middle tube until the gas-liquid interface in the bottom tank of the storage tank is located at a position not less than 3m above the lower end of the middle tube. (2) Then, clean water is continuously injected from the central pipe into the bottom tank of the storage tank at a discharge rate of 10~20m³ / h to dissolve the side wall of the bottom tank of the storage tank; when the gas-liquid interface rises, the rising speed is reduced by injecting gas. (3) When the gas-liquid interface rises to the top plate of the bottom tank of the storage tank, gas is continuously injected to make the gas-liquid interface move down continuously, and the brine inside the bottom tank of the storage tank is discharged through the central pipe and the intermediate pipe until the gas-liquid interface is lowered to a position not less than 3m above the lower end of the intermediate pipe. (4) Repeat steps (2) to (3) until the radius of the top plate of the storage tank bottom is not less than 3m; (5) Continuously inject clean water into the bottom tank of the storage tank through the annulus between the central pipe and the intermediate pipe at a discharge rate of 10~20 m³ / h to dissolve the sidewalls of the bottom tank. At the same time, adjust the discharge rate of clean water according to the concentration of the brine discharged from the central pipe. When the gas-liquid interface rises, reduce the rising speed by injecting gas. The adjustment principle is as follows: when the concentration of brine is 150~180 g / L, the discharge rate of clean water is 25~30 m³ / h. The discharge rate of fresh water is 30-35 m³ / h when the concentration of brine is 180-200 g / L; 35-40 m³ / h when the concentration of brine is 200-220 g / L; 40-45 m³ / h when the concentration of brine is 220-240 g / L; and 45-50 m³ / h when the concentration of brine is greater than 240 g / L. (6) When the gas-liquid interface rises to the top plate of the bottom tank of the storage tank, gas is continuously injected to make the gas-liquid interface move down continuously, and the brine inside the bottom tank of the storage tank is discharged through the central pipe and the intermediate pipe until the gas-liquid interface is lowered to a position not less than 3m above the lower end of the intermediate pipe. (7) Repeat steps (5) to (6) until the radius of the top plate of the storage tank reaches 5 to 10 m; (8) Continuously inject clean water into the bottom tank of the storage tank from the central pipe and intermediate pipe annulus at a discharge rate of 50~55m³ / h to dissolve the side wall of the bottom tank until the gas-liquid interface rises to the top plate of the bottom tank; then gradually increase the discharge rate of clean water. When the gas-liquid interface rises, reduce the gas-liquid interface to the top plate of the bottom tank by injecting gas until the radius of the top plate of the bottom tank reaches the design value.

2. The method for expanding a salt cavern storage tank as described in claim 1, characterized in that, In the method for expanding the salt cavern storage tank, the distance between the lower end of the intermediate pipe and the lower end of the central pipe is controlled to be no less than 5m.

3. The method for expanding a salt cavern storage tank as described in claim 1, characterized in that, In step (2), the discharge rate of the injected water is adjusted according to the concentration of the brine collected from the bottom tank of the storage tank. If the concentration of the discharged brine is greater than 150 g / L, the discharge rate is increased, but the increased discharge rate is not greater than 20 m³ / h.

4. The method for expanding a salt cavern storage tank as described in claim 1, characterized in that, In step (2), the rising speed is reduced by injecting gas as follows: gas is added every 0.4~0.6m when the gas-liquid interface rises so that the gas-liquid interface falls by 0.1~0.3m.

5. The method for expanding a salt cavern storage tank as described in claim 1, characterized in that, In step (5), the rising speed is reduced by injecting gas as follows: gas is added every 0.4~0.6m when the gas-liquid interface rises so that the gas-liquid interface falls by 0.1~0.3m.

6. The method for expanding a salt cavern storage tank as described in claim 1, characterized in that, In step (8), the method for gradually increasing the injection rate of clean water is as follows: when the concentration of brine discharged from the central pipe is 200~220g / L, the injection rate is 55~60m³ / h; when the concentration of brine discharged from the central pipe is 220~240g / L, the injection rate is 60~65m³ / h; when the concentration of brine discharged from the central pipe is 240~260g / L, the injection rate is 65~70m³ / h; when the concentration of brine discharged from the central pipe is 260~280g / L, the injection rate is 70~75m³ / h; when the concentration of brine discharged from the central pipe is not less than 280g / L, the injection rate is 75~80m³ / h.

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