A method for expanding the secondary solution cavity of a salt cavern gas storage

Abstract

The application discloses a secondary solution cavity expansion method for a salt cavern gas storage, which comprises the following steps: step 1, a water injection pipe with a one-way valve is lowered into the salt cavern, water is injected into the gas storage through the water injection pipe, and the stored reserve gas is emptied; step 2, a brine discharge well is drilled beside the salt cavern, and the lower end of the brine discharge well is communicated with the bottom of the salt cavern; step 3, the water injection pipe is continuously lowered to the lower end close to the bottom wall of the salt cavern; step 4, the reserve gas is injected into the salt cavern, and the brine overflows from the brine discharge well until the liquid level in the salt cavern is close to the upper end of the sediment layer; step 5, the water injection pipe is continuously used to continuously inject water into the salt cavern to expand the cavity, and the brine at the bottom of the salt cavern continuously overflows from the brine discharge well; and step 6, after the expansion of the cavity at the bottom of the salt cavern is completed, the water injection pipe is taken out or cut off, the reserve gas is continuously injected through the well hole of the salt cavern, and the liquid level in the salt cavern is lowered to be close to the bottom of the salt cavern until the gas injection and brine discharge operation is completed, so that the expansion effect is good, and the expansion capacity is large.

Description

Technical Field

[0001] This invention belongs to the field of salt cavern gas storage technology, and particularly relates to a method for secondary expansion of the dissolved cavity in a salt cavern gas storage facility. Background Technology

[0002] Currently, most salt cavern gas storage facilities are constructed using a water-soluble cavity-building method. This involves injecting fresh water into salt layers thousands of meters underground through a well, then returning saturated brine to the surface, continuously dissolving and creating a large salt cavern. However, due to the high number of insoluble interlayers and impurity content in terrestrial lacustrine salt deposits, a large amount of insoluble matter is released from the salt layer during the water-soluble cavity-building process and quickly accumulates at the bottom of the cavity, forming a sediment layer. The presence of this sediment layer means that the bottom salt layer of the cavern is buried before it can be fully dissolved, often resulting in low dissolution of the bottom salt layer, a small bottom diameter, and a small volume, severely impacting the storage space. Current cavity-building theories suggest that once the rock salt surface is covered by sediment, the sediment will prevent the diffusion and flow of saturated brine, and the rock salt will no longer dissolve. Therefore, it is generally believed that the lower salt layer buried by sediment in actual salt caverns cannot be further expanded, and no method for continued cavity-building has been proposed. Summary of the Invention

[0003] In order to solve the above-mentioned technical problems, the purpose of this invention is to provide a method for secondary cavity expansion of a salt cavern gas storage tank that is easy to operate and can smoothly expand the cavity at the bottom of a salt cavern with a sediment layer deposited at the bottom.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: a method for secondary expansion of a salt cavern gas storage facility, used to expand an existing salt cavern gas storage facility containing reserve gas, comprising the following steps:

[0005] Step 1: A water injection pipe with a one-way valve is lowered into the wellbore of the salt cavern. Water is injected into the gas storage tank through the water injection pipe until the salt cavern is full, so that the stored gas stored in the salt cavern is vented from the wellbore of the salt cavern.

[0006] Step 2: Drill a brine drain well next to the salt cavern, with the lower end of the brine drain well connected to the bottom of the salt cavern;

[0007] Step 3: Continue lowering the water injection pipe into the sediment layer at the bottom of the salt cave until the lower end of the water injection pipe is close to the bottom wall of the salt cave.

[0008] Step 4: Inject reserve gas into the salt cavern through the wellbore and let brine overflow from the brine discharge well until the liquid level in the salt cavern is pushed down to near the upper end of the sediment layer. Then stop injecting reserve gas and pressurize.

[0009] Step 5: continue to inject water into the salt cavern through the water injection pipe to expand the cavity of the cavity wall covered by the sediment layer at the lower end of the salt cavern, and the brine at the bottom of the salt cavern continuously overflows through the brine discharge well during the water injection process until the secondary cavity expansion operation of the salt cavern is completed;

[0010] Step 6: after the expansion of the bottom of the salt cavern is completed, the water injection pipe is removed or cut off, and the reserve gas is continuously injected through the wellbore of the salt cavern, and the liquid level in the salt cavern is lowered to the bottom of the salt cavern, and during the gas injection process, the brine overflows through the brine discharge well until the gas injection and brine discharge operation is completed.

[0011] In the above technical solution, the lower end of the water injection pipe in step 1 is provided with a downhole power drill.

[0012] In the above technical solution, the water injection pipe needs to be injected during the downhole process to drive the downhole power drill to drill in the sediment layer, and the brine in the salt cavern overflows through the brine discharge well during the drilling process.

[0013] In the above technical solution, the reserve gas is natural gas, helium, hydrogen or compressed air.

[0014] In the above technical solution, the brine discharge well is a horizontal well or a directional well.

[0015] In the above technical solution, a densimeter is arranged at the position of the open hole section at the bottom of the brine discharge well to measure the density of the overflowing brine.

[0016] In the above technical solution, the step 3 needs to add a dissolution inhibitor into the salt cavern through the wellbore in advance to form a dissolution layer on the liquid level in the salt cavern.

[0017] In the above technical solution, the dissolution inhibitor is diesel oil.

[0018] Compared with the prior art, the beneficial effects of the present application are that: by this way, the cavity covered by the sediment at the bottom of the salt cavern can be dissolved and expanded, so that the total volume of the salt cavern is significantly increased, and in the expansion process, the interlaced pores can be formed in the sediment layer, and the reserve gas can also be stored in the pores, so that the total gas storage space of the salt cavern is larger and the utilization rate is higher. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structure schematic view of the initial insertion of the water injection pipe in the salt cavern in the embodiment of the present application;

[0020] Figure 2 It is a structure schematic view of the completion of the water injection and gas discharge in the salt cavern in the embodiment of the present application;

[0021] Figure 3 It is a structure schematic view when the brine discharge well is arranged in the embodiment of the present application;

[0022] Figure 4 This is a schematic diagram of the structure when the water injection pipe is drilled down to the bottom of the salt cave in an embodiment of the present invention;

[0023] Figure 5 This is a schematic diagram of the structure of the salt cavern after expansion at the bottom in an embodiment of the present invention;

[0024] Figure 6 This is a schematic diagram of the structure after the bottom cavity of the salt cave is expanded and filled with reserve gas in an embodiment of the present invention.

[0025] In the diagram: 1. Salt cavern, 11. Sediment layer, 2. Water injection pipe, 21. Check valve, 22. Downhole power drill string, 3. Brine well, 31. Densitometer, 4. Dissolution barrier layer, 5. Gas injection and production tubing string. Detailed Implementation

[0026] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0027] like Figures 1-6 As shown, this embodiment provides a method for secondary expansion of a salt cavern gas storage facility, which is used to expand the capacity of an existing salt cavern 1 gas storage facility containing reserve gas. The method includes the following steps:

[0028] Step 1: A water injection pipe 2 with a one-way valve 21 is lowered into the wellbore of the salt cavern 1. Water is injected into the gas storage tank through the water injection pipe 2 until the salt cavern 1 is full, so that the stored gas stored in the salt cavern 1 is vented from the wellbore of the salt cavern 1.

[0029] Step 2: Drill a brine drainage well 3 next to the salt cave 1, with the lower end of the brine drainage well 3 being drilled to communicate with the bottom of the salt cave 1;

[0030] Step 3: Continue to lower the water injection pipe 2 into the sediment layer 11 at the bottom of the salt cave 1 until the lower end of the water injection pipe 2 is close to the bottom wall of the salt cave 1;

[0031] Step 4: Inject reserve gas into the salt cavern 1 through the wellbore of the salt cavern 1, and let brine overflow from the brine discharge well 3 until the liquid level in the salt cavern 1 is pushed down to the upper end near the sediment layer 11, then stop injecting reserve gas and pressurize.

[0032] Step 5: continue to inject water into the salt cavern 1 through the water injection pipe 2 to expand the cavity wall of the lower end of the salt cavern 1 covered by the sediment layer 11, and the brine at the bottom of the salt cavern 1 continuously overflows through the brine discharge well 3 during the water injection process until the secondary solution cavity expansion operation of the salt cavern is completed;

[0033] Step 6: after the expansion of the bottom of the salt cavern 1 is completed, the water injection pipe 2 is removed or cut off, and the reserved gas is continuously injected through the wellbore of the salt cavern 1, and the liquid level in the salt cavern 1 is lowered to the bottom of the salt cavern 1, and during the gas injection process, the brine overflows through the brine discharge well 3 until the gas injection and brine discharge operation is completed.

[0034] In the step 1, the lower end of the water injection pipe 2 is provided with a downhole power drill 22, and in the step 3, water needs to be injected to drive the downhole power drill 22 to drill in the sediment layer 11 during the lowering process of the water injection pipe 2, and the brine in the salt cavern 1 overflows through the brine discharge well 3 during the drilling process.

[0035] In the step 1, the lower end of the water injection pipe 2 is provided with a downhole power drill 22, and in the step 3, water needs to be injected to drive the downhole power drill 22 to drill in the sediment layer 11 during the lowering process of the water injection pipe 2, and the brine in the salt cavern 1 overflows through the brine discharge well 3 during the drilling process.

[0036] In the step 1, the lower end of the water injection pipe 2 is provided with a downhole power drill 22, and in the step 3, water needs to be injected to drive the downhole power drill 22 to drill in the sediment layer 11 during the lowering process of the water injection pipe 2, and the brine in the salt cavern 1 overflows through the brine discharge well 3 during the drilling process.

[0037] In the step 3, a solution-resistant layer 4 is formed on the liquid surface in the salt cavern 1 by pre-injecting a solution-resistant agent through the wellbore into the salt cavern 1, and the solution-resistant agent is diesel oil, wherein the solution-resistant layer floats on the liquid surface of the brine in the salt cavern, and when the salt cavern is full of water, the salt cavern top is protected to avoid upward expansion of the salt cavern.

[0038] The embodiment mainly expands the cavity of the area where the sediment layer at the lower end of the salt cavern is located.

[0039] The following specific cases are used to explain the doubts:

[0040] Take a certain salt cavern gas storage in Jintan City as an example, the wellbore drilled through salt layer thickness of 191.2 m, the salt layer thickness for cavity making is 166 m, the initial design of the salt cavern volume is 250,000 m3, according to the normal cavity salt layer utilization rate of Jintan 1746 m3 / m, the salt cavern volume can reach 289,000 m3, and the actual salt cavern free volume is only 119,000 m3. The cavity top depth of the well is 1030 m, the cavity bottom sediment depth is 1080 m, and the initial drilling bottom hole depth is 1149 m. According to the analysis of the cavity making history, the bottom of the salt cavern is not fully dissolved during the slotting period, which leads to the shape of the bottom of the salt cavern being an elongated cylinder with a small volume. Therefore, the well has the condition of secondary cavity expansion.

[0041] Step 1: The salt cavern gas storage has been put into production, and initially it is filled with natural gas. The well operating pressure is 7-17 MPa, and the maximum gas storage capacity is 201.7 million m3. The wellbore is embedded with a production casing, and the production casing is embedded with a gas injection and production string 5 (which belongs to the existing structure), as shown in Figure 1 First, a water injection pipe with a downhole power drill and a one-way valve is lowered from the inner hole of the gas injection and production string 5. The water injection pipe and the gas injection and production string 5 have an annular gap to facilitate gas charging or gas discharge of the salt cavern. The water injection pipe is lowered to a depth of 1080 m at the sediment surface position, i.e. the lower end of the water injection pipe is located at the upper end of the sediment layer. The one-way valve only allows fluid to flow downward to prevent natural gas in the well from flowing out to the ground along the water injection pipe, as shown in Figure 2 Then, fresh water is injected into the cavity of the salt cavern through the water injection pipe, and the natural gas in the cavity is discharged from the top of the salt cavern until the natural gas in the cavity is exhausted and is filled with brine.

[0042] Step 2: As shown in Figure 3 A brine discharge well (which can be a horizontal well) is drilled on the side of the salt cavern gas storage to the lowest part of the salt cavern, which can be the bottom of the salt cavern gas storage, at a depth of 1149 m and a position determined according to the initial drilling trajectory of the salt cavern. The brine discharge well is used as a brine discharge well, and a densimeter is lowered in the brine discharge well to measure the density of the overflow brine in the salt cavern gas storage (to determine whether the brine is saturated and whether natural gas is mixed into the brine, the saturated brine range is about 1.1-1.2 g / mL. If the detected brine density is lower than the value, the brine is in an unsaturated state, and the water injection and brine discharge speed can be appropriately reduced).

[0043] Step 3: As shown in Figure 3As shown, high-pressure fresh water 5 is injected from the injection pipe 3, and the injection pipe is lowered at the same time. The downhole power drill carried by the injection pipe is driven to drill into the bottom of the sediment layer. The drilling depth is as low as possible, close to the bottom of the salt cavern at 1149m. At this time, the brine in the salt cavern is discharged from the brine discharge well. In order to protect the salt layer at the production casing shoe from being dissolved, a small amount of anti-dissolution agent (diesel oil) is injected into the salt cavern from the annular gap between the injection and production gas pipe column and the injection pipe before drilling. The anti-dissolution agent floats on the brine surface to protect the top of the salt cavern from being dissolved by the injected fresh water 5.

[0044] Step 4: as shown in Figure 4 , since the upper part of the upper salt cavern has a stable arch shape, in order to protect the upper cavity from being dissolved, it is necessary to reduce the liquid level in the salt cavern by injecting gas to discharge brine. At this time, natural gas is injected back into the salt cavern to squeeze out a part of the brine in the salt cavern well, so that the brine level in the salt cavern just covers the upper end surface of the sediment layer (since the upper part of the sediment layer in the salt cavern is protected by natural gas, the upper part of the sediment layer in the salt cavern will not be dissolved in the subsequent water injection process).

[0045] Step 5: as shown in Figure 5 , continue to inject fresh water into the salt cavern from the injection pipe. Since the density of fresh water is low, it will first flow upward after entering the salt cavern due to the buoyancy of the saturated brine. Then it contacts the salt layer buried in the sediment and dissolves the salt wall of the salt cavern. The saturated brine formed then flows down the salt wall to the bottom of the salt cavern and is discharged from the brine discharge well. This causes the cavity wall of the lower end of the salt cavern corresponding to the sediment layer area to expand on both sides, and the cavity volume at the bottom of the salt cavern increases, causing the sediment surface to sink to some extent.

[0046] Step 6: as shown in Figure 6 , after the second dissolution and expansion are completed, since the injection pipe is deep into the sediment layer and is squeezed or even deformed, it cannot or is difficult to be pulled out to the outside of the salt cavern. At this time, the injection pipe can be cut off by hydraulic cutting. The cut-off injection pipe remains in the salt cavern (without any purpose), and then the gas injection and brine discharge operation continues in the salt cavern. The brine in the salt cavern is discharged through the brine discharge well until the liquid level in the salt cavern drops to a lower position at the bottom of the salt cavern. At this time, the brine discharge well can be closed, and the entire second dissolution and expansion and gas injection operation in the salt cavern is completed.

[0047] Through dissolution and expansion and the use of sediment voids, the effective gas storage volume of the salt cavern can be increased from the current 119,000 cubic meters to 318,000 cubic meters.

[0048] Among them, Figure 1 , Figure 4 and Figure 6 The filling area of the upper layer in the salt cavern represents the reserve gas, Figure 2 The filling area in the salt cavern represents brine, Figure 3 The filling area between the anti-dissolution layer and the sediment layer represents brine,Figure 5 The filling area at the upper end of the middle salt cavern represents reserve gas, and the filling area in the middle represents brine, Figures 1-6 The filling area at the lower end of the middle salt cavern represents a sediment layer.

[0049] The above description is only the preferred embodiment of the present application, and does not limit the present application in any form; any person skilled in the art can easily implement the present application according to the drawings and the above description; however, any slight changes, modifications and equivalent changes made by those skilled in the art within the scope of the technical solutions of the present application, using the above disclosed technical content, are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above embodiments according to the essence of the present application are still within the protection scope of the technical solutions of the present application.

Claims

1. A method for expanding the capacity of a secondary solution cavity of a salt cavern gas storage, which is used to expand the capacity of an existing salt cavern (1) gas storage storing reserve gas, characterized in that, It comprises the following steps: Step 1: a water injection pipe (2) with a one-way valve (21) is lowered into the wellbore of the salt cavern (1), water is injected into the gas storage through the water injection pipe (2) until the salt cavern (1) is filled with water, so as to empty the reserve gas stored in the salt cavern (1) from the wellbore of the salt cavern (1); Step 2: a brine discharge well (3) is drilled next to the salt cavern (1), the lower end of the brine discharge well (3) is drilled to communicate with the bottom of the salt cavern (1); Step 3: the water injection pipe (2) is further lowered into the sediment layer (11) at the bottom of the salt cavern (1) until the lower end of the water injection pipe (2) is close to the bottom wall of the salt cavern (1); Step 4: reserve gas is injected into the salt cavern (1) through the wellbore of the salt cavern (1), and brine overflows from the brine discharge well (3) until the liquid level in the salt cavern (1) is lowered to the upper end of the sediment layer (11), then the injection of reserve gas is stopped and the pressure is built up; Step 5: continue to inject water into the salt cavern (1) using the water injection pipe (2) to expand the cavity wall covered by the sediment layer (11) at the lower end of the salt cavern (1), and the brine at the bottom of the salt cavern (1) continuously overflows from the brine discharge well (3) during the water injection process until the secondary dissolution and cavity expansion operation of the salt cavern is completed; Step 6: after the expansion of the cavity at the bottom of the salt cavern (1) is completed, the water injection pipe (2) is removed or cut off, and reserve gas is continuously injected through the wellbore of the salt cavern (1) until the liquid level in the salt cavern (1) is lowered to the bottom of the salt cavern (1), and the brine overflows from the brine discharge well (3) during the gas injection process until the gas injection and brine discharge operation is completed.

2. The method according to claim 1, wherein, The lower end of the water injection pipe (2) in step 1 is provided with a downhole power drill (22).

3. The method according to claim 2, wherein, In step 3, water needs to be injected to drive the downhole power drill (22) to drill in the sediment layer (11) during the lowering process of the water injection pipe (2), and the brine in the salt cavern (1) overflows from the brine discharge well (3) during the drilling process.

4. The method of claim 1, wherein, The reserve gas is natural gas, helium, hydrogen or compressed air.

5. The method of claim 1, wherein, The brine discharge well (3) is a horizontal well or a directional well.

6. The method of claim 1, wherein, A densimeter (31) is arranged at the position of the open hole section at the bottom of the brine discharge well (3) to measure the density of the overflowing brine.

7. The method according to claim 1, wherein, In step 3, a dissolution inhibitor needs to be added into the salt cavern (1) through the wellbore in advance to form a dissolution inhibitor layer (4) on the liquid surface in the salt cavern (1).

8. The method according to claim 7, wherein, The dissolution inhibitor is diesel oil.

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