Salt-cavern gas storage secondary dissolving cavity expansion method

Abstract

The invention discloses a salt cavern gas storage secondary dissolving cavity expansion method which comprises the following steps: step 1, putting a water injection pipe with a one-way valve into a salt cavern, and injecting water into a gas storage through the water injection pipe so as to empty stored reserve gas; 2, a brine discharging well with the lower end communicated with the bottom of the salt cavern is drilled beside the salt cavern; 3, the water injection pipe continues to descend till the lower end of the water injection pipe is close to the bottom wall of the salt cavern; 4, reserve gas is injected into the salt cavern, and brine overflows from the brine discharging well until the liquid level in the salt cavern is close to the upper end of the sediment layer; 5, continuously injecting water into the salt cavern by using the water injection pipe to expand the cavity, and continuously overflowing brine at the bottom of the salt cavern through the brine discharge well; and 6, after cavity expansion at the bottom of the salt cavern is completed, the water injection pipe is taken out or cut off, reserve gas continues to be injected through the borehole of the salt cavern, the liquid level in the salt cavern is pressed downwards to be close to the bottom of the salt cavern till gas injection and brine discharging operation is completed, the cavity expansion effect is good, and the cavity expansion capacity is large.

Description

Technical Field

[0001] The invention belongs to the technical field of salt cavern gas storage, and in particular relates to a method for expanding the secondary dissolution cavity of a salt cavern gas storage reservoir. Background Art

[0002] At present, most salt cavern gas storages are built by water-dissolving cavitation, that is, fresh water is injected into the salt layer thousands of meters deep underground through a wellbore, and then saturated brine is returned to the ground, continuously dissolving a salt cavern with a huge space. Due to the large number of insoluble interlayers and high impurity content in the salt phase deposited in terrestrial lakes, a large amount of insoluble matter is released from the salt layer during the water-dissolving cavitation process and quickly accumulates at the bottom of the cavity to form a sediment layer. The existence of the sediment layer causes the bottom salt layer of the salt cavern to be buried by the sediment before it can fully dissolve, often resulting in a low degree of dissolution of the salt layer at the bottom of the salt cavern, a small diameter at the bottom of the salt cavern, and a small space volume, which seriously affects the volume of the storage space. The current cavity creation theory believes that once the surface of the rock salt is covered with sediment, the sediment will prevent the diffusion and flow of saturated brine on the surface of the rock salt, and the rock salt will no longer continue to dissolve. Therefore, for the lower salt layer buried by sediment in the actual salt cavern, it is generally believed that the cavity cannot continue to expand, and no one has proposed a method for continuing cavity creation. Summary of the invention

[0003] In order to solve the above technical problems, the object of the present invention is to provide a secondary dissolution cavity expansion method for a salt cavern gas storage which is easy to operate and can smoothly expand the bottom of a salt cavern with a sediment layer deposited on the bottom.

[0004] In order to achieve the above-mentioned purpose, the technical solution of the present invention is as follows: A method for expanding the secondary dissolution cavity of a salt cavern gas storage reservoir, which is used to expand the existing salt cavern gas storage reservoir storing stored gas, comprising the following steps:

[0005] Step 1: a water injection pipe with a one-way valve is lowered through the wellbore of the salt cavern, and water is injected into the gas storage reservoir through the water injection pipe until the salt cavern is filled, so as to discharge the reserve gas stored in the salt cavern from the wellbore of the salt cavern;

[0006] Step 2: drilling a brine drainage well next to the salt cavern, wherein the lower end of the brine drainage well is drilled until it is in communication with the bottom of the salt cavern;

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

[0008] Step 4: injecting reserve gas into the salt cavern through the wellbore of the salt cavern, and allowing brine to overflow from the brine drainage well until the liquid level in the salt cavern is pressed down to the upper end close to the sediment layer, then stopping the injection of reserve gas and holding the pressure;

[0009] Step 5: Continue to use the water injection pipe to continuously inject water into the salt cavern to expand the cavity wall covered by the sediment layer at the lower end of the salt cavern, and during the water injection process, the brine at the bottom of the salt cavern continuously overflows through the brine drainage well until the secondary dissolution 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 pressed down to near the bottom of the salt cavern. During the gas injection process, the brine overflows through the brine drainage well until the gas injection and brine drainage operation is completed.

[0011] The lower end of the water injection pipe in step 1 of the above technical solution is provided with a downhole power drilling tool.

[0012] In the process of lowering the water injection pipe in step 3 of the above technical solution, water needs to be injected to drive the downhole power drill to drill in the sediment layer, and during the drilling process, the brine in the salt cavern overflows through the brine drainage well.

[0013] The stored gas in the above technical solution is natural gas, helium, hydrogen or compressed air.

[0014] The brine drainage well described in the above technical solution is a horizontal well or a directional well.

[0015] In the above technical solution, a densitometer for measuring the density of overflowed brine is provided at the open hole section at the bottom of the brine drainage well.

[0016] In step 3 of the above technical solution, a dissolving agent needs to be added into the salt cavern through the wellbore in advance to form a dissolving agent layer on the liquid surface in the salt cavern.

[0017] The dissolution inhibitor in the above technical solution is diesel.

[0018] Compared with the prior art, the beneficial effect of the present invention is that: through this method, the cavity buried by sediment at the bottom of the salt cavern can be dissolved and expanded, thereby significantly increasing the total volume of the salt cavern. In addition, during the expansion process, staggered pores can be formed inside the sediment layer, and 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 THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the initial insertion of the water injection pipe into the salt cavern according to an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of the structure after water injection and exhaust in a salt cavern are completed in an embodiment of the present invention;

[0021] Figure 3 It is a structural schematic diagram of a brine drainage well provided in an embodiment of the present invention;

[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 cavern in an embodiment of the present invention;

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

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

[0025] In the figure: 1 salt cavern, 11 sediment layer, 2 water injection pipe, 21 one-way valve, 22 downhole power drilling tool, 3 rows of brine wells, 31 density meter, 4 dissolution resistance layer, 5 gas injection and production pipe string. DETAILED DESCRIPTION

[0026] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. The present invention is described in more detail by way of example with reference to the accompanying drawings in the following paragraphs. The advantages and features of the present invention will become clearer according to the following description and claims. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0027] like Figure 1-Figure 6 As shown, this embodiment provides a method for expanding the secondary dissolution cavity of a salt cavern gas storage reservoir, which is used to expand the existing salt cavern 1 gas storage reservoir storing stored gas, and includes the following steps:

[0028] Step 1: a water injection pipe 2 with a one-way valve 21 is lowered through the wellbore of the salt cavern 1, and water is injected into the gas storage reservoir through the water injection pipe 2 until the salt cavern 1 is filled, so as to discharge the reserve gas stored in the salt cavern 1 from the wellbore of the salt cavern 1;

[0029] Step 2: drilling a brine drainage well 3 next to the salt cavern 1, wherein the lower end of the brine drainage well 3 is drilled until it is in communication with the bottom of the salt cavern 1;

[0030] Step 3: Continue to lower the water injection pipe 2 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;

[0031] Step 4: injecting reserve gas into the salt cavern 1 through the wellbore of the salt cavern 1, and allowing brine to overflow from the brine drainage well 3, until the liquid level in the salt cavern 1 is pressed down to the upper end close to the sediment layer 11, then stopping injecting reserve gas and holding the pressure;

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

[0033] Step 6: After the bottom expansion of the salt cavern 1 is completed, the water injection pipe 2 is removed or cut off, and the reserve gas is continuously injected through the wellbore of the salt cavern 1, and the liquid level in the salt cavern 1 is pressed down to near the bottom of the salt cavern 1. During the gas injection process, the brine overflows through the brine drainage well 3 until the gas injection and brine drainage operation is completed.

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

[0035] The stored gas is natural gas, helium, hydrogen or compressed air (when compressed air is stored, the salt cavern gas storage reservoir can be used as an energy storage device, that is, compressed air is sent into the salt cavern gas storage reservoir during low-peak electricity consumption, and during peak electricity consumption, the compressed air in the salt cavern gas storage reservoir is discharged and used to generate electricity).

[0036] The brine drainage well 3 in the above technical solution is a horizontal well or a directional well. A densitometer 31 for measuring the density of overflowing brine is provided at the bottom open hole section of the brine drainage well 3 .

[0037] In step 3 of the above technical solution, an anti-dissolving agent needs to be added into the salt cavern 1 through the wellbore in advance to form an anti-dissolving layer 4 on the liquid surface in the salt cavern 1. The anti-dissolving agent is diesel, wherein the anti-dissolving layer floats on the liquid surface of the brine in the salt cavern. When the salt cavern is full of water, the top of the salt cavern is protected by the anti-dissolving layer to prevent the salt cavern from expanding upward.

[0038] This embodiment mainly performs cavity expansion treatment on the area where the sediment layer at the lower end of the salt cavern is located.

[0039] The following is an explanation of the doubt with a specific case:

[0040] Taking a salt cavern gas storage that has been put into production in Jintan City as an example, the wellbore of the gas storage encountered a salt layer with a thickness of 191.2m, and the thickness of the salt layer section used for cavity building was 166m. The initial design of the salt cavern volume of the well was 250,000 cubic meters. According to the calculation of the utilization rate of the salt layer of the normal cavity in Jintan of 1746m3 / m, the salt cavern volume of the well can reach 289,000 cubic meters, while the actual free volume of the salt cavern is only 119,000 cubic meters. The top depth of the well cavity is 1030m, the depth of the sediment surface at the bottom of the cavity is 1080m, and the initial drilling bottom depth is 1149m. According to the analysis of the cavity building history, the bottom dissolution cavity of the salt cavern was poor during the construction period, and the sediment was buried too quickly, resulting in insufficient dissolution of the salt layer at the bottom of the salt cavern, which resulted in the shape of the dissolution cavity at the bottom of the salt cavern being an elongated cylinder with a small volume. Therefore, the well has the conditions for secondary dissolution cavity expansion.

[0041] Step 1: The salt cavern gas storage that has been put into production is initially filled with natural gas. The operating pressure of the well is 7-17MPa, and the maximum gas storage capacity is 20.17 million cubic meters. A production casing is embedded in the wellbore of the well, and an injection and production gas pipe string 5 (which belongs to the existing structure) is embedded in the production casing. Figure 1 As shown, 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 pipe string 5. There is an annular gap between the water injection pipe and the gas injection and production pipe string 5 to facilitate the inflation or exhaust of the salt cavern. The water injection pipe is lowered to a depth of 1080m at the sediment surface, which means that the lower end of the water injection pipe is located at the upper end of the sediment layer. The one-way valve only allows the fluid to flow downward to prevent the natural gas in the well from escaping to the ground along the water injection pipe. Figure 2 As shown, fresh water is then injected into the salt cavern through a water injection pipe to drain the natural gas in the cavern from the top of the salt cavern until the natural gas in the cavern is emptied and filled with brine.

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

[0043] Step 3: If Figure 3As shown, high-pressure fresh water 5 is injected from the water injection pipe 3, and the water injection pipe is lowered at the same time to drive the downhole power drill carried by the water injection pipe 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 drainage well. In order to protect the salt layer at the production casing shoe from being dissolved, a small amount of dissolving agent (diesel) needs to be injected into the salt cavern from the annular gap between the injection and production gas pipe string and the water injection pipe before drilling. The dissolving agent floats on the brine liquid surface to protect the cavity top of the salt cavern from being dissolved by the injected fresh water 5.

[0044] Step 4: Figure 4 As shown, since the shape of the upper part of the upper salt cavern is already an arch with good stability, in order to protect the upper cavity from being corroded, it is necessary to lower the liquid level in the salt cavern by injecting gas to discharge brine. At this time, natural gas is reinjected into the salt cavern to squeeze out a part of the brine well and the brine discharge well in the salt cavern, so that the brine liquid level in the salt cavern can just cover the upper end surface of the sludge layer (since the upper part of the sludge layer in the salt cavern is protected by natural gas, the salt cavern located on the upper part of the sludge layer will not be corroded again during the subsequent water injection process).

[0045] Step 5: Figure 5 As shown, fresh water is continuously injected into the salt cavern from the water injection pipe. Due to the low density of fresh water, after entering the salt cavern, it is affected by the buoyancy of the saturated brine and first flows upward. Then it contacts the salt layer buried by the sediment and dissolves the salt wall of the salt cavern. The formed saturated brine then flows downward along the salt wall to the bottom of the salt cavern and is discharged from the brine discharge well. In this way, the cavity wall of the lower end of the salt cavern corresponding to the sediment layer expands and dissolves to both sides, the cavity volume at the bottom of the salt cavern increases continuously, and the sediment surface sinks to a certain extent.

[0046] Step 6: Figure 6 As shown in the figure, after the secondary dissolution and expansion is completed, the water injection pipe penetrates into the sediment layer, is squeezed or even deformed by the sediment, and cannot or is difficult to be lifted out of the salt cavern. At this time, the water injection pipe can be cut off by hydraulic cutting. The cut water injection pipe is left in the salt cavern (without any use), and then the salt cavern is continued to be injected with gas to discharge brine. 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 secondary dissolution, expansion and aeration operation in the salt cavern is completed.

[0047] Through dissolution expansion and utilization 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] in, Figure 1 , Figure 4 and Figure 6 The upper filling area in the medium salt cavern represents the reserve gas. Figure 2 The filled areas within the salt caverns represent brine, Figure 3 The filling area between the middle resistance layer and the sediment layer represents brine. Figure 5 The topmost filling area in the middle salt cavern represents the reserve gas, while the middle filling area represents the brine. Figure 1-Figure 6 The filling area at the lower end of the medium salt cavern represents the sediment layer.

[0049] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for expanding the secondary dissolution cavity of a salt cavern gas storage reservoir, which is used to expand the existing salt cavern (1) gas storage reservoir storing stored gas, characterized in that: The steps include: Step 1: A water injection pipe (2) with a one-way valve (21) is lowered through the wellbore of the salt cavern (1), and water is injected into the gas storage reservoir through the water injection pipe (2) until the salt cavern (1) is filled, so as to discharge the reserve gas stored in the salt cavern (1) from the wellbore of the salt cavern (1); Step 2: drilling a brine drainage well (3) next to the salt cavern (1), wherein the lower end of the brine drainage well (3) is drilled until it is in communication with the bottom of the salt cavern (1); Step 3: Continue to lower the water injection pipe (2) 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: injecting reserve gas into the salt cavern (1) through the wellbore of the salt cavern (1), and allowing brine to overflow from the brine drainage well (3), until the liquid level in the salt cavern (1) is pressed down to near the upper end of the sediment layer (11), and then stopping the injection of reserve gas and holding the pressure; Step 5: Continue to use the water injection pipe (2) to continuously inject water into the salt cavern (1) to expand the cavity wall of the lower end of the salt cavern (1) covered by the sediment layer (11), and during the water injection process, the brine at the bottom of the salt cavern (1) continuously overflows through the brine drainage well (3) until the secondary dissolution cavity expansion operation of the salt cavern is completed; 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 reserve gas is continuously injected through the wellbore of the salt cavern (1), and the liquid level in the salt cavern (1) is pressed down to near the bottom of the salt cavern (1). During the gas injection process, the brine overflows through the brine drainage well (3) until the gas injection and brine drainage operation is completed.

2. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 1, characterized in that: The lower end of the water injection pipe (2) in step 1 is provided with a downhole power drilling tool (22).

3. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 2, characterized in that: In the step 3, water needs to be injected during the lowering of the water injection pipe (2) to drive the downhole power drilling tool (22) to drill in the sediment layer (11), and during the drilling process, the brine in the salt cavern (1) overflows through the brine drainage well (3).

4. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 1, characterized in that: The reserve gas is natural gas, helium, hydrogen or compressed air.

5. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 1, characterized in that: The brine drainage well (3) is a horizontal well or a directional well.

6. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 1, characterized in that: A densitometer (31) for measuring the density of overflowing brine is provided at the open hole section at the bottom of the brine drainage well (3).

7. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 1, characterized in that: In the step 3, a dissolving agent needs to be added into the salt cavern (1) through the wellbore in advance to form a dissolving agent layer (4) on the liquid surface in the salt cavern (1).

8. The method for expanding the secondary dissolution cavity of a salt cavern gas storage according to claim 7, characterized in that: The dissolution inhibitor is diesel.

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