Fish bone type horizontal salt cavern cavity group as well as construction method and application thereof

Abstract

The invention provides a fishbone-shaped horizontal salt cavern cavity group and a construction method and application thereof, and the construction method comprises the following steps: step 1, drilling a main vertical well to a target salt rock layer section, and expanding the lower end of the main vertical well; 2, a horizontal well is drilled beside the main vertical well, the horizontal well is the main horizontal well, and the drilling direction of the horizontal section of the main horizontal well faces the main vertical well till the horizontal section of the main horizontal well is communicated with a cavity at the lower end of the main vertical well; 3, cavity expansion is conducted on the horizontal section of the main horizontal well, and a main horizontal cavity is obtained; 4, a plurality of horizontal wells distributed in the length direction of the main horizontal cavity at intervals are drilled in the two sides of the main horizontal cavity respectively, the horizontal wells on the two sides of the main horizontal cavity are branch horizontal wells, and the drilling directions of horizontal sections of the branch horizontal wells face the main horizontal cavity till the horizontal sections are communicated with the main horizontal cavity; and 5, the horizontal section wells of the multiple branch horizontal wells are subjected to cavity expansion, branch horizontal cavities are obtained, in this way, the cavity size of the gas storage can be effectively increased, and the storage building cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of salt cavern gas storage, and in particular relates to a herringbone-shaped horizontal salt cavern group and a construction method and application thereof. Background Art

[0002] For layered salt rock salt mines with poor geological conditions, the thickness of the layer section suitable for cavity making is relatively thin; and the salt rock grade that can be used for cavity making is low, and it also contains a large number of interlayers, which limits the volume of the salt cavity and greatly increases the difficulty of cavity making and reservoir construction. At present, most underground salt cavern gas storages use a single-well and single-cavity water-soluble method to make cavities. Traditional single-well cavity making has high requirements on the site selection of the gas storage area. The volume of the cavity built in the thin salt layer section is small, and the cavity making speed is slow. It is difficult to adapt to the rapid development of domestic underground gas storage. Therefore, it is urgent to find new cavity making methods that are suitable for domestic layered salt layer construction and to increase the cavity making speed. Summary of the invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a method for constructing a strong group of herringbone-shaped horizontal salt caverns. The underground salt cavern cavity group constructed by the method is herringbone-shaped, which can be constructed under the geological conditions of layered salt rock salt mines, and the cavity construction speed is fast.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows: a method for constructing a herringbone-shaped horizontal salt cavern group, comprising the following steps:

[0005] Step 1: Drill a main vertical well to the target salt rock layer, and expand the lower end of the main vertical well;

[0006] Step 2: drilling a horizontal well next to the main vertical well, the horizontal well being the main horizontal well, the main horizontal well being L-shaped, having a vertical section and a horizontal section, and the drilling direction of the horizontal section of the main horizontal well is toward the main vertical well until it is communicated with the chamber at the lower end of the main vertical well;

[0007] Step 3: expanding the horizontal section of the main horizontal well to obtain a main horizontal cavity;

[0008] Step 4: drilling a plurality of horizontal wells spaced apart along the length direction of the main horizontal cavity on both sides of the main horizontal cavity, wherein the plurality of horizontal wells on both sides of the main horizontal cavity are all branch horizontal wells, and the branch horizontal wells are L-shaped, and have a vertical section and a horizontal section, and the drilling direction of the horizontal section of the branch horizontal well is toward the main horizontal cavity until it is connected with the main horizontal cavity;

[0009] Step 5: Expand the horizontal sections of the plurality of branch horizontal wells to obtain branch horizontal cavities, and complete the construction of the herringbone-shaped horizontal salt cavern group.

[0010] The method for expanding the cavity at the lower end of the main vertical well in step 1 of the above technical solution is to use positive circulation to build a groove, open the cavity bottom, and form a dissolution cavity.

[0011] In the above technical solution, the cavity expansion method of the horizontal section of the main horizontal well in step 3 and the cavity expansion method of the horizontal section of the branch horizontal well in step 5 both adopt the backward cavity making method.

[0012] The specific steps of the backward cavitation method described in the above technical scheme are as follows: horizontal segmented cavitation is carried out from the vicinity of the vertical section of the horizontal well to the horizontal section, and in each cavitation process, fresh water or fresh brine is injected into the horizontal well to expand the volume of the cavity, and a dissolving agent is injected into the horizontal well to limit the dissolution of the cavity; after each section of the cavity is cavitated to the shape and volume that meet the standards, the cavitation string in the horizontal well is retreated to enter the next cavitation process until the entire cavitation process of the horizontal section is completed.

[0013] In the above technical solution, the number of branch horizontal wells on both sides of the main horizontal cavity is the same.

[0014] In the above technical solution, the branch horizontal wells on both sides of the main horizontal cavity are arranged correspondingly, and the horizontal sections of the two corresponding branch horizontal wells are aligned with each other.

[0015] In the above technical solution, the horizontal section of each branch horizontal well is perpendicular to the horizontal section of the main horizontal well.

[0016] The number of branch horizontal wells described in the above technical solution is no less than 4.

[0017] The second object of the present invention is to provide a herringbone-shaped horizontal salt cavern group constructed by the above-mentioned construction method.

[0018] In order to achieve the above object, another technical solution of the present invention is as follows: a herringbone-shaped horizontal salt cavern group is constructed by the construction method as described above.

[0019] The third object of the present invention is to provide a herringbone-shaped horizontal salt cavern group constructed by the above-mentioned construction method.

[0020] In order to achieve the above object, another technical solution of the present invention is as follows: an application of the herringbone type horizontal salt caverns as described above, wherein the herringbone type horizontal salt caverns can be used to store gas.

[0021] Compared with the prior art, the beneficial effect of the present invention is that when the herringbone-shaped horizontal salt cavern cavity group constructed by the embodiment of the present invention is used as a gas storage, it can effectively increase the cavity volume of the gas storage, reduce the cost of building a storage, improve the economic efficiency of building a storage, and can effectively increase the cavity building speed, which is conducive to accelerating the construction progress of the underground salt cavern gas storage. At the same time, it can reduce the strict screening requirements for the construction of the salt cavern gas storage, and is particularly suitable for the construction of gas storage in the layered salt rock salt mine area. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a main vertical well and a main horizontal well being connected and expanded to form a main horizontal cavity in an embodiment of the present invention;

[0023] Figure 2 It is a schematic diagram of the structure of a horizontal well in an embodiment of the present invention;

[0024] Figure 3 It is a structural schematic diagram of a main horizontal cavity and two branch horizontal wells that are connected and expanded to form a branch horizontal cavity in an embodiment of the present invention;

[0025] Figure 4 This is a top view of the herringbone-shaped horizontal salt cavern group described in an embodiment of the present invention.

[0026] In the figure: 1 main vertical well, 2 horizontal well, 2a main horizontal well, 2b branch horizontal well, 31 main horizontal cavity, 32 branch horizontal cavity. DETAILED DESCRIPTION

[0027] 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.

[0028] like Figure 1-Figure 4 As shown, an embodiment of the present invention provides a method for constructing a herringbone-shaped horizontal salt cavern group, comprising the following steps:

[0029] Step 1: Drill a main vertical well 1 to the target salt rock layer, and expand the lower end of the main vertical well 1;

[0030] Step 2: Drill a horizontal well 2 next to the main vertical well 1, the horizontal well 2 is a main horizontal well 2a, the main horizontal well 2a is L-shaped, and has a vertical section and a horizontal section, and the drilling direction of the horizontal section of the main horizontal well 2a is toward the main vertical well 1 until it is connected with the chamber at the lower end of the main vertical well 1;

[0031] Step 3: Expand the horizontal section of the main horizontal well 2a to obtain a main horizontal cavity 31;

[0032] Step 4: Drill multiple horizontal wells 2 on both sides of the main horizontal cavity 31 and spaced apart along the length direction of the main horizontal cavity 31. The multiple horizontal wells 2 on both sides of the main horizontal cavity 31 are all branch horizontal wells 2b. The branch horizontal wells 2b are L-shaped and have a vertical section and a horizontal section. The drilling direction of the horizontal section of the branch horizontal well 2b is toward the main horizontal cavity 31 until it is connected with the main horizontal cavity 31.

[0033] Step 5: Expand the horizontal sections of the plurality of branch horizontal wells 2b to obtain branch horizontal cavities 32, and complete the construction of the herringbone-shaped horizontal salt cavern group.

[0034] Among them, the method for expanding the lower end of the main vertical well 1 in step 1 is to use positive circulation to build a groove, open the cavity bottom, and form a dissolution cavity.

[0035] Among them, the cavity expansion method of the horizontal section of the main horizontal well 2a in step 3 and the cavity expansion method of the horizontal section of the branch horizontal well 2b in step 5 both adopt a backward cavity making method, wherein the specific steps of the backward cavity making method are as follows: horizontal segmented cavity making is carried out from the vicinity of the vertical section of the horizontal well 2 to the horizontal section, and in each cavity making process, fresh water or fresh brine is injected into the horizontal well 2 to expand the cavity volume, and a dissolving agent (which can be diesel, which floats on the liquid surface of the brine to form an oil film or oil layer) is injected into the horizontal well 2 to limit the dissolution of the cavity; after each cavity is made to meet the shape and volume requirements, the cavity making tubing in the horizontal well 2 is retreated to enter the next cavity making process until the entire cavity making process is completed in all horizontal sections.

[0036] Among them, the number of branch horizontal wells 2b on both sides of the main horizontal cavity 31 is consistent, and the branch horizontal wells 2b on both sides of the main horizontal cavity 31 are correspondingly arranged, and the horizontal sections of the corresponding two branch horizontal wells 2b are aligned with each other, and the horizontal section of each branch horizontal well 2b is perpendicular to the horizontal section of the main horizontal well 2a, and the number of branch horizontal wells 2b is not less than 4.

[0037] The herringbone-shaped horizontal salt caverns can be used to store gas, and the stored gas can be natural gas, helium, hydrogen or compressed air (when compressed air is stored, the herringbone-shaped horizontal salt caverns can be used as an energy storage device, that is, when electricity consumption is low, excess electric energy is used to do work to deliver compressed air into the herringbone-shaped horizontal salt caverns, and when electricity consumption is high, the compressed air in the herringbone-shaped horizontal salt caverns is discharged and the compressed air is used to generate electricity).

[0038] in, Figure 1 , Figure 3and Figure 4 In the figure, the horizontal section distribution direction of the main horizontal well is the front-to-back direction, while the horizontal section distribution direction of the branch horizontal well is the left-to-right direction.

[0039] The main horizontal cavity is formed by expanding the horizontal section of the main branch well, and the branch horizontal cavity is formed by expanding the horizontal section of the branch horizontal well.

[0040] Of course, the number of branch horizontal wells on both sides of the main horizontal cavity may be inconsistent, and may not be aligned with each other, and may be adjusted specifically according to the structural characteristics of the underground salt layer.

[0041] The following is an analysis of the construction method of the herringbone-shaped horizontal salt cavern group described in the embodiment of the present invention by taking an actual gas storage construction case as an example.

[0042] The target layer for the cavern construction of the Huai'an salt cavern gas storage is the upper salt sub-member of the fourth member of the Paleogene Fuling Formation. The salt layer is stably distributed in layers, with the burial depth and thickness gradually increasing from northeast to southwest. The top boundary is buried at a depth of 1000-2500m and the average thickness is 123.9m. A set of thick interlayers of about 10m is developed under a salt layer in the cavern construction section on the west side of the reservoir area. A salt layer with a thickness of about 20m is developed under the thick interlayer. The salt rock has a good grade and a low content of insoluble matter. It is generally developed within the reservoir area. The salt layer is selected and the construction method of the fishbone-type horizontal cavern salt cavern group is used to simulate the cavern construction. The specific implementation steps are as follows:

[0043] (1) Drill a vertical well (main vertical well) to the pure salt layer section, build a groove in a positive circulation to form a dissolution cavity, and then drill a horizontal well (main horizontal well) to connect with the vertical well. The main vertical well and the main horizontal well form a horizontal docking well group. The horizontal section depth of the main horizontal well is 1-2m above the bottom boundary of the salt layer. The length of the horizontal section of the main horizontal well can reach 300-500m. In this embodiment, 300m is selected.

[0044] (2) A multi-step backward cavity making method is used to inject water into the main horizontal well and drain brine from the main vertical well. The cavity making process is divided into 6 steps, each step is 50m long. During each cavity making process, a blocking agent needs to be injected into the well to below the casing shoe to control the dissolution. After reaching the designed time and cavity volume of the step, the cavity making string in the main horizontal well is withdrawn by withdrawing the pipe, perforating or cutting the pipe to enter the next cavity making process. When dissolving and cavitating in one step, the cavitating pipe mouth needs to keep 10-20m salt rock as a horizontal safety distance from the main horizontal well casing shoe to prevent the casing shoe of the main horizontal well from being damaged by dissolution. Among them, the design time of water injection cavitation for horizontal multi-step cavitation is 280 days, of which the first five steps of cavitation time are 50 days, and the last step design time is 30 days. The height and width of the main horizontal cavity obtained are about 20 meters, the length is 300 meters, the volume of a single cavity is about 100,000 cubic meters, and the water injection rate range is generally 0-300m 3 / h, here select 120m 3 / h. During the cavity construction process, five string adjustments take about 150 days, that is, a total of 430 days to complete the construction of the main horizontal cavity.

[0045] (3) Drilling construction of four branch horizontal wells was completed on both sides of the main horizontal cavity. The horizontal section distance between adjacent branch horizontal wells was 64 meters. The designed cavity diameter of the branch horizontal cavity was 20 meters, the pillar width was 44 meters, and the pillar ratio was 2.2 to meet the safety requirements. Each branch horizontal well was connected to the main horizontal cavity. The above parameters were adopted and the multi-step backward method was used to construct the branch horizontal cavity. Multiple branch horizontal wells on the same side could be constructed at the same time. In this case, the four branch horizontal wells on the same side were simultaneously injected with water to construct the cavity. At this time, the wellheads of the main vertical well and the main horizontal well could be used as brine drainage wells. After the cavity expansion on one side was completed, the four branch horizontal wells on the other side continued to construct the cavity. At this time, the single cavity displacement of the branch horizontal cavity was 120m 3 / h, total displacement on one side 480m 3 / h, it takes a total of 860 days to complete the construction of the 8-branch well cavity, which greatly improves the construction speed of the cavity group. According to production needs, several multi-branch wells can be flexibly selected for cavity construction.

[0046] (4) After the herringbone-shaped horizontal salt cavern cavity group is completed, it enters the gas injection and brine discharge stage. By continuously injecting gas into the cavity group, the brine in the herringbone-shaped horizontal salt cavern cavity group is continuously discharged to form a herringbone-shaped horizontal cavity group gas storage reservoir.

[0047] In this embodiment, the main horizontal cavity and eight branch horizontal cavities together form a herringbone-shaped horizontal cavity group with a total volume of 900,000 cubic meters, which effectively increases the cavity volume of the gas storage, improves the utilization rate of thin salt layers, and broadens the feasibility of thin salt layer construction. Compared with the construction of 9 independent horizontal cavities, which requires drilling 9 vertical wells and 9 horizontal wells, the herringbone-shaped horizontal salt cavern cavity group only requires 1 vertical well and 9 horizontal wells. According to the price of 8 million for a vertical well, this method can reduce the drilling of 8 vertical wells, saving a total of 64 million, greatly reducing the cost of construction, and significantly improving the economic efficiency of construction. At the same time, the method of simultaneously building cavities with multiple horizontal wells effectively improves the cavity group building speed, significantly accelerating the construction of gas storage.

[0048] 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 constructing a herringbone-shaped horizontal salt cavern group, characterized in that: The steps include: Step 1: Drill a main vertical well (1) to the target salt rock layer, and expand the lower end of the main vertical well (1); Step 2: drilling a horizontal well (2) next to the main vertical well (1), the horizontal well (2) being a main horizontal well (2a), the main horizontal well (2a) being L-shaped, having a vertical section and a horizontal section, and the drilling direction of the horizontal section of the main horizontal well (2a) is toward the main vertical well (1) until it communicates with the chamber at the lower end of the main vertical well (1); Step 3: expanding the horizontal section of the main horizontal well (2a) to obtain a main horizontal cavity (31); Step 4: drilling a plurality of horizontal wells (2) on both sides of the main horizontal cavity (31) and spaced apart along the length direction of the main horizontal cavity (31); the plurality of horizontal wells (2) on both sides of the main horizontal cavity (31) are all branch horizontal wells (2b); the branch horizontal wells (2b) are L-shaped and have a vertical section and a horizontal section; and the drilling direction of the horizontal section of the branch horizontal well (2b) is toward the main horizontal cavity (31) until it is connected with the main horizontal cavity (31); Step 5: Expand the horizontal sections of the plurality of branch horizontal wells (2b) to obtain branch horizontal cavities (32), and complete the construction of the herringbone-shaped horizontal salt cavern group.

2. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 1, characterized in that: The method for expanding the lower end of the main vertical well (1) in step 1 is to use positive circulation to build a groove, open the cavity bottom, and form a dissolution cavity.

3. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 1, characterized in that: The method for expanding the horizontal section of the main horizontal well (2a) in step 3 and the method for expanding the horizontal section of the branch horizontal well (2b) in step 5 both adopt a backward cavity making method.

4. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 3, characterized in that: The specific steps of the backward cavitation method are as follows: horizontal segmented cavitation is carried out from the vicinity of the vertical section of the horizontal well (2) to the horizontal section, and in each segment of the cavitation process, fresh water or fresh brine is injected into the horizontal well (2) to expand the volume of the cavity, and a dissolving agent is injected into the horizontal well (2) to limit the dissolution of the cavity; after each segment of the cavity is cavitated to the shape and volume that meet the standards, the cavitation string in the horizontal well (2) is retreated to enter the next segment of the cavitation process until the entire cavitation process is completed in all horizontal segments.

5. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 1, characterized in that: The number of branch horizontal wells (2b) on both sides of the main horizontal cavity (31) is the same.

6. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 5, characterized in that: The branch horizontal wells (2b) on both sides of the main horizontal cavity (31) are arranged correspondingly, and the horizontal sections of the two corresponding branch horizontal wells (2b) are aligned with each other.

7. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 1, characterized in that: The horizontal section of each branch horizontal well (2b) is perpendicular to the horizontal section of the main horizontal well (2a).

8. The method for constructing a herringbone-shaped horizontal salt cavern group according to claim 1, characterized in that: The number of the branch horizontal wells (2b) is no less than 4.

9. A herringbone-shaped horizontal salt cavern group, characterized in that: The method is constructed according to any one of claims 1 to 8.

10. An application of the herringbone-shaped horizontal salt cavern group as claimed in claim 9, characterized in that: The herringbone-shaped horizontal salt cavern group can be used to store gas.

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