Fishbone-shaped horizontal salt cavern cavity group and construction method and application thereof

Abstract

The application 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 straight well to a target salt rock layer section, and expanding the cavity at the lower end of the main straight well; step 2, drilling a horizontal well beside the main straight well, the horizontal well is a main horizontal well, and the drilling direction of the horizontal section of the main horizontal well is towards the main straight well until the horizontal section communicates with the cavity at the lower end of the main straight well; step 3, expanding the horizontal section of the main horizontal well to obtain a main horizontal cavity; step 4, drilling multiple horizontal wells which are distributed along the length direction of the main horizontal cavity on both sides of the main horizontal cavity respectively, the multiple horizontal wells on both sides of the main horizontal cavity are branch horizontal wells, and the drilling direction of the horizontal section of the branch horizontal well is towards the main horizontal cavity until the horizontal section communicates with the main horizontal cavity; and step 5, expanding the horizontal section of the multiple branch horizontal wells to obtain branch horizontal cavities, so that the cavity volume of the gas storage can be effectively increased, and the construction cost of the gas storage can be reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of salt cavern gas storage, and particularly relates to a fishbone-shaped horizontal salt cavern group and a construction method and application thereof. BACKGROUND

[0002] For a salt mine with poor geological conditions of stratified salt rock, the thickness of the layer suitable for cavity construction is thin, and the salt rock in the layer suitable for cavity construction is low in grade and also contains a large amount of interlayer, which limits the volume of the salt cavity and greatly increases the difficulty of cavity construction. At present, most of the underground salt cavern gas storage is constructed by using a single-well single-cavity water solution method, and the traditional single-well cavity construction has high requirements for the site selection of the gas storage area. The cavity constructed in the thin salt layer is small in volume and slow in construction speed, and it is difficult to meet the demand for rapid development of domestic underground gas storage. Therefore, it is urgent to seek a new cavity construction method suitable for the construction of domestic stratified salt layer gas storage to improve the cavity construction speed. SUMMARY

[0003] To solve the above technical problems, the purpose of the present application is to provide a construction method of a fishbone-shaped horizontal salt cavern group, which can construct an underground salt cavern group in the shape of a fishbone-shaped horizontal salt cavern group, and can construct a cavity under the geological conditions of stratified salt rock, and has a fast cavity construction speed.

[0004] To achieve the above purpose, the technical scheme of the present application is as follows: a construction method of a fishbone-shaped horizontal salt cavern group, comprising the following steps:

[0005] Step 1: drilling a main straight well to a target salt rock layer, and expanding the cavity at the lower end of the main straight well;

[0006] Step 2: drilling a horizontal well beside the main straight well, which is a main horizontal well, the main horizontal well 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 is towards the main straight well until the cavity at the lower end of the main straight well is communicated;

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

[0008] Step 4: drilling a plurality of horizontal wells on both sides of the main horizontal cavity, which are distributed along the length direction of the main horizontal cavity, the plurality of horizontal wells on both sides of the main horizontal cavity are branch horizontal wells, 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 towards the main horizontal cavity until the main horizontal cavity is communicated;

[0009] Step 5: expanding the cavity of the horizontal section of the plurality of branch horizontal wells to obtain branch horizontal cavities, and completing the construction of the fishbone-shaped horizontal salt cavern group.

[0010] The cavity expansion method of the lower end of the main vertical well in step 1 is a positive circulation groove forming method, which opens the cavity bottom and forms a solution cavity.

[0011] 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 are both a backward cavity forming method.

[0012] The specific steps of the backward cavity forming method in the technical solution are as follows: horizontal section cavity forming is performed from the vicinity of the vertical section of the horizontal well to the horizontal section direction, and during each cavity forming process, fresh water or fresh brine is injected into the horizontal well to expand the solution cavity volume, and a solution-resistant agent is injected into the horizontal well to limit the cavity expansion; after each cavity forming process reaches the shape and volume standard, the cavity forming string in the horizontal well is retreated, and the next cavity forming process is entered until the entire cavity forming process of the horizontal section is completed.

[0013] The number of branch horizontal wells on both sides of the main horizontal cavity is consistent.

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

[0015] 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 is not less than 4.

[0017] The second purpose of the present application is to provide a fishbone-shaped horizontal salt cave cavity group built by the above-mentioned building method.

[0018] In order to achieve the above-mentioned purposes, another technical solution of the present application is as follows: a fishbone-shaped horizontal salt cave cavity group built by the above-mentioned building method.

[0019] The third purpose of the present application is to provide a fishbone-shaped horizontal salt cave cavity group built by the above-mentioned building method.

[0020] In order to achieve the above-mentioned purposes, another technical solution of the present application is as follows: an application of the fishbone-shaped horizontal salt cave cavity group as described above, which can be applied to store gas.

[0021] Compared with the prior art, the fishbone-shaped horizontal salt cavern cavity group constructed in the embodiment of the present application has the advantages that when the fishbone-shaped horizontal salt cavern cavity group is used as a gas storage, the cavity volume of the gas storage can be effectively increased, the construction cost of the gas storage can be reduced, the economy of the gas storage can be improved, the cavity construction speed can be effectively improved, and the construction progress of the underground salt cavern gas storage can be accelerated. Meanwhile, the strict construction screening requirement of the salt cavern gas storage can be reduced, and the fishbone-shaped horizontal salt cavern cavity group is especially suitable for the construction of a gas storage in a layered salt rock salt mine area. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 FIG. 1 is a structural schematic view of a main vertical well in the embodiment of the present application;

[0023] Figure 2 FIG. 2 is a structural schematic view of a horizontal well in the embodiment of the present application;

[0024] Figure 3 FIG. 3 is a structural schematic view of a main horizontal cavity and two branch horizontal wells in the embodiment of the present application;

[0025] Figure 4 FIG. 4 is a plan view of the fishbone-shaped horizontal salt cavern cavity group in the embodiment of the present application.

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

[0027] The principles and features of the present application are described below in conjunction with the accompanying drawings, and the examples are used only to explain the present application and are not used to limit the scope of the present application. In the following paragraphs, the present application is described in more detail by way of example with reference to the accompanying drawings. The advantages and features of the present application will be more apparent from the following description and claims. It should be noted that the accompanying drawings are very simplified and use non-precise proportions, and are only used to facilitate and clarify the purpose of explaining the embodiment of the present application.

[0028] As shown in FIG. 1, the embodiment of the present application provides a construction method of a fishbone-shaped horizontal salt cavern cavity group, which comprises the following steps: Figures 1-4

[0029] Step 1: drilling a main vertical well 1 to a target salt rock layer, and expanding the cavity at the lower end of the main vertical well 1;

[0030] Step 2: drilling a horizontal well 2 beside the main vertical well 1, wherein 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 towards the main vertical well 1 until the horizontal section communicates with the cavity at the lower end of the main vertical well 1;

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

[0032] Step 4: drilling a plurality of horizontal wells 2 on both sides of the main horizontal cavity 31, the horizontal wells 2 on both sides of the main horizontal cavity 31 being branch horizontal wells 2b, the branch horizontal wells 2b being L-shaped and having vertical sections and horizontal sections, and the horizontal sections of the branch horizontal wells 2b being drilled towards the main horizontal cavity 31 until communicating with the main horizontal cavity 31;

[0033] Step 5: expanding the horizontal sections of the branch horizontal wells 2b to obtain branch horizontal cavities 32, and completing the construction of the fishbone-shaped horizontal salt cavern cavity group.

[0034] In the step 1, the method for expanding the cavity at the lower end of the main vertical well 1 is to open the cavity bottom by positive circulation trenching to form a solution cavity.

[0035] In the step 3, the method for expanding the horizontal section of the main horizontal well 2a and the method for expanding the horizontal section of the branch horizontal well 2b in the step 5 are both the method of backward cavity making, wherein the method of backward cavity making comprises the following steps: making a horizontal section cavity from the vicinity of the vertical section of the horizontal well 2 towards the horizontal section, and in each cavity making process, fresh water or fresh brine is injected into the horizontal well 2 to expand the solution cavity volume, and a solution-resistant agent (which can be diesel oil) is injected into the horizontal well 2 to limit the solution of the cavity; after each cavity making process reaches the standard in shape and volume, the cavity making string in the horizontal well 2 is withdrawn, and the next cavity making process is entered until the entire cavity making process of the horizontal section is completed.

[0036] The number of the branch horizontal wells 2b on both sides of the main horizontal cavity 31 is consistent, the branch horizontal wells 2b on both sides of the main horizontal cavity 31 are correspondingly arranged, the horizontal sections of the corresponding two branch horizontal wells 2b are aligned with each other, 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 the branch horizontal wells 2b is not less than 4.

[0037] The fishbone-shaped horizontal salt cavern cavity group can be applied to store gas, and the stored gas can be natural gas, helium, hydrogen or compressed air (when the stored gas is compressed air, the fishbone-shaped horizontal salt cavern cavity group can be used as an energy storage device, that is, during the low peak of electricity consumption, the excess electricity is used to send compressed air into the fishbone-shaped horizontal salt cavern cavity group, and during the high peak of electricity consumption, the compressed air in the fishbone-shaped horizontal salt cavern cavity group is discharged and used for power generation).

[0038] In the step 1, the method for expanding the cavity at the lower end of the main vertical well 1 is to open the cavity bottom by positive circulation trenching to form a solution cavity. Figure 1 , Figure 3 ​and Figure 4 In the embodiment, the horizontal section of the main horizontal well is distributed in the front-rear direction, and the horizontal section of the branch horizontal well is distributed in the left-right direction.

[0039] In the embodiment, 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 can also be inconsistent, and can also not be aligned with each other, and the specific adjustment is based on the structural characteristics of the underground salt layer.

[0041] The construction method of the fishbone-shaped horizontal salt cavity group is analyzed below by taking an actual gas storage construction case as an example.

[0042] The cavity forming target layer of the Huai'an salt cavity gas storage is the upper salt submember of the Paleogene F4 member, the salt layer is stably distributed in layers, the burial depth gradually increases from northeast to southwest, the thickness gradually increases, the top boundary depth is 1000-2500m, and the average thickness is 123.9m. A 10m-thick interlayer is developed under a certain salt layer on the west side of the cavity forming section, and a salt layer with a thickness of about 20m is developed under the interlayer. The salt rock grade is good, the insoluble content is low, and the salt layer is generally developed in the storage area. The salt layer is selected, and the fishbone-shaped horizontal cavity group salt cavity construction method is used for simulation cavity forming. The specific implementation steps are as follows:

[0043] (1) Drilling a straight well (main straight well) to the pure salt layer section, forming a cavity by positive circulation, then drilling a horizontal well (main horizontal well) connected with the straight well, and forming a horizontal butt joint well group with the main straight well and the main horizontal well. The horizontal section of the main horizontal well is 1-2m above the salt layer bottom boundary, and the length of the horizontal section of the main horizontal well can reach 300-500m, and 300m is selected in this embodiment.

[0044] (2) Using a multi-step back-off cavity forming method, water is injected into the main horizontal well, and brine is discharged from the main straight well, and horizontal step-by-step cavity forming is performed from the vicinity of the main straight well to the main horizontal well. The cavity forming process is divided into 6 steps, each step is 50m long, and during each step, a dissolution control agent is injected into the well below the casing shoe to control the upper dissolution. After reaching the design time and cavity volume of this step, the cavity forming pipe string in the main horizontal well is retreated by means of pipe withdrawal, perforation or pipe cutting, and the next step of cavity forming is entered. When the last step of dissolution cavity forming is performed, the cavity forming pipe port needs to be kept 10-20m away from the casing shoe of the main horizontal well as a horizontal safety distance to prevent the casing shoe of the main horizontal well from being dissolved and damaged. In the horizontal multi-step cavity forming design, the water injection cavity forming time is 280 days, the cavity forming time of the first five steps is 50 days, and the design time of the last step is 30 days. The height and width of the main horizontal cavity obtained are both about 20m, the length is 300m, the single cavity volume is about 100,000m3, and the water injection speed range is generally 0-300m 3 / h, here 120 m 3 / h, in the process of cavity forming, 5 column adjustments are needed to consume about 150 days, i.e. 430 days in total to complete the construction of the main horizontal cavity.

[0045] (3) drilling and construction of 4 branch horizontal wells on each side of the main horizontal cavity are completed, the horizontal section distance of adjacent branch horizontal wells is 64 meters, the cavity diameter of the designed branch horizontal cavity is 20 meters, the pillar width is 44 meters, the pillar ratio is 2.2 to meet the safety requirements, each branch horizontal well is communicated with the main horizontal cavity, using the above parameters, the multi-step back-off method is used to build the branch horizontal cavity, the multiple branch horizontal wells on the same side can be simultaneously formed, the 4 branch horizontal wells on the same side are simultaneously water injected to form cavities, at this time, the wellheads of the main vertical well and the main horizontal well can be used as the brine discharge well, after the expansion of one side is completed, the 4 branch horizontal wells on the other side are continuously formed, at this time, the single cavity discharge of the branch horizontal cavity is 120 m 3 / h, the total discharge on one side is 480 m 3 / h, a total of 860 days are needed to complete the cavity construction of 8 branch wells, which greatly improves the construction speed of the cavity group, and according to the production demand, several branch wells can be selected to form cavities.

[0046] (4) after the fishbone-shaped horizontal salt cavity group is completed, the gas injection and brine discharge link is entered, by continuously injecting gas into the cavity group, the brine in the fishbone-shaped horizontal salt cavity group is continuously discharged to form a fishbone-shaped horizontal cavity group gas storage.

[0047] In the embodiment, the main horizontal cavity and the eight branch horizontal cavities form a total fishbone-shaped horizontal cavity group with a total volume of 900000 square meters, effectively increasing the cavity volume of the gas storage, improving the utilization rate of the thin salt layer, and widening the feasibility of building the gas storage in the thin salt layer. Compared with building 9 independent horizontal cavities, which requires drilling 9 vertical wells and 9 horizontal wells, the fishbone-shaped horizontal salt cavity group only needs 1 vertical well and 9 horizontal wells. According to the price of 800 million for one vertical well, 8 vertical wells can be drilled less, a total of 6400 million is saved, the construction cost of the gas storage is greatly reduced, and the economic efficiency of the gas storage is significantly improved. At the same time, the simultaneous cavity forming of multiple horizontal wells effectively improves the cavity forming speed of the cavity group and significantly speeds up the construction of the gas storage.

[0048] The above is only a preferred embodiment of the present application, and does not limit the present application in any form; any ordinary technical personnel in the industry can smoothly implement the present application according to the drawings and the above description; however, any equivalent changes, modifications and evolution made by the technical personnel familiar with the profession 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 of constructing a fishbone-shaped horizontal salt cavern cavity group, characterized in that, It comprises the following steps: Step 1: drilling a main straight well (1) to a target salt rock section, and expanding the cavity at the lower end of the main straight well (1); Step 2: drilling a horizontal well (2) beside the main straight well (1), which is a main horizontal well (2a), the main horizontal well (2a) is 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 towards the main straight well (1) until it communicates with the cavity at the lower end of the main straight 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) respectively, the horizontal wells (2) on both sides of the main horizontal cavity (31) are branch horizontal wells (2b), the branch horizontal wells (2b) are L-shaped, having a vertical section and a horizontal section, and the drilling direction of the horizontal section of the branch horizontal wells (2b) is towards the main horizontal cavity (31) until it communicates with the main horizontal cavity (31); Step 5: expanding the horizontal section of each of the plurality of branch horizontal wells (2b) to obtain a branch horizontal cavity (32), and completing the construction of the fishbone-shaped horizontal salt cave cavity group.

2. The method of constructing a fishbone crenulation of horizontal salt caverns according to claim 1, characterized in that, The method for expanding the cavity at the lower end of the main straight well (1) in step 1 is to form a solution cavity by opening the cavity bottom and forming a groove with positive circulation.

3. The method of constructing a fishbone-shaped horizontal salt caverns cluster according to claim 1, wherein, The method for expanding the cavity of the horizontal section of the main horizontal well (2a) in step 3 and the method for expanding the cavity of the horizontal section of the branch horizontal well (2b) in step 5 are both the method of backward cavity formation.

4. The method of constructing a fishbone spur-type horizontal salt caverns cluster according to claim 3, wherein, The specific steps of the backward cavity formation method are as follows: from the vicinity of the vertical section of the horizontal well (2) to the horizontal section direction, horizontal section cavity formation is carried out, and during each section cavity formation, fresh water or fresh brine is injected into the horizontal well (2) to expand the solution cavity volume, and a dissolution inhibitor is injected into the horizontal well (2) to limit the cavity dissolution; after each section cavity formation reaches the standard shape and volume, the cavity formation string in the horizontal well (2) is withdrawn, and the next section cavity formation process is entered until the entire cavity formation process of the horizontal section is completed.

5. The method of constructing a fishbone spur-type horizontal salt caverns cluster according to claim 1, wherein, The number of branch horizontal wells (2b) on both sides of the main horizontal cavity (31) is consistent.

6. The method of constructing a fishbone spur-type horizontal salt caverns cluster according to claim 5, wherein, 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.

7. The method of constructing a fishbone crenulation of horizontal salt caverns according to claim 1, wherein, The horizontal section of each branch horizontal well (2b) is perpendicular to the horizontal section of the main horizontal well (2a).

8. The method of constructing a fishbone crenulation of horizontal salt caverns according to claim 1, wherein, The number of branch horizontal wells (2b) is not less than 4.

9. A fishbone-shaped horizontal salt cavern cavity group, characterized by, It is constructed by using the construction method of any one of claims 1-8.

10. Use of a fishbone-shaped horizontal salt caverns cluster according to claim 9, characterized in that, The fishbone-shaped horizontal salt cave cavity group can be applied to store gas.

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