Giant thick interlayer double-well double-cavity salt cavern and construction method and application thereof

Abstract

The invention discloses a super-thick interlayer twin-well double-cavity salt cavern and a construction method and application thereof.The construction method of the super-thick interlayer twin-well double-cavity salt cavern comprises the following steps that 1, a vertical well is drilled to the lower end of the vertical well and drilled into an upper salt layer, then a production casing pipe is put into the vertical well, then the vertical well continues to be drilled, and the production casing pipe is put into the vertical well; the lower end of the vertical well penetrates through the ultra-thick interlayer and enters the lower salt layer; 2, a horizontal well is drilled beside the vertical well, the horizontal well is provided with a vertical section and two horizontal sections, the two horizontal sections are vertically distributed in a spaced mode, the horizontal section located on the upper portion is located in the upper salt layer, the horizontal section located on the lower portion is located in the lower salt layer, and the two horizontal sections communicate with the vertical well; and 3, the two horizontal sections of the horizontal well are subjected to cavity expansion, and an upper salt cavern and a lower salt cavern are formed after cavity expansion is completed. The preparation method is simple and convenient, and the cost is relatively low.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground salt caverns, and in particular relates to a thick interlayer double-well double-cavity salt cavern and a construction method and application thereof. Background Art

[0002] The salt cavern gas storage is built by water dissolution, that is, fresh water is injected into the salt layer thousands of meters underground through a wellbore, and then saturated brine is returned to the ground, which continuously dissolves a salt cavern with a huge space. Since China's salt mines belong to continental lake deposits, the salt layer deposition is discontinuous. There are thick interlayers 22 in the middle of some salt mines, the thickest of which can reach 50m. The thick interlayer 22 divides the salt layer into an upper salt layer 21 and a lower salt layer 23 (such as Figure 1 As shown in the figure, the upper salt layer 21 and the lower salt layer 23 are both relatively thin, and the thickness of the salt layer in some areas is less than 120 m. The conventional vertical well single well single cavity construction method can only utilize the upper salt layer 21 or the lower salt layer 23. Using the 120 m thin salt layer, only a cavity of less than 100,000 cubic meters can be formed. The volume of a single cavity is small, and it is impossible to efficiently build a salt cavern gas storage.

[0003] There are many methods for making caverns or reservoirs in salt mines with thick interlayers. The main methods are to make caverns using a single vertical well, including first fracturing, high-pressure water jetting or blasting the thick interlayers to destroy their structural integrity, and then controlling the collapse of the thick interlayers during the cavity making process; using multi-layer casing to form multiple water injection and brine drainage channels, and making caverns in the upper and lower salt layers at the same time. The disadvantage of this method is that it uses a single single-well cavity making method, which results in the use of complex process technology to expand the volume of the salt cavity, and measures such as fracturing and blasting can easily destroy the sealing of the salt cavity, causing leakage of the salt cavern gas storage. At the same time, the cost of building salt caverns is high, and the existing methods for building reservoirs in salt mines with thick interlayers cannot meet the requirements for the construction of large-scale salt cavern gas storages. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a method for constructing a thick interlayer double-well double-cavity salt cavern with low construction cost.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: A method for constructing a thick interlayer double-well double-cavity salt cavern comprises the following steps:

[0006] Step 1: Drill a vertical well until its lower end enters the upper salt layer, then run a production casing into the vertical well, and then continue to drill the vertical well until the lower end of the vertical well passes through a thick interlayer and enters the lower salt layer;

[0007] Step 2: drilling a horizontal well beside the vertical well, wherein the horizontal well has a vertical section and two horizontal sections, and the two horizontal sections are spaced apart from each other, the upper horizontal section is located in the upper salt layer, and the lower horizontal section is located in the lower salt layer, and both the horizontal sections are connected to the vertical well;

[0008] Step 3: Expand the two horizontal sections of the horizontal well to form an upper salt cavern and a lower salt cavern respectively.

[0009] In the above technical solution, the vertical well in step 1 is lowered into the production casing when it is drilled 20-40m into the upper salt layer.

[0010] After the vertical well in step 1 of the above technical solution is drilled, the vertical distance between its lower end and the bottom of the lower salt layer is 10-15m.

[0011] The drilling order of the two horizontal sections of the horizontal well in step 2 in the above technical solution is to first drill the horizontal section located above and then drill the horizontal section located below.

[0012] The specific steps of step 3 described in the above technical solution are:

[0013] Step 3.1: firstly expand the horizontal section located at the bottom to form a lower salt cavern;

[0014] Step 3.2: Then insert a plug into the vertical section, and the plug is located between the two horizontal sections;

[0015] Step 3.3: Expand the horizontal section located above to form an upper salt cavern;

[0016] Step 3.4: Insert a drill bit into the vertical section to drill through the plug, and then remove the drill bit.

[0017] In the process of expanding the horizontal section in step 3.1 and step 3.3 of the above technical solution, a cavity-making string needs to be lowered into the vertical well and the horizontal well and an anti-solvent solution needs to be injected to protect the wellbore corresponding to the horizontal section from being corroded.

[0018] The dissolution inhibitor in the above technical solution is diesel.

[0019] The horizontal section expansion method in step 3.1 and step 3.3 described in the above technical solution is to expand the cavity by alternately injecting water into the horizontal well and the vertical well or by the horizontal step-back method.

[0020] The present invention also provides a huge thick interlayer double-well double-cavity salt cavern constructed by the construction method as described above.

[0021] The present invention also provides an application of a very thick interlayer double-well double-cavity salt cavern, which can be applied to a salt cavern gas storage or a salt cavern compressed air energy storage power station.

[0022] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that: the construction method provided by the embodiments of the present invention can use a vertical well and a horizontal well to build two salt caverns spaced apart in the upper salt layer and the lower salt layer isolated by a thick interlayer. The well body structure is simple and the construction process is simple. At the same time, the combined volume of the two salt caverns is large. It is preliminarily estimated that the volume of the two salt caverns can reach 400,000 to 600,000 cubic meters, which is 3 to 5 times higher than the volume of a single well and a single cavity of about 100,000 cubic meters. This solves the problem of small volume of a single well and a single cavity, and achieves the purpose of economically and efficiently building a large gas storage facility in a thick interlayer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the distribution of the upper salt layer, thick interlayer and lower salt layer;

[0024] Figure 2 This is a schematic diagram of the structure of a vertical well and a horizontal well underground in Example 1 of the present invention;

[0025] Figure 3 This is a schematic diagram of the structure in which a cavity-making string is lowered into both a vertical well and a horizontal well in Example 1 of the present invention;

[0026] Figure 4 This is a schematic diagram of the interface distribution of water and the barrier solvent after water is injected into the vertical well and the horizontal well and the barrier solvent is added in Example 1 of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure after the lower salt cavern is completed in Example 1 of the present invention;

[0028] Figure 6 This is a schematic diagram of the early stage structure of the upper salt cavern for cavity expansion in Example 1 of the present invention;

[0029] Figure 7 This is a schematic diagram of the structure after the upper salt cavern is completed in Example 1 of the present invention;

[0030] Figure 8 This is a schematic diagram of the structure when the plug is removed and the gas storage is constructed in Example 1 of the present invention;

[0031] Fig. 9 This is a schematic diagram of the structure of the gas storage facility when it is completed in Example 2 of the present invention.

[0032] In the figure: 1 vertical well, 21 upper salt layer, 22 thick interlayer, 23 lower salt layer, 3 horizontal well, 31 vertical section, 32 horizontal section, 41 upper salt cavern, 42 lower salt cavern, 5 plug, 6 cavity-making string, 7 packer, 8 injection and production string. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] This embodiment provides a method for constructing a thick interlayer double-well double-cavity salt cavern, comprising the following steps:

[0035] Step 1: Drill a vertical well 1 until its lower end enters the upper salt layer 21, then lower a production casing 11 into the vertical well 1, and then continue to drill the vertical well 1 until the lower end of the vertical well 1 passes through the thick interlayer 22 and enters the lower salt layer 23 (such as Figure 2 shown);

[0036] Step 2: Drill a horizontal well 3 next to the vertical well 1, the horizontal well 3 having a vertical section 31 and two horizontal sections 32, and the two horizontal sections 32 are spaced apart from each other, the upper horizontal section 32 is located in the upper salt layer 21, the lower horizontal section 32 is located in the lower salt layer 23, and both horizontal sections 32 are connected to the vertical well 1 (e.g. Figure 2 shown);

[0037] Step 3: Expand the two horizontal sections 32 of the horizontal well 3 to form an upper salt cavern 41 and a lower salt cavern 42 respectively.

[0038] Wherein, the production casing 11 is lowered into the vertical well 1 when it is drilled into the upper salt layer 21 at a depth of 20-40 m (preferably 30 m); after the vertical well 1 in step 1 is drilled, the vertical distance between its lower end and the bottom of the lower salt layer 23 is 10-15 m (preferably 10 m).

[0039] Among them, Figure 3-Figure 8 As shown, the drilling order of the two horizontal sections 32 of the horizontal well 3 in step 2 is to first drill the horizontal section 32 located at the upper side, and then drill the horizontal section 32 located at the lower side.

[0040] Wherein, the specific steps of step 3 are:

[0041] Step 3.1: firstly, the horizontal section 32 located at the bottom is expanded to form a lower salt cavern 42;

[0042] Step 3.2: Then, a plug 5 is inserted into the vertical section 31, and the plug 5 is located between the two horizontal sections 32;

[0043] Step 3.3: Expand the horizontal section 32 located above to form an upper salt cavern 41;

[0044] Step 3.4: Insert a drill bit into the vertical section 31 to drill through the plug 5, and then remove the drill bit.

[0045] In the process of expanding the horizontal section 32 in step 3.1 and step 3.3, a cavity-making tubing string needs to be lowered into the vertical well 1 and the horizontal well 3 and an anti-solvent is injected to protect the corresponding wellbore of the horizontal section 32 from being dissolved, wherein the anti-solvent is diesel. In the step 3.1 and step 3.3, the method for expanding the horizontal section 32 is to alternately inject water into the horizontal well 3 and the vertical well 1 to expand the cavity or to expand the cavity by the horizontal step-back method.

[0046] This embodiment also provides a thick interlayer double-well double-cavity salt cavern constructed by the construction method described above.

[0047] The present invention also provides an application of a very thick interlayer double-well double-cavity salt cavern, which can be applied to a salt cavern gas storage or a salt cavern compressed air energy storage power station. The salt cavern gas storage can be used to store natural gas, helium, hydrogen and compressed air (when storing compressed air, it is used as a salt cavern compressed air energy storage power station. When electricity consumption is low, excess electricity is used to do work to store compressed air in the salt cavern, and when electricity consumption is peak, the compressed air in the salt cavern is discharged to generate electricity).

[0048] in, Figure 4 , Figure 5 and Figure 7 The middle dotted line A represents the interface between the dissolving agent and water (brine) (the area below the dotted line A in the horizontal well and the vertical well is filled with water, while the area above the dotted line A is filled with the dissolving agent).

[0049] Example 1

[0050] The following is an example of a domestic salt cavern gas storage. There is a thick interlayer with a thickness of about 50m in the middle of the salt layer of the gas storage. The thickness of the upper salt layer is about 100m, the thickness of the lower salt layer is about 120m, and the depth of the top of the upper salt layer is 900m.

[0051] Step 1, drilling a butt well: Figure 2 and Figure 3As shown, a vertical well is first drilled into the upper salt layer, the drilling depth is 930m, and then a production casing is lowered, the casing diameter is 224.5mm, the depth is 930m, and then a 244.5mm drill bit is used to drill through the salt layer and the thick interlayer in turn, and drill into the lower salt layer, the final drilling depth is 1160m, located at the bottom of the lower salt layer (the distance from the bottom wall of the lower salt layer is 10m); then a horizontal well (including a vertical section and two horizontal sections) is drilled, the horizontal well of the upper salt layer section is first drilled to connect with the vertical well, the depth of the horizontal well is 990m, and the position is at the bottom of the upper salt layer, and then the horizontal well of the lower salt layer section is drilled to connect with the vertical well, the depth of the horizontal well is 1160m, and the position is at the bottom of the lower salt layer, wherein the distance between the vertical well and the horizontal well vertical section is 250-300m;

[0052] Step 2: Building a cavern in the lower salt layer: Figure 4 and Figure 5 As shown, a cavity-making string 6 is lowered into the vertical well to the bottom of the well, and the size of the cavity-making string is 177.8 mm. A cavity-making string 6 is also lowered into the horizontal well to the horizontal section located below, and the size of the cavity-making string is 177.8 mm. The depths of the two cavity-making strings 6 are both 1160 m. In addition, a blocking agent is injected into the horizontal well and the vertical well from the wellheads of the horizontal well and the vertical well. The injection depth of the blocking agent is 1110 m (the area below the depth is water), and it is located at the upper part of the lower salt layer (the upper end of the interior). The dissolving agent is used to protect the lower salt cave from dissolving upward. The lower salt layer is expanded by alternately injecting water into horizontal wells and vertical wells or by horizontal stepping back to expand the horizontal section below (the existing expansion method belongs to the existing technology in this field, which will not be described here) to build a horizontal cavity (lower salt cave). The cavity of the lower salt cave is 110m high, 70-80m wide, about 250-300m long, and has a volume of about 200,000-300,000 cubic meters.

[0053] Step 3, building a cavern in the upper salt layer: Figure 6 and Figure 7As shown, before the cavity is made, the cavity making string in the horizontal well is first pulled out, and a plug is lowered at the position corresponding to the thick interlayer in the vertical section. The plug can be a rubber plug to facilitate drilling in the later stage. Then the cavity making string is lowered into the wellbore of the horizontal section above. The size of the cavity making string is still 177.8 mm, the depth is 990 m, and it is located at the bottom of the upper salt layer. The cavity making string in the vertical well does not move, and the lowering depth is still 1160 m. The blocking agent is continuously injected into the vertical well and the horizontal well to a depth of 910 m (water below the depth). At the top of the upper salt layer (the upper end of the interior), in order to protect the upper salt cavity from dissolving upward, the horizontal section located above is still expanded by alternating water injection of horizontal wells and vertical wells or by the horizontal retreat method (the existing cavity expansion method belongs to the existing cavity expansion method in the field of technology, which will not be described here), so as to build a horizontal cavity (upper salt cavern) in the upper salt layer. The cavity height of the upper salt cavern is about 100 m, and the other dimensions are basically the same as those of the lower salt cavern.

[0054] Step 4, gas injection and brine removal: insert a drill bit into the horizontal well to drill through the plug in the horizontal well, then lower the gas injection and production pipe string 8 and use the packer 7 to isolate it at the wellhead of the vertical section. The gas injection and production pipe string 8 is lowered to a depth of 910m, and the packer is 900m deep. The pipe string steel grade is above N80, and the buckle type is gas-tight. The cavity-making pipe string in the vertical well is different and serves as a brine-removing pipe string. The depth of its lower end is still 990m, but in order to ensure the strength of the brine-removing pipe string, the pipe string steel grade is N80 or above. The stored gas is injected from the gas injection and production pipe string in the horizontal well, and the brine in the salt cavern is discharged from the brine-removing pipe string in the vertical well. After the gas injection and brine removal is completed, the brine-removing pipe string can continue to remain in the well, and gas injection or gas production is carried out from the injection and production pipe string in the horizontal well. Of course, the brine-removing pipe string below the wellhead of the vertical well can also be cut, and gas injection or gas production is carried out from the horizontal well and the vertical well at the same time.

[0055] Among them, the limit of the upward expansion of the upper salt cavern and the lower salt cavern in step 2 and step 3 is the position corresponding to the dotted line A, so that the upper ends of the upper salt cavern and the lower salt cavern will not completely dissolve the upper ends of the corresponding upper salt layer and the lower salt layer, which is beneficial to protect the sealing of the upper salt cavern and the salt cavern. Of course, the dotted line A can be a horizontal line (at this time, the interface between the lower end of the vertical well and the internal resistance solvent of the vertical section is flush), and the dotted line A can also be a small-angle inclined line [at this time, there is a small height difference between the interface between the lower end of the vertical well and the internal resistance solvent of the vertical section (the height difference can be less than 2m)].

[0056] Among them, during the cavity making process, one of the two cavity making pipes is used to inject fresh water, and the other cavity making pipe is used to discharge brine, depending on the cavity making method. However, during the cavity making process of the upper salt cavern, the cavity making pipe in the horizontal well is used to inject fresh water, and the fresh water continuously dissolves the salt layer in the upper salt cavern and becomes concentrated brine until it flows into the lower salt cavern through the vertical well and is discharged through the cavity making pipe in the vertical well (since the brine entering the lower salt cavern is already concentrated brine, the lower salt cavern will not be expanded at this time).

[0057] Example 2

[0058] like Fig. 9 As shown, since some strata have relatively large dip angles, up to 10° in some areas, for the cavity making of the thick interlayer with dip angle, the cavity making method is the same as that in Example 1, with the only difference being that the distribution relationship between the vertical well and the vertical section is consistent with the inclination direction of the thick interlayer, that is, ensuring that the connection between the vertical well and the upper salt cavern and the lower salt cavern is located at the lowest horizontal height inside the upper salt cavern and the lower salt cavern, so that it is convenient to drain the brine in the upper salt cavern and the lower salt cavern, thereby making the gas injection and brine drainage efficiency higher and the cavity utilization rate higher; for example, the thick interlayer is inclined to the lower right, and the vertical well is located to the right of the vertical section.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a thick interlayer double-well double-cavity salt cavern, characterized in that: The following steps are involved: Step 1: Drill a vertical well (1) until its lower end enters the upper salt layer (21), then lower a production casing (11) into the vertical well (1), and then continue to drill the vertical well (1) until the lower end of the vertical well (1) passes through a thick interlayer (22) and enters the lower salt layer (23); Step 2: drilling a horizontal well (3) next to the vertical well (1), wherein the horizontal well (3) has a vertical section (31) and two horizontal sections (32), and the two horizontal sections (32) are spaced apart from each other, the upper horizontal section (32) is located in the upper salt layer (21), and the lower horizontal section (32) is located in the lower salt layer (23), and both of the two horizontal sections (32) are connected to the vertical well (1); Step 3: Expand the two horizontal sections (32) of the horizontal well (3), and after the expansion is completed, form an upper salt cavern (41) and a lower salt cavern (42) respectively.

2. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 1 is characterized in that: In the step 1, the vertical well (1) is lowered into a production casing (11) when the vertical well (1) is drilled 20-40 m into the upper salt layer (21).

3. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 1, characterized in that: After the vertical well (1) in step 1 is drilled, the vertical distance between its lower end and the bottom of the lower salt layer (23) is 10-15m.

4. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 1, characterized in that: The drilling order of the two horizontal sections (32) of the horizontal well (3) in step 2 is to first drill the upper horizontal section (32) and then drill the lower horizontal section (32).

5. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 1, characterized in that: The specific steps of step 3 are: Step 3.1: firstly, the horizontal section (32) located at the bottom is expanded to form a lower salt cavern (42); Step 3.2: Then, a plug (5) is inserted into the vertical section (31), and the plug (5) is located between the two horizontal sections (32); Step 3.3: Expanding the horizontal section (32) located above to form an upper salt cavern (41); Step 3.4: Insert a drill bit into the vertical section (31) to drill through the plug (5), and then remove the drill bit.

6. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 5, characterized in that: During the process of expanding the horizontal section (32) in step 3.1 and step 3.3, a cavity-making string needs to be lowered into the vertical well (1) and the horizontal well (3) and an anti-solvent solution needs to be injected to protect the wellbore corresponding to the horizontal section (32) from being corroded.

7. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 6, characterized in that: The dissolution inhibitor is diesel.

8. The method for constructing a thick interlayer double-well double-cavity salt cavern according to claim 6, characterized in that: The method for expanding the horizontal section (32) in step 3.1 and step 3.3 is to expand the horizontal well (3) and the vertical well (1) by alternately injecting water or by horizontal step-back method.

9. A thick interlayer double-well double-cavity salt cavern, characterized in that: The method is constructed by the construction method described in any one of claims 1 to 8.

10. An application of the thick interlayer double-well double-cavity salt cavern as claimed in claim 9, characterized in that: The ultra-thick interlayer double-well double-cavity salt cavern can be applied to a salt cavern gas storage or a salt cavern compressed air energy storage power station.

Images