A flow control sub and method for controlling the dissolution of a thin interbedded rock salt cavern

Abstract

The application belongs to the technical field of salt cavern gas storage construction, and relates to a flow control short section for water-soluble thin interbedded rock salt cavity construction and a partial dissolution control method. The flow control short section for water-soluble thin interbedded rock salt cavity construction comprises a circular pipe, a plurality of sieve holes are arranged on the pipe wall of the circular pipe, and the distribution proportion of the sieve holes on the two side pipe walls of the circular pipe is 1:COS theta, wherein theta is a stratum dip angle. Different direction outlet flow is distributed through the flow control short section, and a larger fresh water flow is adopted in the downward direction of the stratum, so that the partial dissolution effect is weakened, and a regular salt cavern is formed.

Description

Technical Field

[0001] This invention belongs to the field of salt cavern gas storage construction technology, and in particular relates to a flow control section and a method for controlling partial dissolution in thin interbedded rock salt dissolution cavity construction. Background Technology

[0002] Most rock salt deposits in my country are thin-layered interbedded rock salt deposits. These thin-layered interbedded rock salt deposits are subject to objective geological constraints such as numerous layers, interlayers, and significant grade differences, increasing the difficulty of constructing energy storage facilities within them. During the water-dissolution cavity construction process for salt cavern gas storage, since the rate of upward dissolution is twice that of lateral dissolution, oil or air cushions are typically used to form a protective layer at the top of the salt cavern to prevent fresh water from dissolving the rock salt upwards and to force the salt cavern to expand laterally.

[0003] However, due to the dip angles of the thin interbedded rock salt and insoluble interlayers, under the same freshwater flow rate, the dissolution rate of rock salt in the up-dip direction is greater than that in the down-dip direction, causing partial dissolution of the salt cavern. The side with partial dissolution has a larger contact area with the water flow. If this is not controlled, it will create a vicious cycle, further amplifying the partial dissolution, resulting in irregular shapes of the salt cavern and increased instability of the cavity walls. Figure 3 Furthermore, due to the frequent pressure changes during the injection and extraction process, irregularly shaped gas storage facilities are not conducive to long-term safe operation. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a flow-controlled short section and a method for controlling partial dissolution in thin interbedded rock salt dissolution cavity formation. By distributing the outlet flow rate in different directions through the flow-controlled short section, a larger freshwater flow rate is used in the downdip direction of the formation, thereby weakening partial dissolution and forming a regularly shaped salt cave.

[0005] To this end, the first aspect of the present invention provides a flow control short section for creating a cavity by dissolving thin interbedded rock salt, comprising a circular pipe, wherein a plurality of sieve holes are formed on the pipe wall, and the sieve holes are distributed on both sides of the pipe wall in a ratio of 1:COSθ, where θ is the dip angle of the formation.

[0006] This invention applies the theory of non-uniform flow and the principle of directional differential dissolution during the drilling and water-soluble cavity construction process in thin intersal layers. This balances and counteracts the influence of the heterogeneous monoclinic formation on the morphology of salt caves. By analyzing the distribution characteristics and velocity changes of fluid flow on the profile of the heterogeneous formation, a flow-control short section design is introduced. By using the screen holes with different proportions distributed on both sides of the flow-control short section, the outlet flow rate in different directions is distributed. A larger flow rate is used in the downdip direction of the formation, thereby weakening the partial dissolution effect. By improving the traditional uncontrolled salt cave construction method, better partial dissolution control effect and more regular salt cave morphology are achieved.

[0007] In some embodiments of the present invention, the distribution ratio of the sieve holes on both sides of the circular tube is set according to the specific dip angle of the formation.

[0008] In some embodiments of the present invention, the aperture size of a plurality of the sieve holes is the same.

[0009] In some embodiments of the present invention, one end of the circular tube is closed, and the other end of the circular tube is provided with a threaded joint.

[0010] The second aspect of the present invention provides a method for controlling the partial dissolution of thin interbedded rock salt in a cavity, wherein a flow control sub is lowered to the bottom of the well as described in the first aspect of the present invention, and fresh water is injected into the well through the flow control sub to dissolve the rock salt.

[0011] In some embodiments of the present invention, the side of the flow control section with more distribution sieve holes is aligned with the formation downdip angle.

[0012] In some embodiments of the present invention, the solubility control method includes the following specific steps:

[0013] S1: Drill a vertical well into the rock salt layer, use casing cementing to deepen to the bottom of the rock salt layer, and log to obtain geological structure data;

[0014] S2: Connect the pumping tubing string to the directional gyroscope and the flow control sub in sequence, and lower it to the bottom of the well;

[0015] S3: Adjust the directional gyroscope so that the side of the flow control sub with more distribution screen holes is aligned with the formation downdip angle, and inject fresh water into the well through the flow control sub to dissolve the rock salt;

[0016] S4: When the rock salt dissolves above the casing, inject oil or gas into the well to form an oil cushion or gas cushion, continue to inject fresh water until the return water is close to the fresh water, and then pull out the pumping string.

[0017] In some embodiments of the present invention, in step S1, the cementing location extends at least 1m into the rock salt layer, and after deepening, the bottom of the well is at least 1m away from the bottom boundary of the rock salt layer.

[0018] In some embodiments of the present invention, in step S4, the oil includes crude oil derivatives and the gas includes air.

[0019] In some embodiments of the present invention, the oil is gasoline or diesel.

[0020] The beneficial effects of this invention are:

[0021] (1) The present invention provides a flow control short section for thin interbedded rock salt dissolution cavity construction. According to the actual formation dip angle, screen holes are distributed proportionally on both sides of the pipe wall of the circular pipe to distribute the outlet flow in different directions. A larger fresh water flow is used in the down-dip direction of the formation to weaken the partial dissolution effect and form a regular salt cavern. This can enhance the stability of the salt cavern, reduce the operation risk of the gas storage facility, and improve the safety of long-term operation.

[0022] (2) The present invention provides a flow control short section for thin interbedded rock salt dissolution cavity, which has a simple structure, is easy to manufacture, has a simple installation process, and has a significant effect on controlling the shape of the salt cavern.

[0023] (3) The present invention provides a method for controlling the partial dissolution of salt caverns in thin interbedded rock salt. Using the flow control short section provided by the present invention, the pipe wall of the flow control short section with more distribution screen holes is aligned with the downdip angle of the formation according to the actual formation dip angle, so that the downdip angle direction of the formation has a larger fresh water flow, thereby weakening the partial dissolution effect and forming a regular salt cavern. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a flow-controlled short section for creating a cavity by salt dissolution in thin interbedded rock, provided by the present invention; wherein, a-longitudinal cross-section, b-developed plan view.

[0025] Figure 2 This is a schematic diagram of a salt cavern construction method for controlling partial dissolution in thin interbedded rock salt dissolution cavity construction provided by the present invention.

[0026] Figure 3 A schematic diagram of a salt cavern without controlling partial solubility.

[0027] Reference numerals: 1-flow control short section, 11-round tube, 12-sieve hole, 13-threaded joint, 2-sleeve, 3-pumping string, 4-oil pad, 5-salt layer, 6-jacket, 7-directional gyroscope. Detailed Implementation

[0028] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0029] Example 1

[0030] Depend on Figure 1 As shown, this embodiment provides a flow control section for creating a cavity in thin interbedded rock salt water, including a circular pipe 11. The pipe wall of the circular pipe 11 is provided with a plurality of sieve holes 12. The distribution ratio of the sieve holes 12 on both sides of the pipe wall of the circular pipe 11 is 1:0.87, and the dip angle of the formation is 30°.

[0031] By distributing sieve holes 12 proportionally on both sides of the pipe wall of the circular pipe 11, the outlet flow rate in different directions is distributed. A larger freshwater flow rate is used in the downdip direction of the formation, thereby weakening the dissolution effect and forming a salt cave with a regular shape.

[0032] In this embodiment, all of the sieve holes 12 have the same aperture size. This facilitates controlling the flow rate of each sieve hole 12 to be the same.

[0033] In this embodiment, one end of the circular tube 11 is closed, and the other end of the circular tube 11 is provided with a threaded connector 13. This facilitates connection to the pumping string 3 via the threaded connector 13, and the closure at one end ensures that the liquid flows out from the sieve holes 12 on the side wall of the circular tube 11.

[0034] Example 2

[0035] Depend on Figure 2 As shown, this embodiment provides a method for controlling the partial dissolution of thin interbedded rock salt cavitation, including the following specific steps:

[0036] S1: Drill a vertical well to a depth of 1m into rock salt layer 5. After cementing with casing 2, deepen the well to a depth of at least 1m from the bottom of rock salt layer 5. Locate geological structure data, with the formation dip angle being 30°.

[0037] S2: Connect the pumping tubing string 3 to the directional gyroscope 7 and the flow control sub 1 in sequence, and lower it to the bottom of the well;

[0038] S3: Adjust the directional gyroscope 7 so that the side of the pipe wall with more distribution screen holes 12 of the flow control section 1 is aligned with the formation downdip angle, and inject fresh water into the well through the flow control section 1 to dissolve the rock salt.

[0039] S4: When the rock salt dissolves above the casing 2, gasoline is injected into the well to form an oil pad 4. Fresh water is continued to be injected until the return water is close to the fresh water, and the pumping string 3 is pulled out.

[0040] In this embodiment, the ratio of the number of sieve holes 12 on both sides of the circular tube 11 of the flow control sub 1 is 1:0.87. In other embodiments, the ratio of the number of sieve holes 12 on both sides of the circular tube 11 of the flow control sub 1 can be set according to the actual formation dip angle.

[0041] The distribution ratio of the sieve holes 12 on both sides of the pipe wall of the flow control section 1 is set by the formation dip angle. Then, the pipe wall on the side with more sieve holes 12 of the flow control section 1 is precisely adjusted by the directional gyroscope 7 to align with the formation downdip angle, so that the formation downdip angle direction has a larger freshwater flow, thereby weakening the dissolution effect and forming a regular salt cave.

[0042] In other embodiments, in step S1, the cementing location extends at least 1m into the rock salt layer 5, and after deepening, the bottom of the well is at least 1m away from the bottom boundary of the rock salt layer 5.

[0043] In other embodiments, air may be injected in step S4 to form an air cushion. This forms a protective layer, preventing fresh water from dissolving the rock salt upwards and forcing the salt cavern to expand laterally.

[0044] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for controlling partial dissolution in thin interbedded rock salt-water cavitation, characterized in that, The specific steps include the following: S1: Drill a vertical well into the rock salt layer, use casing cementing to deepen to the bottom of the rock salt layer, and log to obtain geological structure data; S2: Connect the pumping tubing string to the directional gyroscope and the flow control sub in sequence, and lower it to the bottom of the well. The flow control sub includes a circular tube with several sieve holes on the tube wall. The sieve holes are distributed on both sides of the tube wall in a ratio of 1:cosθ, where θ is the formation dip angle. S3: Adjust the directional gyroscope so that the side of the flow control sub with more distribution screen holes is aligned with the formation downdip angle, and inject fresh water into the well through the flow control sub to dissolve the rock salt; S4: When the rock salt dissolves above the casing, inject oil or gas into the well to form an oil cushion or gas cushion, continue to inject fresh water until the return water is close to the fresh water, and then pull out the pumping string.

2. The method for controlling partial solubility according to claim 1, characterized in that, All of the aforementioned sieve holes have the same aperture size.

3. The method for controlling partial solubility according to claim 1, characterized in that, One end of the round tube is closed, and the other end of the round tube is provided with a threaded joint.

4. The method for controlling partial solubility according to claim 1, characterized in that, In step S1, the cementing location extends at least 1m into the rock salt layer, and after deepening, the bottom of the well is at least 1m away from the bottom boundary of the rock salt layer.

5. The method for controlling partial solubility according to claim 1, characterized in that, In step S4, oil includes crude oil derivatives and gas includes air.

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