Method of forming an underground repository in a salt formation

Abstract

The invention relates to the formation of underground tunnel repositories by dissolution of rock salt through vertical and vertical / horizontal boreholes. In the initial step, a production string consisting of two suspended columns is installed in a vertical borehole, a non-solvent is injected into the borehole, and a preliminary opening is created, the size of which allows communication of the vertical borehole and the vertical / horizontal borehole. The point of water supply into the opening formed is periodically moved by installing a packer in the production string of the vertical / horizontal borehole and subsequently perforating the string in front of the packer. The level of the non-solvent in the vertical borehole is periodically raised, thus preventing exposure of the top of the salt formation near the bottom of the casing string. The invention enables to increase the efficiency of the repository formation and provides high repository capacity.

Description

Technical Field

[0001] The technical solution of the present invention relates to the construction of underground reservoirs by drilling and dissolving salt in rock salt, which can be used in the oil, gas and chemical industries to establish underground storage facilities and extract salt through drilling. Background Technology

[0002] The prior art discloses a method for constructing an underground tunnel reservoir in a rock salt stratum of finite thickness. This method involves: drilling vertical and directional (vertical / horizontal) boreholes, wherein the directional (vertical / horizontal) boreholes are horizontal near the bottom of the salt stratum; installing casing and a tubing string in the boreholes and coupling the boreholes through the salt stratum; injecting a non-solvent and supplying water through the tubing string in the directional boreholes to dissolve the rock; and extracting brine through the tubing string in the vertical boreholes (Russian Patent No. 2258652, Publication Date: August 20, 2005, IPC 7B65G 5 / 00, E21B 7 / 06).

[0003] One drawback of this method is the uneven salt dissolution along the length of the tunnel reservoir. The most intense dissolution occurs above the shoe of the directional (vertical / horizontal) borehole, while the least intense dissolution occurs near the vertical borehole, leading to underutilization of formation capacity. Another drawback is the pumping of non-solvents into the directional borehole and the formation of a pre-opening near the casing. Since there are no available instruments to monitor non-solvent levels in the directional borehole, and the lack of reliable level monitoring makes it impossible to maintain the required non-solvent levels near the directional (vertical / horizontal) borehole. This can lead to salt dissolution near the casing, exposure of the salt formation roof, and its potential collapse and loss of underground reservoir sealing. Furthermore, this method is only feasible under strictly level conditions of the salt formation roof, as it presupposes maintaining the non-solvent-salt interface in the vertical borehole at or above the level of the non-solvent-salt interface in the pre-opening or horizontal section during construction, since the completion of construction is marked by the overflow of non-solvents from the horizontal section of the opening into the vertical borehole.

[0004] The closest existing technology is a method for forming underground tunnel reservoirs in salt rock formations with limited capacity, which involves: vertical drilling and vertical / horizontal boreholes, the latter extending horizontally near the bottom of the salt formation; installing casing and production tubing so that the bottom of the tubing reaches the bottom of the salt formation; connecting the boreholes; dissolving the salt by supplying water through the production tubing in the vertical / horizontal boreholes; extracting brine through the production tubing in the vertical / horizontal boreholes; and moving the injection point to the opening as dissolution proceeds (VA Mazurov, “Underground Gas and Oil Reservoirs in Salt Rock Deposits”, Moscow, Nedra Publishing, 1982, pp. 129-132).

[0005] A drawback of this method is the uneven salt dissolution along the length of the tunnel reservoir. Since most of the salt dissolves near the vertical borehole, the dissolution period is long, meaning the salt formation is completely dissolved as the bottom of the vertical borehole casing is exposed before the salt has fully dissolved along the reservoir length. Furthermore, this method involves moving the production string in the vertical / horizontal boreholes, which is challenging and can lead to string breakage. Summary of the Invention

[0006] The problem this invention aims to solve is to improve the efficiency of forming underground tunnel reservoirs in rock salt by controlling reservoir formation.

[0007] Compared with the prototype, the technical solution of the present invention has the following advantages:

[0008] The formation of underground reservoirs is controlled by injecting non-solvents into vertical boreholes;

[0009] For a given thickness of saline strata, underground reservoirs with larger geometric volumes and higher capacities are formed;

[0010] By controllably moving the water injection point to the already formed opening, reliable and continuous reservoir formation is ensured.

[0011] The essence of this invention is a method for forming an underground tunnel reservoir in a rock salt formation of limited thickness. The method includes: drilling a vertical borehole and a vertical / horizontal borehole, the latter extending horizontally near the bottom of the salt formation; installing casing and a production string in the borehole, such that the bottom end of the production string reaches the bottom of the salt formation; connecting the vertical borehole and the vertical / horizontal borehole; extracting brine through the production string in the vertical borehole; and moving the injection point into the formed opening during the next stage of salt dissolution.

[0012] According to the proposed method, the production string installed in the vertical borehole consists of two coaxial outer suspension columns and an inner suspension column. The non-solvent is pumped into the annular space between the casing and the outer suspension column to form a sufficiently large preparatory opening to connect the vertical borehole and the vertical / horizontal borehole.

[0013] Two coaxial suspended columns in a vertical borehole (one pumping water, the other pumping brine) can form a preparatory opening.

[0014] Injecting non-solvents into vertical boreholes can control the rate of salt dissolution at the top of the pre-opening and near the borehole.

[0015] According to the proposed method, in order to periodically move the injection point into the formed opening, a packer is installed in a vertically / horizontally drilled production string, which is then perforated before the packer. The purpose of installing the packer is to prevent water from reaching the previous injection point and to prevent uncontrolled salt dissolution. Another advantage of maintaining the production string in position is that it does not move relative to the opening, which prevents any loss of stability (uncontrolled movement) during water injection.

[0016] During the next stage of dissolution, the non-solvent level in the vertical borehole is raised to slow down the dissolution of salt at the top of the pre-opening and to prevent the exposure of salt formations near the bottom of the vertical borehole casing until the underground reservoir is formed.

[0017] To improve the injection and brine extraction speed after borehole connection, the inner suspension column is removed from the vertical borehole, and the brine is recovered and extracted through the outer suspension column. Attached Figure Description

[0018] The proposed method for forming underground tunnel storage facilities, such as Figure 1 and Figure 2 As shown.

[0019] Figure 1 This illustrates the process of reservoir formation after preparatory openings are formed around a vertical borehole and the boreholes are connected.

[0020] Figure 2 This shows the storage formation process after the final stage of opening formation.

[0021] Figure 1 and Figure 2The diagram shows a vertical borehole 1 and a vertical / horizontal borehole 2, as well as a rock salt formation 3 of limited thickness. The vertical borehole includes a casing 4 and a production string consisting of an outer suspension column 5 and an inner suspension column 6. A non-solvent 7 is located in the annular space between the casing 4 and the outer suspension column 5, with its interface with the brine at level 8. A preliminary opening 9 is formed at the bottom of the vertical borehole 1, connecting the vertical borehole and the vertical / horizontal borehole. The vertical / horizontal borehole 2 is equipped with a casing 10 and a production string 11. The bottom end of the string in the vertical / horizontal borehole 2 is installed at position 12, corresponding to the injection point before the first stage of opening formation. Packers 13, 14, and 15, installed in the second, third, and fourth stages, and their respective injection points 16, 17, and 18, are moved away from the vertical borehole 1. As a result, an opening 19 is formed in the first stage, an opening 20 in the second stage, an opening 21 in the third stage, and a complete underground reservoir 22 is formed after the fourth stage. Detailed Implementation

[0022] The embodiments of the present invention are as follows. First, a vertical borehole 1 is drilled. A casing 4 and two coaxial suspension columns—an outer suspension column 5 and an inner suspension column 6—are installed in the borehole 1. The outer suspension column 5 penetrates to a depth above the bottom of the salt formation 3, and the inner suspension column 6 penetrates to a depth near the bottom of the salt formation 3. A non-solvent 7 is pumped into the borehole 1, maintaining the interface between the non-solvent and the brine at a liquid level 8 at the depth of the outer suspension column 5. Water is pumped through the outer suspension column 5, and brine is extracted through the inner suspension column 6, thereby forming a preliminary opening 9. Then, a vertical / horizontal borehole 2 is drilled until it connects with the preliminary opening 9. A casing 10 and a production string 11 are installed in the borehole 2, with the bottom end of the string located at position 12 at a certain distance from the vertical borehole 1. The liquid level of the non-solvent in the vertical borehole 1 is raised. Water is pumped through the production string 11, and brine is extracted through the suspension columns 5 and 6 in the vertical borehole 1. To reduce hydraulic friction losses and increase the water supply rate, the inner suspension column 6 is removed from the vertical borehole 1 before salt dissolution begins, and brine is extracted through the outer suspension column 5. The first stage is completed after a certain amount of salt is extracted and an opening 19 is formed. Then, a packer 13 is installed in the production tubing 11, and the production tubing 11 is pierced to form a perforation 16. The non-solvent level in the vertical borehole 1 is raised, water is pumped through the production tubing 11, and brine is extracted through the outer suspension column 5. The second stage is completed after a certain amount of salt is extracted and an opening 20 is formed. Then, a packer 14 is installed, forming a perforation 17, raising the non-solvent level, pumping water, and extracting brine while removing a certain amount of salt, thus forming the opening 21 of the third stage. The fourth stage is similar, leading to the formation of the underground reservoir 22.

[0023] Exemplary implementation.

[0024] During the construction of the underground natural gas storage facility, a capacity of 350,000 m³ was formed within the 1150-1200m depth range of the saline stratum 3.3 The underground reservoir 22. Vertical borehole 1 is drilled to a depth 1 meter below the bottom of the salt formation. Casing 4 is installed to a depth of 1150 m, and then suspension columns 5 and 6 are lowered into boreholes 1198 and 1199.5 m, respectively. Non-solvent 7 is pumped to level 8, i.e., 1198 m. Water is pumped through suspension column 5, and brine is extracted through suspension column 6, thereby maintaining non-solvent 7 at level 8. The level of non-solvent is monitored using geophysical methods via vertical borehole 1 using wireline logging tools. A cylindrical preparatory opening 9, 2 m high and 2 m in radius, is flushed away. Subsequently, vertical / horizontal borehole 2 is drilled to a horizontal position near the bottom of the salt formation 3 and connected to preparatory opening 9. In the vertical / horizontal borehole, casing 10 and production string 11 are installed to a depth of 1150 m. The bottom of the string is located 60 m from the vertical borehole. The level of non-solvent in preparatory opening 9 is maintained 10 m above the junction of boreholes 1 and 2. water at 250m 3 A flow rate of / h is pumped into the production tubing 11. The resulting brine is extracted through suspension columns 5 and 6 in a vertical borehole. After extracting 30,000 tons of salt, the first stage is completed, forming opening 19. A packer 13 is installed inside the production tubing 11 at a distance of 150m from the vertical borehole. The column 11 is then perforated before the packer, such that the total perforation area is twice the cross-sectional area of ​​the column 11. This creates a new water injection point 16. The non-solvent level in the prepared opening 9 is raised by 10m. Water flows at 250m... 3 A flow rate of / h is pumped into production tubing 11. The resulting brine is extracted through suspension columns 5 and 6 in vertical borehole 1. After extracting 70,000 tons of salt, the second stage is completed, forming opening 20. A packer 14 is installed in production tubing 11 at a distance of 240m from the vertical borehole. Then, similar to the first step, the column 11 is perforated before the packer. This creates a new water injection point 17. The non-solvent level in the preparatory opening 9 is raised by 10m. Water flows at 250m... 3 A flow rate of / h is pumped into production string 11. The resulting brine is extracted through suspension columns 5 and 6 in a vertical borehole. After extracting 200,000 tons of salt, the third stage is completed, forming opening 21. A packer 15 is installed in string 11 at a distance of 300m from the vertical borehole. Then, similar to the first step, string 11 is perforated before the packer. This creates a new water injection point 18. The non-solvent level in the prepared opening 9 is raised by 15m. Water flows at 250m... 3 A flow rate of / h is pumped into production tubing 11. The resulting brine is extracted through suspension columns 5 and 6 in vertical boreholes. After extracting 340,000 tons of salt, the fourth stage is completed. This completes the formation of underground storage 22.

[0025] Industrial applicability

[0026] The technology described in this article has been implemented in the construction of underground tunnel storage facilities in saline strata of Russian underground gas storage facilities.

Claims

1. A method for forming an underground tunnel reservoir in a rock salt stratum of finite thickness, comprising: Drilling a vertical borehole and a vertical-horizontal borehole, wherein the vertical-horizontal borehole reaches a horizontal position near the bottom of the salt formation; installing a casing and a production string in the borehole, wherein the bottom end of the production string is located near the bottom of the salt formation; forming a preparatory opening; connecting the drilled vertical borehole and the vertical-horizontal borehole; supplying water through the production string of the vertical-horizontal borehole to dissolve the salt in stages and extracting brine through the production string of the vertical borehole; and injecting a non-solvent into the annular space of the vertical borehole, the level of the non-solvent increasing during each stage of salt dissolution, characterized in that the production string of the vertical borehole consists of two coaxial outer suspension columns and an inner suspension column, the non-solvent being injected into the outer suspension column. In the annular space between the float and the casing, a preliminary opening is formed by injecting water through the outer suspension column and extracting brine through the inner suspension column until a sufficiently large preliminary opening is obtained to connect the vertical borehole and the vertical-horizontal borehole; the bottom end of the production string of the vertical-horizontal borehole is installed at a certain distance from the vertical borehole; furthermore, during the staged salt dissolution process, when each next stage of salt dissolution is carried out, a packer is installed in the horizontal portion of the production string of the vertical-horizontal borehole, wherein the distance from the packer to the bottom end of the string gradually increases in each stage, and the string is subsequently perforated, thereby changing the point of water supply to the forming reservoir.

2. The method according to claim 1, characterized in that, After the vertical borehole and the vertical-horizontal borehole are connected, the internal suspension column is removed from the vertical borehole.

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