Cavity building method for thin salt layer double-branch well

Abstract

The invention relates to a thin salt layer double-branch well cavity building method which comprises the following specific steps that a vertical well A and a vertical well D are drilled, and magnetic field generators are placed in the vertical well A and the vertical well D respectively; temporarily plugging the positions of the lower parts of the deflecting points of the vertical well A and the vertical well D, respectively drilling a deflecting section E and a horizontal section F towards the bottom of the vertical well A, drilling a deflecting section B and a horizontal section C towards the bottom of the vertical well D, and forming a communicated common well section at the horizontal sections; the plugging parts of the vertical well A and the vertical well D are removed, the deflecting section B and the deflecting section E are plugged, and finally a communicated well is formed; water injection pipe columns are vertically installed in the vertical well A and the vertical well D respectively, and brine discharging pipe columns are vertically installed in the two water injection pipe columns respectively; and clear water is injected into the vertical well A and the vertical well D alternately, cavity dissolving operation is conducted on the thin salt layer, and brine is discharged from the brine discharging pipe column of the vertical well on the opposite side. According to the double-branch well convection cavity construction method, the utilization rate of the salt rock in the thin salt layer can be increased, the cavity dissolving speed is increased, the cavity construction period is shortened, and efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of the construction method of salt cavern gas storage, and particularly relates to a method for constructing a cavity in a thin salt layer with a double-branch well. Background Art

[0002] As a clean energy source, natural gas has currently received extensive attention globally. It can be predicted from past oil and gas consumption that the proportion of natural gas consumption will increase rapidly. In order to ensure stable gas supply, 40-50% of the gas used in some regions of China in winter comes from underground gas storage. Due to the advantages of high injection and production efficiency and large short-term throughput, salt cavern gas storage has been widely used.

[0003] A salt cavern is an underground space formed after the dissolution of salt rock. Salt rock has characteristics such as low permeability, good creep properties, and strong damage self-recovery ability. Therefore, salt rock formations have become ideal sites for the storage of oil and natural gas and the construction of compressed air energy storage power stations. However, the salt rock deposits in China are mainly formed by lacustrine sedimentation, and the salt layer thickness is relatively thin compared with that in foreign countries. The difficulties and limitations in building gas storage are relatively prominent. At present, the main method for creating cavities in thin salt layers in China is to create cavities with horizontally connected wells, but this method will cause some salt rock below the target point to not dissolve, resulting in insufficient utilization of the limited underground space. In order to increase the cavity space of salt rock in thin salt layers, a method for constructing a cavity in a thin salt layer with a double-branch well is designed. Summary of the Invention

[0004] The present invention provides a method for constructing a cavity in a thin salt layer with a double-branch well, aiming to solve the problems in the prior art.

[0005] The technical solution for the present invention to solve the above technical problems is as follows:

[0006] A method for constructing a cavity in a thin salt layer with a double-branch well includes the following specific steps:

[0007] S1: Drill vertical wells A and D at intervals in the salt rock formation, and place magnetic field generators in the vertical wells A and D respectively;

[0008] S2: According to the designed wellbore trajectory, temporarily block the positions below the kick-off points of the vertical wells A and D, and drill a kick-off section E and a horizontal section F towards the bottom of the vertical well A respectively, and drill a kick-off section B and a horizontal section C towards the bottom of the vertical well D according to the azimuth indication of the magnetic field generator, and form a connected common well section in the horizontal section;

[0009] S3: Remove the blocked parts of the vertical wells A and D, and block the kick-off section B and the kick-off section E to finally form a connected well;

[0010] S4: Vertically install water injection pipe strings in the vertical well A and the vertical well D respectively. The upper ends of the two water injection pipe strings extend outside the vertical well A and the vertical well D respectively, and vertically install brine discharge pipe strings in the two water injection pipe strings respectively. The upper ends of the two brine discharge pipe strings extend outside the two water injection pipe strings respectively;

[0011] Alternately inject clear water into the vertical well A and the vertical well D, perform cavity solution operation on the thin salt layer, and discharge the brine from the brine discharge pipe string of the opposite vertical well.

[0012] The beneficial effects of the present invention are as follows: During the cavity building process, after the vertical well A and the vertical well D are drilled, alternately inject clear water into the vertical well A and the vertical well D, perform cavity solution operation on the thin salt layer, and discharge the brine from the brine discharge pipe string of the opposite vertical well to complete the cavity building operation.

[0013] The double-branch well convection cavity building method adopted by the present invention can improve the utilization rate of salt rock in the thin salt layer, increase the cavity solution speed, shorten the cavity building period, and has high efficiency.

[0014] On the basis of the above technical solutions, the present invention can also be improved as follows.

[0015] Further, the completion drilling depth of the vertical well A and the vertical well D is 5 - 10 m above the lower surface of the thin salt layer.

[0016] The beneficial effect of adopting the above further solution is that the completion drilling depth of the vertical well A and the vertical well D is reasonably designed, ensuring the smooth progress of the cavity solution operation on the thin salt layer to complete the cavity building operation.

[0017] Further, the cementing depth of the vertical well A and the vertical well D is 15 - 20 m below the upper surface of the thin salt layer.

[0018] The beneficial effect of adopting the above further solution is that the cementing depth of the vertical well A and the vertical well D is reasonably designed, ensuring the smooth progress of the cavity solution operation on the thin salt layer to complete the cavity building operation.

[0019] Further, the wellhead spacing between the vertical well A and the vertical well D is greater than 200 m.

[0020] The beneficial effect of adopting the above further solution is that the spacing between the wellheads of the vertical well A and the vertical well D is reasonably designed, which can not only ensure the efficiency of cavity building but also avoid cross-operation.

[0021] Further, the depths of the horizontal well section C and the horizontal well section F are the same, and the distance from the thin salt layer is 5 - 10 m.

[0022] The beneficial effect of adopting the above further solution is that the depths of the horizontal well section C and the horizontal well section F are reasonably designed, which is convenient for connection.

[0023] Further, the magnetic field generator in S1 is an electrode with active magnetic guidance.

[0024] The beneficial effect of adopting the above further solution is that during the operation process, the electrode can release electromagnetic signals and form an electromagnetic field. A probe tube is installed on the drill bit, and the probe tube can detect the information of the magnetic field to judge the orientation.

[0025] Further, the two electrodes are respectively suspended in the vertical well A and the vertical well D through cables.

[0026] The beneficial effect of adopting the above further solution is that the structure is simple, the design is reasonable, and the electrode assembly is convenient.

[0027] Further, in S2, the vertical well sections of the vertical well A and the vertical well D are blocked by open-hole packers.

[0028] The beneficial effect of adopting the above further solution is that the structure is simple, the design is reasonable, and the open-hole packer is used to block the vertical well sections of the vertical well A and the vertical well D, and the blocking operation is convenient.

[0029] Further, in S2, when drilling the build sections E and B, inclinators need to be installed at the build points of the vertical well A and the vertical well D respectively.

[0030] The beneficial effect of adopting the above further solution is that the structure is simple, the design is reasonable, and the cement section is conveniently processed through the inclinator.

[0031] Further, the vertical well A and the vertical well D are respectively three-opening well structures.

[0032] The beneficial effect of adopting the above further solution is that the three-opening well structure is reasonably designed, which can not only improve the drilling efficiency but also reduce the accident risk. Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of the completion stage of the vertical well A and the vertical well D in the present invention;

[0034] Figure 2 It is a schematic structural diagram of the completion stage of the first branch well in the present invention;

[0035] Figure 3 It is a schematic structural diagram of the completion stage of the second branch well section in the present invention;

[0036] Figure 4 It is a schematic structural diagram of the blockage of the build sections B and E in the present invention;

[0037] Figure 5 It is a schematic structural diagram of the convective cavity formation stage in the present invention;

[0038] Figure 6This is the top view of the present invention.

[0039] In the drawings, the list of components represented by each reference numeral is as follows:

[0040] 1. Salt rock formation; 2. Vertical well A; 3. Vertical well D; 4. Electrode; 5. Cable; 6. Open hole packer; 7. Inclinator; 8. Cement section; 9. First connection point; 10. Second connection point; 11. Cavity; 12. Water injection string; 13. Brine discharge string. Detailed implementation manners

[0041] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0042] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installed", "connected", "connected to" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0044] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0045] Embodiment 1

[0046] As Figures 1 to 6 shown, this embodiment provides a method for building a cavity in a thin salt layer double-branch well, including the following specific steps:

[0047] S1: Drill vertical wells A2 and D3 at intervals in the salt rock formation 1, and place magnetic field generators in the vertical wells A2 and D3 respectively;

[0048] S2: According to the designed wellbore trajectory, temporarily block the positions below the kick-off points of the vertical wells A2 and D3, and drill the kick-off section E and the horizontal section F towards the bottom of the vertical well A2 respectively according to the azimuth indication of the magnetic field generator, drill the kick-off section B and the horizontal section C towards the bottom of the vertical well D3, and form a connected common well section in the horizontal section;

[0049] Preferably, perform kick-off and horizontal drilling according to the designed wellbore trajectory so that the horizontal section communicates with the bottom of the opposite vertical well;

[0050] When the bit is unstable when the horizontal well sections C and F are just connected, attention should be paid to controlling the well inclination angle and azimuth angle, and the connected part can also be a point connection;

[0051] S3: Remove the blocked parts of the vertical wells A2 and D3, block the kick-off sections B and E, and finally form a connected well;

[0052] S4: Vertically install water injection pipe strings 12 in the vertical wells A2 and D3 respectively. The upper ends of the two water injection pipe strings 12 extend outside the vertical wells A2 and D3 respectively, and vertically install brine discharge pipe strings 13 in the two water injection pipe strings 12 respectively. The upper ends of the two brine discharge pipe strings 13 extend outside the two water injection pipe strings 12 respectively;

[0053] Alternately inject clear water into the vertical wells A2 and D3, perform cavity solution operation on the thin salt layer, and discharge the brine from the brine discharge pipe string of the opposite vertical well.

[0054] During the cavity building process, after the vertical wells A2 and D3 are drilled, alternately inject clear water into the vertical wells A2 and D3, perform cavity solution operation on the thin salt layer, and discharge the brine from the brine discharge pipe string of the opposite vertical well to complete the cavity building operation.

[0055] Based on the above scheme, the kick-off sections E and B are blocked with cement sections 8 respectively.

[0056] Preferably, in this embodiment, the two vertical wells have two connection points and a common well section, and the length of the common well section is not limited and can also be only one connection point.

[0057] Based on the above scheme, this embodiment uses two drilled vertical wells, and other appropriate numbers of vertical wells can also be used, such as drilling three vertical wells. The specific process is as follows:

[0058] Inject water into one of the vertical wells, and carry out brine drainage operations in the remaining two vertical wells; or, inject water into two of the vertical wells, and carry out brine drainage in the remaining one vertical well.

[0059] The double-branch well convection cavity-forming method adopted in this embodiment can improve the utilization rate of salt rock in thin salt layers, increase the cavity-forming speed, shorten the cavity-forming construction period, and has high efficiency.

[0060] Embodiment 2

[0061] On the basis of Embodiment 1, in this embodiment, the completion depths of the vertical well A2 and the vertical well D3 are 5-10 m above the lower surface of the thin salt layer.

[0062] The completion depths of the vertical well A2 and the vertical well D3 are reasonably designed to ensure the smooth progress of the cavity-forming operation in the thin salt layer to complete the cavity construction operation.

[0063] Preferably, in this embodiment, the completion depths of the vertical well A2 and the vertical well D3 are 7 m above the lower surface of the thin salt layer.

[0064] Embodiment 3

[0065] On the basis of the above embodiments, in this embodiment, the cementing depths of the vertical well A2 and the vertical well D3 are 15-20 m below the upper surface of the thin salt layer.

[0066] The cementing depths of the vertical well A2 and the vertical well D3 are reasonably designed to ensure the smooth progress of the cavity-forming operation in the thin salt layer to complete the cavity construction operation.

[0067] Preferably, in this embodiment, the cementing depths of the vertical well A2 and the vertical well D3 are 17 m below the upper surface of the thin salt layer.

[0068] Embodiment 4

[0069] On the basis of the above embodiments, in this embodiment, the wellhead spacing between the vertical well A2 and the vertical well D3 is greater than 200 m.

[0070] The spacing between the wellheads of the vertical well A2 and the vertical well D3 is reasonably designed, which can not only ensure the efficiency of cavity construction, but also avoid cross operations.

[0071] Embodiment 5

[0072] On the basis of the above embodiments, in this embodiment, the horizontal well section C and the horizontal well section F have the same depth, and the depth from the thin salt layer is 5-10 m.

[0073] The depths of the horizontal well section C and the horizontal well section F are reasonably designed for convenient connection.

[0074] Embodiment 6

[0075] Based on the above embodiments, in this embodiment, the magnetic field generator in S1 is the active magnetic guiding electrode 4.

[0076] During the operation process, the electrode 4 can release electromagnetic signals and form an electromagnetic field. A probe pipe is installed on the drill bit, and the probe pipe can detect the information of the magnetic field to judge the orientation.

[0077] Embodiment 7

[0078] Based on the above embodiments, in this embodiment, the two electrodes 4 are respectively suspended in the vertical well A2 and the vertical well D3 through cables 5.

[0079] This scheme has a simple structure, reasonable design, and convenient electrode assembly. Since the directional accuracy requirement of this well is relatively high, the positioning accuracy of magnetic guidance can be improved by increasing the current.

[0080] It should be noted that the electrode 4 needs to be taken out after the vertical well A2 and the vertical well D3 are processed.

[0081] Embodiment 8

[0082] Based on the above embodiments, in this embodiment, in S2, the vertical well sections of the vertical well A2 and the vertical well D3 are plugged by the open-hole packer 6.

[0083] This scheme has a simple structure, reasonable design, and uses the open-hole packer 6 to plug the vertical well sections of the vertical well A2 and the vertical well D3, and the plugging operation is convenient.

[0084] It should be noted that the above open-hole packer 6 uses the existing technology, and its specific structure and principle will not be elaborated here.

[0085] When the horizontal well section C and the horizontal well section F are just connected, the drill bit is unstable. Therefore, attention should be paid to controlling the well inclination angle and azimuth angle, and the connected part can also be a point connection.

[0086] Embodiment 9

[0087] Based on the above embodiments, in this embodiment, in S2, when drilling the build-up section E and the build-up section B, inclinators 7 need to be installed at the build-up points of the vertical well A2 and the build-up points of the vertical well D3 respectively.

[0088] This scheme has a simple structure, reasonable design, and is convenient to process the cement section through the inclinator 7.

[0089] It should be noted that the above inclinator 7 uses the existing technology, and its specific structure and principle will not be elaborated here.

[0090] In addition, after the drilling operation is completed, both the open-hole packer 6 and the inclinator 7 need to be taken down to avoid affecting the subsequent cavity building operation.

[0091] Example 10

[0092] Based on the above embodiments, in this embodiment, the vertical well A2 and the vertical well D3 are respectively of a three-opening well structure.

[0093] The use of a three-opening well structure for the vertical well A2 and the vertical well D3 is reasonable in design, which can not only improve the drilling efficiency but also reduce the accident risk.

[0094] The process of building a cavity in the present invention is as follows:

[0095] S1: Drill the vertical well A2 and the vertical well D3 at intervals in the salt rock formation 1, and place magnetic field generators in the vertical well A2 and the vertical well D3 respectively;

[0096] S2: According to the designed wellbore trajectory, temporarily block the positions below the kick-off points of the vertical well A2 and the vertical well D3, and drill the kick-off section E and the horizontal section F towards the bottom of the vertical well A2 respectively according to the azimuth indication of the magnetic field generator, drill the kick-off section B and the horizontal section C towards the bottom of the vertical well D3, and form a connected common well section in the horizontal section;

[0097] S3: Remove the blocked parts of the vertical well A2 and the vertical well D3, block the kick-off section B and the kick-off section E, and finally form a connected well;

[0098] S4: Vertically install water injection pipe strings 12 in the vertical well A2 and the vertical well D3 respectively. The upper ends of the two water injection pipe strings 12 extend outside the vertical well A2 and the vertical well D3 respectively, and vertically install brine discharge pipe strings 13 in the two water injection pipe strings 12 respectively. The upper ends of the two brine discharge pipe strings 13 extend outside the two water injection pipe strings 12 respectively;

[0099] Alternately inject clear water into the vertical well A2 and the vertical well D3 to perform cavity operation on the thin salt layer, and discharge the brine from the brine discharge pipe string 13 of the opposite vertical well.

[0100] As Figure 1 shown, this figure is a schematic structural diagram of the stage of drilling vertical wells. Drill the vertical well A2 and the vertical well D3 in the thin salt layer. The well spacing between the two wells is greater than 200 m. The completion depth of the vertical well A and the vertical well D is 5 - 10 m above the lower surface of the thin salt layer. The wellbore is selected with a three-opening structure. Cementing is carried out to 15 - 20 m below the upper surface of the thin salt layer for the three openings, and the standard for qualified cementing quality is that the length of the qualified cement bond quality section should reach more than 70% of the length of the well section to be cemented.

[0101] As Figure 2As shown in the figure, this is the structural schematic diagram of the completed branch I well. After the vertical wells A2 and D3 are completed, an electrode 4 suspended by a cable 5 is placed into the vertical well D3. The cable 5 and the electrode 4 are components of an active magnetic guidance tool, which are used for the azimuth control of subsequent directional wells. Before sidetracking, a barefoot packer 6 and an inclinometer 7 are installed to seal the lower vertical well section of the target point to prevent drilling fluid from directly flowing into the thin salt layer during sidetracking and to achieve well sidetracking. At the same time, the cable is powered on to discharge the electrode, and the current converges on the casing to generate an alternating magnetic field. During the drilling process, the relative position of the probe is judged according to the magnitude of the magnetic field. Finally, the horizontal section C is connected to the bottom of the vertical well D. The directional drilling process includes the build section B and the horizontal section C. After completion, the cable 5 and the electrode 4 are lifted and placed into the build section B.

[0102] As Figure 3 shown in the figure, this is the structural schematic diagram of the completed branch II well. Its completion process is the same as that of the branch I well, and both require the installation of a barefoot packer 6 and an inclinometer 7. During the directional drilling process, with the help of the magnetic guidance tool, the horizontal section C and the horizontal section F are first connected. Subsequently, the cable 5 and the electrode 4 are lifted into the vertical well A and drilling continues to connect the horizontal section F to the bottom of the vertical well A. The directional well section includes the build section E and the horizontal section F. The lengths of the horizontal section C and the horizontal section F are greater than 200m. After the completion of the branch II well, the first connection point 9, the second connection point 10 and a partially shared horizontal well section are formed with the branch I well. The active magnetic guidance technology is currently relatively mature and can fully meet the technical requirements. The accuracy of the relative position between the probe and the target well can be increased by increasing the current. If a drilling deviation causes the well not to be connected, the requirements can be met by dissolving and connecting.

[0103] As Figure 4 shown in the figure, this is the structural schematic diagram of the connection between the branch I well and the branch II well. The lower parts of the build section B and the build section E are sealed with a barefoot packer 6 and cement is injected. The barefoot packer 6 in the vertical well section is opened, and finally a connected well composed of the vertical well A, the horizontal section F, the horizontal section C and the vertical well B is formed. It should be noted that when the horizontal well section C and the horizontal well section F are just connected, the drill bit is unstable. Therefore, attention should be paid to controlling the well inclination angle and azimuth angle, and the connection of the above wells can also be ensured when the connected well section is a single-point connection.

[0104] As Figure 5 shown in the figure, this is the structural schematic diagram of the cavity formation stage. The injection-production string is lowered into the vertical wells A2 and D3. To ensure the stability of the cavity shape, the cavity can be formed by alternately injecting fresh water into the injection pipe string 12 in the two vertical wells and discharging the brine from the opposite side brine discharge pipe string 13, and ensuring that the time for injecting fresh water into the vertical wells A2 and D3 is the same. When a blockage occurs in one side of the brine discharge pipe string, the brine discharge well should be switched in time for backwashing and dredging the brine discharge pipe string. After dredging, the original planned gas injection and brine discharge time plan should be followed. In addition, the cavity shape can also be controlled by injecting a solvent inhibitor.

[0105] It should be noted that Figure 5 In the middle salt rock formation 1, the oval dotted line is the shape of the cavity 11 formed by the dissolution of the thin salt layer, without any other substantial meaning.

[0106] As Figure 6 shown, this figure is a top-view structural schematic diagram of the trajectories of the branch well I (i.e., the vertical well A) and the branch well II (i.e., the vertical well D). Among them, the build-up sections B and E are not part of the connected wells and thus are not fluid flow channels. Fluids can flow in from the vertical well A, flow through the horizontal section F, the common well section, and the horizontal section C, and finally flow out from the vertical well D, or can flow in the reverse direction.

[0107] The advantages of the present invention are as follows:

[0108] 1. In traditional horizontal connection well cavity formation, the salt rock below the target point often fails to be effectively dissolved. Therefore, this part of the underground space usually cannot be utilized, which further limits the development utilization rate and economic benefits of the thin salt layer. The present invention provides a solution for the full utilization of the salt rock resources in the thin salt layer and an innovation in engineering foundation for the improvement of the underground cavity space of the salt cavern.

[0109] 2. The double-branch well convection cavity formation method adopted by the present invention can increase the cavity dissolution speed and shorten the cavity formation construction period. Since the length of the open hole section is generally greater than 200m, the flow-through time of the brine in the horizontal well section is long, the contact area with the salt rock is large, and the concentration of the discharged brine is relatively high.

[0110] 3. The present invention uses the active magnetic guidance technology to judge the well inclination and azimuth of the directional well, and finally connects the horizontal section and the bottom of the vertical well. The accuracy of this technology can meet the construction requirements on site and reduces the construction time of the pre-construction slot.

[0111] The purpose of the present invention is to improve the salt rock dissolution rate in the salt cavern formation stage through the advantages of the drilling process, apply the advantages of domestic branch well drilling technology and active magnetic guidance tools to the field of salt cavern formation in thin salt layers, which can not only improve the underground space utilization rate of thin salt layers, but also expand the site selection range of thin salt layer formations. The method of building a cavity with a double-branch well in a thin salt layer provides a new idea for improving the cavity dissolution of thin salt layers.

[0112] It should be noted that all the electronic components involved in the present invention adopt existing technologies, and the above-mentioned components are electrically connected to the controller. The control circuit between the controller and each component is an existing technology.

[0113] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0114] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, 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 building a double-branch well in a thin salt layer, characterized in that: The specific steps include: S1: drilling a vertical well A (2) and a vertical well D (3) in a salt rock formation (1) at intervals, and placing a magnetic field generator in the vertical well A (2) and the vertical well D (3), respectively; S2: According to the designed wellbore trajectory, temporarily block the position below the inclination point of the vertical well A (2) and the vertical well D (3), and according to the azimuth indication of the magnetic field generator, drill the inclination section E and the horizontal section F to the bottom of the vertical well A (2), and drill the inclination section B and the horizontal section C to the bottom of the vertical well D (3), and form a connected common well section in the horizontal section; S3: Unblocking the plugged parts of the vertical well A (2) and the vertical well D (3), blocking the deflection section B and the deflection section E, and finally forming a connecting well; S4: vertically installing water injection pipe columns (12) in the vertical well A (2) and the vertical well D (3), respectively, with the upper ends of the two water injection pipe columns (12) extending to the outside of the vertical well A (2) and the vertical well D (3), respectively; and vertically installing brine removal pipe columns (13) in the two water injection pipe columns (12), respectively, with the upper ends of the two brine removal pipe columns (13) extending to the outside of the two water injection pipe columns (12); Clean water is alternately injected into the vertical well A (2) and the vertical well D (3) to perform cavity dissolution operations on the thin salt layer, and brine is discharged from the brine drainage pipe column (13) of the vertical well on the opposite side.

2. The method for building a double-branch well in a thin salt layer according to claim 1, characterized in that: The vertical well A (2) and the vertical well D (3) are drilled to a depth of 5-10 m above the lower surface of the thin salt layer.

3. The method for building a double-branch well in a thin salt layer according to claim 1, characterized in that: The cementing depth of the vertical well A (2) and the vertical well D (3) is 15-20 m below the upper surface of the thin salt layer.

4. The method for building a double-branch well in a thin salt layer according to claim 1, characterized in that: The distance between the wellheads of the vertical well A (2) and the vertical well D (3) is greater than 200m.

5. The method for building a double-branch well in a thin salt layer according to claim 1, characterized in that: The horizontal well section C and the horizontal well section F have the same depth, and are 5-10 m deep from the thin salt layer.

6. The method for building a double-branch well in a thin salt layer according to any one of claims 1 to 5, characterized in that: The magnetic field generator in S1 is an active magnetically guided electrode (4).

7. The method for building a double-branch well in a thin salt layer according to claim 6, characterized in that: The two electrodes (4) are respectively suspended in the vertical well A (2) and the vertical well D (3) through cables (5).

8. The method for building a double-branch well in a thin salt layer according to any one of claims 1 to 5, characterized in that: In S2, the vertical well sections of the vertical well A (2) and the vertical well D (3) are plugged using open hole packers (6).

9. The method for building a double-branch well in a thin salt layer according to any one of claims 1 to 5, characterized in that: In S2, when drilling the deflection section E and the deflection section B, it is necessary to install inclinators (7) at the deflection points of the vertical well A (2) and the vertical well D (3), respectively.

10. The method for building a double-branch well in a thin salt layer according to any one of claims 1 to 5, characterized in that: The vertical well A (2) and the vertical well D (3) are respectively three-well structures.

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