A Salt Mine Directional Connecting Well Fully Horizontal Section Suspended Tailpipe Mining System

Abstract

This utility model relates to the technical field of salt mine mining, and more particularly to a fully horizontal section suspended tailpipe mining system for directional docking wells in salt mines. The system includes: a vertical well, with its bottom vertically penetrating the salt layer, and a single well forming a convection channel to create a solution cavity; a directional docking well, comprising a horizontal section and a vertical section; wherein the horizontal section communicates with the solution cavity, the bottom of the vertical section extends into the salt layer, and its end forms a fluid channel with the solution cavity through a tailpipe installed inside the horizontal section, with brine extraction channels arrayed on the tailpipe; casing, respectively installed in the vertical sections of the vertical well and the directional docking well, with cemented sheaths between them and their respective well walls; and a production control unit, including a wellhead device, surface pipelines, and flow and pressure monitoring equipment. The wellhead device is installed at the wellhead positions of both the vertical and directional docking wells, and the surface pipelines connect to the wellhead device to form water injection and brine extraction loops. This system solves the technical problems of low efficiency and poor safety in traditional salt mine mining.

Description

Technical Field

[0001] This utility model relates to the technical field of salt mine mining, and in particular to a salt mine directional docking well full horizontal section suspended tailpipe mining system. Background Technology

[0002] Salt mine water-soluble mining is a mining method that utilizes the water-soluble property of salt minerals. Fresh water or circulating brine is injected into underground ore layers through drilling, dissolving the minerals in situ to form saturated or near-saturated brine. This brine is then extracted to the surface for processing and refining. The drilling methods involved include vertical wells, directional wells, and horizontal wells. Vertical wells are vertically drilled into the salt layer below the surface for injecting fresh water; directional wells are inclined wells with a borehole trajectory deviating from the plumb line for recovering brine; and horizontal wells are near-horizontal brine extraction wells located within the salt layer to connect directional and vertical wells.

[0003] In the field of salt mine karst mining, especially for thick, low-grade rock salt deposits, traditional directional and horizontal well completion methods face two major technical bottlenecks: sand blockage accidents and top salt layer collapse accidents. The technical mechanisms are as follows: In directional wells, due to the large wellbore inclination, the production pipe opening is located at the bottom of the karst cavity. When mining thick, low-grade salt deposits, a large amount of sediment deposits can block the inlet passage of the inclination well. In horizontal wells, the exposed salt layer and roof above the mining layer lose support as the karst cavity expands, leading to collapse and blockage of the horizontal section. Both types of accidents can cause premature decommissioning of the connected well group, severely shortening its service life.

[0004] Therefore, a well completion method is needed that can simultaneously solve the problem of vertical plugging of insoluble material accumulation and the problem of horizontal roof protection. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] This invention provides a fully horizontal section suspended tailpipe mining system for directional docking wells in salt mines, which aims to simultaneously solve the problems of vertical sealing of insoluble material accumulation and roof protection of the horizontal section of the salt layer.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, this utility model proposes a fully horizontal section suspended tailpipe mining system for directional docking wells in salt mines, comprising:

[0009] A vertical well, with its bottom penetrating vertically downwards through the salt layer and communicating with the solution cavity inside the salt layer;

[0010] The directional docking well includes a horizontal well section and a vertical well section that are interconnected; wherein, one end of the horizontal well section is connected to the solution cavity, the bottom of the vertical well section extends into the salt layer, and the end of the vertical well section forms a fluid channel with the solution cavity through a tailpipe set inside the horizontal well section, and the tailpipe has brine extraction channels arrayed on its pipe wall;

[0011] The casing is respectively installed in the vertical shaft section of the vertical well and the directional docking well, and a cementing sheath is provided between it and the well wall of each well.

[0012] The production control unit includes a wellhead device, surface pipelines, and flow and pressure monitoring equipment. The wellhead device is installed at the wellhead of the vertical well and the directional docking well, respectively. The surface pipelines are connected to the wellhead device to form a water injection and brine extraction circuit.

[0013] A further technical solution is that the tailpipe is attached to the bottom of the vertical shaft section and connected to the casing inside the vertical shaft section through a hanger, and a sealing element is also provided between the tailpipe and the casing.

[0014] A further technical solution includes an elastic centralizer corresponding to the hanger, the elastic centralizer being sleeved on the outside of the casing and embedded in the cementing sheath.

[0015] A further technical solution is that the brine extraction channel is a circular hole or a slit, and the circular hole or slit is arranged in a matrix along the pipe wall of the tailpipe.

[0016] A further technical solution is that the bottom of the vertical shaft section has a curved structure, and corresponding to the curved structure, one end of the tailpipe has a matching curved connection part, the curved connection part is matched and connected with the curved structure, and the end of the tailpipe away from the curved connection part is connected to the cavity.

[0017] A further technical solution is that the tailpipe is an oil casing with a wall thickness ≥ 6 mm.

[0018] A further technical solution is that the angle range of the curved structure is 50-60°.

[0019] The salt mine directional docking well fully horizontal section suspended tailpipe mining method using the above mining system includes the following steps:

[0020] S1. Drill a vertical well to 3-5m below the bottom plate of the salt layer, determine the mining layer through well logging, then run in the casing, inject cement slurry to form a cement sheath, and implement single-well convection trenching at the mining layer to form an initial solution cavity.

[0021] S2. Drill a directional docking well to the mining stratum, determine the build-up point, and perform directional drilling at the build-up point to form the inclined structure. Then, run in the casing and cement the well.

[0022] S3. Within the mining layer, drill to the solution cavity through directional drilling along the tangential direction of the opening of the inclined structure to form a horizontal well section;

[0023] S4. Install the tailpipe with the hanger at the bend and angled structure, and seal it.

[0024] S5. Install wellhead equipment, surface pipelines, and flow and pressure monitoring equipment.

[0025] A further technical solution is that the trajectory control of the directional drilling adopts a measurement-while-drilling system.

[0026] (III) Beneficial Effects

[0027] This invention involves installing a tailpipe in the horizontal section of a directional drilling well. The tailpipe effectively supports the horizontal section within the salt layer, preventing collapse accidents induced by the continuous dissolution of the salt layer. Simultaneously, because the tailpipe is equipped with a brine extraction channel, and one end of the tailpipe connects to the melting cavity, brine extraction operations can be carried out simultaneously throughout the entire horizontal section of the well, improving salt mining efficiency. Furthermore, the tailpipe expands the mud and sand accumulation space at the bottom of the directional drilling well. This is particularly beneficial for low-grade salt layers, significantly reducing blockage at the bottom of the well and extending the overall service life of the wellbore. Attached Figure Description

[0028] Figure 1 A schematic cross-sectional view of the directional docking well's fully horizontal section suspended tailpipe mining system;

[0029] Figure 2 for Figure 1 Enlarged view of point A in the middle.

[0030] [Explanation of Labels in the Attached Image]

[0031] 1: Vertical well; 2: Directional docking well; 21: Horizontal section; 22: Vertical section; 221: Inclined structure; 3: Casing; 4: Tailpipe; 41: Brine extraction channel; 42: Inclined connection; 5: Solution cavity; 6: Cementing sheath; 7: Hanger; 8: Salt layer. Detailed Implementation

[0032] To better explain and facilitate understanding of this utility model, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] This embodiment provides a fully horizontal section suspended tailpipe mining system for directional docking wells in salt mines, referring to... Figure 1and Figure 2 As shown, the system includes: a vertical well 1, which penetrates vertically downwards through a salt layer 8 and communicates with a solution cavity 5 inside the salt layer 8; a directional docking well 2, comprising a horizontal well section 21 and a vertical well section 22 that are interconnected; wherein one end of the horizontal well section 21 communicates with the solution cavity 5, the bottom of the vertical well section 22 extends into the salt layer 8, and its end forms a fluid channel with the solution cavity 5 through a tailpipe 4 disposed inside the horizontal well section 21, and the tailpipe 4 has brine extraction channels 41 arrayed on its wall; a casing 3, respectively disposed in the vertical well section 22 of the vertical well 1 and the directional docking well 2, and a cementing sheath 6 is disposed between the casing 3 and the well wall of each well; and a production control unit, including a wellhead device, surface pipelines, and flow and pressure monitoring equipment, wherein the wellhead device is installed at the wellhead positions of the vertical well 1 and the directional docking well 2, and the surface pipelines are connected to the wellhead device to form a water injection and brine extraction circuit.

[0034] It should be noted that in the field of directional drilling, the axis of a horizontal well is not perfectly horizontal, but rather maintains a small angle with the horizontal plane. This is determined based on the orientation of the salt layer during actual production. In this embodiment, the horizontal section 21 of the directional docking well 2 is also not parallel to the horizontal plane; there is an angle between them. Furthermore, the casing 3 inside the vertical well 1 only needs to extend above the top plate of the salt layer 8. The vertical section 22 of the directional docking well 2 has an angle of 0-3° with the plumb line, preferably a vertical 0° angle.

[0035] Specifically, the entire section of vertical well 1 is cemented with casing 3, penetrating the salt layer 8 at the bottom and connecting to the solution cavity 5, which serves the function of water injection for salt dissolution. Vertical well 1 is chosen because its vertical wellbore structure eliminates the need for complex trajectory design and precise directional control technology; it can be implemented quickly and efficiently using conventional drill pipes and drill bits, making it very convenient. The solution cavity 5 is an underground cavity located at the bottom of vertical well 1, used to dissolve and extract salt minerals. Its core principle is based on the fact that salt is easily soluble in water, while the surrounding rocks (such as mudstone, sandstone, gypsum, etc.) are insoluble or sparingly soluble. By injecting fresh water or brine into the salt layer 8, the target salt minerals are dissolved, and the resulting saturated brine is extracted to the surface, while the surrounding rocks remain intact, thus forming an underground cavity. The directional docking well 2 relies on a high-precision measurement-while-drilling system for real-time three-dimensional trajectory adjustment, ensuring that its own wellbore trajectory is precisely connected to another well at a predetermined underground location, ultimately forming a closed fluid channel. The production control unit includes a hydraulically controlled wellhead device, a high-precision electromagnetic flowmeter, and an intelligent pressure transmitter. The wellhead device consists of pipes and valves. A high-precision electromagnetic flowmeter is connected in series with the outlet pipe to monitor the water injection volume, while an intelligent pressure transmitter is installed on the brine extraction branch. All three are connected to the production control system via a bus to form a closed-loop control system: when the flowmeter detects an abnormal water injection, the hydraulic actuator automatically adjusts the valve opening, and the pressure transmitter synchronously feeds back the pressure data from the extraction chamber 5, ensuring injection-production balance and providing real-time production data feedback.

[0036] Furthermore, casing 3 can adopt a three-layer structure: surface casing 3 seals off shallow water, technical casing 3 isolates complex formations, and production casing 3 is mounted on tailpipe 4. The end of the vertical shaft section 22 of the directional docking well 2 is connected to the tailpipe 4 with screen holes by suspension. The screen holes are the brine extraction channels 41 mentioned above. The horizontal section of tailpipe 4 extends to the solution cavity 5, forming a fully horizontal brine extraction operation.

[0037] Traditional directional drilling suffers from long open borehole sections in horizontal wells. During production, if insoluble substances such as mud and sand accumulate to a certain level in the solution cavity 5, it can easily cause slag blockage in the vertical well during well-turning operations. Furthermore, the long open borehole section makes it susceptible to roof collapse during mining, which can also block the channel and severely impact normal production. In contrast, the directional docking well 2 in this design utilizes a suspended perforated tailpipe 4 extending to the solution cavity 5. This enhances the support of the horizontal well section while achieving efficient brine extraction across the entire horizontal segment, significantly improving the efficiency and safety of salt mining. The casing 3 structure isolates complex formations, ensuring stable water injection. The intelligent closed-loop system of the production control unit monitors injection and production parameters in real time, automatically adjusting flow and pressure to prevent pressure imbalances in the solution cavity 5 that could lead to collapse, and also optimizes the purity of the extracted brine. This system maximizes the extraction of resources from salt layer 8 while reducing drilling costs.

[0038] In this embodiment, the tailpipe 4 is attached to the bottom of the vertical shaft section 22 and connected to the casing 3 inside the vertical shaft section 22 via a hanger 7. A seal is also provided between the tailpipe 4 and the casing 3. Specifically, the tailpipe 4 has a certain degree of flexibility, ensuring smooth lowering along the vertical shaft section 22 of the directional docking well 2, and adaptively bending at the bottom of the vertical shaft section 22 to reach the designated position in the horizontal shaft section 21. The hanger 7 is an expansion hanger 7. During installation, the expansion hanger 7 is pressurized using a drill pipe lowering hydraulic device until it is pressed into the casing 3, forming a fitting connection and achieving a firm fixing effect. The cooperation between the tailpipe 4 and the expansion hanger 7 improves the reliability and sealing of the bottom connection of the directional docking well 2. The hydraulic pressure installation method ensures a connection strength far exceeding that of conventional threaded fixing. The seal can be a nickel alloy C-ring, designed to isolate the wellbore from the formation and prevent brine contamination.

[0039] In this embodiment, the system also includes an elastic centralizer corresponding to the hanger 7. The elastic centralizer is sleeved on the outside of the casing 3 and embedded in the cementing sheath 6. Specifically, the elastic centralizer is pre-installed on the outside of the casing 3 before the cementing sheath 6 is poured to ensure that the centering of the casing 3 is ≥80%, thereby ensuring the centering of the tailpipe 4. The elasticity of the elastic centralizer can automatically compensate for wellbore irregularities during cement pouring, ensuring the alignment of the casing 3 with the wellbore.

[0040] In this embodiment, the brine extraction channel 41 is either a circular hole or a slotted pipe, and the circular holes or slotted pipes are arranged in a matrix along the pipe wall of the tailpipe 4. In this embodiment, a slotted pipe is preferred. The matrix-distributed slots can form a uniform fluid inlet, effectively reducing the flow resistance of the brine and preventing local blockage. This structure also enhances the overall strength of the tubing string, making it less prone to deformation under formation pressure, and providing a reliable guarantee for long-term stable mining.

[0041] In this embodiment, the bottom of the vertical shaft section 22 has a bend structure 221. Corresponding to the bend structure 221, one end of the tailpipe 4 has a matching bend connection part 42. The bend connection part 42 is matched and connected to the bend structure 221. The end of the tailpipe 4 away from the bend connection part 42 is connected to the cavity 5. In this embodiment, the angle is preferably 20°. The tailpipe 4 uses API standard N80 oil casing with a wall thickness ≥6mm. The bend angle range of the bend structure 221 is 50-60°. In this embodiment, it is preferably 55°.

[0042] The specific construction method of the above system is as follows: First, drill a vertical well 1 to 3-5m below the bottom plate of salt layer 8, determine the production layer through well logging, then run casing 3, inject cement slurry to form a complete cementing annulus, and implement single-well convection trenching at the production layer to form an initial solution cavity 5. Second, drill a directional docking well 2 to the production layer, determine the build-up point, and perform directional drilling at the build-up point to form a curved structure 221, then run casing 3 and cement. Next, within the production layer, drill directionally to the solution cavity 5 along the tangential direction of the opening of the curved structure 221, forming a horizontal well section 21. Afterwards, install the tailpipe 4 with the hanger 7 at the curved structure 221 and seal it. Finally, install the wellhead equipment, surface pipelines, and flow and pressure monitoring equipment. The trajectory control of the directional drilling uses a measurement-while-drilling (MWD) system to ensure precise docking with the vertical well 1.

[0043] A certain salt mine, with a burial depth of approximately 1000 meters, a ore layer thickness of approximately 40 meters, and an ore grade of approximately 50%, was originally mined using a horizontal docking shaft system with one vertical shaft and one inclined shaft. The inclined shaft casing was lowered to an inclination angle of approximately 55°. After two years of operation, the brine wells experienced varying degrees of blockage, some even completely blocked, making mining impossible. Repairs and side-drilling with open windows were the only options for continued mining, significantly increasing costs. However, using the directional docking shaft fully horizontal section suspended tailpipe mining method described in this embodiment, the brine wells have been operating normally for over five years and are still being mined without any blockages.

[0044] The specific implementation method of the mining system in the above case is as follows:

[0045] Step 1: Drill vertically downwards above salt layer 8 to a depth of 725.86 meters. Then, core drilling begins to 832.97 meters. Next, casing 3 with a diameter of 177.8 mm is run in and cemented. Then, drilling and hole cleaning operations are carried out. After that, tubing with a diameter of 88.9 mm is run in to the bottom of salt layer 8 to form a convection channel 5.

[0046] Step 2: Drill directional docking well 2 to a depth of 676.03 meters. Core drilling begins at 734.58 meters. The salt layer 8 is compared with the salt layer 8 of the planned docking vertical well 1 to determine the mining layer. Inclined drilling begins at 589.15 meters.

[0047] Step 3: directional drilling is carried out using directional drilling technology, with a curvature radius of 150 meters, a build-up angle of 94.85 meters, and a well inclination angle of 55°. Casing 3 with a diameter of 177.8 mm is then run in and cemented.

[0048] Step 4: Using directional drilling technology, continuously drill in the horizontal section 21 of salt layer 8 to a depth of 810.78 meters and connect with the pre-designed vertical well 1 cavity 5 to form a connecting channel.

[0049] Step 5: Lower the combination of hanger 7 and tailpipe 4 into the horizontal well section 21. The combination of the hanging tailpipe 4 includes tailpipe 4 and hanger 7. Tailpipe 4 covers the entire horizontal section to the vertical well 1 cavity 5. After adjusting the position of tailpipe 5, apply pressure to hanger 7 to achieve the fixed installation of tailpipe 5.

[0050] Step 6: Install wellhead equipment and surface pipelines to enable full horizontal mining of salt layer 8.

[0051] It's important to clarify that "coring drilling" is a special drilling technique whose core purpose is to extract as complete as possible cylindrical rock samples that retain their original geological structure and physical properties as possible during the drilling process. "Hole cleaning" is a routine operation in drilling engineering, referring to the process of using a drilling rig and its tools to clean, unclog, and refine an existing borehole from top to bottom. Its core purpose is to restore or maintain the borehole's patency, regular geometry (diameter, verticality / inclination), and stability, creating conditions for subsequent drilling, logging, casing installation, well completion, or other operations. "Single-well convection trenching" refers to the process of running tubing into the well, injecting water into the tubing, and allowing water to drain from the annulus between the tubing and casing or the wellbore, dissolving the underlying salt layer and forming a solution cavity.

[0052] This embodiment achieves complete coverage of the tailpipe 4 across the entire horizontal section of the directional docking well 2 by suspending the tailpipe 4. This effectively prevents salt debris blockage, improves mining efficiency and wellbore stability, and enables efficient and safe mining of the salt layer 8. It solves the technical problems of low efficiency and poor safety in traditional salt mining. Simultaneously, this system can extend the service life of salt wells, reduce subsequent maintenance costs, and generate significant economic and social benefits.

[0053] It should be noted that all directional indicators in this embodiment, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the attached figure. If the specific posture changes, the directional indicator will also change accordingly.

[0054] Furthermore, in this embodiment, the use of terms such as "first" and "second" is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of those features. In the description of this embodiment, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0055] In this embodiment, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this embodiment according to the specific circumstances.

[0056] It should be understood that the above description of specific embodiments of this utility model is only for illustrating the technical route and features of the present invention, and its purpose is to enable those skilled in the art to understand the content of this utility model and implement it accordingly. However, this utility model is not limited to the specific embodiments described above. All changes or modifications made within the scope of the claims of this utility model should be covered by the protection scope of this utility model.

Claims

1. A fully horizontal section suspended tailpipe mining system for directional docking wells in salt mines, characterized in that, include: The vertical well (1) penetrates the salt layer (8) vertically downwards at the bottom and is connected to the solution cavity (5) inside the salt layer (8); The directional docking well (2) includes a horizontal well section (21) and a vertical well section (22) that are interconnected; wherein, one end of the horizontal well section (21) is connected to the solution cavity (5), the bottom of the vertical well section (22) extends into the salt layer (8), and the end of the vertical well section (22) forms a fluid channel with the solution cavity (5) through a tail pipe (4) set inside the horizontal well section (21), and brine extraction channels (41) are arrayed on the pipe wall of the tail pipe (4). The casing (3) is respectively installed in the vertical shaft section (22) of the vertical shaft (1) and the directional docking shaft (2), and a cementing ring (6) is provided between it and the shaft wall of each shaft. The production control unit includes a wellhead device, a surface pipeline, and a flow and pressure monitoring device. The wellhead device is installed at the wellhead positions of the vertical well (1) and the directional docking well (2), respectively. The surface pipeline is connected to the wellhead device to form a water injection and brine extraction circuit.

2. The salt mine directional docking well full-horizontal section suspended tailpipe mining system as described in claim 1, characterized in that, The tailpipe (4) is attached to the bottom of the vertical shaft section (22) and connected to the casing (3) inside the vertical shaft section (22) via a hanger (7). A sealing element is also provided between the tailpipe (4) and the casing (3).

3. The salt mine directional docking well full-horizontal section suspended tailpipe mining system as described in claim 2, characterized in that, It also includes an elastic centralizer corresponding to the hanger (7), the elastic centralizer being sleeved on the outside of the casing (3) and embedded in the cementing sheath (6).

4. The salt mine directional docking well full-horizontal section suspended tailpipe mining system as described in claim 1, characterized in that, The brine extraction channel (41) is a round hole or a slit, and the round hole or slit is arranged in a matrix along the pipe wall of the tail pipe (4).

5. A salt mine directional docking well fully horizontal section suspended tailpipe mining system as described in claim 1, characterized in that, The bottom of the vertical shaft section (22) has a curved structure (221). Corresponding to the curved structure (221), one end of the tail pipe (4) has a matching curved connection part (42). The curved connection part (42) is matched and connected with the curved structure (221). The end of the tail pipe (4) away from the curved connection part (42) is connected to the cavity (5).

6. The salt mine directional docking well fully horizontal section suspended tailpipe mining system as described in claim 1, characterized in that, The tailpipe (4) is an oil casing with a wall thickness of ≥6mm.

7. The salt mine directional docking well full-horizontal section suspended tailpipe mining system as described in claim 5, characterized in that, The angle range of the curved structure (221) is 50-60°.

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