Coal bed gas dual-well linkage integrated workover method

Abstract

The application discloses a coal bed gas double-well linkage integrated well repair method and belongs to the technical field of coal bed gas exploration and development. The method is used for solving the blockage problem of a U-shaped butt joint well cavity section and a horizontal communication section caused by factors such as fracturing interference of a neighboring well, sand production of a coal bed and coal powder settlement. The method comprises the following steps: S1, wellbore pretreatment and blockage drilling and grinding, wherein a roller bit is used to cooperate with a sand setting pipe to positively circulate to drill and grind and break solid blockage; and S2, positively circulating high-pressure jetting and reverse circulating air lifting combined liquid level lowering, wherein special short connections are used to realize the cooperative operation of positively circulating clean water high-pressure jetting and reverse circulating air compressor air lifting. The application breaks the traditional single-well operation mode, proposes a double-well linkage well repair concept of cooperative operation of a vertical well and a horizontal well, realizes synchronous well repair and neighboring well production, shortens a well repair period by about 40% compared with conventional single-well operation, and improves the powder and dust removal efficiency of the cavity section by more than 3 times, so that the application has remarkable economic benefits and application value.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane exploration and development technology, specifically to a method for integrated well workover of two coalbed methane wells. Background Technology

[0002] A U-shaped coalbed methane well consists of a vertical well and a horizontal well (or directional well) connected at a distance through a cavern or horizontal section within the target coal seam, forming a U-shaped wellbore structure. This well type can effectively expand the coal seam drainage area and increase the controlled reserves of a single well, and has been widely applied in coalbed methane blocks such as Qianxi and Qinshui.

[0003] However, after a period of operation, U-shaped wells are prone to blockage in the connecting channels (including the cave section and the horizontal section) between vertical and horizontal wells due to factors such as well-to-well interference from fracturing operations of adjacent wells, coal seam sand production, coal dust settling, and backflow of fracturing proppant. This leads to a significant decrease in gas production or even production stoppage. This application takes the Dingxin 1 well group in the western wing block of the Qianxi syncline as an example. This well group consists of a U-shaped well, namely Dingxin 1 (vertical well) and Dingxin 1-1H (horizontal well), to develop the No. 9 coal seam of the Longtan Formation. After fracturing operations of adjacent wells, the wellhead pressure abnormally increased to 10.5 MPa. After shutting in, the pressure stabilized at 2.2 MPa. A large amount of solid impurities, sand, coal dust, coal slime, and black viscous liquid accumulated in the wellbore, and the connecting channels in the horizontal section were basically lost.

[0004] To address the aforementioned issues, conventional well workover techniques typically employ a single-well operation mode, which involves running a sand flushing string into a vertical well for forward or reverse circulation sand flushing. However, in U-shaped wells, blockages often occur deep within cavernous or horizontal sections, presenting the following technical bottlenecks for single-well sand flushing:

[0005] The flow rate of the flushing fluid is extremely low in the cave and horizontal sections, resulting in poor sand-carrying capacity and difficulty in effectively removing solid impurities such as sand and coal dust. Conventional sand-removing tools encounter severe obstruction in the cave sections, leading to slow progress with a daily advance of only 0.1 to 0.3 meters and low operational efficiency. It is impossible to accurately determine the connectivity between vertical and horizontal wells, resulting in blind well repair operations. During well repair, adjacent wells need to be shut down, affecting the overall production of the well group and damaging economic benefits.

[0006] Therefore, there is an urgent need for an integrated well workover method for coalbed methane wells that can achieve coordinated operation between the two wells, accurately determine the connectivity status, efficiently remove deep blockages, and ensure normal production of adjacent wells during the workover process. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a coalbed methane dual-well linkage integrated well workover method. Through the coordinated operation of vertical and horizontal wells, a combination of processes including positive circulation high-pressure jet flushing, reverse circulation gas lift to lower the liquid level, synchronous monitoring of liquid level in both wells, step-by-step gas lift unblocking, and dual-well water injection verification is adopted to effectively solve the blockage problem of the cavity section and horizontal connecting section of the U-shaped docking well and restore the gas production capacity of the well group.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a coalbed methane dual-well linkage integrated well workover method, based on a docking well, wherein the docking well includes a vertical well and a horizontal well, and the vertical well and the horizontal well are remotely connected in the target coal seam section through a cavern or horizontal section, the method comprising:

[0009] S1: Drilling string is run into the vertical well and the solid blockage in the wellbore and cavern section is broken up by drilling and grinding in a positive circulation manner until the artificial bottom of the well or the designed depth is reached.

[0010] S2: After the drill string is pulled out, a jet flushing string is run into the vertical well. Clean water is used to perform high-pressure jetting through a positive circulation pump to flush the debris at the entrance of the cave section and the horizontal section. At the same time, high-pressure gas is injected into the vertical well through an air compressor to perform reverse circulation air lift, carrying the flushing fluid and debris to the surface.

[0011] S3: Install water level measuring instruments at the wellheads of vertical and horizontal wells respectively, and monitor the liquid level depth of vertical and horizontal wells simultaneously. When the difference between the liquid level difference between vertical and horizontal wells and the difference between the elevation difference at the wellheads of vertical and horizontal wells is within the allowable range of measurement error, it is determined that the liquid levels of vertical and horizontal wells are at the same level, and it is preliminarily inferred that the vertical and horizontal wells have established a hydraulic connection.

[0012] S4: Based on the initial inference of connectivity, continue to use a stepped liquid level reduction method for deep gas lift unblocking; during the gas lift process, monitor the pump pressure and return fluid status of the vertical well and the liquid level changes of the horizontal well; when there are phenomena such as stuck drill handling, large amount of water coming out of the surface pipeline continuously, and a rapid drop in the liquid level of the horizontal well in a short period of time, it is determined that the connection between the vertical well and the horizontal well has been opened.

[0013] S5: Inject a fixed amount of clean water into the horizontal wellhead and monitor the liquid level changes in the vertical well simultaneously; when the liquid level in the vertical well rises significantly within a short period after injection, and the liquid level change pattern is consistent across multiple tests, it is confirmed that the vertical well and the horizontal well are fully connected.

[0014] S6: After the connection verification is completed, a sand-removal tubing string is run into the vertical well to remove the residual sand and debris at the bottom of the well to the designed depth. Then, a completion tubing string and drainage equipment are run into the well to resume well production.

[0015] Furthermore, in step S1, the drilling string includes a roller cone drill bit, a sand setter, and a drill rod; the sand setter is used to collect the debris generated during the drilling process; during the drilling process, the drill bit is slowly reamed up and down 15 to 40 times, with each stroke being 4 to 6 meters, and paused at intervals of 0.5 to 2 hours, so that the broken debris is fully returned.

[0016] Furthermore, in step S1, the drilling and grinding are carried out in stages, including: first, using low drilling pressure and low rotation speed for exploratory drilling and grinding, and after the operation is stable, gradually increasing the drilling pressure and rotation speed; after drilling and grinding to the designed depth, observing the change in sand surface return height through multiple sand surface grinding and washing, and when the sand surface return height tends to stabilize, it indicates that the blockage in the cave section and around the wellbore has been basically cleared.

[0017] Furthermore, in step S2, the jet flushing string includes a special short connector and a drill pipe. The special short connector is a variable diameter short connector that is machined and adapted on-site according to the wellhead equipment and drill pipe specifications. One end of the special short connector is connected to the wellhead flange and seamless pipe, and the other end is connected to the drill pipe, which is used to realize the channel switching between positive circulation high-pressure jet and reverse circulation gas lift.

[0018] The positive circulation pump gradually increases its flow rate from the initial discharge rate to the target discharge rate. The reverse circulation air lift adopts a stepped liquid level reduction method, with each liquid level reduction depth ranging from 130m to 150m, and the effective air lift time for a single cycle is 2 to 3 minutes.

[0019] Furthermore, in step S3, the allowable range of measurement error is ±2m; the elevation difference at the wellhead of the vertical well and the horizontal well is obtained through previous measurement data, and the fluid level difference is the difference between the fluid level depth of the vertical well and the fluid level depth of the horizontal well.

[0020] Furthermore, in step S4, the specific operation of the stepped liquid level reduction is as follows: record the current liquid level depth before each gas lift, measure the actual liquid level reduction depth after the gas lift is completed, and carry out the next gas lift after the wellbore stabilizes; the target depth for deep gas lift dredging is the bottom of the cave section or the entrance of the horizontal section.

[0021] Furthermore, in step S4, when the fluid level in the vertical well drops to near the cave section and a large amount of water continuously sprays out of the surface pipeline after the stuck drill is dealt with, and the fluid level in the horizontal well drops by 80 to 120 meters within 5 to 10 minutes, this is used as a key criterion for opening the connection between the vertical and horizontal wells.

[0022] Furthermore, in step S5, the injection volume of a quantitative amount of clean water is 3-4 m³, the liquid level rise within a short period of time is not less than 50 m, the test is conducted at least twice, and the interval between the two tests is not less than 12 hours.

[0023] Furthermore, in step S5, during the verification process of the experiment, the adjacent well is kept in normal production. The impact of the well repair operation on the adjacent well is judged by monitoring the bottom flow pressure of the adjacent well. The adjacent well is another well in the same well group as the docking well that is currently producing. The adjacent well is kept in normal production throughout the well repair operation. The bottom flow pressure of the adjacent well is monitored in real time. If there is no abnormal fluctuation in the flow pressure, it is determined that the well repair operation has not interfered with the adjacent well.

[0024] Furthermore, in step S6, the sand-removing string includes a sand-removing pen tip, a sand-removing pump, and thickened tubing. The residual debris is carried out of the wellbore using a positive circulation flushing method. After sand is removed to the designed depth, a completion string including a plug, screen pipe, screw pump, pressure gauge support, and thickened tubing is installed, along with a sucker rod and drive unit.

[0025] Compared with the prior art, the present invention achieves the following beneficial effects:

[0026] This invention is the first to propose a U-shaped docking well dual-well linkage well workover concept, breaking the limitations of traditional single-well operations. By coordinating the operation of vertical and horizontal wells and utilizing the hydraulic connection between the two wells, bidirectional removal of blockages is achieved, significantly improving workover efficiency. In the field application of the Dingxin 1 well group, after adopting the method of this invention, the connection between the two wells was restored from a completely blocked state to a fully connected state, and the workover cycle was shortened by approximately 40% compared to conventional single-well operations.

[0027] This invention innovatively employs a combined process of forward circulation high-pressure jet flushing and reverse circulation air lift to lower the liquid level. The forward circulation high-pressure jet effectively impacts solid deposits at the entrances of cave sections and horizontal sections, while the reverse circulation air lift utilizes the gas density difference to create a powerful suction effect, rapidly carrying the broken-up debris and liquid to the surface. The two processes complement each other, solving the technical challenges of low flow velocity and poor sand-carrying capacity in cave sections when using a single flushing method. Field practice shows that the combined process can increase the debris removal efficiency in cave sections by more than three times.

[0028] This invention establishes a connectivity determination method based on synchronous monitoring of liquid levels in two wells. By comparing the consistency between the liquid level difference and the elevation difference at the wellheads of the two wells, the connectivity status is initially inferred. Further verification is achieved through the rapid changes in the liquid level of the horizontal well during a stepped gas lift process and water injection in both wells, ultimately confirming the opening of the connectivity channel. This method changes the passive situation of blind flushing and retrieval in traditional well workover operations, achieving precise and controllable well workover processes. During the workover of the Dingxin 1 well group, the timing of connectivity was successfully predicted using liquid level monitoring data, avoiding ineffective operations.

[0029] The stepped gas lift method for lowering the liquid level proposed in this invention avoids drastic pressure fluctuations and coal seam damage caused by a single large-scale drop in liquid level. This is achieved by controlling the liquid level lowering depth to be 130m-150m and the single gas lift time to be 2-3 minutes. The stepped operation ensures gas lift efficiency while protecting the original stress state of the coal seam, preventing coal seam collapse and increased sand production caused by a sudden drop in pressure.

[0030] This invention enables simultaneous well workover and production from adjacent wells. Throughout the entire well workover process in the Dingxin 1 well group, the Dingxin 1-X2 well in the same group maintained normal pumping. Real-time monitoring of the bottomhole flowing pressure of adjacent wells confirmed that the workover operation did not interfere with them. This minimizes the impact of well workover on the overall production of the well group, resulting in significant economic benefits.

[0031] The process of this invention is highly adaptable and can flexibly adjust the parameter combination of drilling, flushing, and gas lift according to the actual blockage situation downhole. It has good applicability to U-shaped docking wells with different degrees of blockage and different well structures. Attached Figure Description

[0032] Further details, features, and advantages of this application are disclosed in the following description of exemplary embodiments in conjunction with the accompanying drawings, in which:

[0033] Figure 1 This is a flowchart of the method of the present invention;

[0034] Figure 2 This is a schematic diagram of the docking well structure and well workover operation of the present invention;

[0035] Figure 3 This is a schematic diagram illustrating the principle of synchronous monitoring of liquid levels in two wells according to the present invention.

[0036] Figure 4 This is a schematic diagram of the combined operation of forward circulation high-pressure injection and reverse circulation air lift according to the present invention;

[0037] Figure 5 This is a schematic diagram illustrating the principle of dual-well water injection connection verification of the present invention. Detailed Implementation

[0038] Several embodiments of this application will now be described in more detail with reference to the accompanying drawings to enable those skilled in the art to implement this application. This application may be embodied in many different forms and for various purposes and should not be limited to the embodiments set forth herein. These embodiments are provided to make this application thorough and complete, and to fully convey the scope of this application to those skilled in the art. The embodiments described do not limit this application.

[0039] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It will be further understood that terms such as those defined in commonly used dictionaries shall be interpreted as having a meaning consistent with their meaning in the relevant field and / or the context of this specification, and shall not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0040] Example 1:

[0041] Please see Figure 1 A coalbed methane dual-well linkage integrated well workover method, based on docking wells, including a vertical well and a horizontal well, wherein the two wells are remotely connected in the target coal seam section through a cavern or horizontal section. The method includes the following steps:

[0042] S1. Wellbore pretreatment and blockage grinding: A drilling string is lowered into the vertical well. The drilling string includes a roller cone bit, a sand-filled pipe, and a drill pipe. The solid blockage in the wellbore and the cavern section is ground and broken up using a positive circulation method. The drilling is carried out to the artificial bottom of the well or the designed depth. During the drilling process, the hole is slowly reamed up and down 15 to 40 times, with each stroke being 4 to 6 meters, and then paused for 0.5 to 2 hours at intervals to allow the broken debris to be fully returned.

[0043] The drill string assembly consists of a 215.9mm roller cone bit, a 5m long 194mm sand-collecting pipe, and an 89mm drill rod. The sand-collecting pipe is used to collect the debris generated during the drilling process to prevent debris accumulation from causing secondary stuck drill bit.

[0044] The drilling and grinding operation is carried out in stages. First, a small drilling pressure and low speed are used for exploratory drilling and grinding. After the drill bit runs smoothly, the drilling pressure and speed are gradually increased. After drilling to the designed depth, the sand surface is repeatedly tested and washed to observe the changes in the sand surface return height. When the sand surface return height tends to stabilize, it indicates that the blockage in the cave section and around the wellbore has been basically cleared.

[0045] S2. Combined High-Pressure Jetting and Reverse Gas Lift for Liquid Level Reduction: After the drill string is pulled out, a jet flushing string is run into the vertical well. The jet flushing string includes a special connector and drill pipe. High-pressure jetting with clean water is used to flush the debris at the entrance of the cavern section and the horizontal section. At the same time, high-pressure gas is injected into the vertical well through an air compressor for reverse gas lift, carrying the flushing fluid and debris to the surface. The positive circulation pumping rate is gradually increased from the initial discharge rate to the target discharge rate. The reverse gas lift adopts a stepped liquid level reduction method, with the liquid level reduction depth controlled at 130m to 150m each time, and the effective gas lift time controlled at 2 to 3 minutes per cycle.

[0046] Among them, the special short connector is a variable diameter short connector that is processed on-site to fit the wellhead equipment and drill pipe specifications. One end of the special short connector is connected to the wellhead flange and the ∅165mm seamless pipe, and the other end is connected to the drill pipe. It is used to realize the channel switching between positive circulation high-pressure injection and reverse circulation gas lift.

[0047] The pumping rate of the positive circulation high-pressure injection is increased in stages: the initial stage pumping rate is 80-90 L / min, the middle stage is increased to 130-150 L / min, and the later stage is increased to 250-260 L / min; the air compressor pressure of the reverse circulation air lift is not less than 3.0 MPa, and the air lift parameters are dynamically adjusted according to the sand content and color change of the returned liquid during the air lift process.

[0048] S3. Simultaneous monitoring of liquid levels in two wells and preliminary judgment of connection status: Install water level measuring instruments at the wellheads of the vertical well and the horizontal well respectively to simultaneously monitor the liquid level depth of the two wells; when the difference between the liquid level height of the two wells and the difference between the elevation of the wellheads of the two wells is within the allowable range of measurement error, it is determined that the liquid levels of the two wells are at the same level, and it is preliminarily inferred that the two wells have established a hydraulic connection.

[0049] It should be noted that the allowable range of measurement error is ±2m; the elevation difference between the wellheads of the two wells was obtained from previous measurement data, and the fluid level difference is the difference between the fluid level depth of the vertical well and the fluid level depth of the horizontal well.

[0050] S4. Stepped gas lift deep dredging: Based on the initial inference of connectivity, continue to use a stepped liquid level reduction method for deep gas lift dredging; during the gas lift process, closely monitor the pump pressure and return fluid status of the vertical well and the liquid level changes of the horizontal well; when there are phenomena such as stuck drill post-treatment, large amount of water coming out of the surface pipeline continuously, and a sharp drop in the liquid level of the horizontal well in a short period of time, it is determined that the connecting channel between the two wells has been opened.

[0051] The specific operation of the stepped liquid level reduction is as follows: record the current liquid level depth before each gas lift, measure the actual liquid level reduction depth after the gas lift is completed, and carry out the next gas lift after the wellbore stabilizes; the target depth for the depth gas lift dredging is the bottom of the cave section or the entrance of the horizontal section.

[0052] When a stuck drill occurs near the cavern section when the fluid level in a vertical well is lowered, and after the stuck drill is dealt with, a large amount of water continues to gush out of the surface pipeline, while the fluid level in the horizontal well drops by 80 to 120 meters within 5 to 10 minutes, this is a key criterion for opening up the connection between the two wells.

[0053] S5. Verification of Dual-Well Water Injection Connection: Inject a fixed amount of clean water from the horizontal wellhead and simultaneously monitor the liquid level changes in the vertical well. When the liquid level in the vertical well rises significantly within a short period after injection, and the liquid level change pattern is consistent across multiple tests, it is confirmed that the two wells are fully connected. During the verification process, maintain normal drainage and production in the adjacent well, and determine the impact of well repair operations on the adjacent well by monitoring the bottom flow pressure of the adjacent well.

[0054] The injection volume of the quantitative clean water is 3-4 m³, the liquid level rise is not less than 50 m in a short period of time, and the test is conducted at least twice, with an interval of not less than 12 hours between the two tests.

[0055] The adjacent well is another well in the same well group as the U-shaped docking well that is currently being drained; the well workover operation maintains normal drainage of the adjacent well throughout the entire process. By monitoring the bottom flow pressure of the adjacent well in real time, if there is no abnormal fluctuation in the flow pressure, it is determined that the well workover operation has not interfered with the adjacent well.

[0056] S6. Sand Removal Completion: After the connection verification is completed, a sand removal string is run into the vertical well to remove the residual sand and debris at the bottom of the well to the designed depth. Then, a completion string and drainage equipment are run into the well to resume well production.

[0057] The sand-removal string includes a sand-removal pen tip, a sand-removal pump, and thickened tubing. It uses a positive circulation flushing method to carry the residual debris out of the wellbore. After sand is removed to the designed depth, a completion string including a plug, screen, screw pump, pressure gauge support, and thickened tubing is installed, along with a sucker rod and drive unit.

[0058] Example 2:

[0059] A coalbed methane dual-well linkage integrated well workover system includes drilling equipment, an air compressor system, a skid-mounted pump system, a liquid level monitoring device, a special short-connector and wellhead device, and sand removal and well completion equipment.

[0060] Drilling equipment, including XG 360 drilling rigs or XSL20 / 1000 drilling rigs, is used to provide the rotational power and lifting capacity required for drilling operations;

[0061] An air compressor system, comprising at least two air compressors with a single unit pressure of not less than 3.0 MPa, for providing the high-pressure gas required for reverse circulation air lift;

[0062] Skid-mounted pump systems, including the Model 700 pump, are used to provide the pumped-in fluid required for positive circulation high-pressure jet flushing;

[0063] A liquid level monitoring device, including a water level measuring instrument, is installed at the wellheads of the vertical well and the horizontal well, respectively, for synchronously monitoring the liquid level depth of the two wells;

[0064] Specialized shorting and wellhead devices, including field-machined reducing shortings, wellhead flanges, and seamless pipes, are used to achieve channel switching and sealing between positive and reverse circulation.

[0065] Sand removal and well completion equipment, including workover trucks, sand removal tubing, completion tubing and drainage equipment, are used for sand removal and well completion operations in the later stages of well workover.

[0066] Example 3:

[0067] Dual-well coordinated well workover of Dingxin 1 well group: This embodiment takes Dingxin 1 well group in the western wing block of Qianxi syncline in Guizhou Province as an example to explain in detail the specific implementation process of the coalbed methane dual-well coordinated integrated well workover method of the present invention.

[0068] I. Basic Overview of the Well Group: The Dingxin 1 well group consists of a U-shaped docking well, comprising Dingxin 1 (vertical well) and Dingxin 1-1H (horizontal well), with the target formation being the No. 9 coal seam of the Longtan Formation. The basic parameters of the two wells are shown in the table below:

[0069]

[0070] The well group was put into production on December 15, 2024, after the pumping operation was completed. Overflow occurred at the wellhead during the initial pumping operation. After the pump was deepened in March 2025, normal production continued until November 6, 2025, with a daily water production of 3.7 m³, a daily gas production of 2900 m³, and a bottomhole flowing pressure of 0.645 MPa. In November 2025, after fracturing operations in conjunction with an adjacent well, the tubing was pulled out and the well was shut in. After shut-in, the wellhead pressure abnormally increased and stabilized at 2.2 MPa, indicating severe blockage in the cavernous section and the horizontal connecting section.

[0071] II. Well Workover Operation Implementation Process

[0072] (a) Wellbore pretreatment and drilling of blockages

[0073] 1. Equipment Arrival and Drill String Preparation: The XG 360 drilling rig and its supporting facilities will arrive on site. Based on the well structure and the nature of the blockage, a 5m long ∅194mm sand-removing pipe and a sand-retrieving pipe will be fabricated on-site. The drill string assembly will consist of a ∅215.9mm roller cone bit, a 5m (∅194mm) sand-removing pipe, and a ∅89mm drill pipe.

[0074] 2. Drilling and Grinding Operation: Drilling was conducted using a positive circulation method to a depth of 675.26m. During drilling, initial exploratory drilling was performed with low drill pressure and low rotation speed. Once the drill string was running smoothly, parameters were gradually increased. After reaching the designed depth, a sand-finding and grinding operation was carried out: the hole was slowly reamed 15–40 times, each stroke approximately 4–6m, followed by a rest period of 0.5–2 hours before continuing sand-finding and grinding. Through multiple grinding operations, the sand surface rise was successively 0.3m, 0.6m, 0.8m, and 1.4m, indicating that the blockages in the cavity section and around the wellbore were gradually being cleared. Simultaneously, an air compressor was prepared to lower the fluid level.

[0075] (ii) Combined forward circulation high-pressure injection and reverse circulation air lift to lower the liquid level

[0076] 1. Equipment preparation: The air compressor (single unit pressure ≥3.0MPa) is in place, and a special short connector is machined. One end of the special short connector is connected to the wellhead flange and ∅165mm seamless pipe, and the other end is connected to the drill pipe, realizing the channel switching between positive circulation high-pressure injection and reverse circulation air lift.

[0077] 2. Combined Fluid Level Lowering Operation: From January 31st to February 3rd, 2026, the fluid level was lowered to 662m using air compressors. Drilling commenced on February 4th and 5th, employing a combination of high-pressure jetting with positive water circulation and reverse air circulation to remove debris from the wellbore. On February 6th, the sand level was lowered by 0.4m, and flushing was carried out in the well section from 668.86m to 674.86m. The positive circulation pumping rate was increased from the initial 83L / min to 140L / min, and the reverse circulation was used to lower the fluid level to 674.56m. On February 7th, the sand level was lowered by 0.6m, and flushing continued in the well section from 668.86m to 674.66m. The positive circulation pumping rate was increased from 140L / min to 255L / min, and the reverse circulation was used to lower the fluid level to approximately 674.56m. On February 8th, at a depth of 672.26m, the fluid level was directly lowered using air compressors, continuing high-pressure flushing with positive circulation combined with reverse air lift.

[0078] (III) Simultaneous monitoring of liquid levels in both wells and preliminary assessment of connectivity

[0079] The XSL20 / 1000 drilling rig and its supporting facilities arrived on site. The drill string assembly was updated to a ∅215.9mm roller cone bit and a ∅127mm drill pipe. Wellhead flanges were machined, ∅165mm seamless pipes were purchased and installed, and preparations were made for positive circulation to lower the fluid level.

[0080] Before drilling, water level gauges were installed at the wellheads of Dingxin 1 (vertical well) and Dingxin 1-1H (horizontal well) to simultaneously measure the fluid level depth in both wells. The measured fluid level depth in Dingxin 1 was 131m, and in Dingxin 1-1H it was 199m, with a fluid level difference of 68.0m. The elevation difference between the two wellheads was 68.07m. After considering measurement errors, the fluid level difference and elevation difference were basically consistent. Based on this, it was preliminarily inferred that a hydraulic connection had been established between the two wells, and the connecting passage may have been partially restored.

[0081] (iv) Stepped airlift depth dredging

[0082] Based on the initial assessment, a stepped liquid level reduction method was adopted to continue clearing the blockage. Considering the significant force of the positive circulation air lift, for safety reasons, each liquid level reduction was controlled at 130m-150m, and each effective air lift required 2-3 minutes to complete. March 3: The air compressor reduced the liquid level to 460.80m, and the water level of Dingxin 1-1H well was measured at 204.10m; March 4: Before reducing the liquid level, the water level of Dingxin 1-1H well was measured at 204.4m. At 10:00, when the liquid level was further reduced to 644.00m, a stuck drill anomaly occurred, with no water output from the surface pipeline and a large amount of gravel spraying out of the pipeline. During the stuck drill handling process, the torque increased, and after the stuck drill was resolved, a large amount of water continued to spray from the surface pipeline for 30 minutes without stopping. At the same time, the liquid level in the horizontal well dropped sharply by about 100m within about 7 minutes. The above phenomena indicate that the connecting passage between the two wells has been cleared. Subsequently, the drilling reached a depth of 651.8m in the sand surface. After communicating with the client, the liquid level was lowered, and air lifting continued for 25 minutes, with water continuously gushing out. The drilling continued until the sand surface reached 669.05m before the air lifting was stopped.

[0083] (v) Verification of dual-well water injection connection

[0084] To further confirm that the bottoms of the two wells are completely connected, a dual-well water injection verification test was conducted:

[0085] First verification (March 4, 17:30): About 3.5m³ of clean water was injected from Dingxin 1-1H well. At 17:32, the liquid level in Dingxin 1 well rose rapidly from 329.10m to 248.8m, with a rise of 80.3m.

[0086] Second verification (March 5, 14:12): The water injection test continued, and the liquid level change pattern was similar to that of the first test.

[0087] The results of the two tests were consistent, confirming that the two wells were fully connected. Meanwhile, throughout the entire well workover process, the Dingxin 1-X2 well in the same well group maintained normal pumping, and real-time monitoring showed no abnormal changes in the bottom hole flowing pressure, proving that the workover operation did not interfere with the adjacent well.

[0088] (vi) Sand removal and well completion

[0089] The workover truck entered the site to carry out sand removal and pump completion operations. Sand was removed to a depth of 675.33m, and residual sand and debris at the bottom of the well were cleared. The completion string was then run in, from bottom to top: an 89mm plug, one 73mm thickened tubing, a screen (with a 4m 36mm inner tube), an 80mm screw pump, a pressure gauge holder, and 65 73mm thickened tubing sections. The pressure gauge was run to a depth of 650.64m, the pump was run to a depth of 654.68m, and the screen was run to a depth of 656.32m. The following sucker rods were then run in: 79 22mm sucker rods, 3 22mm sucker rod sections (totaling 3.5m), 9.20m of 32mm polished rod, and a remaining 1.50m of polished rod. The lifting distance for preventing impact is 0.40m; the drive unit is hoisted, the water pipeline is connected, the well site is restored, and the well repair operation is completed.

[0090] III. Well Repair Results

[0091] After adopting the dual-well linkage workover process method of this invention, the connection channels between the two wells in the Dingxin 1 well group were restored from a completely blocked state to a fully connected state. During the workover process, the timing of connection was accurately determined by synchronous monitoring of the liquid level in both wells and step-by-step gas lift, avoiding ineffective operations; the combined application of positive circulation high-pressure injection and reverse circulation gas lift effectively cleared solid blockages in the cavern section and horizontal section; the adjacent wells maintained normal production throughout the workover process, without causing any additional impact on the well group's production.

[0092] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A coalbed methane dual-well linkage integrated well workover method, based on docking wells, wherein the docking wells include a vertical well and a horizontal well, and the vertical well and the horizontal well are remotely connected in the target coal seam section through a cavern or horizontal section, characterized in that... The method includes: S1: Drilling string is lowered into the vertical well, and solid blockages in the wellbore and cavern section are broken up by drilling and grinding in a positive circulation manner until the artificial bottom of the well or the designed depth is reached. S2: After the drilling string is pulled out, a jet flushing string is lowered into the vertical well. Clean water is used to perform high-pressure jetting through a positive circulation pump to flush the debris at the entrance of the cave section and the horizontal section. At the same time, high-pressure gas is injected into the vertical well through an air compressor to perform reverse circulation air lift, carrying the flushing fluid and debris to the surface. S3: Install water level measuring instruments at the wellheads of the vertical well and the horizontal well respectively, and simultaneously monitor the liquid level depth of the vertical well and the horizontal well. When the difference between the liquid level difference between the vertical well and the horizontal well and the difference between the elevation difference at the wellheads of the vertical well and the horizontal well is within the allowable range of measurement error, it is determined that the liquid levels of the vertical well and the horizontal well are at the same level, and it is preliminarily inferred that the vertical well and the horizontal well have established a hydraulic connection. S4: Based on the initial inference of connectivity, continue to use a stepped liquid level reduction method for deep gas lift unblocking; during the gas lift process, monitor the pump pressure and return fluid status of the vertical well and the liquid level changes of the horizontal well; when phenomena such as stuck drill handling, large amount of water flowing out of the surface pipeline continuously, and the liquid level of the horizontal well dropping sharply in a short period of time occur, it is determined that the connection channel between the vertical well and the horizontal well has been opened; S5: Inject a fixed amount of clean water into the horizontal wellhead and simultaneously monitor the liquid level change in the vertical well; when the liquid level in the vertical well rises significantly within a short period after injection, and the liquid level change pattern is consistent across multiple tests, it is confirmed that the vertical well and the horizontal well are fully connected. S6: After the connection verification is completed, a sand-removal tubing string is run into the vertical well to remove the residual sand and debris at the bottom of the well to the designed depth. Then, a completion tubing string and drainage equipment are run into the well to resume well production.

2. The integrated well workover method for dual-well coalbed methane operations according to claim 1, characterized in that, In step S1, the drilling string includes a roller cone drill bit, a sand setter, and a drill rod; the sand setter is used to collect the debris generated during the drilling process; during the drilling process, the drill bit is slowly reamed up and down 15 to 40 times, with each stroke being 4 to 6 meters, and paused at intervals of 0.5 to 2 hours, so that the broken debris is fully returned.

3. The integrated well workover method for dual-well coalbed methane operations according to claim 2, characterized in that, In step S1, the drilling and grinding are carried out in stages, including: first, using low drilling pressure and low rotation speed for exploratory drilling and grinding, and after the operation is stable, gradually increasing the drilling pressure and rotation speed; after drilling and grinding to the designed depth, observing the change in sand surface return height through multiple sand surface grinding and washing, and when the sand surface return height tends to stabilize, it indicates that the blockage in the cave section and around the wellbore has been basically cleared.

4. The integrated well workover method for dual-well coalbed methane operations according to claim 1, characterized in that, In step S2, the jet flushing string includes a special short connector and a drill pipe. The special short connector is a variable diameter short connector that is machined and adapted on-site according to the wellhead equipment and drill pipe specifications. One end of the special short connector is connected to the wellhead flange and seamless pipe, and the other end is connected to the drill pipe, which is used to realize the channel switching between positive circulation high-pressure jet and reverse circulation gas lift. The positive circulation pump gradually increases its flow rate from the initial discharge rate to the target discharge rate. The reverse circulation air lift adopts a stepped liquid level reduction method, with each liquid level reduction depth ranging from 130m to 150m and the effective air lift time for a single operation being 2 to 3 minutes.

5. The integrated well workover method for dual-well coalbed methane operations according to claim 1, characterized in that, In step S3, the allowable range of measurement error is ±2m; the elevation difference between the wellheads of the vertical well and the horizontal well is obtained through previous measurement data, and the fluid level difference is the difference between the fluid level depth of the vertical well and the fluid level depth of the horizontal well.

6. The integrated well workover method for dual-well coalbed methane operations according to claim 1, characterized in that, In step S4, the specific operation of the stepped liquid level reduction is as follows: record the current liquid level depth before each gas lift, measure the actual liquid level reduction depth after the gas lift is completed, and carry out the next gas lift after the wellbore stabilizes; the target depth for the depth gas lift dredging is the bottom of the cave section or the entrance of the horizontal section.

7. The integrated well workover method for dual-well coalbed methane operations according to claim 6, characterized in that, In step S4, when the vertical well is lowered to the vicinity of the cave section and a stuck drill occurs, and after the stuck drill is dealt with, a large amount of water continuously sprays out of the ground pipeline, and at the same time the fluid level of the horizontal well drops by 80 to 120 meters within 5 to 10 minutes, this is used as a key criterion for opening the connection between the vertical well and the horizontal well.

8. The integrated well workover method for dual coalbed methane wells according to claim 1, characterized in that, In step S5, the injection volume of the quantitative clean water is 3-4 m³, the liquid level rise is not less than 50 m in a short period of time, the test is conducted at least twice, and the interval between the two tests is not less than 12 hours.

9. A method for integrated well workover of two coalbed methane wells according to claim 8, characterized in that, In step S5, during the verification process of the experiment, the adjacent well is kept in normal production. The impact of the well workover operation on the adjacent well is determined by monitoring the bottom flow pressure of the adjacent well. The adjacent well is another well in the same well group as the docking well that is currently producing. The adjacent well is kept in normal production throughout the well workover operation. The bottom flow pressure of the adjacent well is monitored in real time. If there is no abnormal fluctuation in the flow pressure, it is determined that the well workover operation has not interfered with the adjacent well.

10. The integrated well workover method for dual-well coalbed methane operations according to claim 1, characterized in that, In step S6, the sand-removing string includes a sand-removing pen tip, a sand-removing pump, and thickened tubing. The residual debris is carried out of the wellbore using a positive circulation flushing method. After sand is removed to the designed depth, a completion string including a plug, screen pipe, screw pump, pressure gauge support, and thickened tubing is installed, along with a sucker rod and drive device.

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