Variable diameter reamer bit with pipe drilling through goaf horizontal well drilling technology

Abstract

The present application relates to coal bed gas drilling process technical field, disclose variable diameter reamer drill pipe drilling horizontal well drilling technology of go through mined-out area, the present application through setting go through mined-out area drilling tool, including follow pipe upper part, follow pipe upper part and setting in follow pipe upper part's loose hand part and located follow pipe lower part end head's variable diameter reamer drill bit and conventional drill bit, and using four open well completion mode using the drilling tool go through mined-out area's follow pipe drilling method, by using follow pipe using the no coupling design, reduce the friction when follow pipe drilling, in addition design professional hand structure realizes torque transmission and loose hand, avoid large diameter rock debris appears.Every complete certain footage after full circulation, eye guarantee the stability of wellbore, the present application very goodly solves go through mined-out area and carry out exploitation to lower coal seam problem, same technology can also be used for salt well development, can also go through upper mined-out salt layer, carry out exploitation to lower salt layer.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane drilling technology, specifically to horizontal well drilling technology that uses a variable diameter enlarged drill bit and casing to drill through goaf areas. Background Technology

[0002] Coalbed methane (CBM) has developed rapidly in China as an unconventional energy source. With continuous development, shallow CBM deposits have been largely exhausted, leading to increasingly severe conflicts between CBM and coal mining areas. Areas where coal mines have been established are almost entirely devoid of CBM potential, especially those where coal seams have been completely mined out, rendering CBM development worthless. However, beneath these mined-out areas, potential CBM seams still exist. Due to mining, the roof of the goaf often collapses, creating fracture zones and caving zones near the roof, making the formation highly unstable. Drilling through these sections is prone to loss of return and wellbore collapse, easily causing stuck pipe. If the roof has not collapsed, there is often a venting section, resulting in loss of return. Furthermore, the difference in bending strength between the drill pipe and casing makes it difficult for the casing to enter the bottom wellbore during casing installation. These are the main risks and problems encountered when drilling through goaf areas.

[0003] When drilling through goaf areas, there are risks such as loss of return, leakage, and stuck drill bit. Conventional casing drilling or tubing drilling leaves the drill bit in the well. However, when developing lower coalbed methane, drilling must continue after passing through the goaf. Leaving the drill bit downhole undoubtedly creates a huge obstacle to the next step of drilling, often making it impossible to proceed. This invention aims to solve this problem by allowing casing drilling, leaving the casing in the wellbore, and then retrieving the drill bit after completing the casing drilling, thus isolating a fixed channel free from leakage and collapse for the next step of drilling. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a horizontal well drilling technology for drilling through goaf areas using a variable diameter enlarged drill bit and casing. This technology has advantages such as effectively solving the problem of mining lower coal seams through goaf areas and can also be used for the development of salt wells, thus solving the problems mentioned in the background technology.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution: a horizontal well drilling technology for drilling through goaf areas using a variable diameter reaming drill bit and casing, comprising the following steps:

[0008] 1) Calculate the lengths of the fracture zone and caving zone to determine the pipe running length: The lengths of the fracture zone and caving zone can be calculated using the following formula: caving zone fracture zone

[0009]

[0010] 2) Well depth and wellbore structure design: Based on the need to seal fracture zones and caving zones, we adopted a four-stage well completion method in the design of the well depth structure.

[0011] 3) Conventional drilling: First, conventional drilling tools are used to drill the well. The conventional drilling tools are advanced to the fracture zone of the goaf coal seam to complete this step, and then the conventional drilling tools are pulled out.

[0012] 4) Conduct casing drilling: First, lower the casing assembly (including the upper casing 1 (torque transmission part 5 connected to the drill pipe, upper casing seal 3, and release part 4), and the lower casing 2 (lower casing seal 6, ball-dropping check valve seat 7, and casing guide shoe 8)). Then, lower the conventional PDC drill bit and the variable diameter reamer 9 through the casing. After drilling 5m through the bottom of the goaf coal seam, stop drilling, drop a ball to pressurize and release the casing, and retrieve the variable diameter drill bit and conventional drilling tools.

[0013] 5) Seal the fracture zone and caving zone. Run the cementing string to seal the casing, fracture zone, and caving zone, wait 48 hours for curing, and complete the second casing drilling.

[0014] 6) The lower section will complete the subsequent third and fourth drilling operations according to the conventional drilling procedures.

[0015] Preferably, the drilling tool includes an upper casing 1, a release part 4 disposed on the upper casing 1, a variable diameter reamer 9 and a conventional drill bit 10 located at the end of the lower casing 2, characterized in that: the upper casing 1 and the lower casing 2 are interconnected, the release part 4 is installed at the top of the upper casing 1, the torque transmission part 5 is connected to the front end of the release part 4, the torque transmission part 5 is connected to an external power input end, the ball-dropping single-flow valve seat 7 is disposed inside the lower casing 2, and the variable diameter reamer 9 is disposed at the end of the lower casing 2, and the conventional drill bit 10 is disposed at the end of the variable diameter reamer 9.

[0016] Preferably, an upper outer seal 3 is provided on the outer surface of the upper part 1 of the heel tube, and a lower outer seal 6 is provided on the outer surface of the lower part 2 of the heel tube. The upper outer seal 3 and the lower outer seal 6 have the same structure.

[0017] Preferably, a heel shoe 8 is provided at the end of the lower part 2 of the heel tube. The heel shoe 8 is located outside the front end of the variable diameter reamer 9, and the outer wall of the variable diameter reamer 9 is tapered.

[0018] Preferably, the four-stage well completion method in step 2 is as follows: Stage 1: Drill through the weathered bedrock zone with a drill bit to complete the drilling, and run casing; Stage 2: Drill to the top of the fracture zone with a drill bit, pull out the drill string and replace the casing drilling tool. Drill the casing to a vertical depth of 5m at the bottom of the coal seam, drop the casing and pull out the drill bit, and seal the goaf; Stage 3: Drill to the coal seam landing point with a drill bit (entering the coal seam no more than 5m), run casing and cement the well, and return the cement to the goaf; Stage 4: Drill along the horizontal section with a drill bit to the designed well depth, run in the steel screen pipe and internal flushing pipe, and suspend it using a special hanger.

[0019] Preferably, in step 2, the selection of all drill bit and casing sizes strictly follows the internationally accepted API standard in the petroleum industry, eliminating the need for special-sized casing manufacturing, and the upper casing 1 and lower casing 2 adopt a coupling-free design.

[0020] (III) Beneficial Effects

[0021] Compared with the prior art, the present invention provides a horizontal well drilling technology for drilling through goaf areas using a variable diameter reamerized drill bit and casing, which has the following beneficial effects:

[0022] 1. This variable-diameter reamer drill bit utilizes a casing-following horizontal well drilling technology that employs a coupling-free casing design to reduce friction during drilling. Additionally, a specialized release mechanism facilitates torque transmission and easy release. The variable-diameter drill bit design allows for casing retrieval after drilling completion.

[0023] 2. This variable-diameter reaming drill bit technology for horizontal well drilling through goaf areas requires strict control of the drilling rate during drilling to ensure thorough grinding of rock cuttings and prevent the formation of large-diameter cuttings. After each certain depth of drilling, sufficient circulation and reaming are necessary to ensure wellbore stability. This invention effectively solves the problem of mining lower coal seams through goaf areas, enabling the full development and utilization of numerous high-quality coalbed methane blocks that were previously inaccessible due to coal mining. The same technology can also be applied to the development of salt wells, allowing for the development of lower salt seams through upper goaf areas. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the drill string assembly during casing drilling according to the present invention.

[0025] In the diagram: 1. Upper part of the heel tube; 2. Lower part of the heel tube; 3. Upper outer seal of the heel tube; 4. Release part; 5. Torque transmission part; 6. Lower outer seal of the heel tube; 7. Ball-throwing check valve seat; 8. Heel tube guide shoe; 9. Variable diameter reamer; 10. Conventional drill bit. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example: A drilling tool for traversing a goaf includes an upper casing section 1, a release part 4 located on the upper casing section 1, a variable-diameter reamer 9 and a conventional drill bit 10 located at the end of the lower casing section 2. The upper casing section 1 and the lower casing section 2 are interconnected. The release part 4 is installed at the top of the upper casing section 1. A torque transmission part 5 is connected to the front end of the release part 4 and is connected to an external power input. A ball-dropping check valve seat 7 is located inside the lower casing section 2 and is variable-diameter. The reaming drill bit 9 is located at the end of the lower part 2 of the heel tube, and the conventional drill bit 10 is located at the end of the variable diameter reaming drill bit 9. The upper part of the heel tube 1 is provided with an upper outer seal 3, and the lower part of the heel tube 2 is provided with a lower outer seal 6. The upper outer seal 3 and the lower outer seal 6 have the same structure. The lower part of the heel tube 2 is provided with a heel tube guide shoe 8, which is located outside the front end of the variable diameter reaming drill bit 9. The outer wall of the variable diameter reaming drill bit 9 is tapered.

[0028] The method of drilling through the goaf using a drill string to penetrate the No. 3 coal seam in the Qinshui Basin includes the following steps:

[0029] Step 1: Calculate the lengths of the fracture zone and caving zone to determine the pipe length: The lengths of the fracture zone and caving zone can be calculated using the following formula: Caving Zone fracture zone Based on the maximum thickness of the No. 3 coal seam in the Qinshui Basin, which is 7.49m, the calculation results are as follows: the height H of the caving zone of the No. 3 coal seam. m =13.82m; Height H of the fracture zone in coal seam No. 3 li =64.74m, therefore, the length of the root tube can be determined to be 90m.

[0030] Step 2: Design the well depth and wellbore structure. Because we need to seal fracture zones and caving zones, we adopted a four-stage completion method in the well depth structure design.

[0031] Step 3: First, perform conventional drilling to the fracture zone of the mined-out coal seam, and retrieve the conventional drilling tools. During this process, use a 425.0mm drill bit to drill through the weathered bedrock zone for 10-20m before completing the drilling. Then, run a 339.7mm casing to a depth of not less than 50m.

[0032] Step 3: Conduct casing drilling: First, lower the casing assembly (including the upper casing 1 (torque transmission part 5 connected to the drill pipe, upper casing seal 3, and release part 4), and the lower casing 2 (lower casing seal 6, ball-dropping check valve seat 7, and casing guide shoe 8)). Then, lower the conventional PDC drill bit and the variable-diameter reamer 9 through the casing. After drilling 5m through the bottom of the goaf coal seam, stop drilling, drop a ball to pressurize and release the casing, and retrieve the variable-diameter drill bit and conventional drilling tools.

[0033] Step 4: Sealing the fracture zone and caving zone. The cementing string is lowered to seal the casing, fracture zone, and caving zone. After 48 hours of curing, the second phase of casing drilling is completed. During the second phase, a 311.1mm drill bit is used to drill to the top of the fracture zone (5m). The drill bit is then pulled out and replaced with casing drilling tools (273.1mm casing). Casing drilling continues to the bottom of coal seam #3, reaching a vertical depth of 5m. The casing is then dropped, the drill bit is pulled out, and the goaf is sealed.

[0034] Step 5: The lower section will complete the subsequent third and fourth drilling operations according to the conventional drilling procedure. In the third drilling operation, a 222.2mm drill bit will be used to drill to the No. 15 coal seam (entering the coal seam no more than 5m), followed by running 177.8mm casing for cementing, with cement returned to the goaf. In the fourth drilling operation, a 155.6mm drill bit will be used to drill along the horizontal section to the designed well depth, followed by running 114.3mm steel screen pipe and internal flushing pipe, suspended using a special hanger. Note: The fourth drilling operation will use a guar gum drilling fluid system.

[0035] The beneficial effects of this invention are as follows: This variable-diameter reaming drill bit, used for horizontal well drilling through goaf areas, employs a coupling-free design in the casing, reducing friction during drilling. Furthermore, a specialized release mechanism facilitates torque transmission and release. The variable-diameter drill bit allows for casing retrieval after drilling completion. Strict control of the drilling speed is essential during casing drilling to ensure thorough grinding of cuttings and prevent the formation of large-diameter cuttings. Sufficient circulation and reaming are performed after each certain depth of drilling to ensure wellbore stability. This invention effectively solves the problem of mining lower coal seams through goaf areas, enabling the full development and utilization of high-quality coalbed methane blocks that were previously inaccessible due to coal mining. The same technology can also be applied to the development of salt wells, allowing the development of lower salt seams through upper goaf areas.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A horizontal well drilling method for drilling through a goaf with a variable diameter reamer and casing, characterized in that: Includes the following steps: 1) Calculate the lengths of the fracture zone and caving zone to determine the pipe length: The lengths of the fracture zone and caving zone can be calculated using the following formula: caving zone fracture zone ; 2) Well depth and wellbore structure design: Based on the need to seal fracture zones and caving zones, we adopted a four-stage well completion method in the design of the well depth structure; 3) Conventional drilling: First, conventional drilling tools are used to drill the well. The conventional drilling tools are advanced to the fracture zone of the goaf coal seam to complete this step, and then the conventional drilling tools are pulled out. 4) Conduct casing drilling: First, lower the casing drill assembly, which includes an upper casing and a lower casing. The upper casing includes a torque transmission part connected to the drill rod and an upper outer seal and a release part. The lower casing includes a lower outer seal, a ball-dropping check valve seat, and a casing guide shoe. Then, lower the conventional PDC drill bit and a variable diameter reamer through the casing. After drilling through 5m of the bottom of the goaf coal seam, stop drilling, drop a ball to pressurize and release the casing, and retrieve the variable diameter drill bit and conventional drill tools. The upper and lower parts of the heel tube are connected to each other. The release part is installed at the top of the upper part of the heel tube. The torque transmission part is connected to the front end of the release part. The torque transmission part is connected to the external power input end. The ball-throwing single-flow valve seat is located inside the lower part of the heel tube. The variable diameter reaming drill bit is located at the end of the lower part of the heel tube. The conventional drill bit is located at the end of the variable diameter reaming drill bit. An upper outer seal is provided on the outer surface of the upper part of the tube, and a lower outer seal is provided on the outer surface of the lower part of the tube. The upper outer seal and the lower outer seal have the same structure. A heel shoe is provided at the lower end of the heel tube. The heel shoe is located on the outside of the front end of the variable diameter reamer. The outer wall of the variable diameter reamer is tapered. 5) Seal the fracture zone and caving zone, run the cementing string to seal the casing and fracture zone and caving zone, wait for 48 hours for curing, and complete the second casing drilling. 6) The lower section will complete the subsequent third and fourth drilling operations according to the conventional drilling procedures.

2. The horizontal well drilling method for drilling through a goaf with a variable diameter reamerized drill bit and casing as described in claim 1, characterized in that: The four-stage well completion method in step 2 is as follows: Stage 1: Drill through the weathered bedrock zone with a drill bit and run casing; Stage 2: Drill to the top of the fracture zone with a drill bit, pull out the drill bit and change to casing drilling tools, drill with casing to a vertical depth of 5m at the bottom of the coal seam, drop the casing and pull out the drill bit, and seal the goaf; Stage 3: Drill to the coal seam landing point with a drill bit, enter the coal seam no more than 5m, run casing and cement the well, and return cement to the goaf; Stage 4: Drill along the horizontal section with a drill bit to the designed well depth, run in steel screen pipe and internal flushing pipe, and use a special hanger for suspension.

3. The horizontal well drilling method for drilling through a goaf with a variable diameter reamerized drill bit and casing as described in claim 2, characterized in that: In step 2, the selection of all drill bit and casing sizes strictly follows the internationally recognized API standard in the petroleum industry, eliminating the need for special-sized casing manufacturing. The upper and lower parts of the casing adopt a coupling-free design.

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