Alternating shielded drilling method of soft coal seam with pipe impact and large spiral
By employing a drilling method that combines casing impact with alternating large spiral drilling in ultra-deep coal seams, cavities are formed and coal powder is transported, solving the problems of difficult drilling and poor gas extraction in soft coal seams, and achieving rapid and effective borehole formation and gas control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TAIYUAN UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2023-09-14
- Publication Date
- 2026-07-14
AI Technical Summary
In ultra-deep coal seams, especially when the coal seam is soft, problems such as drilling difficulties, large-area hole collapse, and borehole closure are prominent. Existing technologies have poor hole-forming effects, low drilling efficiency, and unsatisfactory gas extraction results.
The drilling process involves using casing percussion drilling to drill through the rock strata and leaving casing for support. Then, screen pipes are used to drill through the coal seam. Cavities are formed by sealing and injecting water or air. Combined with large spiral drilling technology, cavities are formed in the coal seam and coal powder is transported. Drilling is carried out alternately until the final hole is reached. Finally, the gas is sealed and extracted.
It improves drilling speed and efficiency, reduces the risk of stress on drilling tools, avoids hole collapse, ensures effective gas extraction, and reduces construction costs and labor intensity.
Smart Images
Figure CN117145382B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of drilling and gas control technology in soft coal seams, specifically a method for drilling and gas control in soft coal seams using alternating pipe impact and large spiral shield. Background Technology
[0002] Ultra-deep coal seams are characterized by their great depth (nearly 1000 meters), high ground stress, high gas pressure, large cross-section, small dip angle, and soft texture. Forming boreholes for gas extraction in ultra-deep coal seams is a global challenge, especially when the coal seam is soft, where drilling difficulties, large-area borehole collapse, and borehole closure become even more pronounced. Domestic research has been conducted extensively to address the drilling and borehole formation challenges in soft, high-stress coal seams. In terms of rapid drilling and preventing stuck drill bits, technologies include: high-power, high-torque, low-speed fully hydraulic drilling rigs; PAM aqueous solution-based flocculant-based borehole washing and slag removal technology; large-diameter grooved spiral drill rod composite powder removal technology; and nitrogen-based slag removal pneumatic directional drilling technology. Regarding preventing borehole collapse, two main methods exist: one is to optimize drilling parameters by studying the deformation and collapse patterns of highly plastic coal under high stress; the other is to use casing / casing during the drilling process to prevent collapse. However, when the coal seam is buried too deep (nearly 1000 meters), the high ground stress-pulverized coal coupling effect caused by ultra-deep burial, high ground stress, soft coal seam, large coal seam thickness and small spacing leads to poor hole formation effect and low drilling efficiency of existing technology. Summary of the Invention
[0003] This invention addresses the problems of poor gas extraction in soft coal seams, failure to meet coal uncovering conditions, drilling difficulties, large-area borehole collapse, and borehole closure, thereby improving the borehole formation effect and increasing drilling efficiency in ultra-deep buried soft coal seams. It provides a method for drilling and gas control in soft coal seams using alternating casing impact and large spiral shielding.
[0004] This invention adopts the following technical solution: a method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling, comprising:
[0005] S1: Drilling in the rock formation using the casing percussion drilling method, leaving the casing in the rock formation for support;
[0006] S2: Replace the casing with a screen pipe and use the casing percussion drilling method to drill until the drill bit penetrates the rock formation;
[0007] S3: Continue drilling forward in the coal seam until the friction between the screen and the coal increases to the point that the drilling process cannot continue;
[0008] S4: The sealing plug is sent into the screen tube. After reaching the position, the screen tube is sealed by air or water through the guide tube. Then, water is injected through the water injection pipe to start water impact. The coal powder will flow from the high pressure area to the low pressure area of the screen tube with the water flow.
[0009] S5: After the water impact is completed, the gas release or drainage operation is carried out to remove the sealing plug from the screen tube, and then drilling is carried out, and the coal powder is transported to the outside of the borehole, so that a cavity is formed during the coal seam drilling process;
[0010] S6: Using the casing impact drilling technology, continue drilling forward with the screen pipe, passing through the cavity formed in step S4, and continue drilling until it can no longer continue.
[0011] S7: Repeat steps S4-S6 until the drilling reaches the final hole position, then seal the borehole and extract the coal seam gas.
[0012] In some embodiments, the diameter of the sleeve is larger than the diameter of the screen tube.
[0013] In some embodiments, in step S1, drilling stops when the distance between the drill bit and the coal seam is S1, where S1 ≥ 0.2m.
[0014] In some embodiments, the sealing plug includes two sealing capsules, one at the front and one at the back. The rear sealing capsule is fixed to the water injection pipe. The two sealing capsules are connected by a connecting rod. Both sealing capsules are connected to conduits for inflation and deflation or water filling and drainage operations.
[0015] In some embodiments, in step S5, the cavity length is less than or equal to 0.5m, and the main influencing factors are the coal body's firmness and the degree of collapse.
[0016] In some embodiments, in step S7, the diameter of the sieve tube used gradually decreases each time steps S4-S6 are repeated.
[0017] In some embodiments, in step S7, the diameter of the borehole drilled into the screen tube is insufficient to support the drilling activity of the drill bit.
[0018] In some embodiments, in step S5, drilling is carried out using a large-diameter spiral drilling method, with the large spiral drill rod drilling into the coal body through the casing in the rock strata and the screen pipe in the coal seam.
[0019] In some embodiments, the large spiral drill pipe utilizes specially designed spiral blades with uneven surfaces to increase friction and, combined with water impact, better discharge coal dust, making it easier for the coal body to form cavities.
[0020] Compared with the prior art, the present invention has the following beneficial effects:
[0021] This invention proposes a method of alternating shielding with casing impact technology and large spiral drilling technology, which can create cavities in the coal seam before continuing drilling. The formation of cavities reduces the resistance of the coal body and avoids drilling risks caused by increased drilling depth, increased torque, and increased stress on the drill bit.
[0022] In soft coal seams, protective screens are installed to prevent gas extraction failure due to borehole collapse. The large auger drill rod transports pulverized coal within the protective screen and provides pressure relief during drilling in the coal seam outside the screen. The advantages of this invention include rapid hole formation, large hole diameter, long hole length, excellent borehole wall protection, and reduced risk of drill bit jamming. It effectively solves problems such as ineffective gas extraction in soft coal seams, difficulty in achieving coal uncovering conditions, drilling difficulties, large-area borehole collapse, borehole closure, and drill bit jamming. Furthermore, this invention saves construction costs, reduces labor intensity, effectively improves hole formation results, and increases drilling efficiency. Attached Figure Description
[0023] Figure 1 This is a flowchart of the present invention;
[0024] Figure 2 This is a schematic diagram of the drilling process through rock.
[0025] Figure 3 This is a schematic diagram of the drilling process to enter the coal seam.
[0026] Figure 4 This is a schematic diagram of the coal seam drilling process;
[0027] Figure 5 This is a schematic diagram of the water injection impact process;
[0028] Figure 6 This is a schematic diagram of the large spiral drilling process;
[0029] Figure 7 This is a schematic diagram of the sieve tube extension process;
[0030] Figure 8 A schematic diagram illustrating the continued water injection and impact process;
[0031] Figure 9 A schematic diagram illustrating the continued large spiral drilling process;
[0032] Figure 10 This is a schematic diagram illustrating the continued extension of the sieve tube.
[0033] Figure 11 This is a schematic diagram showing the drilling process after the invention is completed;
[0034] Figure 12 This is a schematic diagram of coal seam gas extraction.
[0035] Figure 13 This is a schematic diagram of the sealing and plugging structure;
[0036] Figure 14 Diagram of water injection for sealing;
[0037] Figure 15 Schematic diagram of the large spiral;
[0038] In the diagram, 1-rock stratum, 2-coal seam, 3-drill tool, 4-casing, 5-screen pipe, 6-sealing plug, 7-large spiral drill rod, 8-cavity, 9-air pump, 10-connecting rod, 11-sealing capsule, 12-water injection pipe, 13-conduit. Detailed Implementation
[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but 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.
[0040] like Figure 1 As shown, a method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling is described, comprising the following steps.
[0041] S1: As Figure 2 As shown, the rock-penetrating process. This process uses casing percussion drilling to penetrate rock stratum 1. Drilling is stopped when the distance between drill bit 3 and coal seam 2 is S1. Drill bit 3 is removed from casing 4, and casing 4 is left in rock stratum 1 to provide support. The diameter of casing 4 is φ1.
[0042] Percussion drilling with casing uses compressed air or water as power. The casing drill bit, under the torque of the impactor and drilling rig, rotates and simultaneously advances the casing, meaning it drills and presses the casing in simultaneously. After drilling is complete, the drill bit is removed from the casing. The casing is used for borehole wall protection, providing significant protection in soft coal seams. The drilling technique involves using a central drill bit and a concentric casing surrounding it to impact and break through rock and coal to create a borehole. Simultaneously, the concentric casing's reaming effect guides the casing into the hole. The concentric casing has a keyway for connection with the drill bit. Once at the predetermined position, the central drill bit reverses and exits from the concentric casing. The concentric casing and casing are connected by a snap-fit mechanism. This invention uses a detachable drill bit, facilitating the replacement of drill bits of different diameters with casings and screens of different diameters. Furthermore, the drill bit, casing, and screen are detachably fitted using a slotted connection, allowing for easy removal of the drill bit from the casing and screen.
[0043] S2: As Figure 3 As shown, the process of entering the coal seam is as follows. This process still uses the casing percussion drilling technology, but the casing 4 is replaced with a screen pipe 5, the diameter of which is φ2 (φ2<φ1). The drill bit 3 reaches a distance S1 from the coal seam through the rock casing 4, and begins drilling in the coal seam 2 after passing through a rock layer of thickness S1, until the drill bit 3 penetrates the rock layer 1.
[0044] S3: As Figure 4The diagram illustrates the coal seam drilling process. After entering the coal seam, drilling continues forward within coal seam 2. When the drilling length in coal seam 2 reaches L1, due to coal collapse and ground stress, the friction between the screen pipe 5 and the coal seam increases to the point that drilling cannot continue.
[0045] S4: As Figure 5 As shown, the water injection and impact process is as follows: The un-air-filled or un-water-filled sealing plug 6 is inserted into the screen tube 5. Once in position, air or water is added through the conduit to seal the screen tube 5. Then, water is injected through the water injection pipe to initiate the water impact. The pulverized coal, impacted by the water, flows from the high-pressure zone to the low-pressure zone with the water flow. After the water impact is complete, air is released or water is drained to remove the sealing plug 6 from the screen tube 5.
[0046] like Figure 13 As shown, the sealing plug 6 includes two sealing capsules 11, one at the front and one at the back. The sealing capsule 11 at the rear is fixed to the water injection pipe 12. The two sealing capsules 11 are connected by a connecting rod 10. Both sealing capsules 11 are connected to a conduit 13 for inflation and deflation or water filling and drainage operations.
[0047] Due to ground stress, friction occurs between the screen pipe and the coal body during drilling, hindering the drilling process. This invention addresses this problem by proposing a sealing and water injection operation in the screen pipe, mimicking a "two-plug-one-injection" sealing method, to perform water impact on the coal body. This invention provides a removable water-filled sealing plug, connecting two sealing capsules 11 via a connecting rod 10. The rear sealing capsule, with a water-filled pipe 12, performs water injection. When drilling cannot continue, the drill bit is removed from the screen pipe, and the uninflated or unwater-filled sealing plug is delivered to the front end of the screen pipe via the casing and screen pipe. The sealing capsule is then inflated or filled with water to seal the screen pipe. After sealing, water is injected through the injection pipe 12 to impact the coal body, creating a gap between the coal body and the screen pipe. After water impact, the sealing capsule is deflated or drained through the guide pipe 13, and removed from the screen pipe, ending the sealing and water injection operation. Unlike the "two-plug-one-injection" method, which suffers from the difficulty of removing the filler, this sealing plug can be easily moved, fixed, or removed from the screen tube via the conduit 13 for inflation and deflation or water filling and drainage, making it convenient and efficient. Due to ground stress, the coal body is inherently a high-pressure zone; under the combined action of water impact and ground stress, a high-pressure zone also forms on the outer wall of the screen tube and its surrounding area, with only the screen tube opening being a low-pressure zone. Coal dust, impacted by water, flows from the high-pressure zone to the low-pressure zone with the water flow, and is subsequently excavated by the large spiral blades. After a period of water injection and impact, gaps appear between the outer wall of the screen tube in the impact section and the coal body, effectively solving the problem of drilling obstruction caused by friction. The sealing and water injection work in conjunction with the subsequent large spiral drilling to create displacement space for further pipe-following impact.
[0048] S5: As Figure 6As shown, this is the large-diameter spiral drilling process. The large spiral drill rod 7 passes through the casing 4 in the rock layer 1 and the screen pipe 5 in the coal seam 2, reaching the front end of the screen pipe 5 to drill into the coal body. Because the drilling tool is a large spiral drill rod, coal dust is transported along the spiral thread to the outside of the borehole, causing the coal body to form cavities 8 during the large spiral drilling process. The specially designed spiral blades with uneven surfaces increase friction, and combined with water impact, better expel coal dust, making it easier for cavities to form in the coal body.
[0049] Large auger drilling is characterized by its fast hole-forming speed, large hole diameter, and suitability for casing drilling, making it a suitable drilling technology for soft coal seams. Large auger drilling is highly efficient, requires no flushing, and features simple equipment, vibration-free operation, low noise, timely sampling, and low cost. It is suitable for drilling various soft strata, including those without water and those with slight water content. Large auger drilling systems are further divided into long and short auger types. Short augers use small auger drilling rigs for engineering geological exploration, while long augers use large auger drilling rigs for engineering construction drilling, with larger diameters and greater depths. The large auger drill rod consists of a solid shaft or hollow tube and pressed spiral blades welded to its outer side. The drill rods are often connected by pins. This invention utilizes large auger drilling with water impact, eliminating the need for fireproof casing. The specially designed spiral blades with uneven surfaces increase friction, and combined with water impact, better expel coal dust, creating cavities in the coal seam. The formation of cavities reduces the resistance of the coal body, avoiding drilling risks caused by increased drilling depth, increased torque, and increased stress on the drill bit.
[0050] S6: As Figure 7 As shown, the screen tube 5 continues to extend. This process uses the casing impact drilling technique to continue drilling forward with the screen tube 5. After passing through the cavity 8 formed in step S4 and continuing to drill for a length of L2, the drilling process can no longer continue due to friction.
[0051] S7: Repeat steps S4-S6 until the drilling reaches the final hole position, then seal the borehole and extract the coal seam gas.
[0052] Specifically, the water impact process is repeated. Because the advance of screen tube 5 is blocked again, operation S4 is performed again to impact the coal body with water.
[0053] The large-diameter spiral drilling rig was used again to drill into the coal seam, forming a second cavity 8.
[0054] The screen tube 5 continues to extend. Drilling continues forward with the screen tube 5, passing through the formed second cavity 8. After drilling for a length of L3, the coal seam collapses during the drilling process, and due to friction, the drilling process can no longer continue.
[0055] The formation of the cavity reduces the resistance of the coal body, avoiding drilling risks caused by increased drilling depth, increased torque, and increased stress on the drill bit. After drilling a distance of A1, the predetermined position is reached, which is the maximum length achievable by the screen pipe 5.
[0056] Continue the drilling process. Select a screen pipe 5 with a suitable diameter and repeat steps S4-S6 until the borehole width D can no longer support the drilling tool for drilling activities.
[0057] Gas extraction process. After the drilling process is completed, the borehole is sealed using a "two-plug-one-injection" sealing process, and the gas extraction pump 9 is used to extract the gas from the coal seam.
[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling, characterized in that... Includes the following steps: S1: Drilling is carried out in the rock stratum (1) using the casing percussion drilling method, and the casing (4) is left in the rock stratum (1) to provide support; S2: Replace the casing (4) with the screen pipe (5) and use the casing percussion drilling method to drill until the drill bit (3) penetrates the rock layer (1). S3: Continue drilling forward in the coal seam (2) until the friction between the screen pipe (5) and the coal body increases to the point that the drilling process cannot continue; S4: Send the sealing plug (6) into the screen tube (5). After reaching the position, perform air or water filling operation through the conduit to complete the sealing of the screen tube (5). Then, start water impact by injecting water through the water injection pipe. The coal powder will flow from the high pressure area of the screen tube (5) to the low pressure area with the water flow. S5: After the water impact is completed, the sealing plug (6) is removed from the screen tube (5) by venting or draining. Then, the coal powder is transported to the outside of the borehole, so that the coal seam (2) forms a cavity (8) during the drilling process. S6: Using the pipe-following impact drilling technology, continue drilling forward with the screen pipe (5), pass through the cavity (8) formed in step S4, and continue drilling until it can no longer continue; S7: Repeat steps S4-S6 until the drilling reaches the final hole position, then seal the borehole and extract the coal seam gas. In step S7, the diameter of the sieve tube (5) used gradually decreases each time steps S4-S6 are repeated. In step S5, the drilling adopts a large-diameter spiral drilling method. The large spiral drill rod (7) drills into the coal body through the casing (4) in the rock layer (1) and the screen pipe (5) in the coal seam (2).
2. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... The diameter of the sleeve (4) is greater than the diameter of the sieve tube (5).
3. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... In step S1, drilling stops when the distance between the drill bit (3) and the coal seam (2) is S1, where S1 ≥ 0.2m.
4. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... The sealing plug (6) includes two sealing capsules (11) at the front and back. The sealing capsule (11) at the rear is fixed to the water injection pipe (12). The two sealing capsules (11) are connected by a connecting rod (10). Both sealing capsules (11) are connected to a conduit (13) for inflation and deflation or water filling and drainage operations.
5. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 4, characterized in that... The water injection process in step S4 is as follows: after sealing the screen tube with the sealing capsule, water is injected to impact the coal body. The sealing plug (6) is ventilated and de-vented or ventilated and drained through the conduit (13) so that it can move, be fixed or removed from the screen tube.
6. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... In step S5, the length of the cavity (8) is less than or equal to 0.5m.
7. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... In step S7, the diameter of the borehole drilled into the screen tube (5) is insufficient to support the drilling activity of the drill bit.
8. The method for drilling and gas control in soft coal seams using alternating impact drilling and large spiral drilling as described in claim 1, characterized in that... The large spiral drill rod (7) utilizes specially designed spiral blades with uneven surfaces to increase friction and, combined with water impact, better discharges coal powder, making it easier for the coal body to form cavities.