A construction method for safe drilling in a goaf and a plugging device thereof

Abstract

The application provides a goaf safety drilling construction method applied to the technical field of goaf drilling safety, and comprises the following steps: S1, accident determination; S2, emergency risk control; S3, static pressure grouting pretreatment; S4, pumping of composite plugging slurry and well shut-in extrusion; S5, cycle recovery and risk isolation; S6, subsequent drilling; and a goaf safety drilling plugging device is also provided, wherein in step S4, before pumping of the reinforced composite plugging slurry, the plugging mechanism is released and used for bearing the reinforced composite plugging slurry. The goaf safety drilling construction method realizes efficient plugging through the cooperation of staged plugging and the plugging mechanism, the plugging mechanism provides rigid bearing, and dry plugging is formed, so that the plugging effect is ensured, the grouting amount is greatly reduced, and the cost is efficiently controlled.

Description

Technical Field

[0001] This application relates to the field of drilling safety technology in goaf areas, and in particular to a construction method for safe drilling in goaf areas and a sealing device thereof. Background Technology

[0002] In the fields of mineral resource extraction and geological exploration, such as coal and metal mining, drilling operations often need to traverse goaf strata. Goaf strata are formed after resource extraction and generally contain numerous cavities, interconnected fractures, and loose filling materials. When the drill bit penetrates the roof of a goaf, it can easily trigger mud return accidents, manifested as a sudden drop in pump pressure, a rapid decline in the mud pit level, and interruption of mud return at the wellhead. If not handled properly, these accidents can easily lead to borehole collapse, stuck drill bits, and drill string burial, not only causing well abandonment and equipment damage but also potentially inducing safety risks such as gas spills and water hazards, severely restricting construction progress and threatening personnel safety.

[0003] Existing mud return treatment technologies for goaf areas have a single plugging process, which often uses a single type of plugging grout for one-time injection. This cannot adapt to the complex leakage channels of small and medium-sized cracks and large-sized cavities. Small and medium-sized cracks are not firmly plugged, while large cavities are easily lost quickly because the plugging grout has no load-bearing capacity, resulting in a low plugging success rate. At the same time, the lack of targeted support structures and the absence of effective load-bearing carriers in the goaf make it difficult for the plugging grout to remain and solidify stably in the leakage channels, thus failing to form a high-strength sealing layer. This results in a large amount of plugging grout loss and high sealing costs.

[0004] To address these issues, a construction method for safe drilling in goaf areas and its sealing device are proposed. Summary of the Invention

[0005] The purpose of this application is to address the problems of existing technologies for handling mud loss in goaf areas, which are limited in scope, have high sealing efficiency, and are costly. Compared to existing technologies, this application provides a construction method for safe drilling in goaf areas, comprising the following steps: S1. Accident Judgment: If, during the drilling process, the pump pressure suddenly drops to zero, the mud level in the mud pit drops rapidly, and the mud return from the wellhead is completely interrupted, it is determined that the drill bit has penetrated the roof of the goaf and entered a large cavity or a fracture zone with excellent connectivity. S2. Emergency Risk Control: Immediately stop drilling and mud pumping, and slowly pull up the entire drill bit to a safe position inside the casing shoe to avoid the drill bit remaining in the goaf section. S3. Static pressure grouting pretreatment: Prepare about 2 cubic meters of high viscosity fiber composite mud. The composite mud is composed of base mud + 3% hard nut shell with a particle size of 2-5mm + 2% wood chips + 1% flaky minerals. It is slowly and continuously poured into the hole through the orifice by the gravity of the slurry itself. After standing for four hours, try a small-volume circulation to verify the leak-stopping effect. S4. Pumping composite plugging slurry and shutting in the well: If static pressure grouting is unsuccessful, prepare 4 cubic meters of reinforced composite plugging slurry. The reinforced composite plugging slurry consists of base slurry + 5% hard nut shell + 3% wood chips + 2% flaky minerals + 3% quick-setting cement. Lower the drill pipe to the top of the goaf and pump the reinforced composite plugging slurry to the predetermined position in one go. After pulling the drill to a safe position, turn off the blowout preventer, apply a wellhead pressure of 1.5-2.0 MPa for 30 minutes, and let it stand for 12 hours to cure. S5. Circulation Recovery and Risk Isolation: After maintenance, drill down to the bottom of the hole, start the pump to circulate and verify the recovery of mud circulation. After confirming recovery, quickly pass through the goaf section with low drilling pressure and high rotation speed. After enlarging the hole, run in the technical casing, so that the technical casing shoe is 2 meters below the bottom plate of the goaf. Pump cement slurry into the surface through the annulus between the technical casing and the hole wall to cement the well, and complete the isolation of the risk section of the goaf. S6. Subsequent drilling: Continue drilling inside the technical casing using a smaller diameter drill bit until the final hole is reached.

[0006] Furthermore, in step S4, the basis for determining that static pressure grouting was unsuccessful is as follows: after static pressure grouting is completed, after standing for 4 hours, the pump is started and circulated at a small displacement. The pump pressure is briefly built up to 0.8MPa. If the pump pressure drops to zero again and the liquid level does not rise, it is determined that the leakage channel is too large and the strength of the mud bridge formed by static pressure grouting is insufficient, and the static pressure grouting is determined to be unsuccessful.

[0007] Furthermore, in step S5, the basis for verifying the recovery of mud circulation is as follows: after the reinforcement of composite plugging slurry is completed, the well is opened, the drill is lowered to the bottom of the hole, the pump is started for circulation, the pump pressure is stabilized at 3.0 MPa, and the mud level in the mud pool is stable, then the mud circulation recovery is determined to be successful.

[0008] Furthermore, in step S5, P.O42.5 grade cement is used for cementing operations, the water-cement ratio of the cement slurry is 0.8-1.0, and the pumping pressure is controlled at 2.5-3.0 MPa to ensure that there is no leakage of cement slurry when it returns to the surface; For rapid traversal of goaf sections, the drilling pressure should be controlled at 50%-60% of the conventional drilling pressure, and the rotation speed at 120%-150% of the conventional rotation speed, to avoid drill bit vibration disturbing the borehole wall.

[0009] Furthermore, in step S4, the wellhead pressure changes are monitored in real time during the shut-in squeezing process. If the pressure is lower than 1.5 MPa, reinforced composite plugging slurry is pumped in to maintain the pressure stable in the range of 1.5-2.0 MPa.

[0010] A plugging device for safe drilling in goaf areas, in step S4, before pumping reinforced composite plugging slurry, the plugging mechanism needs to be released in advance. The plugging mechanism is pre-installed at the bottom of the pre-loading device, and the pre-loading device is set at the bottom of the casing shoe. The sealing mechanism moves freely downwards underground, forming a sealing support in the goaf and well site within the mining area to support the reinforced composite plugging slurry.

[0011] Furthermore, the casing shoe is fixed to the bottom of the casing and is used to bridge the annulus between the casing and the wellbore. The pre-loading device includes an installation ring fixed to the bottom of the casing shoe, a sealing ring fixed to the top outer side of the installation ring, the sealing ring being used to squeeze the well wall to form a seal, the bridging area of ​​the casing being located at the top of the sealing ring, three sets of equally spaced inner tilting frames being provided on the inner wall of the installation ring, the inner tilting frames being rotatably connected to the inner side of the installation ring, a hydraulic mechanism matching the inner tilting frames being provided on the inner wall of the installation ring, and a ball head being fixed to the bottom outer side of the installation ring; The sealing mechanism is clamped between the ball head and the inward flipping frame. The ball head is spherical during the bridging stage. After the bridging is completed, the drill rod drives the drill bit to move down and drill a through hole that matches the drill bit.

[0012] Furthermore, the sealing mechanism includes an upper elastic ring and an outer elastic ring sleeve, with an elastic side liner fixed between the upper elastic ring and the outer elastic ring sleeve, and an outer elastic skeleton sleeved on the outer side of the elastic side liner. The inner side of the outer elastic ring is fixed with three sets of bottom sealing members arranged at equal angles. The bottom of the bottom sealing member is provided with an arc-shaped opening groove. The arc-shaped opening groove is provided with an elastic liner and a cross telescopic member. The cross telescopic member is used to extend the elastic liner downward and cover the bottom of the outer elastic ring.

[0013] Furthermore, the top of the upper elastic ring is provided with several elastic flipping members, the elastic flipping members have elastic force away from the axis of the upper elastic ring, and the elastic flipping members are provided with air chambers. The outer wall of the outer elastic ring is provided with several spiral guide grooves, and the outer diameter of the three sets of bottom sealing parts covered by the outer elastic ring when they are close to the minimum stroke is smaller than the outer diameter of the drill bit.

[0014] Furthermore, the cross telescopic component is composed of multiple sets of X-shaped rotating arc rods, with a return spring fixed between the top arc rod sets, a slider fixed at the rotation node of the second set of top arc rod sets, and an arc-shaped groove that cooperates with the slider in the arc-shaped opening groove. The elastic bottom is fixed to the inner side of the cross telescopic component.

[0015] Compared to existing technologies, the advantages of this application are: This invention achieves efficient sealing through a tiered plugging and sealing mechanism. The fiber composite mud, with the synergistic effect of hard nut shells, wood chips, and flaky minerals, gravity-fills to form a mud bridge, quickly sealing small and medium-sized cracks. Large-sized channels are reinforced with quick-setting cement plugging slurry, which, together with well shut-in extrusion, forms a high-strength sealing layer, providing rigid support for the sealing mechanism and solving the problem of traditional plugging being unsupported and prone to leakage. After grouting, the pressure of the plugging slurry drives the elastic side lining and external elastic skeleton to deform and extend, drying to form an embolus. This significantly reduces the amount of grout injected while ensuring the sealing effect, resulting in high efficiency and cost control. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the location of the pre-loading equipment proposed in this application within the mining area; Figure 2 This is a schematic cross-sectional view of the pre-loading device proposed in this application within the mining area; Figure 3 for Figure 2 Enlarged structural diagram of section A in the middle; Figure 4 This is a schematic diagram of the explosive structure of the sealing mechanism proposed in this application before its lateral contraction. Figure 5 This is a schematic diagram of the sealing mechanism proposed in this application after lateral retraction. Figure 6 This is a schematic cross-sectional view of the sealing mechanism proposed in this application after lateral contraction. Figure 7 This is a schematic diagram of the sealing mechanism proposed in this application after longitudinal stretching; Figure 8 This is a schematic diagram showing the state of the cross-telescopic component and elastic liner before and after telescopic expansion as proposed in this application; Figure 9 This is a schematic diagram showing the state of the cross telescopic component before and after telescopic extension as proposed in this application; Figure 10 This is a schematic diagram showing the state of the sealing mechanism bearing the reinforced composite plugging grout proposed in this application.

[0017] Explanation of the labels in the diagram: 1. Mining area; 11. Goaf area; 2. Sleeve; 21. Sleeve shoe; 3. Drill pipe; 31. Drill bit; 4. Pre-loading fixture; 41. Mounting ring; 411. Hydraulic mechanism; 42. Sealing ring; 43. Inner tilting frame; 44. Ball joint; 5. Sealing mechanism; 51. Upper elastic ring; 511. Elastic flipping component; 512. Air chamber; 52. Bottom sealing component; 521. Arc-shaped opening groove; 522. Arc-shaped sliding groove; 53. Outer elastic ring sleeve; 531. Spiral guide groove; 54. Cross telescopic component; 541. Slider; 542. Return spring; 55. Elastic bottom liner; 56. Elastic side liner; 57. Outer elastic skeleton. Detailed Implementation

[0018] The embodiments will be described clearly and completely with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0019] Example: This invention provides a construction method for safe drilling in goaf areas and a sealing device thereof. Please refer to [link / reference]. Figure 1 - Figure 10 The construction method for safe drilling in goaf areas includes the following steps: S1. Accident Judgment: During the drilling process, the pump pressure, mud level in the mud pit and mud return status at the wellhead are monitored in real time. If the pump pressure suddenly drops to zero, the mud level in the mud pit drops rapidly and the mud return at the wellhead is completely interrupted, it is determined that drill bit 31 has penetrated the roof of goaf 11 and entered a large cavity or a fracture zone with excellent connectivity.

[0020] S2. Emergency Risk Control: Immediately stop drilling and mud pumping, and slowly and uniformly raise the drill bit 31 to a safe position inside the casing shoe 21 at a speed of 0.5-1m / min. The drill bit 31 should be at least 50 meters above the roof of the goaf 11 to prevent the drill bit 31 from getting stuck in the goaf 11 section and to prevent the borehole wall from collapsing or rock cuttings from settling, which could lead to stuck drill bit or buried drill bit.

[0021] S3. Static pressure grouting pretreatment: Prepare approximately 2 cubic meters of high-viscosity fiber composite grout. The composite grout consists of a base grout (in this embodiment, bentonite-based grout is preferred) + 3% hard nutshells with a particle size of 2-5mm + 2% wood chips (dry, mold-free fibrous wood particles) + 1% flaky minerals (flaky structure). The grout viscosity is controlled at 30-40s, and the water loss is ≤10ml / 30min. The grout is slowly and continuously poured into the borehole through the orifice under its own gravity. After standing for four hours, the pump is started at a small flow rate to circulate and verify the leak-sealing effect.

[0022] S4. Pumping composite plugging grout and shut-in squeezing: If static pressure grouting is unsuccessful (judgment criteria: when the pump is started and circulated at a small displacement, the pump pressure briefly builds up to 0.8MPa and then drops to zero again, and the liquid level does not rise, indicating that the leakage channel is too large and the mud bridge strength is insufficient), prepare 4 cubic meters of reinforced composite plugging grout. The reinforced composite plugging grout is composed of base grout + 5% hard nut shell + 3% wood chips + 2% flaky minerals + 3% quick-setting cement.

[0023] It should be noted that, in this embodiment, the hard shell is preferably a walnut shell, the wood chips are preferably sawdust, and the flaky minerals are preferably mica flakes.

[0024] First, the hydraulic mechanism 411 is driven by the drill pipe 3 to release the sealing mechanism 5 pre-installed at the bottom of the pre-loading device 4. The sealing mechanism 5 moves freely downhole to the goaf 11 and the drilling site, automatically forming a sealing support. Then, the drill pipe 3 is lowered to the top of the goaf 11, and the reinforced composite plugging slurry is pumped to the predetermined position in one go. The sealing mechanism 5 carries the plugging slurry. Then, the drill is pulled out to a safe position, the blowout preventer is turned off, and a wellhead pressure of 1.5-2.0 MPa is applied and maintained for 30 minutes. During this period, the pressure is monitored in real time. If the pressure is lower than 1.5 MPa, the reinforced composite plugging slurry is pumped in to maintain the pressure stability. Finally, the well is left to cure for 12 hours to ensure that the plugging slurry is fully solidified.

[0025] S5. Circulation Recovery and Risk Isolation: After maintenance, open the well and drill to the bottom of the hole. Start the pump to verify the recovery of mud circulation (judgment criteria: pump pressure stabilizes at 3.0 MPa, mud level in the mud pit is stable, recovery is considered successful). After confirming recovery, quickly pass through the goaf section at 50%-60% of the conventional drilling pressure and 120%-150% of the conventional rotation speed to avoid drill string vibration disturbing the borehole wall; after reaming, run the technical casing, positioning the technical casing shoe 2 meters below the bottom plate of goaf 11. Use P.O42.5 grade cement for cementing operations, with a cement slurry water-cement ratio of 0.8-1.0 and pumping pressure controlled at 2.5-3.0 MPa to ensure that the cement slurry returns to the surface from the annulus between the technical casing and the borehole wall without leakage, completing the permanent isolation of the risk section of the goaf.

[0026] S6. Subsequent drilling: Drilling continues inside the technical casing using a smaller diameter drill bit until the final hole is reached, with no risk of secondary leakage or hole collapse throughout the process.

[0027] The formulation design of the fiber composite mud in this embodiment is based on the synergistic leakage plugging mechanism of particle gradation + fiber winding + sheet sealing. Hard nut shells, as coarse aggregates, preferentially fill the macroscopic channels of goaf fissures under gravity, forming an initial physical bridge. That is, by utilizing the friction and interlocking between particles, a loose but stable barrier layer is formed at the entrance of the leakage channel, providing support for subsequent fine particles. During the mud flow, wood debris fills the gaps between hard nut shell particles through fiber interweaving and winding, forming a dense fiber network and reducing the filtration loss of the mud. The sheet minerals have good flexibility and water-proof properties. After flowing with the mud to the bridging layer, they adhere to the surface of the fiber network through fluid pressure, forming a sealing layer similar to mud skin, further blocking the mud leakage path.

[0028] Static pressure grouting uses gravity injection to avoid the collapse of the bridging layer caused by pump pressure. The flow of slurry in the hole follows Darcy's law. The flow rate is controlled by adjusting the slurry viscosity to ensure that the material is evenly distributed in the leakage channel, rather than concentrated in a certain area and forming a local blockage.

[0029] In this embodiment, the reinforced composite sealing grout is formulated with 3% quick-setting cement (initial setting time ≤ 30 min, final setting time ≤ 60 min) added to the primary formula. The hydrated calcium silicate (CSH) gel generated by the cement hydration reaction binds aggregates such as hard nut shells, wood chips, and flaky minerals into a high-strength whole. At the same time, an additional quick-setting agent (such as tricalcium aluminate) can be added to accelerate the cement hydration rate and prevent the sealing grout from being lost before solidifying in the leakage channel.

[0030] A high-volume pump (1-1.5 m³ / min) is used to ensure the plugging slurry enters the leakage channel in a plunger flow manner. According to pipe flow mechanics, the high volume prevents the slurry from forming stratification or sedimentation within the drill pipe, filling 1.2-1.5 times the channel volume in one go (with allowance for expansion). During shut-in and squeezing, a pressure of 1.5-2.0 MPa is applied. This pressure value is designed based on the closing pressure of the fractures in the goaf, which can forcefully squeeze the plugging slurry into the depths of the fractures (including micro-fractures invisible to the naked eye) without causing fracture expansion due to excessive pressure. The pressure is maintained for 30 minutes to ensure that the cement slurry completes its initial setting under pressure, forming initial strength (≥3 MPa), and preventing the plugging layer from collapsing after pressure release.

[0031] The sealing mechanism 5 forms a rigid bearing surface within the leakage channel, preventing the sealing grout from flowing freely along the large cavity and allowing the sealing grout to solidify within a confined space, thus solving the problems of traditional sealing techniques that are unsupported and prone to leakage.

[0032] Please see Figure 1 - Figure 10 A sealing device for safe drilling in goaf areas, applicable to the above-mentioned construction method, includes a pre-loading device 4 and a sealing mechanism 5, the specific structure of which is as follows: The pre-loading device 4 is disposed at the bottom of the casing shoe 21, which is fixed to the bottom of the casing 2, and is used to bridge the annulus between the casing 2 and the well wall. The pre-loading device 4 includes an installation ring 41 fixed to the bottom of the casing shoe 21, and a sealing ring 42 is fixed to the top of the outer side of the installation ring 41. The sealing ring 42 is used to squeeze the well wall to form a seal, so that the grouting material during the bridging grouting operation at the casing 2 will not move down to block the pre-loading device 4. The bridging area of ​​the casing 2 is located at the top of the sealing ring 42. The inner wall of the mounting ring 41 is provided with three sets of equally spaced inner tilting frames 43. The inner tilting frames 43 are rotatably connected to the inner side of the mounting ring 41. The inner wall of the mounting ring 41 is provided with a hydraulic mechanism 411 that matches the inner tilting frames 43, which is used to drive the inner tilting frames 43 to tilt. A ball head 44 is fixed at the bottom of the outer side of the mounting ring 41. The ball head 44 is spherical during the bridging stage, which makes it easy for the pre-loading tool 4 to move down in the well synchronously with the casing shoe 21. After the bridging is completed, the drill pipe 3 can drive the drill bit 31 to move down and drill a through hole that matches the drill bit 31, without affecting the subsequent drilling operation.

[0033] The sealing mechanism 5 is clamped between the ball head 44 and the inner flip frame 43, including an upper elastic ring 51 and an outer elastic ring sleeve 53. An elastic side liner 56 is fixed between the upper elastic ring 51 and the outer elastic ring sleeve 53. An outer elastic skeleton 57 is sleeved on the outside of the elastic side liner 56 to enhance the overall structural strength. Three sets of bottom sealing members 52 are fixed on the inner side of the outer elastic ring sleeve 53, which are evenly distributed at equal angles. The bottom of the bottom sealing member 52 is provided with an arc-shaped opening groove 521. An elastic bottom liner 55 and a cross telescopic member 54 are provided in the arc-shaped opening groove 521. The cross telescopic member 54 is used to extend the elastic bottom liner 55 downward and cover the bottom of the outer elastic ring sleeve 53 to form a complete bearing surface.

[0034] The top of the upper elastic ring 51 is provided with several elastic flipping elements 511. The elastic flipping elements 511 have elastic force away from the axis of the upper elastic ring 51. They are provided with air cavities 512 inside. During the downward movement, the air cavities 512 expand under the action of downhole pressure, pushing the elastic flipping elements 511 to open outward and fit and position against the inner wall of the goaf 11 to form a stable material receiving port. At the same time, the buoyancy of the air cavities 512 is used to stretch the upper elastic ring 51 upward and separate it from the sinking bottom sealing element 52, thereby stretching the elastic side liner 56 and the outer elastic skeleton 57 to form a columnar support. The outer elastic ring 53 has a cavity; the outer wall of the outer elastic ring 53 is provided with several spiral guide grooves 531, which are used to form a stable posture and prevent overturning during the sinking process of the outer elastic ring 53; on the other hand, they are used to guide the reinforced composite plugging slurry to be evenly distributed and penetrate into the gap between the plugging mechanism 5 and the leakage channel, thereby improving the sealing performance; the outer elastic ring 53 covers three sets of bottom plugging parts 52 and the outer diameter of the minimum stroke is smaller than the outer diameter of the drill bit 31, ensuring that the plugging mechanism 5 after lateral contraction can sink smoothly in the well drilled by the drill bit 31 of the current size.

[0035] Please refer to this first. Figure 8 - Figure 9 The cross-expansion joint 54 is composed of multiple sets of X-shaped rotating arc-shaped rods. A return spring 542 is fixed between the arc-shaped rods at the top. A slider 541 is fixed at the rotation node of the second set of arc-shaped rods at the top. An arc-shaped groove 522 that cooperates with the slider 541 is provided in the arc-shaped opening groove 521. The elastic base 55 is fixed to the inner side of the cross-expansion joint 54. After the sealing mechanism 5 is disengaged from the inner flip frame 43, the elastic potential energy of the return spring 542 is released. During the process of freely moving down to the goaf 11, the cross-expansion joint 54 extends outward along the arc-shaped groove 522 under the elastic force of the return spring 542, causing the elastic base 55 to form a large-area bearing surface. The three sets of elastic base 55 are staggered and superimposed, which can stably support the reinforced composite sealing grout.

[0036] This method utilizes the synergistic effect of hard nut shells, wood chips, and flaky minerals in fiber-reinforced composite mud to naturally fill leakage channels under gravity, forming a preliminary "mud bridge" for rapid sealing of small and medium-sized cracks. It also provides a positioning basis for subsequent enhanced plugging. For large-sized leakage channels where primary pretreatment failed, the rapid setting characteristics of the quick-setting cement in the composite plugging slurry are enhanced, combined with a shut-in pressure of 1.5-2.0 MPa, to forcibly compact the plugging slurry within the leakage channel, forming a high-strength sealing layer. Simultaneously, the plugging mechanism 5 provides rigid load-bearing support, preventing the plugging slurry from flowing along large cavities, thus overcoming the shortcomings of traditional plugging methods that lack support and are prone to leakage.

[0037] In construction step S4, a signal is transmitted to the hydraulic mechanism 411 through the drill pipe 3. The hydraulic mechanism 411 drives the inner tilting frame 43 to tilt and release the sealing mechanism 5. The sealing mechanism 5 moves freely downward under its own gravity. During the process, the air chamber 512 of the elastic tilting component 511 expands under the downhole pressure, pushing the elastic tilting component 511 to open outward and fit against the inner wall of the goaf 11, thus achieving automatic positioning.

[0038] After the sealing mechanism 5 is positioned, the cross telescopic component 54, under the elastic force of the return spring 542, extends outward along the arc-shaped slide groove 522, causing the elastic bottom liner 55 to move downward and cover the bottom of the outer elastic ring 53, forming a complete and large-area bearing surface; at the same time, the outer elastic skeleton 57 enhances the structural strength of the elastic side liner 56, preventing the sealing mechanism 5 from deforming under the pressure of the leaking grout. Please refer to [reference needed]. Figure 10 After the reinforced composite plugging grout is injected, the pressure of the reinforced composite plugging grout causes the elastic side liner 56 and the outer elastic skeleton 57 located at the intersection of the goaf 11 and the mine shaft to deform and extend into the goaf 11. After the reinforced composite plugging grout dries, it forms a plug. Under the premise of ensuring the sealing effect, the amount of reinforced composite plugging grout injected can be effectively reduced, and accurate sealing can be formed. The sealing efficiency and cost are effectively controlled.

[0039] The above description is only the best implementation method adopted in this application in combination with current practical needs, but the scope of protection of this application is not limited thereto.

Claims

1. A plugging device for safe drilling in goaf, comprising a plugging mechanism (5), characterized in that, The sealing mechanism (5) is pre-installed at the bottom of the pre-loading device (4), which is located at the bottom of the sleeve shoe (21); The sealing mechanism (5) moves freely down into the well and forms a sealing support with the goaf (11) inside the mining area (1) and the well site, which is used to carry the reinforced composite plugging slurry. The casing shoe (21) is fixed to the bottom of the casing (2) and is used to bridge the annulus between the casing (2) and the well wall; The pre-loading device (4) includes an installation ring (41) fixed to the bottom of the casing shoe (21). A sealing ring (42) is fixed to the top of the outer side of the installation ring (41). The sealing ring (42) is used to squeeze the well wall to form a seal. The bridging area of ​​the casing (2) is located at the top of the sealing ring (42). The inner wall of the installation ring (41) is provided with three sets of equally spaced inner flip frames (43). The inner flip frames (43) are rotatably connected to the inner side of the installation ring (41). The inner wall of the installation ring (41) is provided with a hydraulic mechanism (411) that matches the inner flip frames (43). A ball head (44) is fixed to the bottom of the outer side of the installation ring (41). The sealing mechanism (5) is clamped between the ball head (44) and the inner flip frame (43). The ball head (44) is spherical during the bridging stage. After the bridging is completed, the drill rod (3) drives the drill bit (31) to move down and drill out a through hole that matches the drill bit (31). The sealing mechanism (5) includes an upper elastic ring (51) and an outer elastic ring sleeve (53). An elastic side liner (56) is fixed between the upper elastic ring (51) and the outer elastic ring sleeve (53). An outer elastic skeleton (57) is sleeved on the outside of the elastic side liner (56). The inner side of the outer elastic ring (53) is fixed with three sets of bottom sealing members (52) evenly distributed at equal angles. The bottom of the bottom sealing member (52) is provided with an arc-shaped opening groove (521). The arc-shaped opening groove (521) is provided with an elastic base (55) and a cross telescopic member (54). The cross telescopic member (54) is used to extend the elastic base (55) downward and cover the bottom of the outer elastic ring (53). The top of the upper elastic ring (51) is provided with a plurality of elastic flipping members (511), the elastic flipping members (511) have elastic force away from the axis of the upper elastic ring (51), and the elastic flipping members (511) are provided with air chambers (512). The outer wall of the outer elastic ring (53) is provided with several spiral guide grooves (531). The outer diameter of the three sets of bottom sealing parts (52) covered by the outer elastic ring (53) when they are close to each other is smaller than the outer diameter of the drill bit (31). The cross telescopic component (54) is composed of multiple sets of X-shaped rotating arc rods. A return spring (542) is fixed between the arc rods at the top. A slider (541) is fixed at the rotation node of the second set of arc rods at the top. An arc groove (522) that cooperates with the slider (541) is provided in the arc opening groove (521). The elastic bottom liner (55) is fixed to the inside of the cross telescopic component (54). The construction method for safe drilling in goaf areas using the plugging mechanism (5) includes the following steps: S1. Accident determination: During the drilling process, if the pump pressure suddenly drops to zero, the mud level in the mud pit drops rapidly, and the mud return at the wellhead is completely interrupted, it is determined that the drill bit (31) has drilled through the goaf (11) roof and entered a large cavity or a fracture zone with excellent connectivity. S2, Emergency Risk Control: Immediately stop drilling and mud pumping, and slowly pull the drill bit (31) to a safe position inside the casing shoe (21) to avoid the drill bit (31) from staying in the goaf (11) section; S3. Static pressure grouting pretreatment: Prepare about 2 cubic meters of high viscosity fiber composite mud. The composite mud is composed of base mud + 3% hard nut shell with a particle size of 2-5mm + 2% wood chips + 1% flaky minerals. It is slowly and continuously poured into the hole through the orifice by the gravity of the slurry itself. After standing for four hours, try a small-volume circulation to verify the leak-stopping effect. S4. Pumping composite plugging slurry and shutting in the well: If static pressure grouting is unsuccessful, prepare 4 cubic meters of reinforced composite plugging slurry. The reinforced composite plugging slurry is composed of base slurry + 5% hard nut shell + 3% wood chips + 2% flaky minerals + 3% quick-setting cement. Lower the drill pipe (3) to the top of the goaf (11). Before pumping the reinforced composite plugging slurry, release the plugging mechanism (5) in advance. Pump the reinforced composite plugging slurry to the predetermined position in one go. After pulling the drill to a safe position, close the blowout preventer, apply a wellhead pressure of 1.5-2.0 MPa for 30 minutes, and let it stand for 12 hours for curing. S5. Circulation recovery and risk isolation: After maintenance, drill down to the bottom of the hole, start the pump to circulate and verify the mud circulation recovery. After confirming the recovery, quickly pass through the goaf section with low drilling pressure and high speed. After enlarging the hole, run in the technical casing and place the technical casing shoe 2 meters below the bottom plate of the goaf (11). Pump cement slurry into the ground through the annulus between the technical casing and the hole wall to cement the well and complete the isolation of the risk section of the goaf. S6. Subsequent drilling: Continue drilling inside the technical casing using a smaller diameter drill bit until the final hole is reached.

2. The goaf safety drilling plugging device according to claim 1, characterized in that, In step S4, the basis for determining that static pressure grouting was unsuccessful is as follows: after static pressure grouting is completed, after standing for 4 hours, the pump is started and circulated at a small displacement. The pump pressure is briefly built up to 0.8MPa. If the pump pressure drops to zero again and the liquid level does not rise, it is determined that the leakage channel is too large and the strength of the mud bridge formed by static pressure grouting is insufficient, and the static pressure grouting is determined to be unsuccessful.

3. A sealing device for safe drilling in a goaf area according to claim 1, characterized in that, In step S5, the basis for verifying the recovery of mud circulation is as follows: after the reinforcement of composite plugging slurry is completed, the well is opened, the drill is lowered to the bottom of the hole, the pump is started for circulation, the pump pressure is stabilized at 3.0 MPa, and the mud level in the mud pit is stable, then the mud circulation recovery is considered successful.

4. A sealing device for safe drilling in a goaf area according to claim 1, characterized in that, In step S5, P.O42.5 grade cement is used for cementing operations, the water-cement ratio of the cement slurry is 0.8-1.0, and the pumping pressure is controlled at 2.5-3.0 MPa to ensure that there is no leakage of cement slurry when it returns to the surface; The drilling pressure for quickly passing through the goaf (11) section is controlled at 50%-60% of the conventional drilling pressure, and the rotation speed is 120%-150% of the conventional rotation speed, so as to avoid the drilling tool vibration disturbing the hole wall.

5. A sealing device for safe drilling in a goaf area according to claim 1, characterized in that, In step S4, the wellhead pressure changes are monitored in real time during the shut-in squeezing process. If the pressure is lower than 1.5 MPa, reinforced composite plugging slurry is pumped in to maintain the pressure stable in the range of 1.5-2.0 MPa.

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