A ground cementing method for tunnel hole and final hole in coal mine area

Abstract

The present invention discloses a ground cementing method for the final hole of a tunnel borehole in a coal mine. By connecting a packer or cement umbrella to a casing string run at the connection point between the final hole and the tunnel, and then combining casing perforation technology with a high-viscosity cement slurry injection method, a pressure-bearing seal is achieved at the bottom of the annular gap between the final hole casing and the final hole wall. Simultaneously, a graded hoop cementing method and a rubber plug impact pressure method are combined to achieve positive circulation of the cement slurry, thereby efficiently achieving high-quality cementing of the final hole of a tunnel borehole in a coal mine. The present invention establishes positive circulation of cement slurry cementing on the ground after the tunnel final hole is drilled and casing is run, achieving efficient and high-quality cementing.

Description

Technical Field

[0001] The invention belongs to the technical field of through-tunnel drilling engineering in coal mining areas, and relates to a ground cementing method for final hole of through-tunnel drilling in coal mining areas. Background Art

[0002] The application scope of tunnel drilling in coal mining areas is relatively wide, such as gas extraction, cable laying, water supply and drainage, tunnel rescue and material transportation. In order to ensure the permanent use of tunnel holes, the entire section of the tunnel end hole must be casing cemented. However, after the tunnel end hole is drilled, the bottom of the end hole is connected to the tunnel. After the end hole casing is lowered, there is a gap between the end hole casing and the end hole wall. Therefore, it is impossible to use the cement slurry positive circulation method for cementing. Nowadays, in order to ensure that the end hole of tunnel drilling in coal mining areas can be cemented with cement slurry positive circulation, it is proposed to make an artificial bottom in the tunnel below the tunnel point of the tunnel hole in the coal mine to achieve the sealing of the bottom of the annulus between the end hole casing wall and the end hole casing, and at the same time use the graded hoop cementing technology to achieve the cement slurry positive circulation cementing of the tunnel end hole.

[0003] However, in coal mine area tunnel holes are used in special circumstances, and in these circumstances it is impossible to make an artificial well bottom in the coal mine. For example, there is a water storage tank or a sealed and unventilated tunnel directly below the connection point between the tunnel hole and the coal mine tunnel. It is difficult to achieve positive circulation cementing of cement slurry by adopting the existing tunnel hole final hole cementing method in coal mine area. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a ground cementing method for the final hole of a tunnel in a coal mine area, so as to solve the problem that the existing ground cementing method for the final hole of a tunnel in a coal mine area is difficult to achieve positive circulation cement slurry cementing.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A surface cementing method for a tunnel hole in a coal mine comprises the following steps:

[0007] Step 1: Run a final hole casing string into the final hole of the tunnel hole; the final hole casing string includes a blind guide head, a packer or a cement umbrella, a pressure-resistant final hole casing, a pressure-bearing short sleeve and a final hole casing, and a grading collar provided on the inner wall of the final hole casing, which are connected in sequence from bottom to top; the upper end of the final hole casing string is fixed to an open casing by a wellhead seat clamp near the ground; the packer or cement umbrella is located near the connection point between the final hole of the tunnel hole and the tunnel; within 3 to 5 meters above the connection point between the final hole of the tunnel hole and the tunnel, a packer is used when the inner diameter of the final hole is regular, and a cement umbrella is used when the inner diameter of the final hole is irregular;

[0008] Step 2: When the inner diameter of the final hole is regular, high-pressure drilling fluid is pumped into the final hole casing string. The high-pressure drilling fluid is held in pressure to expand the packer. The expanded packer fits tightly against the wall of the final hole of the through-hole, thereby preliminarily establishing an annular bottom seal between the final hole casing string and the final hole wall. When the inner diameter of the final hole is irregular, the cement cap always fits against the final hole wall during the process of running the final hole casing string.

[0009] Step 3: Insert the perforating instrument from the ground to the pressure-resistant end-hole casing, and perform perforating operations on the pressure-resistant end-hole casing to form spirally distributed holes on the pressure-resistant end-hole casing;

[0010] Step 4: Pump high-viscosity cement slurry into the final hole casing string from the surface through a mud pump. After the high-viscosity cement slurry is pumped in, continue to pump drilling fluid into the final hole casing string to the bottom of the pressure-bearing short casing, and then lower a small-sized pressure-holding ball valve to make the final hole casing string in a pressure-holding sealing state. Wait for the high-viscosity cement slurry to solidify for 48 hours to form a high-viscosity cement slurry cementing section. After the high-viscosity cement slurry cementing section is formed between the final hole casing string and the final hole wall, the annulus bottom sealing between the final hole casing string and the final hole wall can be effectively achieved.

[0011] Step 5: Carry out water slurry positive circulation cementing, insert a large-size pressure-holding ball valve into the end hole casing string, and pump high-pressure drilling fluid into the end hole casing string again. The pressure holding makes the large-size pressure-holding ball valve cut the pin of the grader collar, and the sliding sleeve of the grader collar slides along the retaining cylinder to the limit ring. The high-pressure drilling fluid flows out from the side hole of the grader collar and returns to the ground through the annular gap between the end hole casing and the hole wall, thereby establishing normal liquid circulation between the ground and the bottom of the through-tunnel end hole. At the same time, the high-pressure drilling fluid cleans the annular gap between the end hole casing string and the end hole wall; then, the required amount of conventional cement slurry prepared in advance is pumped into the ground through the cementing pump truck to form a positive circulation conventional cement slurry flow line; after the conventional cement slurry is pumped in, A collision plug is lowered into the end hole casing string, and displacement fluid is continuously pumped in through the cementing pump truck. The displacement fluid pushes the pumping plug from the top of the end hole casing string to the bottom of the well. After the collision plug is displaced and pushed to the top of the grading collar, the collision cementing is completed. Then the wellhead is closed on the ground. After the cementing is allowed to solidify for at least 72 hours, a matching drill bit assembly is lowered into the end hole casing string to sweep and break the collision plug, the internal structure of the grading collar, the large-size pressure-holding ball valve, the small-size pressure-holding ball valve and the blind guide head, finally realizing the connection between the ground and the underground tunnel, establishing a permanent channel connecting the ground and the underground tunnel, and realizing the whole process of cementing method of the end hole of the through tunnel in the coal mine area on the ground.

[0012] The present invention also includes the following technical features:

[0013] Specifically, the pressure-bearing short sleeve includes a pressure-bearing short sleeve body and a rubber seat clip embedded inside; the small-size pressure-holding ball valve is directly smaller than the minimum inner diameter of the grading hoop and slightly larger than the minimum inner diameter of the rubber seat clip inside the pressure-bearing short sleeve, so that the small-size pressure-holding ball valve can pass through the grading hoop smoothly and effectively hold pressure at the pressure-bearing short sleeve.

[0014] Specifically, the small-sized pressure-holding ball valve is a drillable pressure-holding ball valve, the interior of which is made of aluminum alloy, and the exterior is wrapped with the same rubber material as the rubber seat inside the pressure-bearing short sleeve.

[0015] Specifically, the large-size pressure-holding ball valve is a drillable pressure-holding ball valve, and its internal and external components are made of the same materials as those of the small-size pressure-holding ball valve. Its outer diameter is the same as the inner diameter of the grading hoop sleeve. After the large-size pressure-holding ball valve is put into the end-hole casing string, it can smoothly enter the interior of the sleeve, hold pressure and remain at the bottom of the sleeve.

[0016] Specifically, in step 4, the high-viscosity cement slurry can fill the space volume in the final hole casing string below the short pressure sleeve and the annular space volume between the final hole casing string and the final hole wall from the packer or cement umbrella to the bottom of the grading collar for 2 to 3 meters.

[0017] Specifically, the cement umbrella includes multiple elastic steel sheets, an annular base, snaps and canvas. The bottom end of the elastic steel sheet is welded to the annular base. Multiple elastic steel sheets form an umbrella-shaped structure with a flared top. The elastic steel sheet has resilience. The bottom end of the canvas is adhered to the annular base, and the upper end is adhered to the elastic steel sheet through snaps.

[0018] Specifically, the cement umbrella is nested on the outside of the pressure-resistant final hole casing through its annular base. During the process of the final hole casing string being lowered into the final hole, the cement umbrella will not slide on the final hole casing string, and can form a preliminary annular bottom seal in the annulus between the final hole casing string and the final hole wall.

[0019] Specifically, the grading hoop includes a sliding sleeve, a retaining cylinder, an outer cylinder, a pin, a sealing ring and a limit ring, wherein the sliding sleeve, retaining cylinder and outer cylinder are sequentially installed from the inside to the outside, the pin passes through the sliding sleeve, retaining cylinder and the upper side walls of the outer cylinder, the retaining cylinder and the outer cylinder are provided with a grading hoop side hole, the grading hoop side hole is located below the pin, the sealing ring is provided between the retaining cylinder and the outer cylinder, the sealing ring is located below the grading hoop side hole, the limit ring is fixed to the inner wall of the outer cylinder and is located at the lower end of the retaining cylinder, the inner diameter of the limit ring is smaller than the outer diameter of the sliding sleeve so that the sliding sleeve falls on the limit ring, the distance between the lower end of the sliding sleeve and the limit ring is greater than the distance between the upper end of the sliding sleeve and the side hole of the grading hoop, so that when the sliding sleeve falls onto the limit ring, the side hole of the grading hoop can connect the inside and outside of the final hole casing.

[0020] Specifically, the grading collar is coaxially fixed to the inner wall of the end hole casing and is connected to the end hole casing by threads or friction welding.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] The present invention establishes a through tunnel final hole on the ground and then runs a casing into the cement slurry for positive circulation cementing, which can achieve high-efficiency and high-quality cementing.

[0023] The present invention can be applied to special circumstances for through-tunnel holes in coal mine areas, such as special conditions where there is a water storage tank or a sealed and unventilated tunnel directly below the connection point between the through-tunnel hole and the coal mine tunnel. In this case, it is impossible to make an artificial well bottom in the coal mine. The method of the present invention can be used to connect a packer or a cement umbrella to the casing string lowered at the connection point between the end hole and the tunnel, and then combine the casing perforation technology and the high-viscosity cement slurry injection method to achieve pressure-bearing sealing of the bottom of the annular space between the end hole casing and the end hole wall; at the same time, the graded hoop cementing method and the rubber plug impact pressure method are combined to achieve positive circulation cementing of the cement slurry, thereby efficiently achieving high-quality cementing of the end hole of the through-tunnel hole in the coal mine area. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a final hole casing string that is lowered into the final hole with a regular aperture of the final hole tunnel section according to the present invention;

[0025] Figure 2 This is a schematic diagram of the packer of the present invention after pressure expansion;

[0026] Figure 3 Schematic diagram of the casing hole after perforation with pressure resistance;

[0027] Figure 4 Schematic diagram of pressure holding during cementing with high viscosity cement slurry according to the present invention;

[0028] Figure 5 Schematic diagram of the pressure-holding activated grading hoop of the large-size pressure-holding ball valve of the present invention;

[0029] Figure 6 This is a schematic diagram of the impact pressure of conventional cement slurry cementing plugs in the final hole through-tunnel section with regular apertures according to the present invention;

[0030] Figure 7 This is a schematic diagram of the wellbore structure of the final hole cementing completion with regular aperture of the final hole through tunnel section of the present invention;

[0031] Figure 8 This is a schematic diagram of a final hole casing string that is lowered into the final hole in an irregular diameter final hole tunnel section according to the present invention;

[0032] Figure 9 It is a schematic diagram of the cement umbrella structure of the present invention;

[0033] Figure 10 This is a schematic diagram of the impact pressure of conventional cement slurry cementing plugs in the final hole through-tunnel section of the present invention with irregular pore diameter;

[0034] Figure 11This is a schematic diagram of the wellbore structure of the final hole cementing completion of the present invention in which the aperture of the final hole through tunnel section is irregular.

[0035] The meanings of the numbers in the figure are: 1. Blind guide head, 2. Packer, 3. Cement umbrella, 4. Pressure-resistant end-hole casing, 5. Pressure-bearing short sleeve, 6. End-hole casing, 7. Grading collar, 8. Wellhead seat clamp, 9. Open casing, 10. Impact rubber plug; 31. Elastic steel sheet, 32. Annular base, 33. Snap button, 34. Canvas; 41. Eyelet; 51. Rubber seat clamp, 52. Small-size pressure-holding ball valve; 71. Sliding sleeve, 72. Stop cylinder, 73. Outer cylinder, 74. Pin, 75. Seal ring, 76. Limit ring, 77. Side hole of grading collar, 78. Large-size pressure-holding ball valve; 20. End-hole of through-hole, 30. Roadway, 40. Ground, 50. Positive circulation conventional cement slurry flow line, 60. High-viscosity cement slurry cementing section, 70. Conventional cement slurry cementing section. DETAILED DESCRIPTION

[0036] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0037] Example:

[0038] This embodiment provides a surface cementing method for a tunnel borehole in a coal mine. After the tunnel borehole 20 in the coal mine connects the ground 40 with the underground tunnel 30, before the final hole cementing operation is performed, a logging instrument is first lowered to measure the aperture of the tunnel borehole 20. Based on the aperture measurement results of the tunnel borehole 20, it is determined whether the aperture is regular within 3 to 5 meters above the connection point between the tunnel borehole and the tunnel 30. The measurement results can be divided into two types: regular and irregular. The method includes the following steps:

[0039] Step 1: insert the Figure 1 The end-hole casing string 6 is shown; the end-hole casing string 6 includes a blind guide head 1, a packer 2 or a cement umbrella 3, a pressure-resistant end-hole casing 4, a pressure-bearing short sleeve 5 and an end-hole casing 6, and a grading hoop 7 arranged on the inner wall of the end-hole casing 6, which are connected in sequence from bottom to top; the upper end of the end-hole casing string 6 is suspended and fixed on an open casing 9 by a wellhead seat clamp 8 near the ground 40, and the open casing 9 is fixed to the upper inner wall of the end hole; the packer 2 or the cement umbrella 3 is close to the connection point between the end hole 20 of the through-tunnel hole and the tunnel 30; within a range of 3 to 5 meters above the connection point between the end hole 20 of the through-tunnel hole and the tunnel 30, if the inner diameter of the end hole is regular, the packer 2 is used, and if the inner diameter of the end hole is irregular, the cement umbrella 3 is used.

[0040] Step 2: When the inner diameter of the final hole is regular, high-pressure drilling fluid is pumped into the final hole casing 6 string. The high-pressure drilling fluid is pressed to expand the packer 2. The expanded packer 2 fits tightly with the wall of the through-hole final hole 20 to preliminarily establish the annular bottom seal between the final hole casing 6 string and the final hole wall. Figure 2 As shown, then stop pumping high-pressure drilling fluid; based on this step method, there is a certain gap or crack between the expanded packer 2 and the end hole wall to achieve a tight fit, and there is a certain gap or crack, and it is impossible to achieve a gapless or crack-free fit. Therefore, the above-mentioned preliminary establishment of the sealing of the bottom of the annulus between the end hole casing 6 strings and the end hole wall cannot meet the pump pressure of the subsequent cement slurry positive circulation cementing process and the cement slurry column pressure between the end hole casing 6 strings and the end hole wall on the upper part of the packer 2. At the same time, the cement slurry will enter the tunnel 30 through the gap or crack between them, and thus the quality and effect of the cement slurry positive circulation cementing cannot be guaranteed; for this reason, before implementing the cement slurry positive circulation cementing, it is necessary to establish a high-viscosity cement slurry cementing section 60 in the annulus between the end hole casing 6 strings and the end hole wall on the upper part of the packer 2, so as to achieve a gapless or crack-free sealing of the bottom of the annulus between the end hole casing 6 strings and the end hole wall. For irregular final hole diameters, after the packer 2 expands and fits against the hole wall, there will be large gaps or clearances, which makes it difficult to support the liquid column pressure after the high-viscosity cement slurry is injected, and thus it is impossible to form a high-viscosity cementing section 60. Therefore, a cement umbrella 3 is used instead of the packer 2.

[0041] When the inner diameter of the final hole is irregular, during the process of running the final hole casing 6 strings, the cement umbrella 3 always fits the final hole wall; Figure 8 As shown; based on this step method, a tight fit between the cement umbrella 3 and the end hole wall is achieved. The canvas 34 structure in the cement umbrella 3 can only withstand the pressure of a certain length of high-viscosity cement slurry column, and cannot ensure that it can withstand the pressure of the cement slurry column in the annulus between the entire end hole section wall and the end hole casing 6 strings and the pump pressure of the cement slurry positive circulation cementing process. Therefore, before implementing the cement slurry positive circulation cementing, it is necessary to establish a certain length of high-viscosity cement slurry cementing section 60 in the annulus between the end hole casing 6 strings and the end hole wall on the upper part of the cement umbrella 3, so as to achieve the bottom sealing of the annulus between the end hole casing 6 strings and the end hole wall, and effectively ensure the smooth implementation of the subsequent cement slurry positive circulation cementing process.

[0042] The cement umbrella 3 includes a plurality of elastic steel sheets 31, an annular base 32, a snap button 33 and a canvas 34. Figure 9 As shown, the bottom end of the elastic steel sheet 31 is welded to the annular base 32, and multiple elastic steel sheets 31 form an umbrella-shaped structure with a flared top. The elastic steel sheet 31 has resilience and always fits with the well wall during and after the six strings of end-hole casing are lowered. Despite irregular hole diameters, it can always fit tightly with the end-hole wall. The canvas 34 is shaped like a bottomless pocket, with the bottom end adhered to the annular base 32 by sealant, and the upper end adhered to the elastic steel sheet 31 by snap fasteners 33.

[0043] The cement umbrella 3 is nested in the outer side of the pressure-resistant end-hole casing 4 through its annular base 32. When the end-hole casing 6 string is lowered into the end-hole, the cement umbrella 3 will not slide on the end-hole casing 6 string. One end of the elastic steel sheet 31 of the cement umbrella 3 with an open trumpet mouth is always tightly fitted with the end-hole wall. One end of the canvas 34 is adhered to the elastic steel sheet 31 through a snap 33, and one end of the canvas 34 is adhered to the annular base 32 through a sealant. Based on the above method, a preliminary annular bottom seal can be formed in the annular space between the end-hole casing 6 string and the end-hole wall.

[0044] Step 3: Lower the perforating equipment from the ground 40 to the pressure-resistant end-hole casing 4, perform perforating operations on the pressure-resistant end-hole casing 4 to form spiral holes 41 on the pressure-resistant end-hole casing 4, and then remove the perforating equipment. Figure 3 As shown, the distribution of the holes 41 can effectively ensure that the high-viscosity cement slurry injected subsequently enters the annular space between the final hole casing 6 and the final hole wall.

[0045] Step 4: Pump the calculated amount of high-viscosity cement slurry into the end hole casing 6 string through the mud pump from the surface 40. After the high-viscosity cement slurry is pumped in, continue to pump drilling fluid into the end hole casing 6 string to the bottom of the pressure short sleeve 5, and then lower the small-sized pressure-holding ball valve 52. Figure 4 As shown, the three-way valve connected to the final hole casing string 6 is then closed at the surface 40, creating a pressure-blocked, sealed state within the final hole casing string 6. After the high-viscosity cement slurry solidifies for 48 hours, a high-viscosity cement slurry cementing section 60 is formed. The three-way valve connected to the final hole casing string 6 is then opened. The formation of the high-viscosity cement slurry cementing section 60 between the final hole casing string 6 and the final hole wall effectively seals the bottom of the annulus between the final hole casing string 6 and the final hole wall, effectively ensuring the smooth implementation of the subsequent cement slurry positive circulation cementing process.

[0046] The pressure-bearing short sleeve 5 includes a pressure-bearing short sleeve 5 body and a rubber seat 51 embedded inside; the small-size pressure-holding ball valve 52 is directly smaller than the minimum inner diameter of the grading hoop 7, and slightly larger than the minimum inner diameter of the rubber seat 51 inside the pressure-bearing short sleeve 5, so that the small-size pressure-holding ball valve 52 can pass through the grading hoop 7 smoothly and effectively hold pressure at the pressure-bearing short sleeve 5.

[0047] The small-sized pressure-holding ball valve 52 is a drillable pressure-holding ball valve, the interior of which is made of aluminum alloy, and the exterior of which is wrapped with the same rubber material as the rubber seat 51 inside the pressure-bearing short sleeve 5 .

[0048] The calculated amount of high-viscosity cement slurry can fill the space volume within the end hole casing 6 string below the short pressure sleeve 5 and the annular space volume between the end hole casing 6 string and the end hole wall from the packer 2 or cement umbrella 3 to the bottom of the grading collar 7 for 2 to 3 meters.

[0049] Step 5: Perform water slurry positive circulation cementing. After opening the three-way valve connected to the end hole casing 6 string based on step 5, a large-size pressure-holding ball valve 78 is inserted into the end hole casing 6 string, and high-pressure drilling fluid is pumped into the end hole casing 6 string from the ground 40 again. The high-pressure drilling fluid pumped into the end hole casing 6 string hole is pressure-holding. The pressure-holding causes the large-size pressure-holding ball valve 78 to cut off the pin 74 of the stage collar 7. The sliding sleeve 71 of the stage collar 7 slides along the retaining cylinder 72 to the limit ring 76. The high-pressure drilling fluid flows out from the side hole 77 of the stage collar and returns to the ground 40 through the annular gap between the end hole casing 6 and the hole wall, thereby establishing normal liquid circulation between the ground 40 and the bottom of the through-tunnel end hole. At the same time, the high-pressure drilling fluid cleans the annular gap between the end hole casing 6 string and the end hole wall. Figure 5 As shown; then, the required amount of conventional cement slurry prepared in advance is pumped into the ground 40 by a cementing pump truck to form a positive circulation conventional cement slurry flow line 50 and a conventional cement slurry cementing section 70; after the required amount of conventional cement slurry is pumped in, a bumping plug 10 is lowered into the end hole casing 6 string, and displacement fluid is continuously pumped into the cementing pump truck. The displacement fluid pushes the pumping plug from the top of the end hole casing 6 string to the bottom of the well. After the bumping plug 10 is displaced and pushed to the top of the grading collar 7, the bumping cementing is completed. Figure 6 、 Figure 10 As shown, the wellhead is then closed on the ground 40. After the cementing is cured for at least 72 hours, the wellhead is opened, and a matching drilling tool assembly is lowered into the end hole casing 6 string to sweep and plug the impact plug 10, the internal structure of the grading collar 7, the large-size pressure-holding ball valve 78, the small-size pressure-holding ball valve 52 and the blind guide head 1 used in the cementing process. Finally, the ground is connected to the underground tunnel 30, and a permanent channel is established between the ground 40 and the underground tunnel 30, as shown in FIG. Figure 7 、 Figure 11 As shown, a cementing method for implementing the entire process of the final hole 20 of the through-tunnel hole in the coal mine area on the ground 40 is implemented.

[0050] The large-sized pressure-holding ball valve 78 is a drillable pressure-holding ball valve. The internal and external components are made of the same materials as the small-sized pressure-holding ball valve 52. Its outer diameter is the same as the inner diameter of the sliding sleeve 71 of the grading hoop 7. After the large-sized pressure-holding ball valve 78 is put into the end hole casing 6 string, it can smoothly enter the interior of the sliding sleeve 71, hold pressure and remain at the bottom of the sliding sleeve 71.

[0051] The grading hoop 7 includes a sliding sleeve 71, a retaining cylinder 72, an outer cylinder 73, a pin 74, a sealing ring 75 and a limiting ring 76. The sliding sleeve 71, the retaining cylinder 72 and the outer cylinder 73 are sequentially mounted from the inside to the outside. The pin 74 passes through the upper side walls of the sliding sleeve 71, the retaining cylinder 72 and the outer cylinder 73. The retaining cylinder 72 and the outer cylinder 73 are provided with a grading hoop side hole 77. The grading hoop side hole 77 is located below the pin 74. The sealing ring 75 is provided between the retaining cylinder 72 and the outer cylinder 73. The sealing ring 75 is located below the side hole 77 of the grading hoop, and the limiting ring 76 is fixed to the inner wall of the outer cylinder 73 and is located at the lower end of the retaining cylinder 72. The inner diameter of the limiting ring 76 is smaller than the outer diameter of the sliding sleeve 71 so that the sliding sleeve 71 falls on the limiting ring 76. The distance between the lower end of the sliding sleeve 71 and the limiting ring 76 is greater than the distance between the upper end of the sliding sleeve 71 and the side hole 77 of the grading hoop. Therefore, when the sliding sleeve 71 falls onto the limiting ring 76, the side hole 77 of the grading hoop can communicate with the inside and outside of the final hole casing 6.

[0052] The grading collar 7 is coaxially fixed to the inner wall of the end hole casing 6 and is connected to the end hole casing 6 by threads or friction welding.

[0053] Based on the above steps and methods, high-quality cementing of the final hole 20 of the tunnel borehole in the coal mine area can be efficiently achieved on the ground 40 throughout the entire process, thereby effectively ensuring the service life of the tunnel borehole.

Claims

1. A ground cementing method for the final hole of a tunnel in a coal mine, characterized in that: The following steps are involved: Step 1: Run a final hole casing string into the final hole of the tunnel hole; the final hole casing string includes a blind guide head, a packer or a cement umbrella, a pressure-resistant final hole casing, a pressure-bearing short sleeve and a final hole casing, and a grading collar provided on the inner wall of the final hole casing, which are connected in sequence from bottom to top; the upper end of the final hole casing string is fixed to an open casing by a wellhead seat clamp near the ground; the packer or cement umbrella is located near the connection point between the final hole of the tunnel hole and the tunnel; within 3 to 5 meters above the connection point between the final hole of the tunnel hole and the tunnel, a packer is used when the inner diameter of the final hole is regular, and a cement umbrella is used when the inner diameter of the final hole is irregular; Step 2: When the inner diameter of the final hole is regular, high-pressure drilling fluid is pumped into the final hole casing string. The high-pressure drilling fluid is held in pressure to expand the packer. The expanded packer fits tightly against the wall of the final hole of the through-hole, thereby preliminarily establishing an annular bottom seal between the final hole casing string and the final hole wall. When the inner diameter of the final hole is irregular, the cement cap always fits against the final hole wall during the process of running the final hole casing string. Step 3: Insert the perforating instrument from the ground to the pressure-resistant end-hole casing, and perform perforating operations on the pressure-resistant end-hole casing to form spirally distributed holes on the pressure-resistant end-hole casing; Step 4: Pump high-viscosity cement slurry into the final hole casing string from the surface through a mud pump. After the high-viscosity cement slurry is pumped in, continue to pump drilling fluid into the final hole casing string to the bottom of the pressure-bearing short casing, and then lower a small-sized pressure-holding ball valve to make the final hole casing string in a pressure-holding and sealing state. Wait for the high-viscosity cement slurry to solidify for 48 hours to form a high-viscosity cement slurry cementing section. After the high-viscosity cement slurry cementing section is formed between the final hole casing string and the final hole wall, the annulus bottom sealing between the final hole casing string and the final hole wall can be effectively achieved. Step 5: Carry out cement slurry positive circulation cementing, insert a large-size pressure-holding ball valve into the end hole casing string, and pump high-pressure drilling fluid into the end hole casing string again. The pressure holding makes the large-size pressure-holding ball valve cut the pin of the grader collar, and the sliding sleeve of the grader collar slides along the retaining cylinder to the limit ring. The high-pressure drilling fluid flows out from the side hole of the grader collar and returns to the ground through the annular gap between the end hole casing and the hole wall, thereby establishing normal liquid circulation between the ground and the bottom of the through-tunnel hole. At the same time, the high-pressure drilling fluid cleans the annular gap between the end hole casing string and the end hole wall; then, the required amount of conventional cement slurry prepared in advance is pumped into the ground through the cementing pump truck to form a positive circulation conventional cement slurry flow line; after the conventional cement slurry is pumped in, a pressure plug is put into the end hole casing string. Continue to pump in the displacement fluid through the cementing pump truck, and the displacement fluid pushes the impact plug from the top of the end hole casing string to the bottom of the well. After the impact plug is displaced and pushed to the top of the grading collar, the impact cementing is completed, and then the wellhead is closed on the ground. After the cementing is allowed to solidify for at least 72 hours, a matching drill bit assembly is lowered into the end hole casing string to sweep and crush the impact plug, the internal structure of the grading collar, the large-size pressure-holding ball valve, the small-size pressure-holding ball valve and the blind guide head, and finally realize the connection between the ground and the underground tunnel, establish a permanent channel connecting the ground and the underground tunnel, and realize the whole process of cementing the end hole of the through tunnel in the coal mine area on the ground; wherein, the grading collar includes a sliding sleeve, a retaining cylinder, an outer cylinder, a pin, a sealing ring and a limit ring.

2. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 1 is characterized in that: The pressure-bearing short sleeve includes a pressure-bearing short sleeve body and a rubber seat clip embedded inside; the diameter of the small-size pressure-holding ball valve is smaller than the minimum inner diameter of the grading hoop and slightly larger than the minimum inner diameter of the rubber seat clip inside the pressure-bearing short sleeve, so that the small-size pressure-holding ball valve can pass through the grading hoop smoothly and effectively hold pressure at the pressure-bearing short sleeve.

3. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 2 is characterized in that: The small-sized pressure-holding ball valve is a drillable pressure-holding ball valve, the interior of which is made of aluminum alloy, and the exterior is wrapped with the same rubber material as the rubber seat inside the pressure-bearing short sleeve.

4. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 3 is characterized in that: The large-size pressure-holding ball valve is a drillable pressure-holding ball valve, and its internal and external components are made of the same materials as those of the small-size pressure-holding ball valve. Its outer diameter is the same as the inner diameter of the grading hoop sleeve. After the large-size pressure-holding ball valve is put into the end-hole casing string, it can smoothly enter the interior of the sleeve, hold pressure and remain at the bottom of the sleeve.

5. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 1 is characterized in that: In step 4, the high-viscosity cement slurry can fill the space volume in the final hole casing string below the short pressure sleeve and the annular space volume between the final hole casing string and the final hole wall from the packer or cement umbrella to the 2-3 m section below the bottom of the grading collar.

6. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 1, characterized in that: The cement umbrella includes multiple elastic steel sheets, an annular base, snaps and canvas. The bottom ends of the elastic steel sheets are welded to the annular base. The multiple elastic steel sheets form an umbrella-shaped structure with a flared top. The elastic steel sheets have resilience. The bottom ends of the canvas are adhered to the annular base, and the upper ends of the canvas are adhered to the elastic steel sheets through snaps.

7. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 6, characterized in that: The cement umbrella is nested on the outside of the pressure-resistant final hole casing through its annular base. When the final hole casing string is lowered into the final hole, the cement umbrella will not slide on the final hole casing string, and can form a preliminary annular bottom seal in the annulus between the final hole casing string and the final hole wall.

8. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 1 is characterized in that: The sliding sleeve, retaining cylinder and outer cylinder are sequentially mounted from the inside to the outside, the pin passes through the upper side walls of the sliding sleeve, retaining cylinder and outer cylinder, the retaining cylinder and the outer cylinder are provided with side holes of the grading hoop, the side holes of the grading hoop are located below the pin, the sealing ring is provided between the retaining cylinder and the outer cylinder, the sealing ring is located below the side holes of the grading hoop, the limiting ring is fixed on the inner wall of the outer cylinder and is located at the lower end of the retaining cylinder, the inner diameter of the limiting ring is smaller than the outer diameter of the sliding sleeve so that the sliding sleeve falls on the limiting ring, the distance between the lower end of the sliding sleeve and the limiting ring is greater than the distance between the upper end of the sliding sleeve and the side holes of the grading hoop, so that when the sliding sleeve falls onto the limiting ring, the side holes of the grading hoop can communicate with the inside and outside of the final hole casing.

9. The surface cementing method for the final hole of a tunnel in a coal mine as claimed in claim 8, characterized in that: The grading collar is coaxially fixed to the inner wall of the end hole casing and is connected to the end hole casing through threads or friction welding.

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