A Coal Mine Downhole Cementing Completion Method Based on Dissolvable Screen Tubes

Abstract

This invention discloses a coal mine well completion method based on soluble screen pipes. The method includes the following specific steps: Step 1, establishing a first-stage borehole and installing a first-stage casing; Step 2, grouting into the first-stage borehole and the first-stage casing; Step 3, establishing a second-stage borehole and installing a second-stage casing; Step 4, grouting into the second-stage borehole and the second-stage casing; Step 5, injecting potassium chloride solution into the second-stage casing; Step 6, pressure testing with clean water; Step 7, gas extraction. This invention artificially creates and expands fractures through hydraulic fracturing, increasing formation permeability and significantly improving gas extraction efficiency compared to conventional open-hole well completion methods that directly run screen pipes. The soluble screen pipes used in this invention technically avoid the safety risks of perforation explosions in coal mines, optimize the perforation and fracturing process, save perforation operation costs, and simultaneously increase gas transport channels through the soluble screen pipes, thereby improving gas extraction efficiency.

Description

Technical Field

[0001] This invention belongs to the field of cementing and completion technology, and relates to soluble screens, specifically to a method for cementing and completion in coal mines based on soluble screens. Background Technology

[0002] Currently, most underground gas drainage boreholes in coal mines use open-hole completion or screen pipe completion methods, resulting in small gas drainage radius and low efficiency per borehole. Hydraulic fracturing technology has been widely applied to surface coalbed methane enhancement and rockburst prevention. The specific process involves cementing the well with ordinary casing, running a perforation string to penetrate the casing and create fractures in the formation, followed by a fracturing string for further fracturing. However, this explosive perforation method is difficult to meet the safety requirements of underground coal mine construction. Furthermore, this process has low overall operational efficiency, high construction costs, and a limited number of perforations, resulting in fewer gas drainage channels and lower drainage efficiency, making it unsuitable for large-scale application of underground gas drainage boreholes in coal mines.

[0003] Therefore, there is an urgent need for a coal mine underground solidification completion method based on soluble screen tubes to make up for the shortcomings of the current gas drainage borehole completion method. This method can improve the gas drainage efficiency of boreholes, save construction costs, and meet the needs of large-scale and safe use in coal mines. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a coal mine underground solidification completion method based on soluble screen tubes, in order to solve the technical problem of low gas extraction efficiency in existing coal mines.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A coal mine underground cementing completion method based on soluble screen tubes, the method comprising the following specific steps:

[0007] Step 1: Drill a hole and install a casing.

[0008] Based on the geological conditions, a first-stage borehole is constructed. A first-stage casing is then lowered into the first-stage borehole to a stable stratum. A centralizer is installed on the first-stage casing. A first-stage flange is connected to the upper outer side of the first-stage casing. A second-stage grouting pipe with a valve is reserved on the side wall of the first-stage casing borehole. A long steel grouting pipe and a short steel grouting pipe are respectively buried near the lower wall of the first-stage casing.

[0009] Step 2: Grouting is performed into the first drilled hole and the first casing.

[0010] First, use cotton yarn soaked in cement-water glass grout to seal the annular zone between the first open sleeve and the borehole wall in step one, and fix the two steel grouting pipes. Inject ordinary silicate cement into the borehole of the short steel grouting pipe and wait for it to set. Then, inject cement grout into the borehole of the long steel grouting pipe. After the grout returns into the first open sleeve, use a blind flange to plug the borehole of the first open sleeve and continue grouting. Pressurize the grout to 2 MPa and then stop grouting. Inject intermittently in multiple spots and wait for it to set.

[0011] Step 3: Establish the two-stage drilling channel and install the two-stage casing:

[0012] The solidified cement slurry in the first casing of step two is removed by drilling. The second borehole is then drilled to the target layer. The second casing is then inserted into the second borehole, and a second flange is connected to the upper outer opening of the second casing.

[0013] The aforementioned double-ended casing is formed by sequentially combining a regular casing, a centralizer, and another regular casing to seal the bottom section of the hole.

[0014] The two-stage casing is composed of a soluble screen pipe, a regular casing, a centralizer, a regular casing, a soluble screen pipe, a regular casing, a centralizer, and a regular casing, which are sequentially combined to form the first combination segment of the target layer of the two-stage casing. The first combination segment of the target layer is sequentially connected to the orifice skewing segment of the first-stage drilled hole.

[0015] Step 4: Grouting into the second-stage drilled hole and the second-stage casing:

[0016] Inject cement grout at a high flow rate through the pre-reserved grouting pipe opening for the second opening on the side wall of the first opening casing. After the grout returns to the second opening casing, plug the opening of the second opening casing with a blind flange and continue grouting. After pressurizing the grout to 12MPa, stop grouting and wait for it to set.

[0017] Step 5: Inject potassium chloride solution into the second-opening sleeve:

[0018] Open the blind flange in step four, drill down to clean the solidified cement slurry in the second-opening sleeve to above the bottom of the hole in the second-opening sleeve, pull up the drill, then connect the second-opening flange to the flange with the grouting hole, inject potassium chloride solution into the grouting hole, seal the opening of the second-opening sleeve, so as to dissolve the gas extraction hole that is temporarily riveted and sealed on the screen pipe.

[0019] Step 6, pressure test with clean water:

[0020] After well completion, at the bottom of the second casing hole, the annular packers are used to seal the front and rear ordinary casings at the first soluble screen pipe. Clean water is injected, pressure is limited during construction, and fracturing and blowout are carried out. After the first stage of fracturing is completed, the fracturing drill string is pulled back to the first soluble screen pipe of the next assembly as the second fracturing stage. The first fracturing process is repeated until fracturing is completed.

[0021] Step 7, Gas Extraction:

[0022] After steps one through six are completed, the milling string is lowered to perform well cleaning operations on the entire well section to ensure the wellbore is unobstructed. Finally, the casing orifice is opened to connect to the negative pressure gas extraction pipeline for joint extraction.

[0023] The present invention also has the following technical features:

[0024] The processing technology of the soluble sieve tube specifically includes the following steps:

[0025] Step 1: On the circular pipe wall 1000mm from both ends of the ordinary casing, four 12mm diameter holes are laser-cut at 90° intervals to obtain gas extraction holes.

[0026] Step 2: Forging is performed simultaneously from both the inner and outer sides of the ordinary casing to form cylindrical grooves with a diameter of approximately 14 mm and a height of approximately 2 mm on both the inner and outer sides of the gas extraction hole of the ordinary casing.

[0027] Step 3: Design the soluble rivet head to have a diameter of 14mm and a height of 2mm, and the soluble rivet shank to have a diameter of 10mm and a height of 8mm. The soluble rivet tail is chamfered to facilitate entry into the gas extraction hole with a cylindrical groove.

[0028] Step 4: Insert the soluble rivet through the gas extraction hole from the inside to the outside of the ordinary casing, and then mechanically pressurize the tail of the soluble rivet to perform the riveting operation, thereby obtaining the soluble screen tube.

[0029] The gas extraction holes of the soluble screen tube are sealed with soluble magnesium-aluminum alloy by riveting.

[0030] In step one, the diameter of the first borehole is Φ246mm, the dimensions of the first casing are Φ219mm×8.33mm×1000mm, and a centralizer is installed every 5m of the first casing.

[0031] In step one, the length of the long steel grouting pipe is 5m, and the length of the short steel grouting pipe is 2m.

[0032] In step one, a casing is lowered into the borehole to a depth of not less than 30m to the stable stratum.

[0033] In step two, ordinary silicate cement is injected through the orifice of the short steel grouting pipe and allowed to set for 24 hours.

[0034] In step two, cement grout is injected through the orifice of the long steel grouting pipe. After the grout returns into the first open sleeve, the orifice of the first open sleeve is blocked with a blind flange. The grouting is then stopped after the pressure is increased to 2 MPa. The grouting is then repeated three times in half-hour intervals, and the curing is allowed to proceed for 48 hours.

[0035] In step three, the diameter of the second-stage drilling channel is Φ193mm, and the dimensions of the ordinary casing and the soluble screen tube are Φ127mm×6.5mm×3000mm. The material of both the ordinary casing and the soluble screen tube is P110 casing.

[0036] In step three, the bottom section of the two-stage casing is formed by sequentially combining three meters of ordinary casing, a centralizer, and another three meters of ordinary casing to seal the bottom.

[0037] The two-stage casing is composed of three meters of soluble screen pipe, three meters of ordinary casing, a centralizer, three meters of ordinary casing, seventy-two meters of soluble screen pipe, three meters of ordinary casing, a centralizer, and three meters of ordinary casing, which are sequentially combined to form the first combination segment of the target layer of the two-stage casing. The first combination segment of the target layer is sequentially connected to the orifice skewing segment of the first-stage drilled hole.

[0038] In step four, grout is first injected from the opening of the casing, and cemented at a pressure of 10 MPa for 48 hours.

[0039] In step four, the cement grout injected at a large flow rate through the pre-reserved second-stage grouting pipe opening on the side wall of the first-stage casing orifice is PO425 cement grout, with a density of 1.80 g / cm³. 3 .

[0040] In step four, after the grout returns to the second-opening sleeve, the opening of the second-opening sleeve is blocked with a blind flange, and grouting continues. After pressurizing the grout to 12MPa, grouting is stopped and allowed to set for 7 days.

[0041] In step five, a 5% potassium chloride solution is injected into the grouting hole to seal the opening of the second-stage casing for 7 days.

[0042] In step six, after wellbore cleaning, annular packers are used to seal the pre- and post-casing sections of the first soluble screen at the bottom of the borehole, and a water injection rate of 6m³ is applied. 3 / min, construction pressure limit 45MPa, carry out fracturing and blowout. After the first stage of fracturing is completed, pull back the fracturing drill bit about 90m to the first soluble screen pipe of the next assembly as the second fracturing stage. Repeat the first fracturing process until fracturing is completed.

[0043] Compared with the prior art, the present invention has the following beneficial technical effects:

[0044] (I) The coal mine underground solidification completion method based on soluble screen tube proposed in this invention increases the formation permeability by artificially creating and expanding the fractures through hydraulic fracturing. Compared with the conventional open-hole direct screen tube completion method, it significantly improves the gas extraction efficiency.

[0045] (II) The soluble screen tube used in this invention technically avoids the unsafe factors of perforation explosion in coal mines, optimizes the perforation and fracturing process, and saves perforation operation costs; at the same time, the soluble screen tube increases the gas transport channel and improves the gas extraction efficiency.

[0046] (III) The soluble screen tube with riveting and sealing used in this invention has a simple structure, is easy to manufacture, has good sealing performance, is easy to achieve large-scale prefabrication in the factory, and has a low cost. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of a two-stage casing in a coal mine.

[0048] Figure 2 This is a schematic diagram of well completion using soluble screens.

[0049] Figure 3 This is a schematic diagram of the structure of a soluble sieve tube.

[0050] Figure 4 This is a schematic diagram of the cross-section at the soluble sieve tube AA.

[0051] Figure 5 This is a schematic diagram of a conventional sleeve opening.

[0052] Figure 6 This is a schematic diagram of simultaneous forging inside and outside the opening of a conventional sleeve.

[0053] Figure 7 This is a schematic diagram of a soluble rivet.

[0054] Figure 8 This is a schematic diagram of the structure of a soluble sieve tube.

[0055] The meanings of the labels in the diagram are as follows: 1-first-opening casing, 2-centralizer, 3-second-opening casing, 4-orifice skewing section.

[0056] 301-Ordinary casing, 302-Dissolvable screen pipe, 303-Gas extraction hole, 304-Cylindrical groove, 305-Dissolvable rivet, 306-Bottom section of hole, 307-First combined section of target layer.

[0057] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0058] It should be noted that, unless otherwise specified, all materials, equipment and components in this invention are made from materials, equipment and components known in the prior art.

[0059] Following the above technical solutions, 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 based on the technical solutions of this application fall within the protection scope of the present invention.

[0060] Example:

[0061] This embodiment presents a method for cementing and completing coal mine shafts based on soluble screens, such as... Figures 1 to 4 As shown, the method includes the following specific steps:

[0062] Step 1: Drill a hole and install a casing.

[0063] Based on the geological conditions, a Φ246mm borehole was constructed. A Φ219mm×8.33mm×1000mm casing 1 was lowered into the borehole to the stable stratum. A stabilizer 2 was installed on the casing 1 every 5m. A flange was connected to the upper outer side of the casing 1. A grouting port with a valve was reserved on the side wall of the casing 1. A long steel grouting pipe and a short steel grouting pipe were buried near the lower wall of the casing 1. The long steel grouting pipe was 5m long and the short steel grouting pipe was 2m long.

[0064] In this embodiment, the main purpose of the casing 1 is to seal the unstable formation in the borehole penetration section and to withstand the pressure of the fracturing string during fracturing; the centralizer 2 keeps the casing in the center.

[0065] Step 2: Grouting is performed into the first drilled hole and the first casing.

[0066] First, use cotton yarn soaked in cement-water glass grout to seal the annular zone between the first open sleeve 1 and the borehole wall in step one, and fix two steel grouting pipes. Inject ordinary silicate cement through the orifice of the short steel grouting pipe and wait for it to set for 24 hours. Then, inject cement grout through the orifice of the long steel grouting pipe. After the grout returns to the inside of the first open sleeve 1, plug the orifice of the first open sleeve 1 with a blind flange and continue grouting. After pressurizing the grout to 2 MPa, stop grouting and inject 3 times in a half-hour interval. Wait for it to set for 48 hours.

[0067] In this specific embodiment, ordinary silicate cement is injected into the short steel grouting pipe to seal the annular zone of the hole wall, so that the cement slurry injected from the orifice of the long steel grouting pipe can enter the interior of an open sleeve 1.

[0068] Step 3: Establish the two-stage drilling channel and install the two-stage casing:

[0069] The solidified cement slurry in the first-opening casing 1 of step two is removed by drilling. A second-opening borehole with a diameter of Φ193mm is drilled to the target layer. The upper outer opening of the second-opening casing 3 is connected to a second-opening flange. The ordinary casing 301 and the soluble screen pipe 302 are both made of P110 casing.

[0070] A Φ127mm×6.5mm×3000mm second-section casing 3 is installed in the second-section drilled hole. The second-section casing 3 consists of three meters of ordinary casing 301, a centralizer 2, and three meters of ordinary casing 301 in sequence as the bottom section 306 of the second-section casing 3.

[0071] The second-stage casing 3 consists of three meters of soluble screen pipe 302, three meters of ordinary casing 301, centralizer 2, three meters of ordinary casing 301, seventy-two meters of soluble screen pipe 302, three meters of ordinary casing 301, centralizer 2, and three meters of ordinary casing 301, which are sequentially combined to form the first combination section 307 of the target layer of the second-stage casing 3. The first combination section 307 of the target layer is sequentially connected to the orifice skewing section 4 of the first-stage drilled hole.

[0072] Specifically, in this embodiment, if the length of the second-stage casing 3 is less than one assembly section, the adjustment is made by reducing the number of soluble screen pipes 302 in the assembly section. A conventional casing 301 is run into the orifice of the second-stage casing 3, adjacent to the orifice of the directional drilling section 4. In this design, 6m of conventional casing 301 and a centralizer 2 are connected to both ends of the pre-fracturing soluble screen pipe 302. The conventional casing 301 provides conditions for sealing and pressurizing the fracturing bridge plug. The centralizer 2 ensures the casing is centered, improving cementing quality and thus guaranteeing the subsequent fracturing effect.

[0073] Step 4: Grouting into the second-stage drilled hole and the second-stage casing:

[0074] PO425 cement grout is injected at a high flow rate through the pre-reserved grouting pipe opening at the side wall of the first borehole of the first casing. The density of the PO425 cement grout is 1.80 g / cm³. 3 After the grout returns to the second-opening sleeve 3, the opening of the second-opening sleeve 3 is blocked with a blind flange, and grouting continues. After the pressure grouting reaches 12MPa, grouting is stopped and allowed to solidify for 7 days.

[0075] Step 5: Inject potassium chloride solution into the second-opening sleeve:

[0076] Open the blind flange in step four, drill down to clean the solidified cement slurry in the second-opening sleeve 3 to above the bottom of the hole in the second-opening sleeve 3, pull up the drill, then connect the second-opening flange to the flange with the grouting hole, inject a 5% potassium chloride solution into the grouting hole, seal the opening of the second-opening sleeve for 7 days, so as to dissolve the gas extraction hole 303 that is temporarily riveted and sealed on the screen pipe 302.

[0077] Step 6, pressure test with clean water:

[0078] After well completion, annular packers were used to seal the pre- and post-annular casing 301 and post-annular casing 301 of the first soluble screen 302 at the bottom of the second casing hole 3, respectively, and a water injection rate of 6m³ was applied. 3 / min, construction pressure limit 45MPa, carry out fracturing and blowout. After the first stage of fracturing is completed, pull back the fracturing drill bit about 90m to the first soluble screen 302 of the next assembly as the second fracturing stage. Repeat the first fracturing process until fracturing is completed.

[0079] In this embodiment, the first fracturing stage and the second fracturing stage are separated by 4 ordinary casing pipes 301 and 26 soluble screen pipes 302 to avoid mutual interference and formation channeling. The soluble screen pipes 302 that have not been fractured are within the coverage area of ​​the fracturing radius, which reduces fracturing costs while also achieving better gas extraction.

[0080] Step 7, Gas Extraction:

[0081] After steps one through six are completed, the milling string is lowered to perform well cleaning operations on the entire well section to ensure the wellbore is unobstructed. Finally, the first opening of the casing is connected to the negative pressure gas extraction pipeline for joint extraction.

[0082] Furthermore in this embodiment, such as Figures 5 to 8 As shown, the processing technology of the soluble sieve tube 302 specifically includes the following steps:

[0083] Step 1: On the circular wall of the ordinary casing 301, 1000mm from both ends, four 12mm diameter circular holes are laser-cut at 90° intervals to obtain the gas extraction hole 303.

[0084] Step 2: Forging is performed simultaneously from both the inner and outer sides of the ordinary casing 301, so that cylindrical grooves 304 with a diameter of about 14 mm and a height of about 2 mm are formed on both the inner and outer sides of the gas extraction hole 303 of the ordinary casing 301.

[0085] Step 3: Design the soluble rivet head to have a diameter of 14mm and a height of 2mm, and design the soluble rivet shank to have a diameter of 10mm and a height of 8mm. The soluble rivet tail is chamfered to facilitate entry into the gas extraction hole 303 with a cylindrical groove 304.

[0086] Step 4: Insert the soluble rivet 305 through the gas extraction hole 303 from the inside to the outside of the ordinary casing 301, and then mechanically pressurize the soluble rivet tail to perform the riveting operation, thereby obtaining the soluble screen tube 302.

[0087] In this embodiment, the gas extraction hole 303 of the soluble screen tube 302 is further sealed by riveting with soluble magnesium-aluminum alloy, such as... Figures 5 to 8As shown, compared to the ordinary casing 301, the gas extraction orifice 303 of the soluble screen pipe 302 is riveted and sealed with soluble magnesium-aluminum alloy. Compared with threaded connection sealing, the riveted screen pipe has a simpler structure, is easier to produce, has good sealing performance, does not require complex thread processing, and has smoother inner and outer walls, which is beneficial for the screen pipe to be lowered into the borehole and for subsequent grouting and hole cleaning operations.

Claims

1. A coal mine underground cementing completion method based on soluble screen tubes, characterized in that, The method includes the following specific steps: Step 1: Drill a hole and install a casing. According to the geological conditions, a first-stage borehole is constructed. A first-stage casing (1) is installed in the first-stage borehole to a stable layer. A stabilizer (2) is installed on the first-stage casing (1). A first-stage flange is connected to the upper outer side of the first-stage casing (1). A second-stage grouting pipe with a valve is reserved on the side wall of the first-stage casing (1). A long steel grouting pipe and a short steel grouting pipe are buried near the lower wall of the casing outside the first-stage casing (1). Step 2: Grouting is performed into the first drilled hole and the first casing. First, use cotton yarn to soak cement water glass grout to seal the annular zone between the first open sleeve (1) and the hole wall in step one and fix two steel grouting pipes. Inject ordinary silicate cement from the hole of the short steel grouting pipe and wait for it to set. Then inject cement grout from the hole of the long steel grouting pipe. After the grout returns to the inside of the first open sleeve (1), use a blind flange to block the hole of the first open sleeve (1) and continue grouting. After pressurizing the grout to 2 MPa, stop grouting and intermittently inject grout multiple times and wait for it to set. Step 3: Establish the two-stage drilling channel and install the two-stage casing: Drill down to remove the solidified cement slurry in the first open casing (1) in step two, drill down to establish a second open borehole channel to the target layer, and insert a second open casing (3) into the second open borehole channel. The upper opening of the second open casing (3) is connected to a second open flange. The two-way sleeve (3) is formed by sequentially combining a regular sleeve (301), a stabilizer (2), and a regular sleeve (301) to seal the bottom as the bottom section (306) of the two-way sleeve (3); The two-stage casing (3) is composed of a soluble screen pipe (302), a regular casing (301), a stabilizer (2), a regular casing (301), a soluble screen pipe (302), a regular casing (301), a stabilizer (2), and a regular casing (301) in sequence as the first combination segment (307) of the target layer of the two-stage casing (3). The first combination segment (307) of the target layer is sequentially connected to the orifice skewing segment (4) of the first-stage drilled hole. Step 4: Grouting into the second-stage drilled hole and the second-stage casing: Inject cement grout at a large flow rate through the grouting pipe reserved on the side wall of the first casing (1). After the grout returns from the second casing (3), block the opening of the second casing (3) with a blind flange and continue grouting. After pressurizing the grout to 12MPa, stop grouting and wait for it to set. Step 5: Inject potassium chloride solution into the second-opening sleeve: Open the blind flange in step four, drill down and clean the solidified cement slurry in the two-way sleeve (3) to the bottom of the hole of the two-way sleeve (3), start drilling, then connect the two-way flange to the flange with the grouting hole, inject potassium chloride solution into the grouting hole, seal the hole of the two-way sleeve (3) to dissolve the gas extraction hole (303) that is temporarily riveted and sealed on the soluble screen pipe (302); Step 6, pressure test with clean water: After well opening, at the first soluble screen pipe (302) at the bottom of the second casing (3), the annular packer is used to seal the front and rear ordinary casing (301) respectively, inject clean water, limit the construction pressure, and carry out fracturing and blowout. After the first stage of fracturing is completed, the fracturing drill bit is pulled back to the first soluble screen pipe (302) of the next combination as the second fracturing stage. The first fracturing process is repeated until the fracturing is completed. Step 7, Gas Extraction: After completing steps one through six, the milling string is lowered to perform well cleaning operations on the entire well section to ensure the wellbore is unobstructed. Finally, the casing (1) orifice is opened to connect to the negative pressure gas extraction pipeline for joint extraction.

2. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, The processing technology of the soluble sieve tube (302) specifically includes the following steps: Step 1: On the circular wall of the ordinary casing (301) 1000mm from both ends, four 12mm diameter circular holes are laser-cut at 90° intervals to obtain gas extraction holes (303). Step 2: Forging is performed simultaneously from both the inner and outer sides of the ordinary casing (301) to form cylindrical grooves (304) with a diameter of about 14 mm and a height of about 2 mm on both the inner and outer sides of the gas extraction hole (303) of the ordinary casing (301). Step 3: Design the soluble rivet head to have a diameter of 14mm and a height of 2mm, and design the soluble rivet shank to have a diameter of 10mm and a height of 8mm. The soluble rivet tail is chamfered to facilitate entry into the gas extraction hole (303) with a cylindrical groove (304). Step 4: Insert the soluble rivet (305) through the gas extraction hole (303) from the inside to the outside of the ordinary casing (301), and then mechanically press the tail of the soluble rivet to perform the riveting operation, thereby obtaining the soluble screen tube (302).

3. The coal mine underground cementing completion method based on soluble screen tubes according to claim 2, characterized in that, The gas extraction hole (303) of the soluble screen tube (302) is sealed by riveting with soluble magnesium-aluminum alloy.

4. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step one, the diameter of the first borehole is Φ246mm, the size of the first casing (1) is Φ219mm×8.33mm×1000mm, and a stabilizer (2) is installed every 5m of the first casing (1). In step one, the length of the long steel grouting pipe is 5m, and the length of the short steel grouting pipe is 2m; In step one, a casing (1) is inserted into the borehole to a depth of not less than 30m to the stable stratum.

5. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step two, ordinary Portland cement is injected through the orifice of the short steel grouting pipe and allowed to set for 24 hours. In step two, cement grout is injected from the orifice of the long steel grouting pipe. After the grout returns into the first open sleeve (1), the orifice of the first open sleeve (1) is blocked with a blind flange. The grouting is stopped after the pressure is increased to 2 MPa. The grouting is then stopped after intermittent injection for half an hour and then 3 times. The curing is allowed to proceed for 48 hours.

6. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step three, the diameter of the second-stage drilling channel is Φ193mm, and the dimensions of the ordinary casing (301) and the soluble screen tube (302) are Φ127mm×6.5mm×3000mm. The material of the ordinary casing (301) and the soluble screen tube (302) is P110 casing. The two-way sleeve (3) is composed of three meters of ordinary sleeve (301), a stabilizer (2) and three meters of ordinary sleeve (301) as the bottom section (306) of the two-way sleeve (3); The two-stage casing (3) consists of a 3-meter soluble screen pipe (302), a 3-meter ordinary casing (301), a centralizer (2), a 3-meter ordinary casing (301), a 72-meter soluble screen pipe (302), a 3-meter ordinary casing (301), a centralizer (2), and a 3-meter ordinary casing (301) as the first combination segment (307) of the target layer of the two-stage casing (3). The first combination segment (307) of the target layer is sequentially connected to the orifice skewing segment (4) of the first-stage drilled hole.

7. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step four, grout is first injected from the orifice of the first casing (1), and cemented at a pressure of 10MPa for 48 hours. In step four, the cement grout injected at a large flow rate from the pre-reserved second-stage grouting pipe opening on the side wall of the first-stage casing (1) is PO425 cement grout, with a density of 1.80 g / cm³. 3 ; In step four, after the grout returns to the second-opening sleeve (3), the opening of the second-opening sleeve (3) is blocked with a blind flange, and grouting continues. After the pressure grouting reaches 12MPa, grouting is stopped and allowed to solidify for 7 days.

8. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step five, a 5% potassium chloride solution is injected into the grouting hole to seal the opening of the second-opening sleeve (3) for 7 days.

9. The coal mine underground cementing completion method based on soluble screen tubes according to claim 1, characterized in that, In step six, after well opening, annular packers are used to seal the pre- and post-casing sections (301 and 302) of the first soluble screen (302) at the bottom of the borehole, respectively, and a water injection rate of 6 m³ / h is applied. 3 / min, construction pressure limit 45MPa, carry out fracturing and blowout. After the first stage of fracturing is completed, pull back the fracturing drill bit 90m to the first soluble screen pipe (302) of the next combination as the second fracturing stage. Repeat the first fracturing process until fracturing is completed.

Images