Coal mine underground well cementation and completion method based on dissoluble screen pipe

Abstract

The invention discloses a coal mine underground well cementation and completion method based on a dissoluble screen pipe. The method comprises the following specific steps that firstly, a first-opening drilling hole channel is established, and a first-opening casing pipe is installed; secondly, grouting is conducted in a first-opening drill hole channel and a first-opening sleeve; thirdly, a second-opening drilling hole channel is established, and a second-opening casing pipe is installed; fourthly, grouting is conducted in the second-opening drilling hole channel and the second-opening casing pipe; 5, a potassium chloride solution is injected into the second-section casing pipe; sixthly, clear water pressure testing is conducted; and seventhly, gas is extracted. According to the method, the fractures are artificially formed through hydraulic fracturing and are expanded, the stratum permeability is improved, and compared with a conventional well completion mode that a screen pipe is directly placed in an open hole, the gas extraction efficiency is greatly improved; the dissolvable screen pipe is adopted, unsafe factors of perforation explosion of an underground coal mine are technically avoided, the perforation and fracturing technological process is optimized, the perforation operation cost is saved, meanwhile, a gas migration channel is increased through the dissolvable screen pipe, and the gas extraction efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of well cementing and completion, relates to a soluble screen pipe, and specifically relates to an underground coal mine well cementing and completion method based on the soluble screen pipe. Background Art

[0002] At present, most of the gas extraction drilling in coal mines adopts the method of open hole completion or screen completion, and the gas extraction radius of a single hole is small and the efficiency is low. Hydraulic fracturing technology has been widely used in the aspects of ground coalbed methane permeability enhancement and rock burst prevention and control. The specific process is: after cementing with ordinary casing cement, a perforating string is first run, the casing is penetrated and the formation is fractured, and then a fracturing string is run for fracturing. However, its explosive perforation method is difficult to meet the needs of safe construction in coal mines. At the same time, the overall operation time efficiency of this process is low, the construction cost is high, and the number of holes for perforation fracturing is limited, resulting in fewer gas extraction channels and low extraction efficiency. It is not suitable for large-scale application of gas extraction drilling in coal mines.

[0003] Therefore, there is an urgent need for a coal mine underground solid completion method based on a soluble screen to make up for the shortcomings of the current gas extraction drilling completion method, which can not only improve the extraction efficiency of drilling gas, but also save construction costs and meet the needs of large-scale and safe use in coal mines. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a coal mine underground solid completion method based on a soluble screen pipe to solve the technical problem of low gas extraction efficiency in coal mines in the prior art.

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

[0006] A method for underground well completion in a coal mine based on a soluble screen, the method comprising the following specific steps:

[0007] Step 1: Create a drilled hole and install a casing:

[0008] A drilling channel is constructed according to geological conditions, an open casing is lowered into the drilling channel to a stable layer, a centralizer is installed on the open casing, an open flange is connected to the upper outer side of the casing, a second grouting pipe opening with a valve is reserved on the side wall of the casing hole, and a long steel grouting pipe and a short steel grouting pipe are buried outside the open casing near the lower wall of the casing.

[0009] Step 2: Grouting into a drilled hole and a casing:

[0010] First, use cotton yarn dipped in cement-water glass slurry to seal the open casing and the annular zone of the hole wall in step one and fix two steel grouting tubes. Inject ordinary Portland cement from the orifice of the short steel grouting tube and wait for it to solidify. Then inject cement slurry from the orifice of the long steel grouting tube. After the slurry returns to the open casing, use a blind flange to block the orifice of the open casing and continue grouting. After the pressure reaches 2Mpa, suspend grouting, inject multiple times intermittently and wait for it to solidify.

[0011] Step 3: Create a second-hole drilling channel and install the second-hole casing:

[0012] Drill down to remove the solidified cement slurry in the first opening casing in step 2, drill down to establish a second opening borehole to the target layer, insert the second opening casing into the second opening borehole, and the outer upper end of the second opening casing is connected with a second opening flange.

[0013] The double-open casing is formed by sequentially combining a common casing, a centralizer and a common casing to seal the bottom as the hole bottom section of the double-open casing.

[0014] The two-open casing is composed of a soluble screen, a common casing, a centralizer, a common casing, a soluble screen, a common casing, a centralizer and a common casing in sequence as the first combination section of the target layer of the two-open casing, and the first combination section of the target layer is connected to the orifice deflection section of the first-open drilling channel in a cycle.

[0015] Step 4: Grouting into the second opening drilling channel and the second opening casing:

[0016] Inject cement slurry in large quantity from the second opening grouting pipe mouth reserved on the side wall of the first opening casing hole. After the second opening casing returns grout, plug the hole of the second opening casing with a blind flange and continue grouting. After the grouting pressure reaches 12MPa, grouting is suspended and wait for setting.

[0017] Step 5: Inject potassium chloride solution into the two-open casing:

[0018] Open the blind flange in step 4, drill down to clean the solidified cement slurry in the second-open casing to the top of the hole bottom of the second-open casing, start drilling, and then connect the second-open flange to the flange with grouting holes, inject potassium chloride solution from the grouting holes, seal the hole of the second-open casing to dissolve the gas extraction holes that are temporarily riveted and sealed on the soluble screen.

[0019] Step 6: Clean water pressure test:

[0020] After the well is dredged, the front and rear common casings of the first soluble screen at the bottom of the second casing hole are sealed with annular packers, clean water is injected, pressure is limited, and fracturing and blowdown are carried out. After the first stage of fracturing is completed, the fracturing drill bit is pulled back to the first soluble screen of the next combination as the second fracturing stage, and the first fracturing process is repeated until the fracturing is completed.

[0021] Step 7: Extraction of gas:

[0022] After completing steps one to six, lower the milling string to clean the entire well section to ensure that the wellbore is unobstructed. Finally, open the casing hole and connect the negative pressure gas extraction pipeline for combined extraction.

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

[0024] The processing technology of the soluble screen tube is specifically divided into the following steps:

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

[0026] Step 2: Forging is performed simultaneously from both the inner and outer sides of the common casing to form cylindrical grooves 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 of the common casing.

[0027] Step 3, design the soluble rivet head to have a diameter of 14 mm and a height of 2 mm, design the soluble rivet handle to have a diameter of 10 mm and a height of 8 mm, and chamfer the soluble rivet tail to facilitate entry into the gas extraction hole with a cylindrical groove.

[0028] Step 4: Pass the soluble rivet through the gas extraction hole from the inside to the outside of the ordinary casing, and then mechanically pressurize the soluble rivet tail to perform riveting operations to obtain a soluble screen pipe.

[0029] The gas extraction holes of the soluble screen pipe are riveted and sealed with soluble magnesium-aluminum alloy.

[0030] In step 1, the aperture of the first drilled hole is Φ246 mm, the size of the first casing is Φ219 mm×8.33 mm×1000 mm, and a centralizer is installed every 5 m of the casing.

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

[0032] In step 1, a casing is lowered into a borehole to a depth of not less than 30 m in a stable layer.

[0033] In step 2, ordinary Portland cement is injected from the orifice of the short steel grouting flower tube and waited for setting for 24 hours.

[0034] In step 2, cement slurry is injected from the hole of the long steel grouting flower tube. After the slurry returns to the open casing, the hole of the open casing is blocked with a blind flange. After the grouting pressure reaches 2Mpa, the grouting is suspended. The grouting is performed 3 times with an interval of half an hour, and the grouting is waited for 48 hours.

[0035] In step three, the aperture of the secondary drilling channel is Φ193mm, the dimensions of the common casing and the soluble screen are Φ127mm×6.5mm×3000mm, and the materials of the common casing and the soluble screen are both P110 casing.

[0036] In step three, the double-open casing is sealed with three meters of common casing, a centralizer and three meters of common casing in sequence as the bottom section of the double-open casing.

[0037] The two-open casing is composed of three meters of soluble screen, three meters of ordinary casing, a stabilizer, three meters of ordinary casing, seventy-two meters of soluble screen, three meters of ordinary casing, a stabilizer and three meters of ordinary casing in sequence as the first combination section of the target layer of the two-open casing, and the first combination section of the target layer is connected to the orifice deflection section of the first-open drilling channel in a cycle.

[0038] In step 4, grouting is first performed from the opening of the casing, cementing is performed at a pressure of 10 MPa, and then the cementing is allowed to proceed for 48 hours.

[0039] In step 4, the cement slurry injected in large volume from the second opening grouting pipe reserved on the side wall of the first opening casing hole is PO425 cement slurry, and the density of PO425 cement slurry is 1.80g / cm 3 .

[0040] In step 4, after the secondary casing is grouted, the orifice of the secondary casing is blocked with a blind flange and grouting is continued. After the grouting pressure reaches 12 MPa, the grouting is suspended and the setting is allowed to continue for 7 days.

[0041] In step 5, a potassium chloride solution with a mass fraction of 5% is injected from the grouting hole to seal the orifice 7d of the second opening casing.

[0042] In step 6, after the well is dredged, annular packers are used to isolate the front and rear common casings of the first soluble screen at the bottom of the hole, and the injection water displacement is 6m 3 / min, with a construction pressure limit of 45MPa, fracturing and blowdown are carried out. After the first stage of fracturing is completed, the fracturing drill bit is pulled back about 90m to the first soluble screen of the next combination as the second fracturing stage, and the first fracturing process is repeated until the fracturing is completed.

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

[0044] (I) The coal mine underground solid completion method based on the soluble screen pipe proposed in the present invention increases the permeability of the formation by artificially creating fractures through hydraulic fracturing and expanding the fractures. Compared with the conventional open-hole completion method of directly lowering the screen pipe, it greatly improves the gas extraction efficiency.

[0045] (II) The soluble screen pipe adopted in the present invention technically avoids the unsafe factors of perforating explosion in coal mines, optimizes the perforating and fracturing process, and saves the cost of perforating operations; at the same time, the soluble screen pipe increases the gas migration channel and improves the gas extraction efficiency.

[0046] (III) The riveted and sealed dissolvable screen tube used in the present invention has a simple structure, is easy to manufacture, has good sealing performance, is easy to implement large-scale prefabrication in a factory, and has a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the structure of the double-opening casing in an underground coal mine.

[0048] Figure 2 Schematic diagram of well completion with dissolvable screen.

[0049] Figure 3 Schematic diagram of the structure of the soluble sieve tube.

[0050] Figure 4 Schematic diagram of the cross section of the soluble sieve tube at AA.

[0051] Figure 5 This is a schematic diagram of the structure of a conventional casing opening.

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

[0053] Figure 7 Schematic diagram of the structure of a soluble rivet.

[0054] Figure 8 Schematic diagram of the structure of the soluble sieve tube.

[0055] The meanings of the numbers in the figure are: 1-first opening casing, 2-centralizer, 3-second opening casing, 4-hole mouth deflection section.

[0056] 301-ordinary casing, 302-soluble screen, 303-gas extraction hole, 304-cylindrical groove, 305-soluble rivet, 306-bottom section of the hole, 307-first combination section of the target layer.

[0057] The specific contents of the present invention are further explained in detail below in conjunction with embodiments. DETAILED DESCRIPTION

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

[0059] In accordance with the above technical scheme, 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 changes made on the basis of the technical scheme of this application fall within the protection scope of the present invention.

[0060] Example:

[0061] This embodiment provides a method for underground coal mine completion based on a soluble screen pipe. Figures 1 to 4 As shown, the method comprises the following specific steps:

[0062] Step 1: Create a drilled hole and install a casing:

[0063] According to the geological conditions, a single-open borehole with a hole diameter of Φ246mm is constructed, and an open casing 1 with a size of Φ219mm×8.33mm×1000mm is lowered into the single-open borehole to the stable layer. A centralizer 2 is installed on the single-open casing 1 for every 5m of casing. An open flange is connected to the upper outer opening of the single-open casing 1, and a second grouting pipe opening with a valve is reserved on the side wall of the hole of the single-open casing 1. A long steel grouting pipe and a short steel grouting pipe are buried outside the single-open casing 1 near the lower wall of the casing. The length of the long steel grouting pipe is 5m, and the length of the short steel grouting pipe is 2m.

[0064] Specifically, in this embodiment, the main purpose of the open casing 1 is to isolate unstable formations in the drilled layer section and withstand the pressure of the fracturing string during fracturing; the centralizer 2 centers the casing.

[0065] Step 2: Grouting into a drilled hole and a casing:

[0066] First, use cotton yarn dipped in cement-water glass slurry to seal the annular zone between the open casing 1 and the hole wall in step 1, and fix two steel grouting tubes. Inject ordinary Portland cement from the orifice of the short steel grouting tube, wait for setting for 24 hours, and then inject cement slurry from the orifice of the long steel grouting tube. After the slurry returns to the open casing 1, use a blind flange to block the orifice of the open casing 1, continue grouting, and suspend grouting after the pressure is held to 2Mpa. Intermittently inject 3 times every half an hour and wait for setting for 48 hours.

[0067] Specifically in this embodiment, ordinary silicate cement is injected into the short steel grouting flower tube to seal the annular zone of the hole wall, so that the cement slurry injected from the orifice of the long steel grouting flower tube can enter the interior of the open casing 1.

[0068] Step 3: Create a second-hole drilling channel and install the second-hole casing:

[0069] Drill down to clear the solidified cement slurry in the first-opening casing 1 in step 2, drill down to establish a second-opening borehole with a hole diameter of Φ193mm to the target layer, and the outer upper end of the second-opening casing 3 is connected with a second-opening flange, wherein the ordinary casing 301 and the soluble screen tube 302 are both made of P110 casing.

[0070] A Φ127mm×6.5mm×3000mm secondary casing 3 is lowered into the secondary drilling channel. The secondary casing 3 is composed of three meters of common casing 301, a centralizer 2 and three meters of common casing 301 in sequence as the bottom section 306 of the secondary casing 3.

[0071] The second-open casing 3 is composed of three meters of soluble screen 302, three meters of ordinary casing 301, a stabilizer 2, three meters of ordinary casing 301, seventy-two meters of soluble screen 302, three meters of ordinary casing 301, a stabilizer 2 and three meters of ordinary casing 301, which are sequentially combined as the first combined section 307 of the target layer of the second-open casing 3. The first combined section 307 of the target layer is connected to the orifice deflection section 4 of the first-open drilling channel in a cycle.

[0072] Specifically, in this embodiment, if the length of the two-open casing 3 is less than one combined section, the length is adjusted by reducing the number of soluble screens 302 in the combined section; the common casing 301 is lowered into the orifice of the two-open casing 3 in the orifice of the orifice-making section 4. In this design, a 6-meter common casing 301 and a centralizer 2 are connected at both ends of the pre-fracturing soluble screen 302. The common casing 301 provides conditions for the plugging and pressure holding of the fracturing bridge plug. The centralizer 2 ensures that the casing is centered, improves the cementing quality, and thus ensures the later fracturing effect.

[0073] Step 4: Grouting into the second opening drilling channel and the second opening casing:

[0074] PO425 cement slurry is injected in large volume from the second grouting nozzle reserved on the side wall of the first opening of the casing 1. The density of PO425 cement slurry is 1.80g / cm 3 After the second-opening casing 3 returns to grout, use a blind flange to block the orifice of the second-opening casing 3 and continue grouting. After the pressure reaches 12MPa, grouting is suspended and waiting for 7 days.

[0075] Step 5: Inject potassium chloride solution into the two-open casing:

[0076] Open the blind flange in step 4, drill down to clean the solidified cement slurry in the second-open casing 3 to the top of the bottom of the second-open casing 3, start drilling, and then connect the second-open flange to the flange with grouting holes, inject a 5% potassium chloride solution from the grouting holes, seal the orifice 7d of the second-open casing, so as to dissolve the gas extraction holes 303 temporarily riveted and sealed on the soluble screen 302.

[0077] Step 6: Clean water pressure test:

[0078] After the well is dredged, the annular packers are used to isolate the front common casing 301 and the rear common casing 301 of the first dissolvable screen 302 at the bottom of the second opening casing 3, and the clean water injection rate is 6m 3 / min, with a construction pressure limit of 45MPa, fracturing and blowdown are carried out. After the first stage of fracturing is completed, the fracturing drill bit is pulled back about 90m to the first soluble screen 302 of the next combination as the second fracturing stage, and the first fracturing process is repeated until the fracturing is completed.

[0079] Specifically, in this embodiment, the first fracturing section and the second fracturing section are separated by 4 common casings 301 and 26 soluble screens 302 to avoid mutual interference and formation pressure channeling. The soluble screens 302 that are not fracturing are within the coverage of the fracturing radius, which reduces the fracturing cost and can also achieve a better gas extraction effect.

[0080] Step 7: Extraction of gas:

[0081] After completing steps 1 to 6, the milling pipe string is lowered to perform well cleaning operations on the entire well section to ensure that the wellbore is unobstructed. Finally, the opening of the casing 1 is connected to the negative pressure gas extraction pipeline for joint extraction.

[0082] In this embodiment, further, Figures 5 to 8 As shown, the processing technology of the dissolvable screen tube 302 is specifically divided into the following steps:

[0083] Step 1: On the circular pipe wall of the common casing 301 at 1000 mm away from the two end pipe openings, four circular holes with a diameter of 12 mm are cut by laser at intervals of 90° to obtain gas extraction holes 303.

[0084] Step 2, forging is performed simultaneously from both the inner and outer sides of the common 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 common casing 301.

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

[0086] Step 4, pass the soluble rivet 305 from the gas extraction hole 303 from the inside to the outside of the common casing 301, and then mechanically pressurize the soluble rivet tail to perform riveting operations to obtain the soluble screen tube 302.

[0087] In this embodiment, the gas extraction holes 303 of the soluble screen tube 302 are further sealed by riveting with soluble magnesium-aluminum alloy. Figures 5 to 8As shown, compared with the common casing 301, the gas extraction holes 303 of the soluble screen pipe 302 are riveted and plugged with soluble magnesium-aluminum alloy. Compared with the threaded connection plugging, the screen pipe plugged by the riveting process has a simple structure, is easy to produce, has good sealing performance, does not require complex thread processing, and the inner and outer walls of the screen pipe are smoother, which is conducive to the lowering of the screen pipe into the borehole and the subsequent grouting and hole sweeping operations.

Claims

1. A method for underground coal mine well completion based on a soluble screen, characterized in that: The method comprises the following specific steps: Step 1: Create a drilled hole and install a casing: According to geological conditions, an open borehole is constructed and established, an open casing (1) is lowered into the open borehole to a stable layer, a centralizer (2) is installed on the open casing (1), an open flange is connected to the outer upper opening of the open casing (1), a second opening for grouting with a valve is reserved on the side wall of the hole of the open casing (1), and a long steel grouting flower pipe and a short steel grouting flower pipe are respectively buried outside the open casing (1) near the lower wall of the casing; Step 2: Grouting into a drilled hole and a casing: First, cotton yarn is dipped in cement water glass slurry to seal the open casing (1) and the annular zone of the hole wall in step 1 and fix two steel grouting flower tubes, ordinary silicate cement is injected from the orifice of the short steel grouting flower tube, and wait for setting, and then cement slurry is injected from the orifice of the long steel grouting flower tube, and after the slurry returns to the open casing (1), the orifice of the open casing (1) is blocked with a blind flange, and grouting is continued. After the pressure is held to 2Mpa, the grouting is suspended, and multiple point injections are intermittently performed and wait for setting; Step 3: Create a second-hole drilling channel and install the second-hole casing: Drilling to remove the solidified cement slurry in the first-open casing (1) in step 2, drilling to establish a second-opening borehole to the target layer, inserting a second-opening casing (3) into the second-opening borehole, and connecting the outer upper end of the second-opening casing (3) with a second-opening flange; The double-open casing (3) is formed by sequentially combining a common casing (301), a centralizer (2) and a common casing (301) to form a bottom seal as a hole bottom section (306) of the double-open casing (3); The double-open casing (3) is composed of a dissolvable screen (302), a common casing (301), a centralizer (2), a common casing (301), a dissolvable screen (302), a common casing (301), a centralizer (2) and a common casing (301) which are sequentially combined as a first target layer combination section (307) of the double-open casing (3), and the first target layer combination section (307) is cyclically connected to a borehole mouth deflection section (4) of a single-open borehole channel; Step 4: Grouting into the second opening drilling channel and the second opening casing: Cement slurry is injected in large volume from the second opening grouting pipe port reserved on the side wall of the hole of the first opening casing (1), and after the second opening casing (3) returns to the grout, the hole of the second opening casing (3) is blocked with a blind flange, and grouting is continued. After the grouting pressure reaches 12 MPa, the grouting is suspended and the setting is waited; Step 5: Inject potassium chloride solution into the two-open casing: Open the blind flange in step 4, drill down to clean the solidified cement slurry in the double-open casing (3) to the top of the bottom of the double-open casing (3), start drilling, and then connect the double-open flange to the flange with the grouting hole, inject potassium chloride solution from the grouting hole, seal the orifice of the double-open casing (3), so as to dissolve the gas extraction hole (303) temporarily riveted and sealed on the soluble screen (302); Step 6: Clean water pressure test: After the well is ventilated, the front common casing (301) and the rear common casing (301) of the first soluble screen (302) at the bottom of the second casing (3) are respectively sealed with annular packers, clean water is injected, pressure is limited, and fracturing and blowout are performed. After the first stage of fracturing is completed, the fracturing drill tool is pulled back to the first soluble screen (302) of the next combination as the second fracturing stage, and the first fracturing process is repeated until the fracturing is completed; Step 7: Extraction of gas: After the completion of step 1 to step 6, the milling pipe string is lowered to perform well cleaning operations on the entire well section to ensure that the wellbore is unobstructed. Finally, the opening of the casing (1) is connected to the negative pressure gas extraction pipeline for joint extraction.

2. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: The processing technology of the soluble screen tube (302) is specifically divided into the following steps: Step 1: on the circular pipe wall of the common casing (301) at a distance of 1000 mm from the two end pipe openings, four circular holes with a diameter of 12 mm are cut by laser at intervals of 90° to obtain gas extraction holes (303); Step 2, forging the common casing (301) from both inside and outside at the same time, so that the gas extraction hole (303) of the common casing (301) forms a cylindrical groove (304) with a diameter of about 14 mm and a height of about 2 mm on both inside and outside sides; Step 3, the soluble rivet head is designed to have a diameter of 14 mm and a height of 2 mm, the soluble rivet handle is designed to have a diameter of 10 mm and a height of 8 mm, and the soluble rivet tail is chamfered to facilitate entry into the gas extraction hole (303) with the cylindrical groove (304); Step 4, passing the soluble rivet (305) from the gas extraction hole (303) from the inside to the outside of the common casing (301), and then mechanically pressurizing the soluble rivet tail to perform riveting operations to obtain a soluble screen tube (302).

3. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 2, characterized in that: The gas extraction holes (303) of the soluble screen tube (302) are riveted and sealed with soluble magnesium-aluminum alloy.

4. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 1, the aperture of the first drilled hole is Φ246 mm, the size of the first casing (1) is Φ219 mm×8.33 mm×1000 mm, and a centralizer (2) is installed every 5 m of the first casing (1); In step 1, the length of the long steel grouting flower pipe is 5m, and the length of the short steel grouting flower pipe is 2m; In step 1, a casing (1) is lowered into a borehole to a depth of not less than 30 m to a stable layer.

5. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 2, ordinary Portland cement is injected from the orifice of the short steel grouting flower tube and waited for setting for 24 hours; In step 2, cement slurry is injected from the orifice of the long steel grouting flower pipe, and after the slurry returns to the open casing (1), the orifice of the open casing (1) is blocked with a blind flange, and the grouting is suspended after the pressure reaches 2Mpa, and the grouting is performed three times with an interval of half an hour, and the grouting is waited for 48 hours.

6. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 3, the aperture of the second drilling channel is Φ193 mm, the dimensions of the common casing (301) and the dissolvable screen tube (302) are Φ127 mm×6.5 mm×3000 mm, and the materials of the common casing (301) and the dissolvable screen tube (302) are both P110 casing; The double-open casing (3) is composed of three meters of common casing (301), a centralizer (2) and three meters of common casing (301) as a bottom hole section (306) of the double-open casing (3); The double-open casing (3) is composed of three meters of a soluble screen (302), three meters of a common casing (301), a centralizer (2), three meters of a common casing (301), seventy-two meters of a soluble screen (302), three meters of a common casing (301), a centralizer (2) and three meters of a common casing (301) as the first target layer combination section (307) of the double-open casing (3), and the first target layer combination section (307) is connected to the orifice deflection section (4) of the first-open drilling channel in a cycle.

7. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 4, grouting is first performed from the orifice of an open casing (1), cementing is performed at a pressure of 10 MPa, and then the cementing is waited for 48 hours; In step 4, the cement slurry injected in large volume from the second opening grouting pipe port reserved on the side wall of the hole of the first opening casing (1) is PO425 cement slurry, and the density of PO425 cement slurry is 1.80g / cm 3 ; In step 4, after the double-open casing (3) is slurried back, the orifice of the double-open casing (3) is blocked with a blind flange, and grouting is continued. After the pressure is held to 12 MPa, grouting is suspended and the setting is waited for 7 days.

8. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 5, a potassium chloride solution with a mass fraction of 5% is injected from the grouting hole to seal the orifice 7d of the double-open casing (3).

9. The method for underground coal mine well consolidation and completion based on a soluble screen according to claim 1, characterized in that: In step 6, after the well is dredged, the front common casing (301) and the rear common casing (301) of the first soluble screen (302) at the bottom of the hole are respectively sealed with annular packers, and the injection water displacement is 6m 3 / min, with a construction pressure limit of 45MPa, fracturing and blowdown are carried out. After the first stage of fracturing is completed, the fracturing drill bit is pulled back 90m to the first soluble screen (302) of the next combination as the second fracturing stage, and the first fracturing process is repeated until the fracturing is completed.

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