FRACTURING RELIEF METHOD FOR STRESS CONCENTRATION OF REMAINING ORE PILLARS IN OVERLYING GOAF

Abstract

Provided is a fracturing relief method for stress concentration of remaining ore pillars in an overlying goaf, including first, performing directional fracturing on a roof to optimize the stress of the roof and reduce the source of force; secondly, performing pulse fracturing on a coal pillar to produce a crack network, weaken the stiffness of the coal pillar and reduce the bearing capacity of the coal pillar; and finally, performing pulse fracturing on a floor strata of the coal pillar to reduce the ability of transferring stress concentration thereof. A drilling machine is used for separately constructing fracturing drill holes in a roadway to a set depth at an interval in a direction oblique to the coal pillar in an upper goaf. The roof, the coal pillar and the floor can be fractured by an oblique fracturing hole in a sublevel retreating manner. The position of the directional fracturing of the roof is approximately 1 m above the middle of a main roof above the coal pillar. The method reduces the width of the lower coal pillar, improves the coal mining rate, reduces the deformation of the lower coal roadway, effectively solves the problems of mine pressure passing through the coal pillar on the working face of the lower coal seam, rock burst, and coal and gas outburst in the mining of the lower coal seam, and simultaneously has the advantages of high safety factor, simple method, convenient construction and low cost.

Claims

1. A fracturing relief method for stress concentration of remaining ore pillars in an overlying goaf, comprising the following steps: step 1: separately constructing three rows of fracturing drill holes in a roadway to a set depth at an interval in a direction oblique to a coal pillar in an upper goaf by using a drilling machine, wherein a position of a final hole of a first row of the fracturing drill holes is 1 m above a middle of a main roof above the coal pillar, a position of a final hole of a second row of the fracturing drill holes is 1 mm above a middle of the coal pillar, and a position of a final hole of a third row of the fracturing drill holes is at a section of ¾ of the coal pillar; step 2: mounting and commissioning a hydraulic fracturing high-pressure pump and a hydraulic fracturing pulse pump; step 3: sending a packer to a to-be-fractured area of a to-be-fractured drill hole, sequentially connecting a high-pressure seal mounting rod, a transfer joint and a high-pressure pipeline, and separately connecting the high-pressure pipeline to the hydraulic fracturing pulse pump and the hydraulic fracturing high-pressure pump through a three-way valve; step 4: performing high-pressure hydraulic fracturing on a main roof area in the first row of the fracturing drill holes, and then performing pulse hydraulic fracturing on a coal pillar area in the first row of the fracturing drill holes; step 5: performing pulse hydraulic fracturing on the second row of the fracturing drill holes; and step 6: performing pulse hydraulic fracturing on the coal pillar area in the third row of the fracturing drill holes, and then performing pulse hydraulic fracturing again on a floor area in the third row of the fracturing drill holes.

2. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 1, wherein, in step 4, specific step of performing hydraulic fracturing on the first row of the fracturing drill holes comprises following steps: (a) connecting the high-pressure seal mounting rod with the packer, sending the packer to a corresponding first-row drill hole main roof fracturing zone in a first fracturing drill hole of the first row, then connecting the high-pressure pipeline connected to the hydraulic fracturing high-pressure pump and the hydraulic fracturing pulse pump onto the high-pressure seal mounting rod, and using a hand pump to infuse high-pressure water into the packer through a high-pressure thin hose to expand the packer and seal the hole, wherein a pressure relief valve and a hydraulic fracturing measuring and controlling instrument are arranged on the high-pressure pipeline; (b) closing a switch valve II, opening a switch valve I, turning on the hydraulic fracturing high-pressure pump, and infusing high-pressure water into the drill hole through the high-pressure pipeline to perform hydraulic fracturing; when a construction pressure monitored by the hydraulic fracturing measuring and controlling instrument is smaller than 5 MPa or when a coal seam sweats for more than 5-7 minutes, turning off the hydraulic fracturing high-pressure pump and opening the pressure relief valve; (c) retreating the packer to a corresponding first-row drill hole coal pillar fracturing zone by adopting sublevel retreating fracturing, sealing the hole again, closing the switch valve I, opening the switch valve II, and performing fracturing again by using the hydraulic fracturing pulse pump; and (d) removing the packer and the high-pressure seal mounting rod.

3. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 1, wherein, in step 5, specific step of performing hydraulic fracturing on the second row of the fracturing drill holes comprises following steps: (a) connecting the high-pressure seal mounting rod with the packer, sending the packer to a corresponding second-row drill hole coal pillar fracturing zone in a first fracturing drill hole of the second row, then connecting the high-pressure pipeline connected to the hydraulic fracturing high-pressure pump and the hydraulic fracturing pulse pump onto the high-pressure seal mounting rod, and using a hand pump to infuse high-pressure water into the packer to expend the packer and seal the hole, wherein a pressure relief valve and a hydraulic fracturing measuring and controlling instrument are arranged on the high-pressure pipeline; (b) closing a switch valve I, opening a switch valve II (25), turning on the hydraulic fracturing pulse pump, and infusing pulse water into the first fracturing drill hole of the second row through the high-pressure pipeline (15) to perform hydraulic fracturing; when a construction pressure monitored by the hydraulic fracturing measuring and controlling instrument is smaller than 5 MPa or when a coal seam sweats for more than 5-7 minutes, turning off the hydraulic fracturing pulse pump and opening the pressure relief valve; and (c) removing the packer and the high-pressure seal mounting rod.

4. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 1, wherein, in step 6, specific step of performing hydraulic fracturing on the third row of the fracturing drill holes comprises following steps: (a) connecting the high-pressure seal mounting rod with the packer, sending the packer to a corresponding third-row drill hole coal pillar fracturing zone in a first fracturing drill hole of the third row, then connecting the high-pressure pipeline connected to the hydraulic fracturing high-pressure pump and the hydraulic fracturing pulse pump onto the high-pressure seal mounting rod, and using a hand pump to infuse high-pressure water into the packer to expand the packer and seal the hole, wherein a pressure relief valve and a hydraulic fracturing measuring and controlling instrument are arranged on the high-pressure pipeline; (b) closing a switch valve I, opening a switch valve II, turning on the hydraulic fracturing pulse pump, and infusing pulse water into the first fracturing drill hole of the third row through the high-pressure pipeline to perform hydraulic fracturing; when a construction pressure monitored by the hydraulic fracturing measuring and controlling instrument is smaller than 5 MPa or when a coal seam sweats for more than 5-7 minutes, turning off the hydraulic fracturing pulse pump and opening the pressure relief valve; (c) sublevel retreating fracturing being adopted, retreating the packer to a corresponding third-row drill hole floor fracturing zone, sealing the hole again, closing the switch valve I again, opening the switch valve II, and performing fracturing again by turning on the hydraulic fracturing pulse pump; and (d) removing the packer and the high-pressure seal mounting rod.

5. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 1, wherein both drill holes and hydraulic fracturing are constructed sequentially according to a sequence of a first fracturing drill hole of the first row, a first fracturing drill hole of the second row, a first fracturing drill hole of the third row, a second fracturing drill hole of the first row, a second fracturing drill hole of the second row, a second fracturing drill hole of the third row . . . an Nth fracturing drill hole of the first row, an Nth fracturing drill hole of the second row and an Nth fracturing drill hole of the third row; a hydraulic fracturing sequence and a hole drilling construction sequence are the same, hydraulic fracturing and hole drilling are synchronously performed in parallel, and a construction speed matches.

6. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 5, characterized in that a group of fracturing areas for directional fracturing are arranged in the main roof above the coal pillar; three groups of fracturing areas are arranged in the coal pillar; and a group of fracturing areas are arranged in the floor below the coal pillar.

7. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 2, wherein both drill holes and hydraulic fracturing are constructed sequentially according to a sequence of a first fracturing drill hole of the first row, a first fracturing drill hole of the second row, a first fracturing drill hole of the third row, a second fracturing drill hole of the first row, a second fracturing drill hole of the second row, a second fracturing drill hole of the third row . . . an Nth fracturing drill hole of the first row, an Nth fracturing drill hole of the second row and an Nth fracturing drill hole of the third row; a hydraulic fracturing sequence and a hole drilling construction sequence are the same, hydraulic fracturing and hole drilling are synchronously performed in parallel, and a construction speed matches.

8. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 3, wherein both drill holes and hydraulic fracturing are constructed sequentially according to a sequence of a first fracturing drill hole of the first row, a first fracturing drill hole of the second row, a first fracturing drill hole of the third row, a second fracturing drill hole of the first row, a second fracturing drill hole of the second row, a second fracturing drill hole of the third row . . . an Nth fracturing drill hole of the first row, an Nth fracturing drill hole of the second row and an Nth fracturing drill hole of the third row; a hydraulic fracturing sequence and a hole drilling construction sequence are the same, hydraulic fracturing and hole drilling are synchronously performed in parallel, and a construction speed matches.

9. The fracturing relief method for the stress concentration of the remaining ore pillars in the overlying goaf according to claim 4, wherein both drill holes and hydraulic fracturing are constructed sequentially according to a sequence of a first fracturing drill hole of the first row, a first fracturing drill hole of the second row, a first fracturing drill hole of the third row, a second fracturing drill hole of the first row, a second fracturing drill hole of the second row, a second fracturing drill hole of the third row . . . an Nth fracturing drill hole of the first row, an Nth fracturing drill hole of the second row and an Nth fracturing drill hole of the third row; a hydraulic fracturing sequence and a hole drilling construction sequence are the same, hydraulic fracturing and hole drilling are synchronously performed in parallel, and a construction speed matches.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is a construction plan of hydraulic fracturing drill holes in the present invention.

[0048] FIG. 2 is an A-A sectional view in FIG. 1.

[0049] FIG. 3 is a drawing of hydraulic fracturing equipment used in the method provided by the present invention.

[0050] In the drawings: 1—roadway; 2—first fracturing drill hole of first row; 3—first fracturing drill hole of second row; 4—first fracturing drill hole of third row; 5—main roof above coal pillar; 6—immediate roof above coal pillar; 7—floor below coal pillar; 8—coal seam; 9—first-row drill hole coal pillar fracturing zone; 10—third-row drill hole floor fracturing zone; 11—second-row drill hole coal pillar fracturing zone; 12—first-row drill hole main roof fracturing zone; 13—third-row drill hole coal pillar fracturing zone; 14—coal pillar; 15—high-pressure pipeline; 16—hydraulic fracturing measuring and controlling instrument; 17—pressure relief valve; 18—transfer joint; 19—high-pressure thin hose; 20—high-pressure seal mounting rod; 21—packer; 22—hand pump; 23—hydraulic fracturing high-pressure pump; 24—switch valve I; 25—switch valve II; 26—hydraulic fracturing pulse pump; 27—three-way valve.

DESCRIPTION OF THE EMBODIMENTS

[0051] The present invention will be described below in detail with reference to the drawings.

[0052] The average thickness of the lower coal seam of a particular mine is 10 m; the roof of the lower coal seam is coarse sandstone with an average thickness of 6 m; the thickness of the upper coal seam is 4 m; the immediate roof of the upper coal seam is gravel-bearing coarse sandstone with an average thickness of 4 m; the main roof of the upper coal seam is sandstone with an average thickness of 4 m. The cross sections of the two crossheadings in the working face are rectangular cross sections, the supporting mode is bolt, cable and metal mesh combined support, and the two crossheadings are tunneled along the floor; the specification of the air intake roadway is: width*height=(5.3*3.5)m.sup.2, the specification of the air return roadway is: width*height=(4.6*3.5)m.sup.2; the two layers of coal pillars are overlapped, and the width of the coal pillars in the two working faces is 35 m.

[0053] A fracturing relief method for stress concentration of remaining ore pillars in an overlying goaf is provided, and the specific steps are as follows:

[0054] As illustrated in FIG. 1 and FIG. 2, in step 1, three rows of fracturing drill holes are separately constructed in a roadway 1 at an interval in a direction oblique to the coal pillar in an upper goaf by using a drilling machine, where the hole drilling position is 1.2 m far away from the floor, the position of the final hole of the first row of fracturing drill holes is approximately 1 m above the middle of the main roof 5 above the coal pillar, the position of the final hole of the second row of fracturing drill holes is approximately 1 m above the middle of the coal pillar 14, and the position of the final hole of the third row of fracturing drill holes is at ¾ of the section of the coal pillar 14; the length of the drill holes is respectively 28 m, 23 m and 25 m, and the diameter of the drill holes is 75 mm. The arrangement of the drill holes is required to avoid the geological structure zones such as faults as much as possible according to geological information, so as to avoid the influence of the geological structure on the fracturing effect of the coal pillar.

[0055] In step 2, a hydraulic fracturing high-pressure pump 23 and a hydraulic fracturing pulse pump 26 are mounted and commissioned.

[0056] In step 3, a packer 21 is sent to the to-be-fractured area of a to-be-fractured drill hole, a high-pressure seal mounting rod 20, a transfer joint 18 and a high-pressure pipeline 15 are sequentially connected, and the high-pressure pipeline 15 is respectively connected to the hydraulic fracturing pulse pump 26 and the hydraulic fracturing high-pressure pump 23 through a three-way valve 27.

[0057] In step 4, first the hydraulic fracturing pulse pump 26 is turned off and the hydraulic fracturing high-pressure pump 23 is turned on to perform high-pressure hydraulic fracturing on the first drill hole of the first row, and then the hydraulic fracturing high-pressure pump 23 is turned off and the hydraulic fracturing pulse pump 26 is turned on to perform pulse hydraulic fracturing on the first drill hole of the first row.

[0058] The specific steps are as follows: [0059] (a) the high-pressure seal mounting rod 20 is connected to the packer 21, the packer 21 is sent to a corresponding first-row drill hole main roof fracturing zone 12 in the first fracturing drill hole 2 of the first row, then the high-pressure pipeline 15 connected to the hydraulic fracturing high-pressure pump 23 and the hydraulic fracturing pulse pump 26 is connected onto the high-pressure seal mounting rod 20, and a hand pump 22 is used to infuse high-pressure water into the packer 21 through a high-pressure thin hose 19 to enable the packer 21 to be expanded and seal the hole, where a pressure relief valve 17 and a hydraulic fracturing measuring and controlling instrument 16 are arranged on the high-pressure pipeline 15; [0060] (b) a switch valve II 25 is closed, a switch valve I 24 is opened, the hydraulic fracturing high-pressure pump 23 is turned on, and high-pressure water is infused into the drill hole through the high-pressure pipeline 15 to perform hydraulic fracturing; when the construction pressure monitored by the hydraulic fracturing measuring and controlling instrument 16 is smaller than 5 MPa or when the coal seam “sweats” for more than 5-7 min, the hydraulic fracturing high-pressure pump 23 is turned off and the pressure relief valve 17 is opened; [0061] (c) sublevel retreating fracturing is adopted. the packer 21 is retreated to a corresponding first-row drill hole coal pillar fracturing zone 9, the hole is sealed again, the switch valve I 24 is closed, the switch valve II 25 is opened, and fracturing is performed again by using the hydraulic fracturing pulse pump 26; and [0062] (d) the packer 21 and the high-pressure seal mounting rod 20 are removed.

[0063] In step 5, the hydraulic fracturing high-pressure pump 23 is turned off and the hydraulic fracturing pulse pump 26 is turned on to perform pulse hydraulic fracturing on the first drill hole of the second row.

[0064] The specific steps are as follows: [0065] (a) the high-pressure seal mounting rod 20 is connected to the packer 21, the packer 21 is sent to a corresponding second-row drill hole coal pillar fracturing zone 11 in the first fracturing drill hole 3 of the second row, then the high-pressure pipeline 15 connected to the hydraulic fracturing high-pressure pump 23 and the hydraulic fracturing pulse pump 26 is connected onto the high-pressure seal mounting rod 20, and a hand pump 22 is used to infuse high-pressure water into the packer 21 to enable the packer 21 to be expanded and seal the hole, where a pressure relief valve 17 and a hydraulic fracturing measuring and controlling instrument 16 are arranged on the high-pressure pipeline 15; [0066] (b) a switch valve I 24 is closed, a switch valve II 25 is opened, the hydraulic fracturing pulse pump 26 is turned on, and pulse water is infused into the first fracturing drill hole 3 of the second row through the high-pressure pipeline 15 to perform hydraulic fracturing; when the construction pressure monitored by the hydraulic fracturing measuring and controlling instrument 16 is smaller than 5 MPa or when the coal seam “sweats” for more than 5-7 min, the hydraulic fracturing pulse pump 26 is turned off and the pressure relief valve 17 is opened; and [0067] (c) the packer 21 and the high-pressure seal mounting rod 20 are removed.

[0068] In step 6, the hydraulic fracturing high-pressure pump 23 is turned off and the hydraulic fracturing pulse pump 26 is opened to perform pulse hydraulic fracturing on the first drill hole of the third row. The specific steps are as follows: [0069] (a) the high-pressure seal mounting rod 20 is connected to the packer 21, the packer 21 is sent to a corresponding third-row drill hole coal pillar fracturing zone 13 in the first fracturing drill hole 4 of the third row, then the high-pressure pipeline 15 connected to the hydraulic fracturing high-pressure pump 23 and the hydraulic fracturing pulse pump 26 is connected onto the high-pressure seal mounting rod 20, and a hand pump 22 is used to infuse high-pressure water into the packer 21 to enable the packer 21 to be expanded and seal the hole, where a pressure relief valve 17 and a hydraulic fracturing measuring and controlling instrument 16 are arranged on the high-pressure pipeline 15; [0070] (b) a switch valve I 24 is closed, a switch valve II 25 is opened, the hydraulic fracturing pulse pump 26 is turned on, and pulse water is infused into the first fracturing drill hole 4 of the third row through the high-pressure pipeline 15 to perform hydraulic fracturing; when the construction pressure monitored by the hydraulic fracturing measuring and controlling instrument 16 is smaller than 5 MPa or when the coal seam “sweats” for more than 5-7 min, the hydraulic fracturing pulse pump 23 is turned off and the pressure relief valve 17 is opened; [0071] (c) the packer 21 is retreated to a corresponding third-row drill hole floor fracturing zone 10 by adopting sublevel retreating fracturing, the hole is sealed again, the switch valve I 24 is closed again, the switch valve II 25 is opened, and fracturing is performed again by turning on the hydraulic fracturing pulse pump 26; and [0072] (d) the packer 21 and the high-pressure seal mounting rod 20 are removed.

[0073] Step 4 to step 6 are repeated till hydraulic fracturing of all three rows of fracturing drill holes is sequentially completed; the hydraulic fracturing sequence and the hole drilling construction sequence are the same, hydraulic fracturing and hole drilling are synchronously performed in parallel, the construction speed matches and the drill holes can be constructed in advance.

[0074] The first and third rows of fracturing holes are fractured by adopting sublevel retreating hydraulic fracturing, which further improves the utilization rate of drill holes. The specific steps are as follows: [0075] (a) the hydraulic fracturing high-pressure pump 23 or the hydraulic fracturing pulse pump 26 is turned on; [0076] (b) water is infused into a fracturing drill hole and a cycle of hydraulic fracturing is performed; [0077] (c) when the hydraulic fracturing measuring and controlling instrument 16 monitors that the water pressure of the fracturing drill hole is smaller than 5 MPa or the coal seam “sweats” for more than 5-7 min, the hydraulic fracturing high-pressure pump 23 or the hydraulic fracturing pulse pump 26 is turned off, and the pressure relief valve 17 is opened to complete this cycle of hydraulic fracturing; [0078] (d) the packer 21 is retreated for 5-20 m towards the hole mouth of the drill hole, and a cycle of hydraulic fracturing is performed again; and [0079] (e) the packer 21 is retreated to complete the sublevel retreating hydraulic fracturing.

[0080] Although the present invention has been described according to a limited number of embodiments, benefiting from the above description, one skilled in the art understands that other embodiments may be conceived within the scope of the present invention described herein. In addition, it should be noted that the language used in this description is selected mainly for readability and teaching purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Therefore, without departing from the scope and spirit of the attached claims, many modifications and changes are obvious to one skilled in the art. For the scope of the present invention, the disclosure of the present invention is descriptive rather than restrictive, and the scope of the present invention is limited by the attached claims.