Method for constructing artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in roof aquifer

Abstract

A method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer includes constructing an artificial water-conducting channel in a sandstone fissure aquifer through arrangement of drainage boreholes and pulse hydraulic fracturing, which improves the permeability of dense and intact sandstone rock masses. The artificial water-conducting channel formed through arrangement of drainage boreholes is connected to discontinuous water-bearing areas and water-rich areas, and water from roof sandstone fissures is diverted to the drainage boreholes through the artificial water-conducting channel, thereby achieving effective drainage of the boreholes and expanding a radiation range of single-borehole drainage. The method not only avoids the arrangement of excessive drainage boreholes and significantly improves the drainage efficiency of prospecting and drainage boreholes, but also facilitates advance drainage during the mining process. The method enables effective control of mine water hazards, thereby ensuring safe production of the mine.

What is claimed is: 
     
         1 . A method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer, comprising the following steps:
 S 100 , collecting hydrogeological information of a mining area, and exploring a specific stratigraphic horizon and water volume of a roof sandstone fissure aquifer;   S 200 , extracting rock samples from the roof sandstone fissure aquifer for a segmented pulse hydraulic fracturing simulation experiment to study the relationship of a pulse pressure peak, a pulse frequency, a segment length, a segment interval length, and a fracturing duration with fracture development, so as to determine an optimal pulse frequency, an optimal pulse pressure peak, an optimal segment length, an optimal segment interval length, and an optimal fracturing duration for segmented pulse hydraulic fracturing in a drainage operation area;   S 300 , determining drainage borehole arrangement parameters, drainage borehole arrangement forms, and segmented pulse hydraulic fracturing parameters according to a fracture development law and the specific stratigraphic horizon and water volume of the roof sandstone fissure aquifer derived from the segmented pulse hydraulic fracturing simulation experiment;   S 400 , drilling according to the drainage borehole arrangement parameters and the drainage borehole arrangement forms, and surveying a site after the drilling, to determine placement positions of pulse hydraulic fracturing equipment;   S 500 , installing a water-stopping casing and a matching spherical orifice water shutoff valve at an orifice of the drainage borehole drilled, externally connecting the spherical orifice water shutoff valve to a return flowmeter to monitor a water return volume at the orifice, determining whether the artificial water-conducting channel formed by pulse hydraulic fracturing is connected to water from roof fissures according to the difference between a water injection volume of a pulse hydraulic fracturing pump, a filtration loss of a rock stratum, and the water return volume at the orifice, and estimating a water volume of a water-bearing area of the roof connected to the artificial water-conducting channel;   S 600 , before a fracturing operation, arranging an artificial water-conducting trough in a roadway near the orifice of the drainage borehole; and after the pulse hydraulic fracturing equipment is transported to a designated operation location, checking equipment quantity and integrity, and connecting the equipment;   S 700 , after checking connections of the pulse hydraulic fracturing equipment, sequentially advancing a shutoff valve, a downhole packer, a check valve, a near-orifice packer, and a high-pressure sealed drill rod to a designed first-segment hydraulic fracturing position through a drilling rig to start a segmented pulse hydraulic fracturing operation; after the first-segment pulse hydraulic fracturing is completed, retracting part of the high-pressure sealed drill rod through the drilling rig, wherein a total length of the retracted high-pressure sealed drill rod is equal to a segment interval length; and then performing next-segment pulse hydraulic fracturing, and repeating the above operations for segmented pulse hydraulic fracturing of a single borehole until the pulse hydraulic fracturing of all fracturing segments designed in the single borehole is completed;   S 800 , after the pulse hydraulic fracturing operation is completed, turning off the pulse hydraulic fracturing pump, opening a pressure relief valve in a pipeline to release residual fracturing fluid in the pipeline, and after a pressure in the pipeline drops to 0, sequentially retracting the high-pressure sealed drill rod, the near-orifice packer, the check valve, the downhole packer, the shutoff valve, and other equipment, and checking their integrity; repeating the above pulse hydraulic fracturing process and sequentially completing the segmented pulse hydraulic fracturing of all boreholes; and   S 900 , after completing the pulse hydraulic fracturing operation, monitoring and counting the water return volumes and other parameters of the drainage boreholes, evaluating the effect of pulse hydraulic fracturing on optimizing the drainage of water from the roof sandstone fissure aquifer, and adjusting the spherical orifice water shutoff valve in time to control water outflow from the drainage borehole.   
     
     
         2 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 1 , wherein in the step S 100 :
 hydrogeological information of the mining area is collected through hydrogeological survey, three-dimensional seismic exploration, geographic information system spatial analysis, and the like; and   the specific stratigraphic horizon and water volume of the roof sandstone fissure aquifer are explored in advance by arranging prospecting boreholes in the mining area.   
     
     
         3 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 1 , wherein in the step S 300 :
 the drainage borehole arrangement parameters comprise a borehole length, a dip angle, a spacing, an azimuth angle, and a diameter; and   a terminal end of the drainage borehole arrangement is located at a geometric center point of a geometric figure formed by connecting center points of a plurality of potential discontinuous water-bearing areas facing a radiation zone of pulse hydraulic fracturing-induced fracture development.   
     
     
         4 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 3 , wherein in the step S 300 :
 a spacing of drainage boreholes is designed based on the distribution and continuity of water-bearing areas;   when the water-bearing areas are evenly distributed and have good continuity, the spacing between the drainage boreholes is 30-50 m;   when the water-bearing areas are unevenly distributed and have poor continuity, the drainage boreholes are arranged in a way that a single borehole, after pulsed hydraulic fracturing, is fully connected to the water-bearing areas inside the radiation zone of pulse hydraulic fracturing-induced fracture development, and the spacing between adjacent drainage boreholes ensures that all discontinuous water-bearing areas between two adjacent boreholes fall within a fracture development radiation range.   
     
     
         5 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 4 , wherein in the step S 300 :
 the azimuth angle of the drainage borehole is offset by 30-60° toward an open-off cut of the working face, such that the drainage boreholes enable advance drainage during the mining of the working face; the drainage boreholes have a diameter of 94-120 mm; and a single-segment hydraulic fracturing duration is 20-60 min.   
     
     
         6 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 1 , wherein in the step S 300 :
 The drainage borehole arrangement forms comprise trans-stratal straight borehole arrangement, directional long borehole arrangement, and combined arrangement of trans-stratal straight boreholes and directional long boreholes.   
     
     
         7 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 6 , wherein in the step S 300 :
 the trans-stratal straight borehole arrangement comprises fan-shaped borehole arrangement, parallel borehole arrangement, and a combination of the fan-shaped borehole arrangement and the parallel borehole arrangement.   
     
     
         8 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 7 , wherein in the step S 300 :
 the fan-shaped borehole arrangement refers to arrangement of a plurality of boreholes in a drilling site, and the boreholes are distributed in a fan shape; and   the parallel borehole arrangement refers to arrangement of a plurality of groups of alternately long and short boreholes obliquely toward the open-off cut of the working face in two entries of the working face of a coal mine, and plane projections of the alternately long and short boreholes are parallel to each other.   
     
     
         9 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 6 , wherein in the step S 300 :
 the directional long borehole arrangement refers to arrangement of directional long boreholes in a roof sandstone aquifer of the coal seam using a directional drilling rig in a working face entry;   the boreholes have a length of greater than 200 m, and a borehole strike is parallel to an advancing direction of the working face.   
     
     
         10 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 6 , wherein in the step S 300 :
 the combined arrangement of trans-stratal straight boreholes and directional long boreholes refers to arrangement of both the trans-stratal straight boreholes and the directional long boreholes in the working face entry; first, segmented pulse hydraulic fracturing of the directional long boreholes is performed to form a large range of artificial water-conducting fissures for overall drainage of the roof sandstone fissure aquifer; and then, pulse hydraulic fracturing of the trans-stratal straight boreholes is performed in the water-bearing areas not radiated by the directional long boreholes or highly localized water-bearing areas for local drainage of water.   
     
     
         11 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 1 , wherein in the step S 600 :
 the connecting the equipment comprises: a water tank is connected to a water supply pipeline through a water tank supply hose to supply liquid to the water tank; the pulse hydraulic fracturing pump is connected to the water tank through a pulse pump return hose and a pulse pump supply hose to supply liquid to the pulse hydraulic fracturing pump; the pulse hydraulic fracturing pump is connected to a high-pressure hose to output pulsed hydraulic fracturing water and inject same into the borehole; the high-pressure hose is connected to a first three-way joint and a pressure relief valve for releasing water pressure in the pipeline; a pressure sensor and a flow sensor are connected to the high-pressure hose to monitor a pulse pressure and flow rate in the pipeline during the pulse hydraulic fracturing process; the pressure sensor is connected to a hydraulic fracturing measurement and control instrument through a pressure sensor signal transmission line, and the flow sensor is connected to the hydraulic fracturing measurement and control instrument through a flow sensor signal transmission line, which is configured to transmit the pulse pressure and flow signals monitored in the pipeline to the hydraulic fracturing measurement and control instrument, display the pulse pressure and flow curves in real time, and store data.   
     
     
         12 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 11 , wherein in the step S 600 :
 the spherical orifice water shutoff valve and the return flowmeter are connected, the return flowmeter is fixed to a roadway sidewall through a steel band clamp, the return flowmeter is connected to an orifice drainage hose, and the orifice drainage hose is connected to drainage ditches of the two entries.   
     
     
         13 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 1 , wherein in the step S 900 :
 monitoring operation effects comprise monitoring pulse hydraulic fracturing effects of roof sandstone fissure aquifers and monitoring water drainage effects;   the monitoring pulse hydraulic fracturing effects of roof sandstone fissure aquifers comprises monitoring the number and distribution of pulse hydraulic fracturing fractures on drainage borehole walls, and monitoring a propagation range of pulse hydraulic fracturing fractures; and   the monitoring water drainage effects mainly comprises counting water return volumes of the drainage boreholes after pulse hydraulic fracturing, and water seepage of a roadway roof during normal mining of the working face.   
     
     
         14 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 13 , wherein in the step S 900 :
 the monitoring a propagation range of pulse hydraulic fracturing fractures of drainage boreholes is performed by an observation method of taking adjacent boreholes as observation boreholes, and when water outflow or more water outflow occurs in adjacent boreholes during the pulse hydraulic fracturing process, it indicates that pulse hydraulic fracturing fractures have propagated to the adjacent boreholes; and   the monitoring the number and distribution of pulse hydraulic fracturing fractures on drainage borehole walls is performed by observing through a borehole inspection apparatus, after borehole drilling is completed, a morphology of borehole walls of the fracturing segments is observed through the borehole inspection apparatus before pulse hydraulic fracturing, and after the pulse hydraulic fracturing, the borehole walls of the fracturing segments are observed again to compare and analyze the number and distribution of pulse hydraulic fracturing fractures on drainage boreholes.   
     
     
         15 . The method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer according to  claim 13 , wherein in the step S 900 :
 the counting water return volumes of the drainage boreholes refers to monitoring a pumping flow rate during fracturing through the flow sensor, calculating the filtration loss of a rock stratum according to an indoor hydraulic fracturing similarity simulation experiment in a laboratory, monitoring the water return volume at the orifice after the pulse hydraulic fracturing through the return flowmeter at the orifice, determining whether the artificial water-conducting channel formed by pulse hydraulic fracturing is connected to water from roof fissures according to the difference between the water injection volume of a pulse hydraulic fracturing pump, the filtration loss of a rock stratum, and the water return volume at the orifice, and estimating a water volume of the water-bearing area of the roof connected to the artificial water-conducting channel; and   the counting water seepage of the roadway roof during normal mining of the working face refers to observing and recording the water seepage of the roof before and after fracturing and during the mining of the working face, and intuitively evaluating the effect of pulse hydraulic fracturing on optimizing the drainage of water from water-bearing areas of the roof sandstone fissures according to macroscopic phenomena.