Segmented hydraulic fracturing technology by multi-hole synchronous drilling in low permeability coal seams
In order to improve the permeability improving efficiency of coal seams,we researched on hydraulic fracturing technology with multi-hole synchronous drilling.Based on the basic principle of this technology,we did a laboratory test for the compressive strength of high-pressure sealing capsule and the automatic control process of hydraulic fracturing system with multi-hole synchronous drilling.The test shows the minimum failure strength is 35 MPa;the automatic control system of this technology can monitor real time pressure data of each hole;the fracturing process is controlled automatically in this system.We made an on-site industrial test at Sanyuan Coal Mine.The industrial test shows that the starting pressure of No.3 coal seam is 23.3～25.4 MPa;when the fracturing distance is 10 m,the crack extension time of a fracturing hole is 26～38 min and the cracks connecting time is 28～40 min;the data shows the fracturing efficiency is effectively improved.In a 30 d statistic period,the average gas concentration after fracturing is 1.12 times,the average mixing flow is 2.17 times,and the average gas purity is 2.44 times,that of the unfractured coal seam.This technology is proved to effectively increase the permeability of coal seams and improve the gas extraction effect.
multi-hole synchronous drillingsegmented hydraulic fracturingpermeabilitypressure relief and gas permeability improvementgas extraction
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