Comparison analysis on permeability improved effect of single and multi section hydraulic fracturing in deep depth seam

Zhang Chunhua; Zhang Yongzhi; Li Jiangtao; Li Tengda

doi:10.13199/j.cnki.cst.2017.06.008

Abstract：In order to compare the permeability effects of a single section and multi section hvdraulic fracturing in the deep seam boreholes,based on the deposition conditions of the proposed opened No.8 seam in Xieqiao Mine,a single section and multi section hydraulic fracturing and permeability improved models were individually established.A RFPA2D-Flow software was applied to simulate and analyze the features and law of the in-seam water pressure field,stress field,crack field and permeability field within the hydraulic fracturing influence zone and the effect verifications were conducted.The results showed that the pore pressure in the coal mass at the initial fracturing of the single section fracturing was 7 MPa and the pore pressure of the coal mass at the initial fracturing of the multi section fracturing was 16 MPa.When the fracturing operation started in the seam,during the single section fracturing,there was an obvious stress concentration occurred in the borehole middle part of the seam.And when a multi section fracturing was in operation,the stress distribution of the coal mass would have ups and downs and would not have an obvious stress concentration.During the single section fracturing operation,the cracks would be expanded from the middle location of the borehole to the roof and floor,the effective fractured area would be small.In the multi section fracturing operation,each fracturing section would cause a similar crack field and the effective fracturing area would be large.During the single section fracturing operation,the permeability coefficient of the coal mass would be 249 times higher than the initial value.During the multi section hvdraulic fracturing operation,the permeability coefficient of the coal mass would be 263 times higher than the initial value.In comparison with the single section hydraulic fracturing of the borehole,the multi section hydraulic fracturing could effectively improve the gas drainage effect of the borehole.