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| Initiation pressure model for liquid CO2 fracturing through upward penetrating boreholes and its engineering verification |
| FAN Shixing1,WEN Hu1,JIN Yongfei1,CHEN Jian2,TONG Xiaozhang1,2,CHENG Xiaojiao1,YU Zhijin1 |
| (1. College of Safety Science and Engineering,Xi¢an University of Science and Technology,Xi¢an,Shaanxi 710054,China;2. Huainan Mining Group Co.,Ltd.,Huainan,Anhui 232001,China) |
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Abstract Determining the initiation pressure of coalseam in liquid CO2(L-CO2) fracturing technology is a fundamental scientific issue. According to the stress superposition principle and maximum tensile failure criterion and combined with the weakening effect of low viscosity of L-CO2 on the tensile strength of coal,an initiation pressure model for L-CO2 fracturing was established by superimposing the horizontal principal stress,the fracturing fluid pressure and the circumferential stress caused by the percolation effect,and the upper and lower limits of the initiation pressure model were determined by the limit assumption of fracturing fluid viscosity. A set of high pressure(30 MPa) L-CO2 fracturing equipment with a three-stage L-CO2 injection process was firstly developed to be implemented in underground coal mine,and the first permeability enhancement field test through L-CO2 fracturing was carried out in Pansan coal mine in Huainan. The initiation pressure calculated by the theoretical model ranges from 15.4 to 21.4 MPa,which is not only compatible with the four measured values of two fracturing boreholes(22.9 MPa,16.2 MPa and 21.3 MPa,20.1 MPa,respectively) but also consistent with 65%–70%(15.6–23.2 MPa) of the initiation pressure using hydraulic fracturing,showing the correctness of the initiation pressure theoretical model. The research results have a certain guidance meaning for the application of L-CO2 fracturing.
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