The Correlation between the Fluid Injection Pressure and the Unit Fluid Injection Quantity during Hydraulic Fracturing

Hydraulic fracturing (HF) technology has been widely used in the coal mining industry. This technology can effectively increase the permeability coefficient of low-permeability coal seams, thereby enhancing the gas drainage efficiency and increasing the safety of coal mining. To study the correlation between the fluid injection pressure (FIP) and the unit fluid injection quantity (UFIQ) during hydraulic fracturing and considering the limitations of laboratory and numerical simulation methods, this study employs a field engineering experiment at the 1703 mining working face of Jin’zhong Coal Mine in Sichuan Province as the test site. Through the monitoring and analysis of the FIP and the UFIQ during the whole HF process of coal seam drilling, it is found that there is a certain correlation between the FIP and the UFIQ, the FIP will appear obvious “decreases-recovery” phenomenon when the coal cracks and cracks propagation. And in this process, the UFIQ will appear the corresponding “rise-recovery” phenomenon. At the same time, the fracturing process is divided into three stages according to the variation law of UFIQ in the HF process: liquid filling stage, energy storage and coal cracking cycle stage, and stop cracking stage. In addition, through the arrangement of holes stress gauges around the fracturing hole, it is found that the transfer of disturbance stress formed in the coal mass due to HF behavior is mainly attenuation, and its change stage in the whole HF process is mainly divided into the original stress stage, the stress response stage, and the stress stabilization stage. These results inform the design and optimization of fracturing parameters in hydraulic fracturing processes and aid in understanding the mechanisms of earthquake induction by HF.