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Fluid injection-induced earthquakes have been a scientific and social issue of wide concern, and fluid pressurization rate may be an important inducement. Therefore, a series of stepwise and conventional injection-induced shear tests were carried out under different fluid pressurization rates and effective normal stresses. The results show that the magnitude of fluid pressure is the main factor controlling the initiation of fracture slipping. The contribution of fluid pressure heterogeneity and permeability evolution on the initiation of fracture slipping is different with the increase of fluid pressurization rate. When the fluid pressurization rate is small, permeability evolution plays a dominant role. On the contrary, the fluid pressure heterogeneity plays a dominant role. The increase of fluid pressurization rate may lead to the transition from creep slip mode to slow stick-slip mode. Under the laboratory scale, the fluid pressure heterogeneity causes the coulomb failure stress to increase by about one times than the predicted value at the initiation of fracture slipping, and the coulomb stress increment threshold of 1.65 MPa is disadvantageous to the fracture stability. [ABSTRACT FROM AUTHOR]

Hydraulic sand-fracturing experiments are conducted at different proppant content and fracturing fluid viscosities on samples obtained from the shale reservoirs in the Guanyinqiao Member. The characteristics of the obtained sand-fracturing curve and proppant distribution are investigated. The test results establish that the fracture morphologies and proppant distribution after sand fracturing have significant differences. Although the proppant is favorable for increasing the fracture width, the fracture width does not increase gradually with the increase in proppant content. For both acoustic emission localization and proppant distribution, the sand fracture effect is best at a proppant content of 10%. [ABSTRACT FROM AUTHOR]

In this study, a series of laboratory fracturing experiments were conducted on samples mined from reservoirs of the Guanyinqiao Member shale in Xishui County, Guizhou Province, using a traditional triaxial fracturing simulation system. Based on the experimental results, the breakdown pressure and effective stimulated reservoir volume were obtained for four fracturing fluids (supercritical carbon dioxide, water, NO-sand, and sand). The fracture mechanism was then analyzed using acoustic emission monitoring data. Based on the curves of pressure vs injection time for different fracturing fluids, the breakdown pressure increased with increasing fracturing fluid viscosity. When sands with different viscosities were used as the fracturing fluid, the breakdown pressure first increased and then decreased with an increase in the sand viscosity. The distribution of the tracer or proppant was not only correlated with the fracturing effect, but also promotes the filling crack of the tracer and proppant at a certain viscosity as the best fracturing effect. During sand fracturing, the proppant mainly formed shear cracks. The results provide a valuable technical reference for shale gas mining. [ABSTRACT FROM AUTHOR]