Experimental Investigation of the Growth Law of Multi-Fracture during Temporary Plugging Fracturing within a Stage of Multi-Cluster in a Horizontal Well

Temporary plugging fracturing in a horizontal well with multi-stages and multi-clusters is usually used to improve stimulation efficiency and increase the gas production from shale gas reservoirs. However, the fracture propagation geometry and the mechanism of temporary plugging are still unclear, which restricts the further optimization of temporary plugging fracturing scheme. In this study, taking the Longmaxi shale as the research object and considering the intrafracture and intrastage temporary plugging, the true tri-axial hydraulic fracturing system was used to put forward an experimental method for simulating the temporary plugging fracturing in a horizontal well with multi-stages and multi-clusters. Afterward, the effects of the size combination and concentration of temporary plugging agents and the cluster number in a stage on the fracture geometry created in the secondary fracturing were investigated in detail. The results show that an optimal fracture propagation geometry tends to be obtained by using the combinations of 100 to 20/70 mesh, and 20/70 to 10--18 mesh temporary plugging agents for the intrafracture and intrastage temporary plugging, respectively. Increasing the proportion of the temporary plugging agent of a larger particle size can improve the effectiveness of intrafracture and intrastage temporary plugging fracturing, and tends to open new fractures. With the increase in temporary plugging agent concentration and the cluster number within a stage, both the number of diverting fractures formed and the overall complexity of fractures tend to increase. After fracturing, the rock specimen with a high peak in the temporary plugging pressure curve has more transverse fractures, indicating a desirable diversion effect. By contrast, the fractured rock specimen with a low peak pressure has no transverse fracture, generally with fewer fractures and poor diversion effect.