Fracture Propagation Behavior of Bedding Shale in the Process of Multistage Cluster Fracturing considering the Intercluster Stress Interference

Abstract

Abstract Staged multicluster fracturing in horizontal wells is the key technology for forming complex fractures in shale reservoirs. The existence of shale bedding plays a conspicuous role for the propagation path of hydraulic fractures, affecting the propagation of the fracture height direction prominently. A 3D finite element model containing three clusters signed as side clusters and middle cluster was established based on the cohesive zone model and the dynamic distribution mechanism of interfracture flow. And the correctness of the model was verified by literature comparison. Some factors including cluster spacing, horizontal stress difference, shale bedding strength, perforation density, injection rate, and viscosity of fracturing fluid which influenced fracture propagation behavior of bedding shale were simulated. The results indicate that the stress interference of the middle cluster by the clusters on both sides will be prominently obvious when the cluster spacing is less than 10 m. Multiclusters will penetrate across the shale bedding when the horizontal stress difference is more than 4 MP, which will conspicuously reduce the activated probability of discontinuities and the complexity of fracture geometry. In correspondence with increase of horizontal stress difference, the interference between clusters also increases prominently, which will conspicuously decrease the propagation of the middle cluster. In order to comprehensively equalize the length of multiclusters, the inhibition of intercluster stress interference on the middle cluster propagation can be counteracted by improving pressure drop in perforation. The high injection rate and viscosity of fracturing fluid will contribute to the shale bedding shear slip increasingly, which is conducive to the formation of complex fractures in areas with well-developed bedding. The study has a certain guiding significance for the operation parameter design of multicluster fracturing in bedded shale.