The staged fracturing and microseismic monitoring techniques are used for horizontal well stimulation in the Fuling shale gas field. From the analysis of the microseismic data, most of the wells are well stimulated. However, there are still some zones which are not broken thoroughly between adjacent two clusters. When decreasing the cluster space in the adjacent well, this bad phenomenon can be avoided. The cluster space is the key factor for the multi-stage hydraulic fracturing. How to choose it? Two things must be concerned, one is the fracture geometry, and the other is the induced stress field between each two adjacent fractures.
A three-dimensional (3D) multi-fracture propagation model was developed. The mixed boundary element method was used to describe the propagation of the 3D fractures. The fluid flow in a fracture was modeled by the lubrication equation and the Navier-Stokes equations. The fluid flow in the wellbore was considered as the one-dimensional flow. Newton-Raphson and Picard iterative methods were used to discrete the 3D multi-fracture propagation model. Based on the geomechanics parameters of the Fuling shale reservoir, the fracture geometry and stress interference between each two adjacent fractures are studied.
Numerical simulations are carried out to study the influences of the cluster arrangements, fluid displacement and viscosity, bedding plane, shale anisotropic, etc. on the fractures geometry, net pressure inside the fractures and induced stress fields, which reveals the fracture propagation interference mechanism of multi-stage hydraulic fracturing. An optimized cluster space exits for a specific well. 20-25 meter cluster space is recommended for the shale gas formation with well-developed bedding planes, and 25-35 meter recommended for the shale gas formation with non-developed bedding planes. The results are used for the on-site perforation cluster spacing optimization in about ten shale gas wells in Fuling shale gas field, the microseismic signals are full in the shale formation between two adjacent fractures.
The 3D multi-fracture propagation model are established, and the fractures geometry and induced stress fields are studied, which can help to optimize the perforating cluster space and hydraulic fracturing parameters.