Simulation Study On Fracture Extension Of Horizontal Well Segmental Fracturing In Shale Reservoir

As an unconventional resource, shale gas has become the focus of China’s natural gas development. By the influence of low porosity and ultra low permeability properties, the economic production of shale gas must rely on horizontal drilling and hydraulic fracturing. The natural fractures would be activated by the continuous propagating hydraulic fracturing, which results in secondary fractures. As further propagation of fractures, the connection and extension will lead to large-scale and asymmetric fracture pattern in shale gas reservoirs. Accurate prediction the scope of complex fracture network is a key link in the process of shale gas reservoir hydraulic fracturing optimization design. This paper based on fluid mechanics, elasticity mechanics and percolation mechanics, establishes the pressure drop equation and continuity equation in fracture and fracture deformation equation, then considering the intersection model of hydraulic fracture and natural fractures; we established a complex fracture network model. Finite difference solution on the network model, and analyzed the influence of formation parameters and construction parameters to the reconstruction volume. The paper mainly includes the following aspects:(1) According to various rupture when hydraulic fracture intersect natural fracture, we establish failure criteria based on the theory of elastic mechanics and rock mechanics, and make a comprehensive analysis and calculation of intersection point’s possibility fracture situation by using the established criteria. The criteria provides means for the study of the extension path of hydraulic fracture after intersecting natural fracture(2) Based on percolation mechanics, elastic mechanics and fluid mechanics theory, we established complex fracture network propagation model which was controlled by liquid flow equation, material balance equation, continuity equation and fracture deformation equation. Through the finite difference numerical method and language of VB, we compile the simulation calculation program of fracture network volume.(3) Through the simulation program, we make a sensitivity analysis to geological and engineering factors affecting the network volume. The results show that the larger stimulation reservoir volume (SRV) can be obtained by using greater amount of fluid, lower fracturing fluid viscosity and displacement; under the same construct condition, high elastic modulus and low stress difference of reservoir contribute to bigger SRV. The greater of natural fracture density, the smaller of SRV. In addition, according to the fracture width data in the intersection point, obtained the width distribution in the affected areas.