A 3-D hydraulic fracture propagation model applied for multiple-layered formation
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2019, International Petroleum Technology Conference Rock layering, a critical factor in determining fracture height growth, is pervasive in the Silurian Longmaxi shale formation in the southwest of China. From field studies, engineers found that the created fracture height is lower than the required height even after they enhanced the pumping rate to a very high value. This paper introduces a coupled three-dimensional hydraulic fracture propagation model considering the effect of bedding layers and investigate the effect of shear displacements along the bedding planes on fracture height growth. Our fracture propagation models address rock deformation and fluid flow. Rock deformation is governed by a fully three-dimensional displacement discontinuity method (3D DDM). The fluid flow model employs a finite difference method able to capture fluid movement along vertical fractures and bedding planes. Additionally, a propagation criteria determines whether the fracture would penetrate bedding planes. The Longmaxi shale formation has characteristics of large burial depth, low porosity and multiple bedding layers that hamper reaching the target fracture height even after increasing the pumping rate and treatment size. Hence, our fracture propagation model is applied to study the effect of bedding layers on fracture height growth. In this paper, we selected two different fracture geometries and analyzed profiles of fracture width, pressure and two types of shear displacement discontinuities. From numerical investigations, we found that the maximum width can be obtained at the junction after the vertical fracture penetrates the bedding planes as a result of the decrement of the compressive stress acting on the bedding planes. As the fracture penetrates the bedding planes, a certain amount of fluid would leak into the planes, which leads to fracture height containment. Moreover, the slope utilized for characterizing the correlation between leak-off volume and fracture height, is regarded as a tool to identify the number of BPs that fracture penetrates through. This paper illustrates the extensive application of our coupled hydraulic fracture propagation model for the Silurian Longmaxi shale formation with multiple bedding layers. Shear displacements along the bedding planes are regarded as a primary mechanism of fracture height containment.
