Hydraulic fracture energy considerations: a 3D numerical simulation compared to microseismic imaging

Summary Hydraulic fracture creation, in unconventional resources, is essential for optimizing hydrocarbon recovery. Microseismic events are mainly small shear failures that occur adjacent to the hydraulic fracture as it propagates and destabilizes the reservoir. When these microseismic events are recorded and mapped, measurements of the hydraulic fracture dimensions in time are possible. With knowledge of reservoir parameters such as: in-situ stress, barrier layer stress contrasts, payzone and layered elastic and material properties and location of layered interfaces, the fracture geometry can also be modeled. We have developed a numerical algorithm that simulates three-dimensional fracture growth using these input parameters along with the concept of energy balance. Our work is based on Advani’s (1990) approach that uses a symmetric three-layered homogeneous geologic model. The fracture is assumed to be a single planar elliptical tensile (Model I) crack that experiences several episodes of energy loss and transformation during propagation. Though many forms of energy losses occur during the hydraulic fracturing process, the ones mainly associated with tensile failure are considered: potential energy, the energy applied to open the fracture; strain energy, the energy used to deform the formation; and surface energy, the energy required to create a new fracture surface. The modeled fracture length, width, height and effective crack opening pressure are solved at different injection times. The calculated dimensions are compared to the mapped microseismic geometries and effective borehole treatment pressure. By sequentially adjusting the input parameters and comparing the model response to the microseismic image, we determine their influence on the resulting fracture geometry and pressure profile. This shows that energy considerations can serve as a practical method for determining fracture geometry.