Thermal-Mechanical Modeling of a Rock/Proppant System to Investigate the Role of Shale Creep on Proppant Embedment and Fracture Conductivity

Under high temperature and stress reservoir conditions, proppant embedment induced by the time-dependent creep behavior of shale rocks has posed great challenges to the long-term maintenance of fracture conductivity in unconventional reservoirs. In this study, a numerical workflow combining a 3D continuum-discrete mechanical coupling approach with the lattice Boltzmann (LB) method is developed to simulate the coupled thermal-mechanical process in a rock/proppant system and to investigate the role of the time-dependent deformation of shale rocks on proppant embedment and fracture conductivity loss under varying temperature and stress conditions. The numerical workflow is first compared with an experiment under varying temperature and stress conditions to calibrate the elastic, plastic, viscoelastic, and thermal properties of the shale rock, as well as the proppant properties. Then, the effect of fracture axial and confining stress, numbers of proppant layers, proppant size, proppant spatial distribution, and proppant crushing is systematically investigated. The simulation results indicate that when the rock creep is significant, large size and a multilayer of proppant structure are suggested to maintain the fracture conductivity. The small percentage of particle breakage in a proppant assembly plays a less important role in the long-term maintenance of fracture conductivity. The findings of this study will shed light on the creep-induced proppant embedment mechanisms at reservoir conditions as well as their influence on the sustainability of fracture conductivity over long periods of time.