Investigation of hydraulic fracture propagation in conglomerate reservoirs using discrete element method

Hydraulic fracturing has been widely used in the development of conglomerate reservoirs in the Karamay oilfield Xinjiang, China. Understanding the influences of large and irregular conglomerate particles on the fracture propagation behavior is crucial for the fracturing design of reservoirs of this type. This study numerically captured the associated fracturing process and thoroughly analyzed the impact of conglomerate particles by adopting the discrete element method. The simulation results indicated that the existence of conglomerate particles conspicuously increase the breakdown pressure of the conglomerate formations. Several scenarios were designed to investigate the influence of content and strength of conglomerate particles, respectively. It was found the fitting relationship was nonlinear between breakdown pressure and particle content and was linear between breakdown pressure and particle strength. Conglomerate particles affected fracture behavior in two patterns, namely penetration and circumvention. However, under certain in-situ stress condition, the conglomerate particles had negligible impact on the principal direction of fracture propagation. The simulation results are advantageous to instruct the field fracturing operations, such as the selection of hydraulic fracturing site and injection parameters.