FDEM-BEM simulation of hydraulic fracture propagation and control factors in conglomerate reservoirs

Owing to the existence of gravel of tight sand conglomerate, the law of propagation and main factors of hydraulic fracture have not been understood perfectly. Firstly, the finite-discrete element method (FDEM) was used to investigate the ductile behavior of hydraulic fractures when they met gravel. Then, the main geological and engineering factors affecting hydraulic fracture propagation are determined, such as difference of horizontal principal stress, gravel size, viscosity of fracturing fluid and displacement. Subsequently, the boundary element method (BEM) was used to demonstrate that the propagation process of macroscopic artificial fractures in conglomerate can be simulated by equivalent natural fractures. The results indicated that: (1) The fracture morphology of sand conglomerate reservoir was determined by stress state and gravel, mainly dominated by gravel-bypassing and bifurcation under low stress difference; (2) The spacing of natural fracture has the greatest positive influence on the length of hydraulic fracture, while the minimum horizontal principal stress has the greatest negative influence; (3) The smaller the angle of natural fracture is, the greater the frequency of branching fracture occurs; 4)The hydraulic fractures in tight conglomerate reservoir are mainly characterized by bi-wing fractures on the macro levels. The results can provide some reference for revealing the propagation mechanism of hydraulic fracture and selection of fracturing section in conglomerate reservoir.