Numerical simulation on hydraulic fracture propagation in glutenite under the effect of unsteady seepage

Due to the existence of gravels, the propagation mechanisms of hydraulic fractures in glutenite reservoirs are not defined and fracture morphology can be hardly controlled. In this paper, the gravel in glutenite reservoirs was characterized as a three-phase complex structure of matrix-interface-gravel. Then, the mathematical model for the propagation of hydraulic fractures in glutenite reservoirs under the joint effect of stress field and unsteady seepage field was established by means of fracturing mechanics and damage mechanics comprehensively, and it was solved. Finally, the effects of principal stress difference, gravel particle diameter, gravel content and flow rate on fracture propagation morphology and rock fracturing pressure were analyzed. The following research results were obtained. First, the hydraulic fractures in glutenite reservoirs are morphologically complex with developed secondary pinnate fractures. When hydraulic fractures meet gravels, gravel bypassing, gravel penetrating and crack arresting occur, and gravel bypassing propagation is dominant.Second, the length of hydraulic fractures in the study area increases with the increase of principal stress difference, gravel particle diameter and flow rate and with the decrease of gravel content. Third, the rock fracturing pressure in the process of hydraulic fracturing is proportional to principal stress difference, gravel content and flow rate and is in inverse proportion to gravel particle diameter.