Abstract: A set of mixed shale oil reservoirs deposited in a littoral-shallow lacustrine environment is developed in the fourth member of the Shahejie Formation in the Leijia Area of the Liaohe region.The rocks are lithologically diverse with well-developed laminae and natural fractures,leading to complex and variable hydraulic fracture geometries.To reveal the effects of laminae and natural fractures on hydraulic fracture propagation in shale oil reservoirs,based on typical geological and mechanical parameters of shale oil in the Leijia Area,this study combined the continuous-discontinuous element method(CDEM) and the finite volume method(FVM) to establish a numerical simulation model coupling block deformation,fracture failure and fracture flow.Three representative geological models,namely,laminae-dominated,natural-fracture-dominated and interlayer-dominated,were constructed.Under a fixed injected-fluid volume,the effects of injection rate and fracturing-fluid viscosity on hydraulic fracture propagation in these three geological models were investigated.The results show that increasing injection rate can significantly enhance the maximum aperture of the main fracture,and increasing viscosity also helps enlarge fracture aperture.In natural-fracture systems,medium-to-low injection rates or low-viscosity conditions more readily promote fracture propagation along natural fractures,whereas under high injection rates and high viscosity the main fracture is more likely to cross natural fractures and alter branch connectivity patterns.In interlayer systems,increasing injection rate and viscosity helps reduce differences in fracture aperture between layers and improve the average aperture of the main fracture.The results can provide technical support for hydraulic fracture geometry design and pumping-parameter optimization in similar shale oil reservoirs.

Key words: shale, hydraulic fracturing, fracture propagation, continuous-discontinuous element method, finite volume method, Leijia Area