3D Fracture Propagation Simulation of Shale Oil Reservoirs with Bedding Planes and Natural Fractures Development

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ABSTRACT: The development of shale oil reservoirs has received extensive attention from countries around the world. Shale oil reservoirs are often distributed with a large number of horizontal bedding planes (BPs) and natural fractures (NFs), the presence of both have a greater impact on the propagation of hydraulic fractures. The continuous-discontinuous element method (CDEM) integrates the advantages of the finite element method and discrete element method, which is very suitable for the numerical simulation of complex fracture propagation in shale oil reservoirs. According to the geological characteristics of shale oil reservoirs in Longdong area of Ordos Basin, a three-dimensional fracture propagation model of double BPs and a three-dimensional mine-scale fracture propagation model considering the BPs and NFs were established based on CDEM, the width and range of the opening of BP under the influence of different factors were analyzed, and the fracture propagation law under different factors was clarified. The results show that (1) With the increase of difference between vertical stress and minimum horizontal stress, the BP opening width and the BP opening range both decreases; With the increase of BP cohesion, the BP opening range is reduced. (2) Increased displacement, increased BP opening width and opening range. As viscosity increases, the maximun BP opening width increases but the BP opening range decreases significantly. (3) Under the combined influence of BPs and NFs, the asymmetry of the two wings of hydraulic fracture is significant at low displacement, while the spread non-uniformity of the two wings decreases at high displacement; when the viscosity is high, the NF opening range is small, and the spread of the two wings is non-uniform. (4) At NF approach angles >60°, hydraulic fractures tend to cross through NF, and NF opening range is small. This study provides theoretical guidance for realizing efficient development of target shale oil reservoirs. 1. INTRODUCTION At present, conventional oil and gas resources are difficult to meet the increasing energy demand of human beings. The shale oil and gas revolution, represented by breakthroughs in the exploration and development technology of unconventional oil and gas resources, has triggered a major change in the international energy landscape (Feng et al. 2020; Tong et al. 2018; Wang et al. 2016). In 2022, China's shale oil production exceeds 300×104 t, a nearly three-fold increase compared to 2018, strongly contributing to the growth of shale oil production, which is currently an important part of China's oil and gas energy mix.