## 1 Introduction  
Shale oil, characterized by the integration of source rocks and reservoirs, refers to the prospective hydrocarbon resources that exist in shale in a free or adsorbed state [1; 2; 3]. The exploration and development of abundant shale oil resources are crucial globally. Energy independence has been achieved by the United States through the Black Shale Revolution, significantly increasing shale oil production, which now constitutes 50% of the nation's total crude oil production [4]. In recent years, China has also made substantial progress in exploiting shale oil resources. Commercial shale oil reserves have been discovered in the Junggar Basin, Ordos Basin, Qaidam Basin [5; 6; 7], and numerous other petroliferous basins (Figure 1). However, shale oil reservoirs present challenges due to their poor physical properties, complex pore structures, rapid lithological changes, and strong heterogeneity. These factors contribute to the considerable challenges of exploitation [7; 8]. Fracturing based on the natural fracture networks of shale oil reservoirs during later stages of development has proven effective in enhancing industrial oil and gas production. Previous studieshave highlighted the significant influence of rock mechanical properties and in situ stress on fracture propagation, underscoring the critical importance of studying these factors for shale oil development. Currently, research on the tectonics, mineral composition, and organic geochemistry of shale oil reservoirs in the Mahu Sag has been comprehensive [9; 10; 11]. However, research on the distribution of in situ stress, which is crucial for predicting sweet spots and determining well trajectories in shale oil reservoirs, remains insufficient. This gap in understanding hampers shale oil reservoir exploration and development. Therefore, urgent research is needed on rock mechanics analysis and precise stress quantification to address the challenges in hydrocarbon exploitation and generate economic value [12]. In recent years, research has proven the widespread presence of source rocks with rich organic matter in the lower Permian Fengcheng Formation of Mahu Sag. Due to the superposition of multiple tectonic movements, the stress distribution in the research area is complex [13]. Additionally, the strong reservoir heterogeneity poses challenges in identifying sweet spots. Exploiting industrial oil and gas from unconventional reservoirs often involves deploying directional and horizontal wells [14; 15]. However, the poor reservoir quality poses challenges for maintaining stable production, despite the deployment of horizontal wells. Therefore, establishing effective fracture network systems through fracturing transformation, which are significantly influenced by in situ stress, is advisable [16]. Previous research on in situ stress in this region has primarily focused on logging calculations and mechanical experiments. While these methods accurately reflect in situ stress to some extent, they do not capture the stress distribution across the entire research  
Figure 1: Continental shale oil distribution in China. Reprinted with permission from ref. [7]. Copyright 2019 Elsevier. area. Furthermore, typical 3D numerical simulations of stress fields often concentrate on regional faults and terrain undulations. Homogeneous geomechanical parameter models are employed during the simulation process, which means the influence of these complex variables has not been fully considered. Consequently, the stress state in the formation cannot be adequately represented by numerical simulation results. Nowadays, the technology for simple 3D in situ stress simulations has significantly advanced. Accurately depicting geomechanical models with strong anisotropic characteristics and constructing in situ stress models under complex geological conditions are pressing issues that require solutions. Mechanical experiments, seismic data, volume attributes, and other data were used in the numerical simulation process to enhance the results.