Dynamic response characteristics of reservoir in-site stress induced by the tridimensional development of shale oil

Shale oil has become one important oil and gas development field in China, and the tridimensional development mode based on horizontal well and hydraulic fracturing can improve the recovery efficiency of shale oil effectively. In the process of tridimensional development, reservoir pressure drops to induce the complicated change of reservoir in-situ stress state, which interferes in the engineering operation in the formations at the similar depth. In order to study the influences of tridimensional development on the evolution of reservoir in-situ stress, this paper established a 3D in-situ stress evolution mathematical model of shale oil reservoir according to the pore elasticity theory, combined with reservoir seepage, linear elastic deformation of rock skeleton and field data. Then, vertical and lateral time-space evolution characteristics of reservoir pore pressure and in-situ stress were described, and the influences of the stimulated reservoir volume (SRV) in the three-dimensional space on these response characteristics were analyzed. The research results show that SRV can enhance the response of reservoir in-situ stress. The influence of tridimensional development on the reservoir in-situ stress increases as it approaches to the SRV center vertically. Both the magnitude of in-situ stress and the direction of principal stress change as the formation depth changes. The phenomenon of interlayer stress interference occurs, causing the disturbance of formation fracturing pressure. The fracturing difficulty changes in different positions of tridimensional space. The results provide a theoretical basis for the three-dimensional development of shale oil in China.