Casing Stress Analysis Under Dynamic Change of In-Situ Stress

ABSTRACT During hydraulic fracturing of shale oil wells, fracturing fluid enters the formation causing dynamic changes in in-situ stress in the near-wellbore region, which in turn affects the wellbore stress. This paper takes into account the change of in-situ stress caused by fracturing fluid pumped into the formation, derives the analytical solution of wellbore stress under non-uniform in-situ stress conditions, and analyzes the effects of surface pumping pressure, delivery rate, casing wall thickness, formation Young's modulus and Poisson's ratio on casing stress. The results show that: with the increase of pump pressure and Poisson's ratio of the formation, the Mises stress increase of the casing inner wall increases, and the non-uniformity of stress increases; with the increase of delivery rate and Young's modulus of the formation, Mises stress of the casing inner wall increases, and the non-uniformity of stress decreases sharply; With the increase of the casing wall thickness, the Mises stress in the inner wall of the casing decreases, but the non-uniformity increases slightly; When the Young's modulus and Poisson's ratio of the formation is high, the pumping pressure and displacement should be reasonably controlled and the wall thickness of the casing should be increased to reduce the risk of casing change. INTRODUCTION In recent years, more and more shale oil resources have been discovered with the continuous development of China's economy and the continuous updating of exploration technology (Xu et al., 2021; Wang et al., 2018; Ning et al., 2021). The typical terrestrial mixed-phase shale oil developed in the Lucaogou Formation of the Jimsar region has great exploration potential, and the first national terrestrial shale oil demonstration region was built in China (Kuang et al., 2012; Li et al., 2021; Wang et al., 2020; Li et al., 2021). The shale oil formation conditions in the Lucaogou Formation of the Jimsar region are complex, the reservoir is non-homogeneous, the field has a poor ability to sustain stable production, and the economic benefits of preliminary development are poor (Shen et al., 2021; Xie et al., 2020; Zhang et al., 2020; Wu et al., 2019).