Integrity Evaluation of Cement Ring during Fracturing and Flowback of Horizontal Well in Jimsar Shale Oil

Horizontal well volume fracturing has become the main technology for effective development of unconventional oil and gas. In the process of fracturing and flowback of horizontal wells, the changes of wellbore temperature and pressure will affect the magnitude and distribution of stress in cement sheath, which may lead to compression or tensile failure of cement sheath, or a microclearance between casing and cement sheath. Therefore, based on the elastic theory of thick-walled cylinder, the elastic model of casing cement sheath and formation combination is established, and the finite difference program FLAC3D (Fast Lagrangian Analysis of Contimua in Three-Dimensional) was used to solve the model. The simulation evaluation of several horizontal wells in Jimusar shale oil shows that the main failure mode of cement sheath in horizontal well section is radial compression or circumferential tensile failure in fracturing period, and the main failure mode is a microclearance failure in flowback period. Taking Jimusar shale oil horizontal well JHW00421 as an example, the critical values of wellbore pressure and mechanical parameters of cement when cement sheath fails during fracturing flowback and their relationship are predicted or evaluated. The findings of this study are helpful to better understand and evaluate how different fracturing or flowback operation parameters affect the integrity of cement sheath and the effectiveness of interlayer sealing in horizontal well sections.