This paper aims to solve the issue of differential pressure in the annulus commonly existed in shale gas and deep oil & gas well drilling. The reasons for cement sheath integrity failures mainly caused by a high differential pressure in the exploration and development
process of deep, low-permeability, unconventional oil and gas resources were achieved from theoretical research and experimental simulation. Then, in the case studies of shale gas wells, HTHP wells in the Anyue gasfield, Sichuan Basin, and the Kuche Shanqian block in the Tarim Basin, differential pressures during drilling, fracturing and production process were sorted and quantitative calculation was made to further interpret the above achievement, that is, the cement sheath integrity failure by micro-annulus resulted from tensile stress under gravity-free condition in the solidification period of cementing, plastic deformation in the cement-sheath under loading and unloading
working conditions, tensile stress in the interfaces in the process of unloading. Patterns of cement sheath integrity failures under a high differential pressure were analyzed, and the risks of integrity failures during different periods of a wellbore full life cycle were summarized.
Preliminary measures and techniques to ensure cement-sheath integrity were proposed as follows: to improve the deformation resistivity of cement stones and to enhance the cementing force of the primary and the second interfaces as well as the force of interface contact.