Mechanism of Cement Stone Porosity and Permeability Structures for Downhole Fluid Packing.

Cement ring is the main barrier for downhole fluid sealing. The sealing properties of the cement ring include two aspects: sealing off the cement ring itself and the interface. Numerous studies have been conducted on interface sealing failure. However, there are few studies considering the structural perspective of the sealing performance of the complete cement ring itself. Therefore, this study explores pore structure characteristics of cement stone at the microscopic scale, the influencing factors of fluid flow in the cement stone, and the mechanism of sealing performance of the cement stone. The studies have shown that G-grade and ultra-fine cement stones present high porosity and low permeability. Cement stone pores containing free water represent the prerequisite for effective sealing performance. Capillary pressure, resistance caused by ultimate static shear stress, pore fluid pressure, and additional pressure difference produced by the "Jamin effect" are the main driving factors of cement stone sealing fluid. Likewise, as the main driving factors and the length of the cement stone increase, the sealing ability of the cement stone to fluid will follow Enhanced. Considering that water is a non-Newtonian fluid, when the interfacial tension of gas–water is 47 mN/m, the pore diameter is 0.05 μm, the length of the cement stone is 1000 m, the wetting angle is 100°, and the limit dynamic shear stress is 0.01 Pa, the sealing pressure of the cement stone is 543.66 MPa. Our findings provide a foundation for sealing oil and gas reservoirs with different pressure and permeability characteristics. [ABSTRACT FROM AUTHOR]