Mechanical properties of high-ferrite oil-well cement used in shale gas horizontal wells under various loads

Abstract

As a heterogeneous porous and brittle composite material, oil-well cement cannot withstand the heterogeneous load caused by perforation and fracturing of shale gas horizontal wells, and it is easy to damage the integrity of cement sheath. High-ferrite oil-well cement (HFOC), as a high sulfate-resistant cement, has received extensive attention due to its unique mechanical properties. Based on the service conditions of shale gas horizontal wells, this study discussed the mechanical properties and strengthening and toughening mechanism of HFOC under various loads. The results show that appropriately increasing the content of ferrite in oil well cement can improve the strength and toughness of cement paste. Compared with the Class-G sample, the 28-day compressive strength and tensile strength of the HFOC-3 sample are increased by 19.24% and 51.1%, respectively. The elastic modulus of the HFOC-3 sample is reduced to 6.48 GPa, and the cement paste still has a certain deformation ability under the action of multiple loads. The cement sheath integrity test shows that the HFOC-3 cement sheath can still effectively ensure the cementing quality between the casing and the cement sheath when the cement sheath is damaged. Under impact conditions, the HFOC-3 sample exhibited higher strength and deformation during the energy accumulation stage and the unstable stage. The strengthening and toughening mechanism of ferrite is a synergistic effect of chemistry and physics.