The Role of Water and Strain Rate in the Deformation of Limestone

Abstract

Fluids are pervasive throughout the Earth’s crust. Fluid-rock interaction can significantly alter the mechanical and petrophysical properties of host rocks. This study focuses on the role of fluids in weakening porous carbonate rocks. High solubility of calcite can cause chemically-induced weakening and lead to time-dependent deformation in carbonate rocks. To quantify the effect of hydro-chemo-mechanical coupling on the deformation behavior and failure mode of carbonate rocks, limestone was deformed under both dry and water-saturated conditions. To elucidate the deformation mechanisms, the deformation experiments were conducted at different strain rates. The experimental data shows that while the shear strengths of water-saturated limestone increase with increasing strain rate, the effect of strain rate on the dry samples is negligible. Quantitative microstructural analyses reveal that the grain-scale damage is primarily in forms of stress-induced microcracking and mechanical twinning under both dry and wet conditions. However, with the presence of water, the extent of intergranular pressure solution increases with increasing confinements. The positive correlation between the extent of intergranular pressure solution and the magnitude of weakening suggests that intergranular pressure solution exerts important controls in time-dependent deformation of carbonate rocks.