Effect of rock-fluid interaction and heterogeneities on the tensile, uniaxial strength and elastic behaviour of Dinantian carbonate intact rocks

Abstract

Carbonate rocks, which often serve as geo-energy reservoirs, are prone to fluid-assisted deformation, which is susceptible to fluid chemistry. Acknowledging the impact of fluids and fluid chemistry on the mechanical behaviour of rocks substantiates the safety of exploiting the geo-energy reservoirs. We saturated Dinantian carbonate samples overnight at a similar fluid mass with 4 different fluids: deionised water, calcium carbonate saturated solution, sulfuric acid, and a sodium chloride-rich geothermal brine, which cover a range of redox potentials, pH, and ionic strength. After saturation, we conducted Brazilian Disc and uniaxial compressive tests from which we obtained tensile strength, Young's modulus, Poisson’s ratio and Uniaxial Compressive Strength (UCS). The tensile strength of the sample depends on both sample porosity and fluid chemistry, and tensile strength decreases with decreasing fluid ionic strength. In contrast, Young’s modulus doesn’t exhibit a clear dependence on pH, and instead correlates with the ionic strength of the fluids used, just as UCS. Poisson’s ratio is affected by pH, redox potential and ionic strength. This correlation implies that the ionic strength induces more deformation and lowers UCS. Additionally, given the differences in the effect on Young’s modulus and Poisson’s ratio, the magnitude and direction of the local stress field determine if further fluid complexity affects elastic deformation and hence local stress transfer.