Mechanical properties of reservoir rock and caprock under varying brine saturation for application of geological carbon storage in deep saline aquifers

In order to mitigate the greenhouse gas emission level largely in the atmosphere the best possible solution is storing the CO2 in deep saline confined aquifers having impermeable caprock material on the top. However, such deep sedimentary rocks in the presence of water and brine saturation undergo degradation in their mechanical properties – elastic modulus and toughness. Therefore, it is very important to understand and quantify the degree of degradation of mechanical properties of those rocks under varied brine concentration. For this purpose, a detailed experimental work is carried out in this paper. The specimens are saturated under varying brine (0% NaCl to 30% NaCl) and water of different degree of saturation (0% DOS to 100% DOS) saturated sandstone and siltstone rocks, respectively. The rock samples namely, sandstone and siltstone material used in this work collected from Gosford, New South Wales and Eidsvold, Queensland, respectively in Australia. The mechanical properties, namely elastic modulus, E and fracture toughness, KIC estimated using Uniaxial Compressive Strength (UCS) and Three-Point Bending (TPB) tests, respectively. From the powdered X-ray diffraction (XRD) analysis, the sandstone material mineralogical composition has 65.5% quartz, 27.6% kaolinite, 5.4% montmorillonite and 1.4% anatase. Similarly, the siltstone material mineralogical composition has 35% quartz, 53% kaolinite, 8% muscovite, 3% alunite and 1% other minerals.