Elastic, Viscoelastic, and Permeability Response of Kentucky Sandstone in the Presence of scCO2

ABSTRACT: We performed a series of hydrostatic and triaxial creep experiments on a Kentucky Sandstone sample using 1% NaCl brine as the pore fluid, before and after interaction with supercritical carbon dioxide (scCO2). We conducted the hydrostatic creep tests at three different pore pressures of 10, 20, and 30 MPa and three different effective stresses of 10, 20, and 30 MPa at each pore pressure, in both loading and unloading conditions. The triaxial creep tests consisted of two levels of pore pressures of 10,20 MPa, under the same confining pressure and differential stress. The bulk moduli showed strong and weak dependency on effective stress and pore pressure, respectively. As expected, creep deformation was notably larger in the triaxial tests compared to hydrostatic tests, which led to an increase in Young's modulus and a gradual loss of permeability during the triaxial tests. After interaction with scCO2, we observed a significant increase in permeability, a significant decrease in Young's modulus, and a modest increase in bulk modulus. Moreover, the triaxial creep deformation was larger after interaction with scCO2. 1. INTRODUCTION Geological carbon storage has been proposed by many as one of the solutions to the issue of climate change, and as a bridge to transition from hydrocarbon production to renewable and clean geo-resources (Bouckaert et al., 2021). Storage of large volumes of CO2 can be achieved in porous sandstone formations, either in depleted hydrocarbon reservoirs or saline aquifers. However, there are some considerations when CO2 is injected into these sandstone formations (Orr, 2009). The role of geomechanics has often been neglected when the interplay between mechanical and transport characteristics of depleted reservoirs that are then repressurized with CO2 is considered. In particular, how the injection-induced change in the state-of-stress would affect the (i) mechanical (elastic) characteristics of the reservoir over shorter time periods, and (ii) transport characteristics (i.e., permeability) of the reservoir over longer time periods.