Abstract
Injection of CO2 into the subsurface requires consideration of the poromechanical behavior of reservoir rock saturated with aqueous fluid. The material response is usually assumed to be elastic, to avoid consideration of induced seismicity, or viscoelastic, if long-term deformations are needed to be taken into the account. Both elastic and viscous behavior may be influenced by the chemical reactions that are caused by the acidic mixture formed as high-pressure CO2 enters the pore space saturated with aqueous fluid. In this study, we conduct laboratory experiments on a fluid-saturated porous rock - Berea sandstone, and evaluate its poromechanical properties. Subsequently, the specimens are treated with liquid CO2 for 21 days and the corresponding variations in their properties are determined. The constitutive model considering the elastic time-dependent behavior of porous rock is validated by comparing the measured and predicted specimen deformation. Presented data indicate that the effect of CO2 injection on the long-term response is more significant compared to the short-term response. It is suggested for the constitutive models that predict long-term reservoir behavior during CO2 storage to include not only the poroelastic response and its change due to treatment, but also the time-dependent deformation and its evolution caused by the changes in chemistry of the pore fluid.
Highlights
The primary purpose of geologic carbon storage (GCS) is to inject large volumes of CO2 into subsurface reservoirs sealed with low-permeable layers
During the CO2 injection, either in liquid or supercritical state, multiphysical processes may occur in the saturated reservoir as a result of overpressure, thermal stress, and chemical reactions caused by the high acidity of CO2 and aqueous fluid mixture [2, 3]
It becomes essential to properly understand the effect of CO2 injection on the mechanical behavior of reservoir rock and predict the associated deformations to evaluate the safety of the carbon storage operations [4]
Summary
The primary purpose of geologic carbon storage (GCS) is to inject large volumes of CO2 into subsurface reservoirs sealed with low-permeable layers. Considering the permanent time scale of carbon storage (up to thousands of years), the elastic response of reservoir rock must be examined for both short-term (poroelasticity) and long-term deformation (poroviscoelasticity) [5, 6]. The latter one is characterized as the elastic time-dependent behavior of Despite the existing studies on the poromechanical response of reservoir rock, there is a lack of consistent understanding of the effect of CO2 treatment on both poroelastic and poroviscoelastic behavior of silica-rich rock. The volume strain rate can be decomposed into elastic and viscoelastic parts (Equation 1) and expressed through the increments of mean stress and pore pressure and the poroviscoelastic parameters (Equation 2)
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