Abstract
CO2-foam injection is a promising technology for reducing gas mobility and increasing trapping within the swept region in deep brine aquifers. In this work, a consistent thermodynamic model based on a combination of the Peng-Robinson equation of state (PR EOS) for gas components with an activity model for the aqueous phase is implemented to accurately describe the complex phase-behavior of the CO2-brine system. The phase-behavior module is combined with the representation of foam by an implicit-texture (IT) model with two flow regimes. This combination can accurately capture the complicated dynamics of miscible CO2 foam at various stages of the sequestration process. The Operator-Based Linearization (OBL) approach is applied to improve the efficiency of the highly nonlinear CO2-foam problem by transforming the discretized nonlinear conservation equations into a quasi-linear form based on state-dependent operators. We first validate our simulation results for enhanced CO2 dissolution in a small domain with and without the presence of a capillary transition zone (CTZ). Then a 3D unstructured reservoir is used to examine CO2-foam behavior and its effects on CO2 storage. Simulation studies show good agreement with analytical solutions in both cases with and without CTZ. Besides, the presence of a CTZ enhances the CO2 dissolution rate in brine. Foam simulations show that foams can reduce gas mobility effectively by trapping gas bubbles and inhibit CO2 from migrating upward in the presence of gravity, which in turn improves the sweep efficiency and opens the unswept region for CO2 storage. In the long run (post-injection), with the increasing effects of dissolution, the mechanism of residual trapping, due to the presence of foam, may not be significant. This work suggests a possible strategy to develop an efficient CO2 storage technology.
Highlights
Due to various anthropogenic activities, the concentration of carbon dioxide (CO2) in the atmosphere is having significant and observable effects on the environment
We investigate the behavior of the CO2 plume with brine-assisted and foam-assisted CO2 injection, including the plume footprint, the amount of CO2 dissolved and resid ually trapped, storage capacity and efficiency using an unstructured 3D reservoir with homogeneous properties
Elenius et al (2012, 2014) investi gated the full problem of two-phase flow with gravity currents and convective dissolution in the absence and presence of the capillary transition zone (CTZ), and these results can be used as a benchmark for verification of our simulation approach
Summary
Due to various anthropogenic activities, the concentration of carbon dioxide (CO2) in the atmosphere is having significant and observable effects on the environment. This effect causes very poor sweep efficiency of CO2 (i.e., lowering storage capacity) These issues can be overcome or minimized by reducing gas mobility and increasing trapping within the pore space of the swept region. The implicit-texture (IT) model (CMG-STARS, 2012) used in this study as sumes that foam generation and destruction reach a local steady-state instantaneously and represents the effect of foam bubbles implicitly by introducing a mobility-reduction factor This mobility-reduction factor, used to rescale gas mobility with foam, is a function of water saturation, oil saturation, surfactant concentration, capillary number and salinity. To accurately simulate these highly nonlinear coupled foam-assisted CO2 storage processes, a new approach, named Operator-Based.
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