IMPACT OF METHANE ON CARBON DIOXIDE SEQUESTRATION WITHIN MULTISCALE AND HIERARCHICAL FLUVIAL ARCHITECTURE

Geological heterogeneity affects flow and transport in porous media, including the migration and trapping patterns of carbon dioxide (CO₂) during both geological carbon sequestration (GCS) and CO₂-enhanced oil recovery. Such effects are only understood fundamentally through their relation to a hierarchy of aquifer heterogeneities over a range of scales. Thermodynamic phase behavior adds further complexity to this problem. For example, in the context of GCS, CO₂ is often injected into brine formations that may contain dissolved light hydrocarbons, such as methane (CH₄). Thus, the CO₂ sequestration problem easily becomes a multicomponent, multiphase displacement process in which CO₂ competes with other components such as CH₄ during dissolution. In this case, CH₄ is not dissolved and instead exsolves from the aqueous phase into a gaseous phase. This has important implications for the risk assessment of GCS projects. We show how the CH₄ and CO₂ transport in brine formations is controlled by different scales of heterogeneity and the associated spatial distribution of sedimentary facies types, and the resulting connectivity of high-permeability pathways across different scales of the sedimentary architecture. We use a three-dimensional digital model that was developed based on field studies of the hierarchy of fluvial forms within channel-belts of gravelly braided rivers. We will show the effects of facies-related capillarity and hysteresis processes on CH₄ and CO₂ fate and transport.