Influence of small‐scale fluvial architecture on CO₂ trapping processes in deep brine reservoirs

Abstract

Abstract A number of important candidate CO 2 reservoirs exhibit sedimentary architecture reflecting fluvial deposition. Recent studies have led to new conceptual and quantitative models for sedimentary architecture in fluvial deposits over a range of scales that are relevant to CO 2 injection and storage. We used a geocellular modeling approach to represent this multiscaled and hierarchical sedimentary architecture. With this model, we investigated the dynamics of CO 2 plumes, during and after injection, in such reservoirs. The physical mechanism of CO 2 trapping by capillary trapping incorporates a number of related processes, i.e., residual trapping, trapping due to hysteresis of the relative permeability, and trapping due to hysteresis of the capillary pressure. Additionally, CO 2 may be trapped due to differences in capillary entry pressure for different textural sedimentary facies (e.g., coarser‐grained versus finer‐grained cross sets). The amount of CO 2 trapped by these processes depends upon a complex system of nonlinear and hysteretic characteristic relationships including how relative permeability and capillary pressure vary with brine and CO 2 saturation. The results strongly suggest that representing small‐scale features (decimeter to meter), including their organization within a hierarchy of larger‐scale features, and representing their differences in characteristic relationships can all be critical to understanding trapping processes in some important candidate CO 2 reservoirs.