CO2 trapping in reservoirs with fluvial architecture; sensitivity to heterogeneity and hysteresis in characteristic relationships for different rock types

A number of important candidate CO (sub 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 (sub 2) injection and storage, led to new geocellular modelling approaches for representing this architecture, and led to new computational studies of CO (sub 2) plume dynamics during and after injection. The processes of CO (sub 2) trapping depend upon a complex system of non-linear and hysteretic characteristic relationships including how relative permeability and capillary pressure vary with brine and CO (sub 2) saturation. New computational studies of capillary trapping in conglomeratic reservoirs strongly suggest that representing small-scale (decimeter to meter) textural facies among different rock types, including their organization within a hierarchy of larger-scale stratification, representing differences in characteristic relationships between rock types, and representing hysteresis in characteristic curves can all be critical to understanding trapping processes. In this context, CO (sub 2) trapping was evaluated in conglomeratic reservoirs with fluvial architecture including different rock types with different and hysteretic characteristic curves and with capillary pressure defined for each rock type using two different conventional approaches, i.e. Brooks-Corey and van Genuchten. The results show that in these reservoirs the capillary trapping rates are quite sensitive to differences between the Brooks-Corey and van Genuchten approaches, and that heterogeneity and hysteresis in characteristic relationships must both be represented in either case.