CAPACITY INVESTIGATION OF BRINE-BEARING SANDS FOR GEOLOGIC SEQUESTRATION OF CO_2

摘要

The capacity of brine-bearing formations to sequester carbon dioxide (CO_2) is investigated using mathematical modeling of CO_2 injection and storage. CO_2 is injected in a supercritical state that has a much lower density and viscosity than the brine it displaces. In situ, it forms a gas-like phase, and also partially dissolves in the aqueous phase. The capacity factor is defined as the volume fraction of the subsurface available for CO_2 storage and is conceptualized as a product of four factors that account for 1) two-phase flow and transport processes, 2) formation geometry, 3) formation heterogeneity, and 4) formation porosity. The key properties that impact the capacity factor include permeability anisotropy and relative permeability, brine/CO_2 density and viscosity ratios, brine salinity, the shape of trapping structure, formation porosity, and the presence of low-permeability layering. The space and time domains used to define capacity factor must be chosen carefully to obtain meaningful results. Often, there is no unique choice for the volume on which to base the capacity factor. One possible convention is to define a dynamic capacity factor that makes use of the self-similar nature of the Buckley-Leverett solution for the propagation of the CO_2 front away from the injection well.