Using stratigraphic heterogeneity to improve containment and capacity in thegeological storage of CO_2

摘要

Stratigraphic heterogeneities affect the migration flow paths of injected CO_2, and can be utilised to improve CO_2 geological storage containment and capacity. An example is presented from the Kingfish Field area in the Gippsland Basin, Australia. The potential injection targets are the sediments of the Paleocene-Eocene upper Latrobe Group, regionally sealed by the Lakes Entrance Formation. The sequence stratigraphic study suggests that there are several packages of sand separated by locally effective but regionally non-extensive intraformational seals, comprised of siltstones, shales and coals. The MICP analysis indicates that the intraformational seals have the potential to hold back an average CO_2 column height of 517 m. Thus, the interbedded siltstones and shales will behave as flow baffles and barriers that will hinder or slow vertical migration. Based on the structural geometry of the intra-Latrobe Group succession, CO_2 is predicted to migrate upwards and eastwards by a tortuous pathway created by the stratigraphic heterogeneity until it accumulates at the top of the Latrobe Group beneath the regional seal. The low permeability Gurnard Formation at the top of the Latrobe Group provides additional containment security by further slowing migration rates vertically and laterally and potentially promoting permanent mineralogical trapping of CO_2 through precipitation of ferroan carbonate minerals. Numerical simulation models verified how stratigraphic heterogeneities create localised traps throughout the stratigraphy, which allow more time for dissolution into the formation water and geochemical reactions to take place, and by reducing the effective vertical permeability create a more tortuous migration pathway for injected CO_2, resulting in greater CO_2 storage via residual gas trapping. These effects all increase the potential CO_2 storage capacity and containment security, and should be considered when devising injection scenarios to optimise the geological CO_2 storage process.