Predicting CO2 storage performance in heterogeneous shallow marine reservoirs through integrated depositional and diagenetic controls

The successful geological storage of CO2 in heterogeneous shallow marine reservoirs at greater depths requires a predictable subsurface characterization. The integrated core-based analysis in this study examines the CO2 storage potential of the Cretaceous Lower Goru Formation, a proven gas-producing reservoir, as an analog and highlights how sedimentary systems with hydrocarbon potential can be reused as CO2 storage sites. The high porosity at depths greater than 3000 m is preserved by early chlorite rims and is restricted to medium-coarse-grained sandstones of proximal delta front settings. Chlorite coatings and quartz cementation control porosity preservation, injectivity, and fluid flow behavior at greater depths in these reservoirs. The transgressive unit above and the lower shoreface underlying are pervasively cemented, forming top and bottom seals that demonstrate long-term containment. The high storage capacity and injectivity are confined to chlorite-coated delta front settings. There is a systematic downdip transition from high storage capacity to saline and tight lower shoreface deposits, significantly impacting storage inactivity and containment. The discontinuous and thin chlorite rims create low-permeability intra-reservoir barriers that further complicate the predictive modeling. The secure and efficient geological storage of CO2 in these deeply buried depleted reservoirs relies on mapping the chlorite fairway and taking into consideration intra-reservoir-scale heterogeneity. The integrated workflow suggests predicting CO2 plume behavior, capacity, and storage depends on first reconstructing the depositional settings and then mapping their diagenetic imprints, a workflow essential for de-risking CO2 storage in complex shallow marine systems worldwide.