Effects of fluvial sedimentary heterogeneity on CO2 geological storage: Integrating storage capacity, injectivity, distribution and CO2 phases.

• An optimal amount of low-permeable layers can increase the swept area of CO 2 plume. • An optimal amount of low-permeable layers can reduce the ratio of CO 2 in free phase. • Proximal-medial fluvial lithofacies associations are more suitable for CO 2 storage. Fluvial system deposits often form suitable reservoirs for CO 2 geological storage (CGS). These potential storage sites usually present heterogeneous fluvial architectures at multiple scales. This heterogeneity can exert varied effects on different aspects of CGS, resulting in significant storage efficiency variability. Here, we investigate the effects of variable fluvial lithofacies associations on CO 2 storage, using the Puig-reig anticline in the SE Pyrenees (Spain) as a reservoir analog. To test this, we employ a multidisciplinary approach that integrates field sedimentology, reservoir modeling, and numerical simulation of CO 2 injection to produce models akin to different fluvial lithofacies associations. The storage volume and injectivity of CO 2 are found to decrease in reservoirs with decreasing fractions and sizes of high-permeable facies from the proximal to the medial-distal lithofacies associations. The flow barriers created by low-permeable facies can hinder the vertical migration of the CO 2 plume and prevent it from reaching the reservoir top, hence reducing the direct contact between the CO 2 plume and the overlying caprock. Furthermore, an optimal amount of low-permeable layers (around 30% in this study) can increase the swept area of CO 2 and reduce the proportions of free CO 2 phase. These aspects can collectively increase the amount of permanently trapped CO 2 and reduce the leakage risks of the injected CO 2. Based on the characteristics of the resulting models (i.e., storage volume, injectivity, distribution and phases of CO 2), a multi-criteria decision-making method has been used to quantitatively rank the different lithofacies associations according to their suitability for CO 2 storage. In this analysis, the proximal-medial fluvial lithofacies associations are assessed to be the most suitable ones because they feature low proportions of the injected CO 2 reaching the reservoir top and in free phase while maintaining the high storage volume and injectivity. This study reveals that heterogeneous reservoir architectures have mixed effects on CO 2 storage, and that reservoirs featuring moderately heterogeneous architectures (i.e., fractions of low-permeable facies ranging from 30% to 40%) are beneficial to keeping the balance among different aspects of CO 2 storage. This provides new insights for the screening and selection of potential geological sites for CO 2 storage. [ABSTRACT FROM AUTHOR]