The impact of heterogeneous mixed carbonate-siliciclastic systems on CO2 geological storage

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The impact of heterogeneous mixed carbonate-siliciclastic systems on CO2 geological storage
Azadeh Pourmalek1, Andrew J. Newell2, Seyed M. Shariatipour1, Adrian M. Wood3
Fluid and Complex Systems Research Centre, Faculty of Engineering, Environment and Computing, Coventry University, CV1 2NL
British Geological Survey, Maclean Building, Wallingford, OX10 8BB
School of Energy, Construction and Environment, Coventry University, CV1 2LT
Three different outcrops are selected in this study, each representing a shallow marine system with varying heterogeneity provided by carbonate-siliciclastic mixing that may form a small or large stratigraphic trap and contribute to secure CO2 geological storage. The impact of these styles of mixed facies on CO2 storage is relatively poorly known but may be an important factor in many target formations. The three 3D models are based on the: 1. Grayburg Formation (US), which displays spatial permeability linked to variations in the mixture of siliciclastic–carbonate; 2. Lorca Basin outcrop (Spain), which demonstrates the interfingering of clastic and carbonate facies; and 3. Bridport Sand Formation outcrop (UK), an example of a layered reservoir, which has thin carbonate-cemented horizons.
This study demonstrates the significance of these systems for safe CO2 geological storage, as stratigraphic traps are likely to be a significant feature of many future storage sites. It demonstrates that facies interplay and associated sediment heterogeneity have a varying effect on fluid flow, storage capacity and security. In the Grayburg Formation, storage security and capacity are not controlled by heterogeneity alone but influenced mainly by the permeability of each facies (i.e., permeability contrast), the degree of heterogeneity, and the relative permeability characteristic of the system. In the case of the Lorca Basin, heterogeneity through interfingering of the carbonate and clastic facies improved the storage security regardless of their permeability. For the Bridport Sand Formation, the existence of extended sheets of cemented carbonate contributed to storage security but not storage capacity, which depends on the continuity of the sheets. These mixed systems specially minimize the large buoyancy force that act on the top seal and reduce the reliance of the storage security on the overlying caprock. They also increase the contact area between injected CO2 and brine, thereby promoting the CO2 dissolution processes. Overall, mixed systems contribute to the safe storage of CO2.
Original languageEnglish
JournalPetroleum Geoscience
Publication statusSubmitted - 2020

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