Potential structures for CO₂ geological storage in the Baltic Sea: Case study offshore Latvia

This study is focused on two structures in the Baltic offshore region (E6 and E7 structures in Latvia) prospective for the geological storage of carbon dioxide (CO 2 ). Their CO 2 storage capacities were estimated recently with different levels of reliability. Petrophysical, geophysical, mineralogical and geochemical parameters of reservoir rocks represented by quartz sandstones of the Deimena Formation of Middle Cambrian in two wells and properties of Silurian and Ordovician cap rocks were additionally studied and interpreted in the present contribution. Extended methodology on rock measurements and estimation of conservative and optimistic storage capacity are presented. Uncertainties and risks of CO2 storage in the offshore structure E6 estimated as the most prospective for CO2 geological storage in the Baltic Region, and the largest among all onshore and offshore structures studied in Latvia, were discussed. We re-estimated the previous optimistic capacity of the E6 structure (265–630 Mt) to 251–602 Mt. Considering fault system within the E6 structure we estimated capacity of two compartments of the reservoir separately (E6-A and E6-B). Estimated by the optimistic approach CO2 storage capacity of the E6-A part was 243–582 Mt (mean 365 Mt) and E6-B part 8–20 Mt (mean 12 Mt). Conservative capacity was 97–233 Mt (mean 146 Mt) in the E6-A, and 4–10 Mt (mean 6 Mt) in the E6-B. The conservative average capacity of the E6-B part was in the same range as this capacity in the E7 structure (6 and 7 Mt respectively). The total capacity of the two structures E6 and E7, estimated using the optimistic approach was on average 411 Mt, and using the conservative approach, 159 Mt