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

Abstract

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 CO 2 storage in the offshore structure E6 estimated as the most prospective for CO 2 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 CO 2 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.

Experimental modeling of CO2‐fluid‐rock interaction: The evolution of the composition and properties of host rocks in the Baltic Region

“…These two rock samples have similar geochemical properties. Samples E6‐1 and E6‐3 were selected from two different depth intervals of the well E6‐1/84 (Table ), characterized by various lithological and petrophysical properties [ Shogenov et al ., ]. Sample E6‐2 (from the same depth as sample E6‐3) showed an increase in effective porosity and, contrary to E6‐3, petrophysical alterations after the experiment, thus proving the influence of rock heterogeneity on the obtained results.…”

“…Three‐dimensional geological models of the top of the Cambrian Series 3 Deimena Formation with location of the studied wells are shown (modified after Shogenov et al . [, ]).…”

“…Four geological structures, located onshore (South Kandava and Dobele) and offshore Latvia (E6) and Lithuania (E7) and serving as prospective CGS sites in the Baltic Region (Figure ), were previously described in detail by Shogenov et al . [, ]. All the studied structures are situated within the tectonically dislocated Liepaja‐Saldus zone of highs (Figure ).…”

“…The deepest Deimena Formation rocks occur in the offshore E7 structure (Figure ). This structure is also characterized by the highest temperature of 46°C and water salinity of 125 g/L [ Shogenov et al ., , ]. The shallowest offshore structure E6 shows a lower temperature (36°C) and the lowest salinity of Cambrian fluids (99 g/L).…”

“…The selected structures have an average porosity of 12–21%, permeability of 40–360 mdarcy, and mean reservoir thickness of 42–58 m. The average CO 2 storage potentials (conservative‐optimistic) of the Dobele, South Kandava, E7 and E6 structures were, respectively, 20–106, 25–95, 7–34, and 152–377 Mt. We estimated the E6 offshore structure as the largest suitable trapping structure prospective for CGS offshore Latvia with the highest CO 2 storage capacity [ Shogenov et al ., , ]. Based on unpublished exploration report data, stored in Latvian Environmental, Geology and Meteorology Centre (LEGMC), we have treated E7 as a Latvian offshore structure in our earlier publications.…”