Lithofacies analysis and heterogeneity study of the subsurface Rhaetian-Pliensbachian sequence in SW Skåne and Denmark

Abstract: The geological setting of Skåne is the outcome of successive phases of transtensional tectonics, block-faulting, subsidence, transpression and inversion focused around the Sorgenfrei-Tornquist Zone. The Höllviken Halfgraben is one of the major blocks in southwestern Skåne with a Rhaetian–Pliensbachian succession characterized by interbedding of arenaceous and argillaceous facies of local and regional extent. This study aims at analysing the heterogenous Rhaetian–Pliensbachian strata and is part of a major project focused on assessing the suitability of this succession for CO2 storage and/or geothermal energy production. Investigation of the lithofacies distribution has been done using Gamma Ray, Self Potential, Resistivity, Sonic, Neutron and Density data from 11 Swedish and Danish boreholes. Five boreholes have been selected for a northwest–southeast transect that is interpreted in a sequence stratigraphic approach supported with outcrop data from Kulla Gunnarstorp and Norra Albert, the Höllviken-2 core, and sidewall cores from the FFC-1 well. The study presents an eustatically controlled Rhaetian deposition and a tectonically controlled Hettangian–Pliensbachian deposition. A generally transgressive sequences dominate the Rhaetian–Pliensbachian succession. A distinctive similarity between the Rhaetian–Pliensbachian succession in southwestern Skåne and northwestern Skåne, though some differences in the relative sea level fluctuation occur during the Hettangian–Sinemurian owing to differential subsidence. Moreover, the Rhaetian–Pliensbachian succession in the Höllviken Halfgraben shows a dominance of fine-grained facies, and thus rendered less favorable conditions for geothermal water production. However, the succession is proved convenient for CO2 storage having adequate porosities (>20%), enough permeability (>100 mD), occurring at a depth of more than 800 m and sealed by tight claystone layers.