Geophysical well log-motifs, lithology, stratigraphical aspects and correlation of the Ordovician succession in the Swedish part of the Baltic Basin

Abstract

The geophysical characteristics of the carbonate-dominated Ordovician succession is described using wire-line logging data from exploration wells located within the Swedish part of the Baltic Basin, both offshore and from the island of Gotland. The petrophysical properties and log-motifs are compared and correlated with the lithology of cores from the Hamra-10, Skåls-1 and Grötlingbo-1 wells on southern Gotland. The 80-125-m-thick Ordovician succession is divided into five log stratigraphic units O a-O e , which are correlated throughout the study area. The proposed log stratigraphy and wire-line log characteristics are evaluated and compared with the established Ordovician stratigraphy from the adjacent areas of Öland, Östergötland and South Estonia. The newly established log stratigraphy is also linked to the existing seismic stratigraphic framework for the study area and exemplified with a selection of interpreted seismic type sections from Gotland and the south Baltic Sea. The presented characterization, division and correlation provide a basis for understanding the lateral and vertical variation of the petrophysical properties, which are essential in assessing the sealing capacity of the Ordovician succession, in conjunction with storage of CO 2 in the underlying Cambrian sandstone reservoir.