GEOCHEMISTRY OF LITHUANIAN OILS AND SOURCE ROCKS - A PRELIMINARY ASSESSMENT

A series of oils and potential petroleum source-rock samples has been analysed from exploration wells on-and offshore Lithuania. Despite the limited amount of data, the results indicate the possible existence o f partly-exhausted source rocks within the Cambrian succession. Furthe rmore, possible source rocks are present within the Ordovician success ion, and excellent source rocks occur within the Silurian in several w ells. The source rocks are all present within a few hundred metres of stratigraphic succession and the thermal maturity roughly follows the actual depth of burial, despite the fact that most of the subsidence a nd maturation took place in the latest Palaeozoic. The most important reservoir rocks are Middle Cambrian sandstones, but petroleum accumula tions also occur in Ordovician limestones and Silurian reefal carbonat es. Petroleum accumulations in Lithuania probably result from the pool ing of oil derived from several sources, with the Lower Silurian (Llan doverian) shales being the most important single contributor.