Geology and hydrocarbon prospects of the Paleozoic in the Baltic region

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Abstract
Within the East Baltic region the main prospective area for hydrocarbons is the Peribaltic Depression (‘Baltic Syneclise’). Four sedimentary successions are developed, separated by major tectonic hiatuses. Total sedimentary thickness ranges from less than 1 km to over 8 km. Hydrocarbon occurrences are limited to the Paleozoic section where rich oil-prone source rocks are found. These contain TOC of 11–23% in the alum shale facies of the Cambrian, with 13% and 16% in the Ordovician and Silurian, respectively. Oil window maturity is reached on burial to 2000 m, with the main kitchen being in the Gdansk–Kura Depression. Main reservoir development is within Middle Cambrian sandstones, where porosities of 20–30% and permeabilities of a few Darcies are preserved. Fields are combined structural/stratigraphic traps associated with fold noses and fault blocks providing structural closure. Ordovician and Silurian carbonates contain abundant shows, with current limited production from the Swedish island of Gotland. These traps are associated with algal mudmounds draped by organic-rich clays. Most new prospects have been identified in the offshore Baltic Basin, where 35 wells have been drilled, resulting in the discovery of eight oil and gas fields, one of which is the largest found to date in the Baltic region.

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