The Jantar Shale.
he Jantar Formation is bituminous shale of the lower Llandovery (lower Silurian) age. The average TOC content of this shale in the Żarnowiec and Wejherowo concession blocks is relatively high, equal to 3-5 wt. %. Domination of the II type of kerogen, favourable for shale gas and oil systems, is observed, however, due to locally elevated oxygen index a development of kerogen type transitional between the II and the III is also identified. The high TOC content coeval with the high RockEval S1+S2, allows to qualify the shale as a good or very good source rock.
In the Żarnowiec and Wejherowo concession blocks the Llandovery shale has gross thickness of 40-65 m. However, the Jantar Shale represents it’s lower part only, and thus its net organic-rich interval thickness is in a range of 8-24 m, depending on location. In that zone the thermal maturity of the Jantar Formation is an equivalent of oil to condensate window. The high oil saturation index, often ranging between 100-200, indicate high shale oil potential.
The Jantar Formation is characterized by moderate to high brittleness. The formation is relatively rich in clay mineral, content of which is as high as 45-60 %. Quartz content is in a range of 25-35 %, while carbonate content does not exceed 10 %.
In the Baltic Basin, few oil/gas production tests were performed for the Jantar Shale, therefore the formation remains underexplored. In the Żarnowiec and Wejherowo concession blocks, the Jantar Shale reservoir is separated from the Sasino one by TOC-lean marls of thickness equal to 6-10 m only, therefore, the two formations have potential to be fractured together at one time.