The Piaśnica Foration.
The Piaśnica Formation of the upper Cambrian to Tremadocian age, is an lateral equivalent of the SW Scandinavian Alum Shale. This formation is characterized by very high TOC content, often in a range of 5 to 12 wt. %. Together with coeval high RockEval S1+S2, this qualifies the shale as good, very good or excellent source rock, depending on a location. The Piaśnica Shale is characterized by presence of the II type of kerogen, favourable for development of shale gas and oil accumulations.
Presence of organic-rich shale of the Piaśnica Formation in onshore Baltic Basin is limited to its northern part (northern Łeba Elevation), mainly to the Żarnowiec and Wejherowo concession blocks, and the area adjacent to the west. In that zone, the maximum onshore thickness of the Piaśnica Formation is documented, reaching up to 22 m. It decreases considerably westward, southward and eastward, and in the major part of the onshore Baltic Basin it is missing, and the upper Cambrian to lower Tremadocian is represented by hiatus. In the most prospective zone, the thermal maturity of the Piaśnica Formation varies from the equivalent of oil in the east, though the condensate window, to the dry gas window in the west.
The Piaśnica Formation is characterized by moderate brittleness. Mineralogical composition is variable, both laterally and in vertical section. Clay minerals, quartz and carbonates content is in a range of 20-40 %, 20-30 %, and 0-45 %, respectively. Locally very high pirite contents, exceeding 30 %, is observed.
The Piaśnica Formation is highly underexplored, from the shale oil/gas point of view. There was only one vertical well with single frac stage, and one horizontal multi-stage fractured well completed within this formation, although, the later one was mechanically junked. Therefore, the shale oil/gas potential of the formation still remains to be constrained.