Habitat and hydrocarbon potential of the lower Paleozoic source rocks in the Polish part of the Baltic region

The quantity, genetic type and maturity of organic matter dispersed in the Lower Cambrian to the uppermost part of the Silurian (Pridoli) sequence of the Polish part of the Baltic region was determined based on the results of geochemical analyses of a total of 1377 rock samples collected from 38 onshore and offshore boreholes. The best source rocks were found in the Upper Cambrian-Tremadocian succession where present and initial total organic carbon (TOC) contents are up to ca. 18 and 20 wt.%, respectively. Caradocian (Ordovician) strata can be considered as an additional source of hydrocarbons. In the individual boreholes median present and initial TOC contents vary from 0.5 to 3.3 wt.% and from 1 to 6 wt.%, respectively. The Llandovery (Silurian) strata reveal moderate and locally high hydrocarbon potential of the source rocks. The present TOC content reaches locally 10 wt.% (usually 1-2 wt.%). Another source of hydrocarbons can be clayey intercalations within the Middle Cambrian strata. Their organic matter content rarely exceeds 1 wt.%, being often a result of advanced organic matter transformation. In all lower Paleozoic strata investigated from the Polish part of the Baltic region oil-prone, low-sulphur Type-II kerogen occurs, deposited in anoxic or sub-oxic conditions. The maturity of all source rocks changes from the initial phase of the low-temperature thermogenic processes in the northeastern part to the overmature stage in the southwestern part of the study area.