Petroleum families in the Baltic Sea Basin: Source rock-oil correlations

Petroleum in Lower Palaeozoic rocks including Ordovician carbonate mounds and Cambrian sandstones is known from southern Scandinavia, northern Poland and the Baltic States. According to Sivhed (2004), around 100,000 cubic metres of oil was produced on Gotland from 1972-1992, and currently new wells are being drilled by Gripen Gas&Oil. Oil produced from early Palaeozoic reservoirs in the Baltic basin share many similarities and the accumulation process appears to be very complex as there is no definite answer about the main contributing source rock.

Key questions regarding the oil-source correlation in Baltic basin are:

  1. How heterogeneous is the oil potential and the oil composition of Palaeozoic source rocks -especially within the Alum shale- which increase in thickness towards the south-western part of the basin (over 100meters).
  2. Which significance have controls like ,e.g., difference source contribution, migration fractionation and biodegradation on the produced oil?
  3. Which key signals can be extracted to relate the petroleum to its early Palaeozoic source rocks which are all marine shale with type II kerogen? 

The PhaseKinetic approach which includes a series of open- and close-system pyrolysis techniques provides a systematic way to evaluate the hydrocarbon generation properties of the source rocks. Besides GC-MS analysis on the biomarkers, FT-ICR MS which is very capable in identifying detail compositions of the oil is applied to screen the connection of source rock and oil in NSO compounds.

Goals:

  • to classify possible source rocks into different organic facies
  • to analyse biomarkers (GC-MS) and NSO compounds (FT-ICR-MS) dependent on the stratigraphically different source rocks
  • to correlate the produced oil from Ordovisian carbonate reservoirs to their potential main source rocks. 
The investigation area in the Baltic Sea region (left) and potential source rocks from the Lower Palaeozoic (right).

Participants:

  • Shengyu Yang
  • Hans-Martin Schulz
  • Brian Horsfield

Partners:

  • Gripen Oil and Gas, Sweden
  • Niels H. Schovsbo, Geological Survey of Denmark and Greenland.

Key publications:

  • Dahl, J., Chen, R., Kaplan, I., 1989. Alum Shale bitumen maturation and migration: Implications for Gotland’s oil. J. Pet. Geol. 2, 465–476.  
  • O. Zdanavikiute, Bojesen-Koefoed, J.A., 1997. Geochemistry of Lithuanian oils and source rocks: a preliminary assessment. J. Pet. Geol. 20, 381–402.
  • Sivhed, U., 2004. Upper Ordovician carbonate mounds on Gotland, central Baltic Sea: distribution, composition and reservoir characteristics. J. Pet. Geol.

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