Poland Shale Gas/Oil Play: Integrating Old and New Disciplines to Interpret Unconventional Resource Potential of an Early Paleozoic Source Rock
Hardy, Martine J.1; Davis, Cara L.2;
Kaufman, Jon 1; Molyneux, Stewart G.3; Klimentidis,
Robert E.2; Ferguson, Innes J.1
(1)Exploration, ExxonMobil International Ltd, Leatherhead, United Kingdom. (2) ExxonMobil Upstream Research Company, Houston, TX. (3) Centre for Biostratigraphy, British Geological Survey, Nottingham, United Kingdom.
Poland has recently experienced increased exploration activity associated with an emerging shale gas/oil play developed in thick Upper Ordovician to Lower Silurian shales. The prospective section is part of the southwestern margin of Baltica (East European Platform). ExxonMobil has acquired a large acreage position to test the potential of the play. As part of this evaluation, reservoir and source studies were performed on samples from an extensive collection of conventional core archived in Poland.
Eighty samples were analyzed for palynology, bulk organic and inorganic geochemistry (total organic carbon, Rock Eval pyrolysis, XRD mineralogy, elemental analyses), and GRI porosity / matrix permeability. A subset of samples were selected for advanced biomarkers characterization and nanometre-scale pore imaging using SEM on BIB- (Broad Ion Beam milling) prepared samples.
Relative distance to shore, expressed as paleo-water depths, were interpreted from palynological assemblages. Integrating palynological results with organic geochemistry allowed classification of source facies from restricted shallow marine (excellent oil-prone) to open marine (good gas-prone and poor oil-prone) to deep marine (poor gas-prone). Molecular signatures of solvent extracts and pyrolyzates contribute to interpreting source facies and character of generated hydrocarbons. These were consistent with deposition of primitive marine algae in dysoxic conditions, either as algal bloom or dispersed organic matter.
Shale matrix mineralogy, porosities, and permeabilities have thus far not been linked to source facies or level of thermal maturation. However, SEM imaging revealed nanometer-scale pore architecture comprising voids in select organic matter clasts, as well as intercrystalline and intracrystalline pore networks in the mineral matrix. On-going research is examining the relationship between mineral and organic elements.
The integration of palynology with modern rock characterization techniques is a significant advance in the resource evaluation of early Paleozoic source. Despite the paucity of land plants in the Ordovician / Silurian, marine source rocks have the hydrocarbon potential of being both oil-prone, as expected for such rocks, and gas-prone of primary generation. Areal and stratigraphic variations in source rock quality may exert a major control over “sweetspot” development in the play.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.