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Wagner Ryszard, Polish Geological Institute (Poland)
Kotarba Maciej, AGH-Univeristy of Science and Technology (Poland)
Jaworowski Krzysztof, Polish Geological Institute (Poland)
Slowakiewicz Miroslaw, Polish Geological Institute (Poland)
Mikolajewski Zbigniew, Polish Gas and Oil Company (Poland)
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The search for hydrocarbon resources in the Zechstein Main Dolomite (Ca2) of Poland is continuing in more and more complex structural and geological conditions. The latest developments in technology and geological thought must be used to achieve successful exploration results. Besides using 3D seismic surveys to determine trapping geometries, the search for oil and gas must be targeted in the most prospective regions; that is in areas where source rocks directly neighbour reservoir rocks.
The latest interdisciplinary results of geological-petrological-sedimentological studies have helped to define precisely the basic genetic types of source rocks in the Ca2. The main source of organic matter was shown to be cyanobacteria with a minor algal component.
The studies were associated with an elaboration of the architectural of the Ca2 basin together with its basic elements such as lithological, sedimentological and palaeogeographical characteristics. Studies on cyanobacterial microstructures and trace elements related to life processes of algae and bacteria were done.
Geochemical analyses of Ca2 rocks were carried out, including pyrolytic Rock-Eval, biomarkers, stable isotope compositions and sulphur contents in kerogen. Results of lithofacies studies together with geochemical analyses of organic matter help to characterize in detail the maturity of the Ca2 strata and determine the position of mature intervals in the borehole cores studied. Using analytical geochemical studies of petroleum fluids (especially stable isotopes and biomarkers), their genetic identification and correlation with source rocks was possible.
Results of geochemical analyses of natural gases (stable isotope composition in methane, ethane, propane, butanes, and carbon dioxide, stable isotopes of hydrogen in methane) helped to identify gas genesis and to characterize a primary organic source substance (genetic type and state of transformation). Using one- (1-D) and two-dimensional (2-D) numerical models it was possible to reconstruct generation processes, expulsion and hydrocarbon migration over geologic time and to evaluate the volumes of hydrocarbons expelled for migration and, hence the possibility of their accumulations in potential traps in the study area. This is an important factor used for estimation of prognosed reserves. A new kinetic model of the Ca2 kerogen was worked out for 1-D and 2-D modelling of generation and expulsion processes based on analyses of sulphur contents in kerogen correlated with hydrous pyrolysis.
A complex elaboration of the Ca2 petroleum system, together with the determination of generation processes, timing, expulsion, migration and filling the traps, helped to estimate the petroleum and natural gas prospective resources. Integration of the aforementioned information and use of risk and uncertainty analyses helped to rank accumulation zones of hydrocarbons as a good reason for economical evaluation of future exploration works.
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