Title : Hydrocarbon exploration in different oil and gas basins
Abstract:
Some aspects of research on fluid inclusions (FI) in quartz cements and in the carbonates in the reservoir rocks in two areas have been discussed aiming at presentation of microscale search on hydrocarbons. The research areas comprise boreholes from N and Central Poland the Baltic Sea and the BMB regions. The analytical methods applied are those microscopic ones: fluorescence; microthermometry and CL analyses, SEM studies as well. Most studies were performed on double-sided polished sections prepared as the routine for the FI studies. Computer calculations and simulation followed the studies. Two types of inclusions have been distinguished in the sandstones in one borehole in the siliciclastic basin, while only one type in another. They are aqueous inclusions (AQFI) that occur at the boundary of detrital and authigenic quartz, in the early cement and in late filling of microfractures, and the hydrocarbon inclusions (HCFI) present in the late filling of the fractures. The HCFI show UV luminescence in colors from blue-white to yellow, while the AQFI do not fluoresce. Late cementation was connected with an increasing burial and fluids of more negative isotopic composition. Contrary to these results, the rocks in the cements in the second borehole contain only AQFI. That is the proof that there is no petroleum in this borehole, despite the similar petrographic characteristics. Carbonate deposits from the Main Dolomite horizon, often altered due to diagenesis, where the pore space has been filled by dolomite and anhydrite, were the study object in the second type of the basin. Standard petrological analysis was performed (Mo-1), wide fluid inclusion analyses and Rock-Eval determinations. In this case, based on the phase and fluorescence criteria, three types of FI have been distinguished: single phase not fluorescing, two phase not fluorescing and two phase fluorescing inclusions. These three types were further analyzed. The fluids distinguished are: oil, gas (methane with admixtures),and brine in different contents and mutual relations. The variation of fluids in the vertical column has been interpreted. The results may be interpreted in the context of fluid evolution and diagenesis of the studied rocks that is a step in the hydrocarbon exploration in the regions. The methodology of petrographic studies including fluid inclusions should be a standard in the search for oil and gas.
