RESUMO
Understanding the spatial variation in lithology is crucial for characterizing reservoirs, as it governs the distribution of petrophysical characteristics. This study focuses on predicting the lithology of carbonate rocks (limestone, argillaceous limestone, marly limestone, and marl) within the Kometan Formation, Khabbaz Oil Field, Northern Iraq, using well logs. Precise lithology prediction was achieved by applying multivariate regression method on neutron, sonic, and density logs. Gamma-ray and elemental concentrations from bulk-rock X-ray fluorescence spectroscopy were employed to identify clay minerals, paleoenvironments, and quantify the shale content. The results indicate that the Kometan Formation predominantly comprises limestone, marl, marly limestone, and argillaceous limestone in the middle section. The middle part exhibits a higher shale content compared to the lower and upper parts. A statistically significant correlation (R2 = 0.83-0.85) between described and predicted lithology was established. The model with a higher coefficient of determination (0.85) was tested for further predictions in other wells in the Kirkuk Oil Field. This research can be valuable for lithological and petrophysical characterization of carbonate reservoirs and electrofacies analysis, particularly in situations where core data is unavailable.
RESUMO
A previous cultivation-independent investigation of the microbial community structure of natural oil and asphalt seeps in the Kurdistan Region of Iraq (KRI) revealed the dominance of uncultured bacterial taxa belonging to the phyla Deferribacterota and Coprothermobacterota and the orders Thermodesulfobacteriales, Thermales, and Burkholderiales. Here we report on a cultivation-dependent approach to identify members of these groups involved in hydrocarbon degradation in the KRI oil and asphalt seeps. For this purpose, we set up anoxic crude oil-degrading enrichment cultures based on cultivation media known to support the growth of members of the above-mentioned taxonomic groups. During 100-200 days incubation periods, nitrate-reducing and fermentative enrichments showed up to 90% degradation of C8-C17 alkanes and up to 28% degradation of C18-C33 alkanes along with aromatic hydrocarbons. Community profiling of the enrichment cultures showed that they were dominated by diverse bacterial taxa, which were rare in situ community members in the investigated seeps. Groups initially targeted by our approach were not enriched, possibly because their members are slow-growing and involved in the degradation of recalcitrant hydrocarbons. Nevertheless, the enriched taxa were taxonomically related to phylotypes recovered from hydrocarbon-impacted environments as well as to characterized bacterial isolates not previously known to be involved in hydrocarbon degradation. Marker genes (assA and bssA), diagnostic for fumarate addition-based anaerobic hydrocarbon degradation, were not detectable in the enrichment cultures by PCR. We conclude that hydrocarbon biodegradation in our enrichments occurred via unknown pathways and synergistic interactions among the enriched taxa. We suggest, that although not representing abundant populations in situ, studies of the cultured close relatives of these taxa will reveal an unrecognized potential for anaerobic hydrocarbon degradation, possibly involving poorly characterized mechanisms.
