AAPG Middle East Region GTW, Regional Variations in Charge Systems and the Impact on Hydrocarbon Fluid Properties in Exploration

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Petroleum (Hydrocarbon and Non-Hydrocarbon) Composition: Current Modeling Capabilities and Future Needs


Prior talks in Session 1 by Pepper and Laigle et al proposed a methodology integrating source rock Organofacies, organic richness and hydrogen index together with the individual layering and internal architecture of the source bed, and showed how this can lead to more realistic mapping of source bed UEP (UEO, UEG); and calculated volumes and compositions expelled from OM in source beds. These compositions can in turn be used to calculate important fluid properties, as we show using the Shaikan field in northern Iraq. However, a number of important processes are not yet in the mainstream modeling capability: • Modeling gas composition and isotopes. Models of isotopic composition are largely empirical - divorced from fundamentals. Four origins of gas - three occurring in OM and one in the reservoir fluid need to be modeled. We show a new, preliminary model (and a poster is available) • Current models of volume and composition are for the most part calibrated on pyrolysis hydrocarbon measures and so are limited to predicting hydrocarbon volumes and compositions. Generation and expulsion of [HC+NSO] compounds in resin and asphaltene fractions is not yet explicitly modeled. • Examples from Pakistan and the Williston and Permian basins of the US to show the importance of non-hydrocarbons in the viability of gas plays, the most volumetrically significant being H2S, CO2, N2. We need better capability to predict non-hydrocarbons gases • Mineral-fluid interactions are still not part of our models, for example in the Smackover Formation of the US Gulf Coast, H2S from TSR depends on magnesium in dolomite to proceed • Water-fluid interactions: most petroleum compounds can be (conveniently) considered insoluble in water. Geochemists have appealed to water washing of oils but for the most part the most soluble light aromatic components (BTX) are dense and in many cases the effect will be to increase - not decrease - API gravity. The more important impact on reservoir fluid properties such as compressibility and viscosity comes from the removal of solution gas in aquifer water. We show examples from Iraq and Cano Limon in Colombia.