Genetic Correlations
Determining genetic petroleum families and their correlation with source rocks are critical to defining petroleum systems and interpreting the processes that are controlling the generation, migration and accumulation of petroleum within sedimentary basins. Geochemical parameters based predominantly on biomarker technology have been established to genetically correlate crude oils and their sources and aid in defining petroleum systems (see Peters et al., 2005). However, crude oil is not the only petroleum product exploited in sedimentary basin; condensates and gases are also significant. In order to more thoroughly and completely understand the dynamic petroleum processes operating within sedimentary basins, reliable and scientifically sound geochemical parameters are needed to perform (1) condensate-source rock and condensate-oil correlations, (2) gas-source correlations, and (3) identify and quantify mixing of genetically unrelated crude oils, natural gas and condensates. The absence of biomarkers in most condensates precludes the interpretation of the origin of condensates, correlation with sources and the identification of mixtures using established methods. Thus, new tools that integrate molecular and isotopic data to interpret source facies and mixing processes are required. Previous studies have attempted to decipher mixed petroleum systems (Peters and others, 1989; Jiang and Li, 2002; Chen and others, 2003) with some success. However, challenges remain due to the effects of maturity, source rock facies variation, secondary alteration, and migration fractionation. Currently, no established methodology exists to unequivocally differentiate these mixtures. The issue of differentiating crude oils that represent genetic end-members and varying mixtures is particularly important in determining total petroleum systems and their assessment units.
Gas-rich petroleum systems are receiving more attention, as natural gas becomes a more dominant component of our energy mix. Currently, characterizing natural gases is limited to molecular concentrations and stable isotopes of C1 to C5 hydrocarbons. Condensates commonly coexist with natural gases in many accumulations, but correlation of this type of petroleum with natural gases and crude oils to define petroleum systems and assessment units that are dominated by natural gas and condensate is in the early stages of development (Gurgey et al., 2005). Figure T4-1 (Gurgey et al. 2005) demonstrates how isotopic data can be used to correlate gases and condensates with oils. Integration of genetic molecular interpretations with this type of isotopic data will enhance petroleum system and process interpretation capabilities.
Migration distance/pathways, thermal maturity, and reservoir alteration can affect the geochemical parameters used to correlate natural gas, condensate, and crude oil to their source rock. A robust suite of geochemical parameter parameters that are not affected by these geological factors remains to be established to unequivocally determine the sources of genetically related natural gases, condensates, and crude oils of a petroleum system.
Figure T4-1: Correlation of condensates and gases with oils based on isotopic data (From Gurgey et al., 2005).
Determining genetic petroleum families and their correlation with source rocks are critical to defining petroleum systems and interpreting the processes that are controlling the generation, migration and accumulation of petroleum within sedimentary basins. Although a variety of geochemical parameters are currently available for correlating oils to oils and their source rocks, there is a definite need to establish geochemical parameters to correlate gas and condensate to one another and to their related oils and source rocks. Results from this research are essential in defining petroleum systems that are gas or oil dominated.
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