Question

Advancements in source rock technology and geochemical software in petroleum geochemistry and exploration

Answer 1

Organic matter is isotopically heterogeneous. Lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite. The C and H isotopic composition of kerogens is determined by many factors, such as environmental conditions during formation and deposition and variability of sources of organic matter. Stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition. Isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction. A basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the Toarcian of Central Europe. Coals are isotopically heterogeneous due to different isotopic composition of macerals. Inertinite and vitrinite tends to be enriched in deuterium as compared to exinite. Also Boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials. Petroleums can be genetically classified through the patterns of covariance of their compound classes. Carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content. The general, world-wide applicability of such genetic differentiations needs still to be proved. Carbon and hydrogen isotope variations in methane are genetically controlled. Bacterial methane in freshwater environments is characteristically depleted in deuterium. Even complex origins of natural gases can be unraveled using compositional and isotopic variations. New analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration. A discussion reveals that processes such as isotope effects during degassing and bacterial oxidation, as well as indigenous formation of hydrocarbons, may completely obscure the results.