Sedimentary Biomarkers and Their Stable Isotope Proxies in Evaluation of Shale Source and Reservoir Rocks

Abstract

Organic-matter present in shales is the source of gaseous hydrocarbons and its quantity and quality determines the gas generative capacity of the rock. It is represented by the total organic carbon (TOC) content. There exist two important organic fractions, the kerogen, which amounts to the bulk of organic-matter (~80–90%), and the second are the free molecules of lipids ‘the biomarkers’ (10–20%), which include the hydrocarbons and related compounds. The molecular compositions and stable isotope signatures determined using organic and isotope ratio mass spectrometry provide important attributes of the organic-matter such as organic richness, type and thermal maturity. This chapter presents an account of the minor fraction of the sedimentary organic carbon content, the biomarkers, its origin and occurrence in shale source and reservoir rocks, the transformations that occur with successive burial, its isotopes and the crucial information provided on the organic-matter provenance (source), depositional environment and thermal maturity along with the contemporary analytical approaches for its characterization.