ZenToks Publication

Chapter 2

Petrographic Analysis of Kerogen Types and Their Depositional Environments: Implications for Oil and Gas Exploration

Abstract/Preface

Kerogen, the insoluble organic fraction of sedimentary rocks, represents the fundamental precursor to petroleum hydrocarbons and is critical to the generation of oil and natural gas. It forms through the progressive transformation of biological organic matter via early diagenetic processes and thermal maturation stages—collectively known as diagenesis and catagenesis—under conditions of increasing temperature and pressure over geological time (Peters et al., 2015; Mahlstedt & Horsfield, 2012). As such, kerogen serves as both a geochemical archive of past biological productivity and a predictive tool in hydrocarbon exploration.
The characterization of kerogen is central to evaluating the petroleum generation potential of source rocks. The type of kerogen present in a rock—classified broadly into Type I, II, III, and IV—controls not only the quantity but also the quality of hydrocarbons that may be generated. Type I kerogen, typically derived from lacustrine algal material, is highly hydrogen-rich and considered highly oil-prone. Type II kerogen, usually of marine planktonic origin, generates both oil and gas under appropriate thermal conditions. Type III kerogen, dominated by terrestrial woody material, is primarily gas-prone, while Type IV kerogen, composed largely of inert carbon, is non-generative and of little petroleum interest (Bohacs et al., 2010; Behar et al., 2017).