Properties of gases and petroleum liquids derived from terrestrial kerogen at various maturation levels

This study deals mainly with shale-sandstone series in which the disseminated kerogen is mostly composed of land-derived debris. Organic matter was characterized by microscopic and chemical techniques. The kerogen maturity was assessed by microscopic studies, mainly by means of vitrinite reflectance measurements. The chemical properties of shale kerogens and of oil and gas shows, were examined in several sedimentary basins in different parts of the world.Oil and gas properties were tentatively interpreted in terms of maturity, using a comparison of oil properties with the kerogen features of shales interbedded in the impregnated sandstone reservoirs. The synthesis is documented in several case histories including those from New Zealand, Colombia, Australia, Indonesia.In low maturity stages (immature zone), dry gas with minor condensate is observed, whereas in higher maturity levels (oil window), wet gas with high paraffinic crudes is generally recorded. Pristane to n-C₁₇ ratios allow a distinction to be made between immature (often > 1.0) and mature (< 1.0) condensates, i.e. intensively cracked crude oils. I-C₄ to n-C₄ ratios enable an adequate discrimination to be made between gases produced with immature condensates ($\text{i-C}{}_4\text{n-C}{}_4\text{> 0.80}$) and those produced with high wax crudes or mature condensates ($\text{i-C}{}_4\text{n-C}{}_4\text{< 0.80}$). Shallow depth condensates and their related gases have been identified as immature fluids. Properties of some mature condensates are given as references.This study offers a maturity framework as a guide for oil and gas show prediction in shale-sandstone sequences containing land-derived kerogen.