Abstract

The present study deals mainly with shale sandstone series in which the disseminated kerogen is mostly composed of land-derived debris. The organic matter characterization was performed by means of microscopic and chemical techniques. The kerogen maturity was assessed by microscopic studies, mainly using vitrinite reflectance measurements. Chemical properties of shale kerogens, as well as 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. For this purpose, oils properties were compared to the kerogen characteristics of shales interbedded with the impregnated sandstone reservoirs. This synthesis is documented in several case histories form New Zealand, Colombia, Australia, Indonesia, ...................

In low maturation stages (immature zone), dry gas with minor condensate is observed, whereas in higher maturity levels (oil window), wet gas with high paraffinic crudes are generally recorded. Pristane to n-C₁₇ ratios permit differentiation between immature (> 1.0) and mature (> 1.0) condensates i.e. intensively cracked crude oils. i-C₄ to n-C₄ ratios enable an adequate discrimination between gases produced with immature condensate (i-C₄/n-C₄ > 0.80) and those produced with high wax crudes or mature condensates (i-C₄/n C₄ > 0.80). Shallow depth condensates and their related gases have also been identified as immature fluids. Properties of some mature condensates are given as references.

This study should provide a maturity framework as a guide for oil – and gas – show prediction in shale-sandstone sequences containing landderived kerogen.