The decomposition of posidonia shale and green river shale kerogens using microscale sealed vessel (MSSV) pyrolysis

Abstract

Microscale sealed vessel (MSSV) pyrolysis was used to simulate the compositional evolution of products generated from Posidonia Shale and Green River Shale kerogens with increasing maturity. Conversion was measured using a pseudo-Rock-Eval approach. Temperatures in the range 300–350°C and heating times between 1 and 10 days resulted in a 10–90% conversion of Posidonia Shale kerogen and 3–60% conversion of Green River Shale kerogen into volatile products. Single step GC analysis (C 1–C 30 range) revealed the presence of aliphatic hydrocarbons, aromatic hydrocarbons, sulphur-containing compounds and a complex mixture of unresolved components. The Posidonia Shale kerogen was inferred to have generated mainly heavy bitumen for all low temperature (300°C) experiments and for higher temperature experiments of short duration. At higher temperatures and longer heating times this material, possibly derived from alkyl-substituted naphthenoaromatic units in the kerogen, decomposed to yield products, detectable by gas chromatography, with an enhanced “gas to oil” ratio. Bitumen generated from Green River Shale appears to have a lower average molecular weight and/or polarity. Normal alkanes with a fixed chain length distribution were generated from what appears to be biopolymeric structures in both kerogen types.