VARIATION IN PYROLYSATE COMPOSITION OF SEDIMENTS FROM THE JURASSIC WALLOON COAL MEASURES, EASTERN AUSTRALIA AS A FUNCTION OF THERMAL MATURATION

Examination of a natural maturity sequence from the Jurassic Walloon Coal Measures by quantitative flash pyrolysis-gas chromatography (Py-GC) and low temperature sealed tube pyrolysis reveals systematic changes in pyrolysate composition. In particular, gas to oil ratios, composition of gas and liquid normal hydrocarbons, aromatic and heteroatom content are examined for this immature oil prone rock as it is taken artificially and naturally through the oil window. Liquid hydrocarbon generation, giving a product with a high wax content, is shown to occur over a relatively narrow range of maturation. Significant quantities of gas are generated and the gas to oil ratio remains relatively constant during the main phase of oil generation. This reflects a uniform distribution of oil and gas precursors in the original labile kerogen. At higher rank, where increasing generation from the residual refractory kerogen occurs there is a progressive decrease in the yield of liquid hydrocarbons concomitant with an increase in the gas to oil ratio.