Predicting the quantities of oil and gas generated from Australian Permian coals, Bowen Basin using pyrolytic methods

The aim of the study was to establish kinetic parameters for gas and oil generation and to test the applicability of the kinetic models to petroleum generation through comparisons with natural maturity coal sequences (433 degrees C < T-max < 547 degrees C; 0.53% < Ro < 2.59%) and field observations in the Bowen and Surat basins. From bulk pyrolysis and py-gc, the quantities and composition of coal-derived products have established that the 'oil window' is between 440 and 465 degrees C (0.7% < Ro < 1.2%). This compares favourably with the oil window defined using the chemical kinetics model (0.1 < TR < 0.5; 0.65-0.7% < Ro modelled < 1.05-1.2%) applied to the geohistory model as well as encompassing the range in chemical maturities of the oils (0.65 < Ro calculated < 1.05%) in the Bowen and Surat basins. Furthermore, field observations on gas maturity (1.05% < Ro calculated < 1.4%) support the kinetic predictions that the bulk of the gas generation mainly occurs after bulk oil generation. However, there are specific discrepancies that question the current kinetic treatment for coal and its ability to accurately predict petroleum generation in the subsurface. For example, the naturally matured coals are more oil prone, as a result of re-incorporation of H-rich volatile components into the coal matrix, compared with predictions from the immature analogue. Furthermore, cumulative GORs determined from modelling significantly underestimate GOR found for recoverable gas and oil from the Bowen and Surat basins. Here, uncertainties in the extent of gas and oil preservation arising from multiple phases of, petroleum generation during a complex burial history model may also be significant. (C) 1999 Elsevier Science Ltd. All rights reserved.