Some Predicted Effects of Minerals on the Generation of Petroleum in Nature

The presence of some minerals can strongly influence the composition of laboratory pyrolysates. The question is whether similar effects may also occur in nature, thereby influencing, the gas-oil ratio and other bulk compositional characteristics. A series of experiments have been conducted at varying heating-rates to examine this issue. Three source rocks that vary significantly in mineralogy (a quartz-rich, a calcite-rich, and a clay-rich sample), namely, the Alum shale, Bowland shale, and Toolebuc oil shale, respectively, were tested by Rock-Eval pyrolysis, open-system pyrolysis gas chromatography (PyGC). and bulk kinetic parameters to check for the existence or otherwise of mineral matrix effects (MMEs). Kerogen and whole-rock samples were then pyrolyzed at three heating rates using closed-system [microscale sealed vessel (MSSV)] pyrolysis to examine the heating rate dependency upon hydrocarbon aromaticity, gas-oil ratio, and total yield. The solvent extract of one Bowland shale sample was used as a reference material for the natural system when extrapolating the results from laboratory experiments to nature. A comparison of the natural reference sample with kerogen and whole-rock pyrolysates using, Fourier transform ion cyclotron resonance mass spectrometry was also made, providing insights into NSO compounds in laboratory and natural environments. The MME in Alum shale, Toolebuc oil shale, and Bowland shale has negligible, weak, and strong influences on Rock-Eval, PyGC, and bulk kinetic results, respectively. MMEs on the hydrocarbon aromaticity total yield are heating-rate dependent; with decreasing heating rates, the effect is weakened. Bowland kerogen pyrolysate resembles natural products more in certain NSO class ratios compared with its whole-rock counterpart. The MME is speculated to be induced by the fast heating rates and higher temperatures in the laboratory, and it is concluded that the effects do not occur in the geological maturation process.