PYROLYSIS DERIVED MOLECULAR INDICATORS FOR THE THERMAL ALTERATION OF OIL: POTENTIAL MATURITY AND GOR INDICATORS?

Determining the thermal maturity of oils and condensates, in particular, can be difficult. Biomarker indicators are well studied and extremely useful for oils, but have limited usefulness for condensates. Confined, dry pyrolysis laboratory experiments of a saturate-rich Devonian oil were performed at T=350°C to 400°C, P=650 bars and times ranging from 3 to 33 days, vitrinite reflectance (%Ro) calculated from experimental conditions and potential thermal maturity indicators investigated. The objective of this study was to identify compounds or compound ratios that can be used as indicators for thermal maturity of an oil and hence a proxy for gas yield, gas-oil-ratio (GOR), and pyrobitumen yield. Experimental gas yield, GOR, and pyrobitumen yield increase with increase in calculated %Ro. The alkycyclohexanes and C4-benzenes show promise as thermal maturity indicators for oils and condensates. Percent dimethylethylbenzene isomers (% of measured C4-benzenes) increases and percent tetramethylbenzene isomers (% of measured C4-benzenes) decreases with increase in %Ro. Percent methylcyclohexane and ethylcyclohexane (% of sum of methyl to pentylcyclohexane) also increase with increasing %Ro. The application of C4-benzenes and alkycyclohexanes as maturity indicators in natural systems remains to be tested, but represent a potential tool provided the relationships are validated. These compounds may also have use in determining mixtures of condensates and light oils.