Maturity Determination of Contaminated Source Rocks by Pyrolysis and Thermal Oxidation Methods: A Review

Open system pyrolysis (e.g., Rock–Eval) is widely used screening technique for hydrocarbon source rock characterization. It is preferred because it is rapid, practical and cost-effective. However, some pitfalls exist due mainly to sample conditions and care must be exercised. One of the major problems occurs when source rock samples are contaminated by organic additives from the drilling fluids. Analyses of contaminated samples inevitably result in misrepresentative conclusions, possibly leading to incorrect directions. This paper revisits some previously reported problems due to contamination and discusses available remedies. Decontaminating source rock samples is conventionally accomplished by solvent extraction. However, a recent method called thermo-vaporization is equally successful in decontaminating samples prior to pyrolysis. In the case of concern about determining the true thermal maturity of samples contaminated with persistent contaminants, we remind the reader and discuss a recently proposed method, namely Oxidation Tmax. Finally, although pyrolysis is a rapid screening technique, sole dependence upon pyrolysis for petroleum source rock characterization must be avoided. At the least, for some selected samples, assessments should be based on integrated organic geochemical and organic petrographic analysis methods.