Thermo-vaporization for decontaminating hydrocarbon source rocks

Although use of oil based mud (OBM) benefits drilling engineers, it creates complications for analyses and interpretations of geochemical samples. Pyrolysis of such samples frequently displays masking effects on the true pyrolysis Tmax (e.g., true maturity). When this phenomenon goes undetected, erroneously reported Tmax-based thermal maturity may wrongly influence exploration efforts. The consequences can be even more dramatic when such data is used for calibration of basin models that aim to reconstruct burial and temperature histories and determine hydrocarbon generation from source rock(s). Solvent extraction is generally an effective and commonly employed method for removal of solvent-soluble organic contaminants from samples, but it is expensive and time consuming. Here, we report a new and a faster method called “thermo-vaporization” (TV) that is capable of replacing solvent-extraction processes, thereby eliminating the need for lengthy solvent extraction. This can lead to further contamination. Careful thermo-vaporization conducted below kerogen cracking temperatures guarantees that the solid organic matter (kerogen) is not affected, excluding low level effects determined for immature sulfur-rich kerogen containing samples. The thermo-vaporization method saves time and reduces the potential effect of sample contamination. It provides a rapid workflow to assess thermal maturity with greater confidence. The study described in this article confirms that solvent extractable organic contaminants can be removed from samples by the novel thermo-vaporization method. The method is based on programmed pyrolysis and can be performed with a variety of available pyrolysis apparatus. After optimization, it was found that TV at 350 °C for 60 min or 375 °C for 30 min are both sufficient for removal of contaminants similar to the traditional solvent extraction method. A workflow for a thermo-vaporization based sample cleaning prior to pyrolysis is provided.