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Thermovaporisation: A screening tool for the gas-sorptive properties of source rocks

Mahlstedt, Nicolaj, Horsfield, Brian
Organic geochemistry 2019 v.131 pp. 1-4
data collection, gas chromatography, logging, methane, pyrolysis, rocks, screening, sorption
We have developed a new geochemical logging method to evaluate the amount and composition of sorbed gas within source rocks quickly and inexpensively, thereby providing a practical tool for the rapid identification of “sweet spots” or heterogeneities within vertical profiles. Thermovaporisation GC-FID (Tvap) forms the basis of the screening method and can be easily run alongside Rock-Eval pyrolysis in high resolution. A fairly good correlation of S2 normalised Tvap gas yields with the rocks TOC normalised measured Langmuir amounts (nL) assessed using standard petrophysical methods (e.g., excess sorbed methane versus pressure curves) demonstrates that Tvap is capable of defining the basic sorption characteristics of source rocks or gas shales. The Tvap screening tool excels at detecting zones (organofacies/lithofacies) and related heterogeneities in the sorption behaviour of the respective rocks, but not in directly detecting sorption properties. Nevertheless, adsorptive property profiling is possible for large data sets by including direct integration of Langmuir parameters.