THERMAL BEHAVIOR OF HYDROCARBON-BEARING ROCKS DETERMINED BY SIMULTANEOUS THERMAL ANALYSIS/QUADRUPOLE MASS SPECTROMETRY

Hydrocarbon-bearing shale and limestone samples were analyzed by Simultaneous Thermal Analysis/Quadrupole Mass Spectrometry, which combines calorimetry, thermogravimetry, and evolved gas analysis. This technique has not seen wide use in the geosciences; however, results of this study demonstrate its great potential in the characterization of a wide range of geological materials. The instrument design (ours was manufactured by Netzsch, GmbH) involves a skimmer coupling that allows direct sampling of gases from the sample surface and prevents their condensation, a problem that is commonly observed in systems utilizing transfer lines. Samples were heated at a constant rate (from 25 to 1100 °C) in a helium atmosphere. An array of phase transitions was observed that were accompanied by mass loss, exothermic/endothermic reactions, and/or evolution of volatiles.

Limestone samples exhibit different mass losses, with most of the mass lost at temperatures greater than 650 °C. This mass loss corresponds to endothermic reactions, and the evolution of CO₂, N₂, and CH₄. Shale samples experienced total mass losses ranging from 17% to 45%. The wide range in total mass loss between samples is probably a reflection of different clay contents. The shales exhibit different gas release patterns and temperatures, but all of them released H₂O, CO₂, N₂, CH₄, C₂H₆, and SO₂.

This study illustrates the usefulness of this method for the analysis of hydrocarbon-bearing rocks. This technique could be applied to characterize the behavior of rocks subjected to enhanced thermal recovery methods.