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TitleHydrocarbon evaporative loss from shale core samples as revealed by Rock-Eval and thermal desorption-gas chromatography analysis: Its geochemical and geological implications
AuthorJiang, C; Chen, Z; Mort, A; Milovic, M
SourceMarine and Petroleum Geology vol. 70, 2015 p. 294-303, https://doi.org/10.1016/j.marpetgeo.2015.11.021
Year2015
Alt SeriesEarth Sciences Sector, Contribution Series 20150321
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
Subjectseconomic geology; geochemistry; sedimentology; fossil fuels; petroleum resources; hydrocarbon gases; hydrocarbon geochemistry; hydrocarbon maturation; hydrocarbons, light; hydrocarbon migration; organic carbon analyses; shale, commodity; oil shales; Rock-Eval; S1 Peak; Thermal desorption-gas chromatography; TD-GC; Evaporative loss; Light hydrocarbons; TOC; Adsorption; Devonian; Ordovician
Illustrationstables; graphs; geochemical charts
ProgramShale-hosted petroleum ressource assesment, Geoscience for New Energy Supply (GNES)
AbstractThe S1 peaks generated by Rock-Eval analysis of source rock and reservoir interval core and cuttings samples have been routinely employed for in-place hydrocarbon resources assessment by petroleum geochemists, geologists and even engineers. Due to the evaporative loss of gaseous and light hydrocarbons during core and cuttings collection and storage as well as sample preparation in the laboratory before instrumental analysis, a correction to the S1 values is needed in order to obtain a more accurate estimate of the resources. To investigate the effect of evaporative loss on both the amount and the composition of the hydrocarbons retained in shale, a time-series of Rock-Eval and thermal desorption-gas chromatography (TD-GC) analyses have been carried out on an organic-rich Duvernay Formation shale core sample from the Western Canada Sedimentary Basin (WCSB) and an organic-lean Lorraine Formation shale core sample from Quebec, Canada. The results suggest that the content of total organic carbon (TOC) may play an important role in preserving hydrocarbons in sedimentary rocks. A total loss of gaseous and light liquid hydrocarbons up to C9 is shown to take place within 21 hours of sample preparation for the low TOC (<1%) Ordovician Lorraine shale when the powdered sample was left exposed to the open air, accounting for a 38% decrease in its Rock-Eval S1 peak. The Rock-Eval S1 peak can be reduced by 29% even if the powdered sample has been stored in a sealed container for just over a week. In contrast, the volatile loss has been found to be at a much slower rate for the high TOC (> 11%) Devonian Duvernay shale core sample. After 360 hours of exposure to the open air, the powdered Duvernay shale sample shows only 15% decline in its Rock-Eval S1 peak, and still contains high relative concentrations of C7?C9 hydrocarbons. In addition, the evaporative loss of some isomers of C5?C7 hydrocarbons from the organic-rich shale is not fully in agreement with their GC retention/elution behavior, but appears to be partially controlled by their adsorption/desorption process on the organic matter and mineral matrix as well. This suggests that the C5-C8 gasoline range light hydrocarbon parameters should be used with caution for oil-oil correlation for unconventional shale and tight petroleum systems. While the findings in this work validate the current industrial practice that targets organic-rich and mature shale intervals for unconventional shale gas and oil exploration because of their large hydrocarbon storage capacity, the study also has an important implication that high TOC content may adversely affect the production efficiency of shale and tight hydrocarbon reservoirs due to the strong adsorption of hydrocarbons by the high maturity organic matter.
Summary(Plain Language Summary, not published)
The S1 peaks generated by Rock-Eval analysis of source rock and reservoir samples have been routinely used for hydrocarbon resources assessment by petroleum geologists and engineers. Due to the evaporative loss of volatile hydrocarbons during sample collection, storage and preparation before instrumental analysis, a correction to the S1 values is needed in order to obtain a more accurate estimate of the resources. In addition to Rock-Eval, thermal desorption-gas chromatography (TD-GC) analyses have also been carried out on shale core samples from Alberta and Quebec basins at different times after sample preparation to investigate the effect of volatile loss. The results indicate that the organic matter in shale may help to retain hydrocarbons especially the volatile components through adsorption, thus preventing their evaporative loss.
GEOSCAN ID297380