| Titre | The stable carbon isotope geochemistry of natural gas after 20 years of shale gas development |
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| Auteur | Cesar, J ; Mayer,
B; Ardakani, O H |
| Source | Conference proceedings, 30th International Meeting on Organic Geochemistry (IMOG 2021); 2021 p. 1-2, https://doi.org/10.3997/2214-4609.202134075 |
| Image |  |
| Année | 2021 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20210162 |
| Éditeur | European Association of Geoscientists and Engineers |
| Réunion | International Meeting on Organic Geochemistry; Septembre 12-17, 2021 |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.3997/2214-4609.202134075 |
| Media | en ligne; numérique |
| Formats | pdf; html |
| Sujets | ressources pétrolières; hydrocarbures; gaz; production d'hydrocarbure; études des isotopes stables; isotopes de carbone; roches reservoirs; perméabilité; maturation thermique; géochimie organique; ethane;
roches mères; combustibles fossiles; géochimie; Sciences et technologie |
| Programme | Les géosciences pour les nouvelles sources d'énergie Caractérisation des réservoirs de schiste |
| Diffusé | 2021 09 12 |
| Résumé | (disponible en anglais seulement)
After completion of numerous studies of hydrocarbon generation processes in petroleum basins, the generation of natural gas is well understood, and represents a
process of simple non-catalytic thermal cracking (e.g. Snowdon, 2001). From the perspective of conventional hydrocarbon accumulations, natural gas has been characterized as part of a dynamic system where generation, migration, and accumulation of
hydrocarbons affect not only the molecular composition of the gas but also the isotopic composition of the individual molecules. Stable carbon isotopes are known to distribute according to kinetic isotope fractionation as a consequence of thermal
cracking and migration of hydrocarbons from the source rock (e.g. Clayton, 1991).
During the rapid development of shale gas (and low-permeability reservoirs in general) in the last twenty years, the carbon isotope concepts that were conceived for
conventional petroleum systems were also applied to these new types of hydrocarbon reservoirs. However, geochemical evidence has shown that shale gas exhibits different isotope fractionation phenomena. On the one hand, a well-documented distinct
isotope feature of gases from low-permeability reservoirs is the occurrence of ethane carbon isotope reversal (delta-13Cethane< delta-13Cmethane), typically found in gases with thermal maturity above 2.0 %Ro. The isotope reversal has been attributed
to partly reversible free radical reactions under kinetic isotope fractionation (Xia and Gao, 2018). On the other hand, at lower thermal maturity in shale gas plays, it is yet a question whether the processes governing the carbon isotope distribution
are the same as those conceived for conventional hydrocarbon accumulations, especially in the wet-gas window, which defines condensate rich trends of major economic significance in producing low-permeability hydrocarbon reservoirs around the
world.
Recently, we have found that stable carbon isotopes of natural gas from low-permeability reservoirs display a tendency towards equilibrium isotopic fractionation in the oil window and wet-gas window (Cesar et al., 2020). Carbon isotope
quasi-equilibrium has also been proposed for gases from conventional accumulations using clumped-isotope geochemistry (Thiagarajan et al., 2020). The possibility of tendencies towards isotope equilibrium does not change the understanding of gas
generation as a kinetic process via thermal cracking of kerogen and/or other hydrocarbons, but it implies the likelihood of other processes facilitating isotope equilibration of the generated gas that is retained in the source rock in unconventional
hydrocarbon reservoirs over extended residence times.
In this study, we present new compound-specific carbon isotope evidence suggesting a tendency towards isotope equilibration in gases from low-permeability hydrocarbon reservoirs in North
America. We also discuss how these isotope proxies are related to the molecular composition of the gas and the evolution of key molecular parameters such as the ethane to propane ratio (C2/C3) during the thermal maturation process. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Dans cette étude, nous présentons de nouvelles preuves isotopiques du carbone suggérant une tendance à l'équilibrage isotopique dans les gaz
provenant de réservoirs d'hydrocarbures à faible perméabilité en Amérique du Nord. Nous discutons également de la manière dont ces proxies isotopiques sont liés à la composition moléculaire du gaz et à l'évolution des paramètres moléculaires clés au
cours du processus de maturation thermique. |
| GEOSCAN ID | 328591 |
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