Rhenium–osmium geochronology and oil–source correlation of the Duvernay petroleum system, Western Canada sedimentary basin: Implications for the application of the rhenium–osmium geochronometer to petroleum systems

Abstract

The rhenium-osmium (Re-Os) geochronometer has been applied to many petroleum systems worldwide. However, it is debated if the Re-Os systematics in petroleum actually records the timing of oil generation. Here, we investigate the Re-Os isotope systematics of the Duvernay petroleum system in the Western Canada sedimentary basin, which has been shown to be a relatively simple petroleum system that is associated with oil generated during the Late Cretaceous-Early Eocene Laramide orogeny from a single source. The organic geochemistry of the Duvernay oils (pristane/phytane ratios of ~1.5, smooth homohopane profile, C 29 >C 27 >C 28 regular sterane distribution, and predominance of diasteranes over regular steranes) strongly suggest the oil source to be that of Type I-II marine organic matter of the Late Devonian Duvernay Formation. The asphaltene fraction Re-Os isotope data of the Duvernay oil yield an age of 66 ± 31 Ma, which is in excellent agreement with the timing of the main-stage hydrocarbon generation of the Duvernay Formation based on basin models. Further, the similarity between the 187 Os/ 188 Os compositions of the Duvernay Formation source rock (0.46 to 1.48) and the oil (0.55 to 1.06) at the time of oil generation supports the hypothesis that the 187 Os/ 188 Os composition of an oil is inherited from the source unit at the time of oil generation, and therefore shows no, or limited influence from interaction with basin fluids. This study supports that the Re-Os isotope systematics of an oil can yield the timing of oil generation, and be used to trace its source.

Remotely constraining the temporal evolution of offshore oil systems

“…A major concern when assessing material released from hydrocarbon seeps is the continued integrity of its Re-Os system despite exposure to formation waters and the marine environment. Studies of weakly to heavily biodegraded crude oils have repeatedly shown that their Re-Os system is not significantly affected by microbial alteration 10,11,13,14 . However, laboratory experiments have demonstrated rapid transfer of Re and Os to liquid oils from an enriched aqueous solution 30 .…”

“…Although an improvement from the regression of all asphaltite Re-Os data, the revised regression also yields a date that is still relatively imprecise (68 ± 15 Ma, 22%). Such a spread in a Re-Os generation age is not abnormal 11,13,14 , and likely the result of prolonged generation over millions of years, combined with variation in the initial 187 Os/ 188 Os composition of the source unit 11,12,14 . Potential mixing of variable 187 Os/ 188 Os values across a source rock may be particularly applicable to oils and bitumen derived from OAE2 deposits, given the extent of variability at metre to centimetre scale across the interval (Fig.…”

“…A major recent advance in petroleum geochemistry has been the ability to directly determine the timing of hydrocarbon generation from the source rock using the decay of 187 Re to 187 Os within the produced oil 9–14 . Studies using naturally formed oils and those produced via artificial maturation of source rocks in a laboratory setting have also demonstrated that the initial 187 Os/ 188 Os composition of an oil (Os i ) is inherited directly from the source rock at the time of generation 13–15 .…”

“…Studies using naturally formed oils and those produced via artificial maturation of source rocks in a laboratory setting have also demonstrated that the initial 187 Os/ 188 Os composition of an oil (Os i ) is inherited directly from the source rock at the time of generation 13–15 . Therefore, comparison of this Os i value of an oil to the 187 Os/ 188 Os composition of a proposed source rock at the time of generation (Os g ) may be used to aid oil-to-source correlations, should data on the source rock be available 11,14,16 . However, previous applications of Re-Os dating using oils and bitumens have been restricted to samples collected in-situ , rather than examples released from the subsurface into the marine environment through natural seepage.…”

Neoproterozoic–Cambrian petroleum system evolution of the Micang Shan uplift, northern Sichuan Basin, China: Insights from pyrobitumen rhenium–osmium geochronology and apatite fission-track analysis

“…The latter, combined with the analytical challenge of isolating the Ar from the gas inclusions has limited the available results (Liu et al, 2011;Qiu et al, 2011). Compared to K-Ar and Ar-Ar dating on associated minerals, for example illite, K-feldspar and quartz fluid inclusions, rhenium-osmium (Re-Os) dating directly of the oil or solid bitumen, has shown promise to determine the absolute timing of hydrocarbon (oil and gas) generation (Cumming et al, 2014;Finlay et al, 2011;Ge et al, 2016;Georgiev et al, 2016;Lillis and Selby, 2013;Liu et al, 2017;Selby et al, 2007).…”