Carbon Isotopes in Petroleum Science

Whiticar, Michael J.

doi:10.1007/978-3-319-02330-4_310-1

Cited by 1 publication

(4 citation statements)

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“…The carbon and deuterium (CD) diagram of δ 13 CH 4 vs. δ 2 H-CH 4 (Figure 12C, Whiticar, 2021) demonstrates the progressive addition of microbial methane to the thermogenic gas. In addition, the data trend in the CD diagram (dashed line) indicates that 1) the thermogenic methane endmember of the mixture is likely derived from a humic, Type III kerogen source, rather than marine or lacustrine Type I or II kerogen, and 2) the microbial endmember is likely methanogenesis by the hydrogenotrophic pathway (Whiticar, 2020), typical of anoxic marine sediments, rather than a more freshwater, land-based acetoclastic methanogenic pathway.…”

Section: Geochemistry Of Oil Samplesmentioning

confidence: 99%

“…The determined sulfate flux rates at the gas hydrate mound (Supplementary Figure S9) where the pore-fluid array was located indicate an average downward sulfate flux rate of 75 mM cm −2 yr −1 , equivalent to an average methane gradient of 58 mM m −1 , which is about 50 times the average background fluxes distal to the seepage area. Whiticar, 2021) illustrating the mixture of recent, microbial methane with migrated thermogenic methane. The expected thermogenic δ 13 CH 4 vs. δ 2 H-CH 4 endmember is shown (D) Carbon isotope difference plot (modified from Jenden et al, 1993) reinforces that interpretation of a lower maturity, thermogenic gas mixed with a microbial gas.…”

Section: Gas Hydrate Moundsmentioning

confidence: 99%

“…However, these generalizations are viewed as guidelines. Recent reviews and studies have shown the boundaries for gas classification overlap (e.g., Milkov and Etopie, 2018;Whiticar 2021), making interpretation of gas sources more complex.…”

Section: Introduction and Geological Backgroundmentioning

confidence: 99%

“…The expected δ 13 CH 4 from a humic, Type III kerogen source is indicated along with the shift due to the addition of microbial methane. (C) expanded CD diagram (δ 13 CH 4 vs. δ 2 H-CH 4 fromWhiticar, 2021) illustrating the mixture of recent, microbial methane with migrated thermogenic methane. The expected thermogenic δ 13 CH 4 vs. δ 2 H-CH 4 endmember is shown (D) Carbon isotope difference plot (modified fromJenden et al, 1993) reinforces that interpretation of a lower maturity, thermogenic gas mixed with a microbial gas.…”

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Barkley Canyon Gas Hydrates: A Synthesis Based on Two Decades of Seafloor Observation and Remote Sensing

et al. 2022

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Barkley Canyon is one of the few known sites worldwide with the occurrence of thermogenic gas seepage and formation of structure-II and structure-H gas hydrate mounds on the seafloor. This site is the location of continuous seafloor monitoring as part of the Ocean Networks Canada (ONC) cabled observatory off the west coast off Vancouver Island, British Columbia, Canada. We combine repeat remotely operated vehicle (ROV) seafloor video observations, mapping with an autonomous underwater vehicle (AUV), ship-, ROV-, and AUV-based identification of gas flares, as well as seismic and Chirp data to investigate the distribution of fluid migration pathways. Geologically, the site with the prominent gas hydrate mounds and associated fluid seepage is covering an area of ∼0.15 km2 and is situated on a remnant of a rotated fault block that had slipped off the steep flanks of the north-east facing canyon wall. The gas hydrate mounds, nearly constant in dimension over the entire observation period, are associated with gas and oil seepage and surrounded by debris of chemosynthetic communities and authigenic carbonate. The formation of gas hydrate at and near the seafloor requires additional accommodation space created by forming blisters at the seafloor that displace the regular sediments. An additional zone located centrally on the rotated fault block with more diffuse seepage (∼0.02 km2 in extent) has been identified with no visible mounds, but with bacterial mats, small carbonate concretions, and clam beds. Gas venting is seen acoustically in the water column up to a depth of ∼300 m. However, acoustic water-column imaging during coring and ROV dives showed rising gas bubbles to much shallower depth, even <50 m, likely a result of degassing of rising oil droplets, which themselves cannot be seen acoustically. Combining all observations, the location of the gas hydrate mounds is controlled by a combination of fault-focused fluid migration from a deeper reservoir and fluid seepage along more permeable strata within the rotated slope block. Fluids must be provided continuously to allow the sustained presence of the gas hydrate mounds at the seafloor.

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Section: Geochemistry Of Oil Samplesmentioning

confidence: 99%

Section: Gas Hydrate Moundsmentioning

confidence: 99%

Section: Introduction and Geological Backgroundmentioning

confidence: 99%

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