Decrease in natural marine hydrocarbon seepage near Coal Oil Point, California, associated with offshore oil production

Quigley, D.; Hornafius, J. Scott; Luyendyk, Bruce P.; Francis, Robert D.; Clark, J. M.; Washburn, Libe

doi:10.1130/0091-7613(1999)027<1047:dinmhs>2.3.co;2

Cited by 88 publications

(55 citation statements)

References 18 publications

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“…Studies on the amount of seep gas captured by two large steel tents open to the seafloor at 80 m depth ∼1 km offshore in the COP seep field suggested a long-term influence of offshore oil production (Quigley et al 1999), and an imprint of tidal patterns (Boles et al 2001). These studies demonstrated that the seepage rate varied by a factor of 3 over a 17-year collection period.…”

Section: Gas Fluxmentioning

confidence: 86%

“…For seeps located in deep water and containing dissolved hydrocarbons, important factors include the advective flux of pore fluid through the subsurface (Tryon et al 2002), the formation of gas hydrate in the subsurface (Suess et al 1999), and the efficiency of anaerobic, methane-oxidizing communities (Boetius and Suess 2004). Factors known to impact gas seeps in shallow water include the pressure of the underlying gas reservoir (Quigley et al 1999), blockages or constrictions in fractures and subsequent large "blow-out" events (Leifer et al 2004), and an imprint of tides on seepage rates (Boles et al 2001).…”

Section: Introductionmentioning

confidence: 99%

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Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

et al. 2010

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The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ∼200 m 2 area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ∼450 moles of CH 4 per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO 2 , which should act to dissolve carbonates. The average δ 13 C of the carbonates was −29.2±2.8‰ VPDB, compared to a range of −1.0 to +7.8‰ for CO 2 in the seep gas, indicating that CO 2 from the seep gas is quantitatively not as important as 13 Cdepleted bicarbonate derived from methane oxidation. Methane, with a δ 13 C of approximately −43‰, is oxidized and the resulting inorganic carbon precipitates as highmagnesium calcite and other carbonate minerals. This finding is supported by 13 C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ 13 C ranged from −84 to −25‰). The inconsistency in δ 13 C between the carbonates and the seeping CO 2 was resolved by discovering pockets of gas trapped near the base of the sediment column with δ 13 C-CO 2 values ranging from −26.9 to −11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment-bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.

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Section: Gas Fluxmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

et al. 2010

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“…On the upper slope above the better developed gullies, an east-west trending zone of pockmarks exists, which lies below a zone of carbonate buildup on the continental shelf (14a). This is in the area of extensive gas venting offshore of Goleta Point (Quigley et al, 1999). Near the base of the slope where the gullies are best developed, a bulge of sediment, here called the Goleta bulge, has formed, perhaps the result of downslope creep (Fig.…”

Section: Propagating Head Scarp -Goleta Bulgementioning

confidence: 99%

“…The seeps we observed are contin- uous or intermittent and release gas bubbles and to a lesser extent oil droplets from crevices in rocky substrate or from circular openings within muddy substrate. At Coal Oil Point, gas seeps occur along two linear trends following faulted anticlines that trap hydrocarbons in the fractured Monterey Formation (Quigley et al, 1999;Fig. 9).…”

Section: Fluid Flowmentioning

confidence: 99%

Submarine landslides in the Santa Barbara Channel as potential tsunami sources

Greene

Murai

Watts³

et al. 2006

Nat. Hazards Earth Syst. Sci.

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“…Sonar is an effective tool for mapping seeps, because gas bubbles in water are strong acoustic scatterers (e.g., Hornafius et al 1999;Quigley et al 1999). A chirp sonar (model 424 Edgetech, 4 to 16 kHz) was towed along a series of parallel transect lines that cover the seep field.…”

Section: Sonar Surveysmentioning

confidence: 99%