• journal_title：Environmental Geosciences
• Contributor：Marlene Duffy ; Franklin S. Kinnaman ; David L. Valentine ; Edward A. Keller ; Jordan F. Clark
• Publisher：American Association of Petroleum Geologists (AAPG)
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.1306/eg.07110707010
• journal_abbrev：Environmental Geosciences
• issn：1075-9565
• volume：14
• issue：4
• firstpage：197
• section：ARTICLES

The atmospheric fluxes of methane (CH₄), carbon dioxide (CO₂), and reactive organic gases (ROGs) were determined for natural terrestrial petroleum seeps in the Upper Ojai Valley, California, by measuring the emission rates from five vents and scaling these measurements with the known distribution of seeps within the valley. The Upper Ojai Valley seeps emit about 55 m³/day (1942 ft³/day) of gas, of which about 15 m³/day (529 ft³/day; 3.6 Mg/yr) is CH₄, about 40 m³/day (1412 ft³/day; 27 Mg/yr) is CO₂, and less than 0.05 m³/day (1.765 ft³/day; 0.04 Mg/yr) are ROGs. CH₄ and ROG fluxes in the Upper Ojai Valley are, respectively, three and five orders of magnitude less than at the well-characterized Coal Oil Point field, a large offshore seep field located approximately 70 km (43 mi) to the west of the valley. The CO₂ flux from these two fields is about the same. The compositions and δ¹³C values of seep and reservoir gases were also quantified and indicate extensive biodegradation of gaseous hydrocarbons and the input of isotopically enriched CO₂ during ascent from the reservoir. Unlike the nearby CH₄-dominated marine seeps, the largest percentage of gas emitted by seeps in the Upper Ojai Valley is CO₂.