COMPARING AND CONTRASTING NATURAL CARBON DIOXIDE ACCUMULATIONS IN SOUTHERN CALIFORNIA
Gases sampled for this study were analyzed for both CO2 concentration and the carbon isotope ratio δ13C (CO2), as possible source indicators. CO2 gas concentrations at DSF ranged from 93.4 to 98.4 percent and concentration at La Brea reached 20.8 percent with the remaining gas being mostly methane. The ratio for δ13C (CO2) at DSF ranged from -3.8 to -3.3 per mil and the ratio at La Brea reached 26.3 per mil. Based on these results, the rift system may host geothermal or volcanic sources of CO2, whereas the petroliferous sedimentary basin may host a source of CO2 enriched through biodegradation or methanogenesis. The volcanic origin of CO2 occurs through degassing of magmatic bodies, though this process may be complicated by decarbonation reactions in the geothermal system. The origin of CO2 due to biodegradation typically occurs in mature oil and gas fields, and is not necessarily due to exploration practices. In contrast to preliminary results from the Santa Maria and Ventura Basins presented last year, less overlap of δ13C (CO2) ratios exits in this study, making for less complicated identification of the CO2 source in these accumulations.