Light hydrocarbons in Gulf of Mexico water: Sources and relation to structural highs |
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Authors: | RH Reitsema FA Lindberg AJ Kaltenback |
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Institution: | Marathon Oil Company — Denver Research Center, Littleton, Colo. 80160 U.S.A. |
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Abstract: | Analyses of Gulf of Mexico water samples indicate that methane arises from both biologic and thermal sources. Thermal generation of methane and other light hydrocarbons found in the water is demonstrated by: (1) the ratio of methane to ethane of less than 500 is below that expected for bacterial gases; (2) vertical profiles of hydrocarbon concentrations indicate multiple sources for methane, but not for ethane or propane; (3) the correlation between ethane, propane and butane is high indicating a common source, whereas methane correlates in only some areas suggesting multiple sources assumed to be bacterial and thermal; and (4) carbon isotope ratios. Hydrocarbons in the water result from seepage from the sea floor, and a relationship between hydrocarbons and fault systems can be observed. Petroleum production activities did not increase the hydrocarbon content of the non-surface water beyond that often found above petroliferous structures. To avoid surface contamination, analyses were made on water samples taken from near the sea floor. Special equipment for analyses was designed for the survey in the Gulf of Mexico offshore from Galveston, Texas, to Grand Isle, Louisiana, at water depths to 120 m. |
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