Publikationsdatum:
2007-04-01
Beschreibung:
Detailed biomarker and light hydrocarbon geochemistry confirm that the marine Mississippian Barnett Shale is the primary source rock for petroleum in the Fort Worth Basin, north-central Texas, although contributions from other sources are possible. Biomarker data indicate that the main oil-generating Barnett Shale facies is marine and was deposited under dysoxic, strong upwelling, normal salinity conditions. The analysis of two outcrop samples and cuttings from seven wells indicates variability in the Barnett Shale organic facies and a possibility of other oil subfamilies being present. Light hydrocarbon analyses reveal significant terrigenous-sourced condensate input to some reservoirs, resulting in terrigenous and mixed marine-terrigenous light hydrocarbon signatures for many oils. The light hydrocarbon data suggest a secondary, condensate-generating source facies containing terrigenous or mixed terrigenous-marine organic matter. This indication of a secondary source rock that is not revealed by biomarker analysis emphasizes the importance of integrating biomarker and light hydrocarbon data to define petroleum source rocks. Gases in the Fort Worth Basin are thermogenic in origin and appear to be cogenerated with oil from the Barnett Shale, although some gas may also originate by oil cracking. Isotope data indicate minor contribution of biogenic gas. Except for reservoirs in the Pennsylvanian Bend Group, which contain gases spanning the complete range of observed maturities, the gases appear to be stratigraphically segregated, younger reservoirs contain less mature gas, and older reservoirs contain more mature gas. We cannot rule out the possibility that other source units within the Fort Worth Basin, such as the Smithwick Shale, are locally important petroleum sources. Ronald Hill specializes in petroleum geochemistry and has more than 12 years of professional experience, which includes his years in ExxonMobil and Chevron. Currently, he is a research geologist for the U.S. Geological Survey. His interests include the investigation of shale-gas resources and the processes that control petroleum generation. He holds geology degrees from the Michigan State University (B.S. degree), the University of California, Los Angeles (Ph.D.), and a geochemistry degree from the Colorado School of Mines (M.S. degree). Dan Jarvie is an analytical and interpretive organic geochemist. He works on conventional hydrocarbon systems and has worked on unconventional shale-oil and shale-gas hydrocarbon systems since 1984 and the Barnett Shale since 1989. He earned a B.S. degree from the University of Notre Dame and was mentored in geochemistry by Wallace Dow and Don Baker of Rice University. He is the president of Humble Geochemical Services. John E. Zumberge is a cofounder of GeoMark Research in Houston and has been vice president since GeoMark was founded in 1991. He was manager of geochemical and geological research for Cities Service–Occidental, general manager for Ruska Laboratories, and director of geochemical services for Core Laboratories. He has global experience in petroleum geochemistry, focusing on crude-oil biomarkers. He obtained a B.S. degree in chemistry from the University of Michigan and a Ph.D. in organic geochemistry from the University of Arizona. Mitchell Henry received a Bachelor of Science degree in biology from Midwestern University, Wichita Falls, Texas, in 1969. He was awarded a Master of Science degree in Oceanography from Texas A&M University, College Station, Texas, in 1974, and earned a Ph.D. also from Texas A&M in 1982. He joined the U.S. Geological Survey in 1974 and retired from that organization in 2005. His primary interests were in remote sensing, direct detection of geochemical anomalies related to petroleum microseepage, and the application of computer analysis to basin studies. His most recent assignments were related to domestic and international petroleum resource assessments, basin analysis, and hydrocarbon source rock studies. Rich Pollastro received an M.A. degree in geology from the State University of New York at Buffalo in 1977. Rich joined the U.S. Geological Survey in 1978 and serves as a province geologist on the national and world energy assessment projects. His recent accomplishments include petroleum system assessments of the Fort Worth, Permian, and South Florida basins and the Arabian Peninsula.
Print ISSN:
0149-1423
Digitale ISSN:
1943-2674
Thema:
Geologie und Paläontologie
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