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Geothermal gradient and temperature of hydrogen sulfide-bearing reservoirs, Alabama continental shelf

¹ Department of Geosciences, Texas Tech University, Lubbock, Texas 79409-1053; seiichi.nagihara{at}ttu.edu
² Minerals Management Service, New Orleans, Louisiana 70123-2394; michael.smith{at}ttu.edu

Seiichi Nagihara is an assistant professor at the Department of Geosciences, Texas Tech University. He received his B.S. degree in 1985 and his M.S. degree in 1987, both from Chiba University in Japan. He received a Ph.D. in geological sciences in 1992 from the University of Texas at Austin. His area of specialty includes geophysics, basin analysis, and geographic information science.Mike Smith is the Minerals Management Service Operations geologist responsible for geological reviews of all exploration and development plans and drilling permits for the deep-water Gulf of Mexico. He has also worked as a petroleum geologist, geochemist, and manager for the U.S. Geological Survey, Getty Oil, Texaco, and Geo-Strat.

Present-day formation temperatures of the hydrogen sulfide (H₂S)-bearing reservoirs in the James Limestone and the Norphlet Sandstone in the continental shelf off Alabama have been determined to be 138–149 and 191–217°C, respectively. Hydrogen sulfide gas in those reservoirs is generated by thermochemical sulfate reduction, a process sensitive to the ambient temperature. Bottom-hole temperature data from 135 wells in the offshore lease areas of Mobile, Main Pass East Addition, and the northern section of Viosca Knoll were examined in the estimation of formation temperatures. The bottom-hole temperatures were corrected for the thermal effect of drill-fluid circulation. Estimation of formation temperatures permitted the determination of the geothermal gradient representative for the study area, leading to a temperature range estimation for the H₂S-bearing James and Norphlet reservoirs. Temperatures of offshore Norphlet reservoirs are higher than those reported previously for Norphlet reservoirs onshore. Temperatures of the James Limestone are close to the low-temperature limit for thermochemical sulfate reduction previously suggested.

This article has been cited by other articles:

				P. J. Mankiewicz, R. J. Pottorf, M. G. Kozar, and P. Vrolijk Gas geochemistry of the Mobile Bay Jurassic Norphlet Formation: Thermal controls and implications for reservoir connectivity AAPG Bulletin, October 1, 2009; 93(10): 1319 - 1346. [Abstract] [Full Text] [PDF]

				S. Nagihara and M. A. Smith Regional overview of deep sedimentary thermal gradients of the geopressured zone of the Texas Louisiana continental shelf AAPG Bulletin, January 1, 2008; 92(1): 1 - 14. [Abstract] [Full Text] [PDF]