Bottom-Hole Temperature Data in the Outer Continental Shelf off Alabama

S. Nagihara
Department of Geosciences, Texas Tech University, Lubbock, TX

Bottom-hole temperature data are routinely obtained during wire-line logging operations. The data are typically lower than the true virgin rock temperature of the formation due to the cooling effect of drill fluid circulation. However, if a bottom hole temperature can be measured several times at a fixed depth while the well is shut in, it is possible to monitor the well bore temperature as it recovers toward its pre-drilling state, thus permitting extrapolation to virgin rock temperature. In this study, 207 bottom hole temperatures from 91 wells were examined from the federal protraction areas of Mobile, Main Pass East Addition, and Viosca Knoll off Alabama. Forty-six virgin rock temperature estimates were obtained for 37 wells, using the so-called Horner plot method.

In characterizing the geothermal profile at a well, it is preferable to have at least 4 virgin rock temperature estimates, but only one well met the criteria. Thus, geothermal gradient was obtained collectively by grouping data from wells that are located close to one another. Such a technique can be justified, because no salt structure seems evident in this area and little horizontal variation in thermal conductivity is expected. Thermal gradient values were determined at three locations on the continental shelf and they are between 0.026 and 0.030 Kelvin per meter. The finding may be useful in assessing the potential for the H₂S and other high temperature hazards associated with deep drilling.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004