Thermal structure of the Anadarko basin

The Anadarko basin of Oklahoma is a two-stage Paleozoic cratonic basin with as much as 12 km (7.5 mi) or more of sedimentary fill. We present a presen t-day thermal model of the basin based on lithologic analysis at 3-m (10-ft ) intervals in 63 wells, heat flow measurements at seven sites, and in-situ thermal conductivity calibration of the sediment section at two sites. We do not use BHT (bottom-hole temperature) information in the process, but we do, at the end of the process, compare the independently predicted tempera tures to BHT information. The in-situ calibration of thermal conductivity w as accomplished using detailed temperature logs and represents a new practi cal application for evaluating basin thermal characteristics. Shale exerts the most control on the temperature distribution because it is the most abu ndant lithology and has the lowest thermal conductivity. Shale comprises 47 % by volume of rock in the basin and represents 75% of total thermal resist ance, directly related to temperature gradient; therefore, shale dominates the thermal structure of the basin. Thus, the problems in sampling and in c haracterizing the in-situ thermal conductivity of shale from laboratory mea surements represent a major limitation in basin thermal analysis; are use t he in-situ calibration approach as a way to address the difficulty: The tem peratures calculated do not mimic the structure of the sediments; i.e., the hottest area on a given age horizon in the lower Paleozoic is not in the m ost deeply buried part of the Anadarko basin. The combination of decreasing heat flow toward the Wichita Mountains and the facies changes in the Penns ylvanian units from marine shale (low thermal conductivity) in the basin to the granite wash (high thermal conductivity) toward the uplift results in the highest temperatures being displaced about 50 km (31 mi) northward into the basin. The pattern of vitrinite reflectance in the Woodford Shale is v irtually identical to the present-day reconstructed temperature pattern; th erefore, we conclude that the thermal pattern is and has been dominated by conductive heat transport.