Undisturbed temperature in the main drillhole of the German Continental Deep Drilling Program predicted from temperature logs recorded after shut-in

Three high resolution temperature logs recorded after shut-in of the main borehole KTB-Oberpfalz HE of the German Continental Deep Drilling Program are used to determine a first estimate of the undisturbed formation temperature, using the line source model of Bullard [Bullard, E.C., 1947. The time necessary for a borehole to attain temperature equilibrium. Monthly Notices Royal Astronomical Society, Geophysical Supplement 5, 127-130.]. The resulting formation temperature profile and the corresponding temperature gradient, deviate from previous estimates [Wilhelm, H., Baumann, C., Zoth, G., 1995. Some results of temperature measurements in the KTB main borehole, Germany. Geothermics 24, 101-113; Clauser, C., Giese, P., Huenges, E., Kohl, T., Lehmann, H., Rybach, L., Safanda, J., Wilhelm, H., Windloff, K., Zoth, G., 1997. The thermal regime of the crystalline continental crust: implications from the KTB. Journal Geophysical Research 102, 18,417-18,441; Wilhelm, H., 1998. Comparison of predicted and logged temperatures in the KTB main hole. In: Popov, Yu, Pimenov, V. (Eds.), Proc. Int. Conf. The Earth's Thermal Field and Related Research Methods. Moscow State Geological Prospecting Academy, Moskow, pp. 280-281], which were derived from bottomhole measurements and from multiple temperature logs recorded during drilling pauses at 4500, 6000 and 7200 m depth. Although the database is not large enough to allow a formal error estimate, the noise in the extrapolated formation temperature indicates a mean error of about +/-0.15 K between 2500 and 5200 m depth and a mean error of +/-0.5 K below 5200 m depth. (C) 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.