PARAMETER-IDENTIFICATION AND UNCERTAINTY ANALYSIS FOR HEAT-TRANSFER AT THE KTB DRILL SITE USING A 2-D INVERSE METHOD

The German continental deep-drilling program (KTB) provided a unique o pportunity for studying heat transfer processes in deep continental cr ust. We used an inversion technique based on the Bayesian parameter es timation to constrain parameters involved in crustal heat transfer at the KTB site and their standard deviations. Measurements in the two de ep KTB boreholes and on rock material recovered from these holes were used to compile a set of a priori information for a 2-D cross-section of 40 km x 30 km. Thermal and hydraulic parameters were determined in a steady-state inverse finite-element model for a simplified geologica l structure. The inversion algorithm yielded a posteriori information for thermal conductivity, permeability, and heat production rate as we ll as for temperature and hydraulic head. Because of the large tempera ture range (up to 800 degrees C), we introduced the variation of therm al conductivity with temperature into the numerical algorithm. While t hermal conductivity could be well resolved, the distribution of heat p roduction rate was relatively poorly resolved. The uncertainties for t he parameters varied depending on the number of free parameters. If he at production rate was constrained tightly, the resolution of the ther mal conductivity was improved. A zone of higher heat production rate b etween 3.8 km and 10 km combined with a reduced thermal conductivity a bove it provided the best fit to the measured temperatures in the bore hole. The steady-state inversion yielded a better solution when paleoc limatic temperature perturbations, such as those caused by the last ic e age, were removed from the temperature data. (C) 1998 Elsevier Scien ce B.V. All rights reserved.