Abstract. An extensive geothermal research program within the German Continental Deep Drilling Program (KTB) covered an almost complete spectrum of experimental and theoretical aspects. The main results and conclusions are as follows: (1) Equilibrium temperature is 118.6øC at 4000 m in the KTB pilot borehole (KTB-VB) and will be around 260øC at 9100 m in the KTB main borehole (KTB-HB). Time required for thermal equilibration of the KTB-HB to within 1% of the initial perturbation will be about 13-16 years. for large rock volumes, but simple numerical models indicate that the associated temperature regimes are imcompatible with KTB borehole data. (6) Heat production rate shows no systematic variation with depth and is related to lithology at the KTB as in other deep boreholes in crystalline rock. Numerical models, using heat production rate derived from seismic velocities, yield temperatures compatible with KTB borehole data.

[1] The borehole Yaxcopoil-1, drilled within the Chicxulub meteoritic impact structure (Mexico), was completely cored from 404 to 1511 m through postimpact Tertiary limestones underlain by impactites. The impactites comprise impact melt-rich, suevitic breccia followed by megablocks of Cretaceous limestones, calcarenites, dolomites, and anhydrites. Measurements of porosity, density, and thermal parameters on 450 samples (equidistant sampling, complete depth range) and of ultrasonic velocities and electric resistivity on 80 representative samples are used to investigate the physical properties of carbonate rocks and to study the influence of the impact. Experiments under elevated pressure, calculations using frequency-dependent Biot-Gassmann theory, and crosschecking with borehole logs, where available, show that ultrasonic laboratory and sonic in situ data correspond. Sonic and electric quasi-continuous logs are obtained from empirical correlations with thermal conductivity, density, and porosity and consideration of mineralogical composition and microstructure. These data give constraints on interpretation and geophysical modeling of, e.g., seismic and gravity data. In the Tertiary postimpact limestone section, the rock fabric (porosity) influences the physical properties. The upper boundary of the impactites is distinctly determined by the high inhomogeneity factor and anisotropy coefficient of thermal conductivity and by the temperature gradient from high-resolution borehole temperature measurements. All physical properties indicate that the upper part of the suevitic breccia can be distinguished from the lower suevite unit. In the Cretaceous megablocks, a high variability of all properties (particularly, thermal conductivity, density of solid material, and temperature gradient) due to the high variability in the mineral composition (calcite, dolomite, anhydrite) is observed.

Abstract-Physical properties were determined in a first step on post-impact tertiary limestones from the depth interval of 404-666 m of the Yaxcopoil-1 (Yax-1) scientific well, drilled in the Chicxulub impact crater (Mexico). Thermal conductivity, thermal diffusivity, density, and porosity were measured on 120 dry and water-saturated rocks with a core sampling interval of 2-2.5 m. Nondestructive, non-contact optical scanning technology was used for thermal property measurements including thermal anisotropy and inhomogeneity. Supplementary petrophysical properties (acoustic velocities, formation resisitivity factor, internal surface, and hydraulic permeability) were determined on a selected subgroup of representative samples to derive correlations with the densely measured parameters, establishing estimated depth logs to provide calibration values for the interpretation of geophysical data. Significant short-and long-scale variations of porosity (1-37%) turned out to be the dominant factor influencing thermal, acoustic, and hydraulic properties of this post impact limestone formation. Correspondingly, large variations of thermal conductivity, thermal diffusivity, acoustic velocities, and hydraulic permeability were found. These variations of physical properties allow us to subdivide the formation into several zones. A combination of experimental data on thermal conductivity for dry and water-saturated rocks and a theoretical model of effective thermal conductivity for heterogeneous media have been used to calculate thermal conductivity of mineral skeleton and pore aspect ratio for every core under study. The results on thermal parameters are the necessary basis for the determination of heat flow density, demonstrating the necessity of dense sampling in the case of inhomogeneous rock formations.

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