PETROPHYSICAL PROPERTIES OF THE 9-KM-DEEP CRUSTAL SECTION AT KTB

Petrophysical properties of drill core and drill cuttings samples from both bore holes of the German Continental Deep Drilling Program (KTB) measured at atmospheric pressure and room temperature in the field la boratory are presented, along with data of core samples measured at si mulated in situ conditions by other laboratories, Most of the petrophy sical properties show a bimodal frequency distribution corresponding t o the two main lithologies (gneiss and metabasite), except electrical resitivity and Th/U ratio which are lithology independent (monomodal d istribution). Low resistivities are mainly associated with fractures z ones enriched in fluids and graphite. The most abundant ferrimagnetic mineral is monoclinic pyrrhotite. Below 8600 m, hexagonal pyrrhotite w ith a Curie temperature of 260 degrees C is the stable phase. Thus the Curie isotherm of the predominant pyrrhotite was reached (bottom hole temperature about 265 degrees C). The highest values of magnetic susc eptibility are linked with magnetite. Microcracks grow due to pressure and temperature release during core uplift. This process continues af ter recovery and is documented by the anelastic strain relaxation and acoustic emissions. The crystalline rocks exhibit marked reversible hy dration swelling. Anisotropy of electrical resistivity, permeability, P and S wave velocity is reduced significantly by applying confining p ressure, due to closing of microcracks. Fluids within the microcracks also reduce the P wave velocity anisotropy and P wave attenuation. Ani sotropy and shear wave splitting observed in the field seismic experim ents is caused by the foliation of rocks, as confirmed by laboratory m easurements under simulated in situ conditions. The petrophysical stud ies provide evidence that microfracturing has an important influence o n many physical rock properties in situ.