FACTORS CONTROLLING THE VARIANCES OF SEISMIC VELOCITY, DENSITY, THERMAL-CONDUCTIVITY AND HEAT-PRODUCTION OF CORES FROM THE KTB PILOT HOLE

This paper presents a statistical analysis of about 50000 petrophysica l data measured on core samples from the Continental Deep Drilling Pro ject (KTB) of the Federal Republic of Germany. The scattering of the d ata must be taken into consideration using empirical relationships bet ween pairs of parameters, e.g., sound velocity, density, heat producti on and thermal conductivity. Such covariances of parameters were calcu lated and used to find the principle components by applying factor ana lysis. The reduction of parameters by factor analysis may help other s cientists to concentrate on the essential parameters to be measured. A bout 50% of the variance of all data can be explained by one backgroun d variable, the so-called ''lithology factor''. The variables that loa d a factor are either highly correlated or anticorrelated. The litholo gy factor combines gamma spectroscopy data, density and the mineral co ntents of quartz, amphibole, garnet and white mica. Seismic velocities and porosity data, however, were less well related to the lithology f actor. Therefore, the KTB data indicate that correlation between seism ic velocity and one of the lithology factor loading variables is unlik ely. The lithology factor distinguishes 3 major ''rock types'': metaba sites, gneisses and an intermediate type. The variance of the petrophy sical parameters within the rock types, plotted in crossplots, show th e level of validity of commonly used relationships among these paramet ers. Measurements under ambient and simulated in-situ conditions are i ncluded to enable discussion of chemical, mineralogical and microstruc tural characteristics of the rocks.