Abstract

Log responses in crystalline rocks are a function of the lithology (rock matrix), macro- and microfractures. Basically, the porespace-geometry dependent petrophysical parameters (porosity, internal surface area, permeability, formation factor) are similarly interrelated as in sediments, but mineralogy and fractures exert greater control than in sediments.

A qualitative log interpretation method was developed and tested. Fractured and otherwise deteriorated zones with anomalous properties are identified, using a suitable combination of five standard logs. Before a quantitative well-log analysis of petrophysical parameters is possible, the logs are corrected for lithology effects, using a quick-look lithology identification program. For lithology identification seven logs are considered sufficient. Their mean lithology-dependent response in the German KTB borehole is reported.