Drilling data-calibrated shale compaction models for pore pressure evaluation from geophysical well logs in the North Alpine Foreland Basin, SE Germany

Abstract

This paper combines quality-controlled pore pressure measurements and indicators with geophysical well logs of 310 deep wells to evaluate the pore pressure distribution in the overpressured North Alpine Foreland Basin, in southeast Germany. Previous studies relied chiefly on low resolution checkshots and vertical seismic profiles calibrated to only a few pore pressure measurements. Current study based on sonic and electrical resistivity logs indicates that more than one shale normal compaction trend is required to appropriately assess pore pressure from geophysical well logs. Thereby, the necessary adjustments of the derived compaction trends apply to both sonic and resistivity data, which possibly reflect a gradual change in mineralogical composition with decreasing clay content or progressing cementation from north to south or an increase of horizontal loading driven compaction towards the North Alpine Thrust Front. The newly derived compaction-based pore pressure distribution is combined with drilling data-based pore pressure evaluations and offers a comprehensive update of previous pore pressure investigations in the North Alpine Foreland Basin. Our study is therefore of key importance for optimised well planning and cost-effective drilling in the course of the recent expansion of deep geothermal energy exploration in the overpressured North Alpine Foreland Basin.