The Rhine Graben Revisited

Harthill, Norman, Dietfried Bruss, Christian Hecht, HotRock Engineering GmbH, Karlsruhe, Germany

The Rhine graben is currently the focus of intense geothermal exploration which has shown that the internal structure of the graben is much more complicated than previously thought. In 2003 and 2004, HotRock Engineering commissioned 60 km of 2D seismic; 80km will be shot in spring 2005. Data quality is excellent and good reflections were obtained to depths of 4,000 m. The sections show that the graben is dominated by a series of strike-slip fault flower structures which vertically offset beds from Quaternary to basement. Deeper lay­ers are offset by 500m. The flower structures narrow and become vertical at depth and growth faulting is obvious. The amount of horizontal displacement appears to be significant. The graben contains significant marine and non-marine source and reservoir rocks ranging in age from lower Trias to Late Tertiary and oil and gas fields were developed in widely scat­tered, small, mainly Oligocene, structural traps which occupy only about 300 km? of the total 5,500 km? area of the middle and northern Rhine graben. Hydrocarbon generation is believed to be related to fault-controlled upwelling geothermal waters. However, re-interpre-tation of BHT data shows that high temperatures may be widespread and oil may have been generated throughout the 5,000 km? middle and northern part of the graben. New seismic data could define traps, faulting and migration pathways and lead to significant oil and gas development. In early 2005, HotRock will drill a 2,700 m geothermal test well to the Muschelkalk and will also test oil and gas possibilities.