(Fig.29)
The physical parameters responsible for the crustal reflectivity were quantified by modelling the petrophysical borehole data and by integrating the data from surface experiments and borehole measurements. By using this approach we could come up with a new processing method. Based on a reflection concept we developed a - as shown in the next slide - a pre-stack true amplitude migration procedure. The figure shows the re-processed data of the old KTB profiles which were done in 1986. You can see that with this method it is easy to recognize the fault systems which were penetrated by the boreholes. You see the sediments in the foreland, the neighbouring granite, and a large number of structural features in the lower crust with a very high and very good resolution.
We are presently reprocessing all the old DEKORP data which were obtained 10 years ago.
(Fig.30)
The drilled crustal segment is distinguished by abundant free fluids which occur in numerous distinct zones up to several tens of meters in width from the surface down to the bottom of the borehole. There is a systematic variation of the composition of these fluids from fresh water down to 1 kilometer; underneath low salinity, sodiumchloride-dominated formation waters to 3 kilometers; and below that depth we encountered highly saline calciumchloride-dominated brines, with an increasing salinity to 3 Mol at bottom-hole depth. These saline brines contained a high amount of dissolved gas. Per liter of brine there was almost 1 liter of gas dissolved which was composed of two-thirds of nitrogen, about 30% of methane, and a little helium.
(Fig.31,32)
It could be shown by a number of experiments that we encountered a complex polymetamorphic terrane with free fluids especially in fault zones as shown in the 3-dimensional schematic diagram. We could reconstruct that the frequent fluids were ultimately derived from Mesozoic sediments from the foreland. They were drawn down along major fault systems to the present depth and then - in connection with tectonic processes - tectonically brought up to the surface again. We did a number of pumping tests, draw-down and pumping experiments which indicated that the formation pressures throughout the profile are almost hydrostatic. This together with the observation that there is a hydraulic connection between the pilot hole and the main borehole clearly indicates that we encountered an active hydrothermal circulation system which is highly interconnected and which is also connected to the surface.
(Fig.33)
The permeability is relatively high in the crust. As I already mentioned, the formation pressures are near hydrostatic and there is a hydraulic communication between the boreholes.
(Fig.34)
Despite of the abundance of saline brines, the electrical behaviour of the continental crust is essentially determined by the distribution of graphite. Graphite was found coating many of the old fault zones. Graphite was definitely formed by a reaction of methane plus CO2 to form graphite and water. You can even see the reaction here by the alteration of the neighbouring gneisses.
