FROM FACIES VARIATIONS TO PETROPHYSICAL PROPERTIES: EXAMPLES FROM THE LOWER TRIASSIC OF THE NORTH-EASTERN GERMAN BASIN

The Buntsandstein is stratigraphically the lowermost part of the tripartite German Triassic which is characterised by multiple successions of reddish to brownish sandstones and claystones. In the north-eastern German Basin these sediments are typically deposited by fluvial to brackish environmental systems.

This work describes lower Triassic sediments with the help of geophysical measurements from deep boreholes. From lithological descriptions clastic, fluvial to lacustrine and brackish deposits could be depicted showing grain size variations from clay to sand. By the construction of an E-W/N-S profile the variability of the sediment composition and their respective facies could be depicted together with the according petrophysical properties.

The basis for our correlation is a borehole set taken from Hoth et al. (1993) together with their geophysical log measurements like gamma ray, acoustic and resistivity logs. With the use of these logs porosity and grain-size distribution have been calculated by petrophysical methods as used as standard method in hydrocarbon exploration. Finally, these results will be compared to regional maps that have been elaborated geothermal studies for the working area by Diener et al. (1989).

First results of the well correlation show on the one hand that the porosity and the lithology vary with respect to the basin rim and basin centre but on the other hand as well from older to younger stratigraphic levels, i.e.Volpriehausen to Solling Formation.

Additionally to the ‘manual’ well correlation we aim to correlate the logs based on a statistical method introduced by Olea (2002) to fit the log pattern of distinct lithological intervals between the boreholes.

References

Diener, I. et al. (1989), Geothermische Ressourcen im Nordteil der DDR. ZGI Berlin, 72p..

Hoth, K.; Rusbült, J.; Zagora, K.; Beer, H.; Hartmann, O. (1993), Die tiefen Bohrungen im Zetralabschnitt der Mitteleuropäischen Senke – Dokumentation für den Zeitabschnitt 1962 – 1990. Verlag der Gesellschaft für Geowissenschaften e. V. (i. G.). Berlin. Schriftenreihe für Geowissenschaften

Olea, R. A. (2002), Correlator 5.2 – Computer program and user’s manual. Open File Report No. 2002-52, December 2002