Malmfacies

Integrated Project MAFA: Parameterization of facies, diagenesis, structure and stress field as well as optimization of the test sequences in the Malm for reduction of the performance risk (research project no. 0325673A)

The reduction of the performance risk involved in the exploration of geothermal reservoirs in the Bavarian Molasse Basin has been the overall objective of this integrated R&D project.

The target horizon in Bavaria are the Upper Jurassic carbonates (Malm) in a depth of up to 5,000 m. However, the matrix porosities and permeabilities of these carbonates are very low (<10 % and <1 mD). Therefore, the high inflows must come from fissures or faults. Through the investigation of samples from surface developments (analogous development studies) and cuttings it could be determined that the dolomitisation of the pure calcites is tied to particular features. Futhermore it varied partly locally (Malm delta), but was mainly associated with fault zones. It can be identified through the existence of „fractured dolomites“ and „fractured calcites“ in the cuttings, so that inflow zones in a well can be proven already by analysing the cuttings. Furthermore, it could be proven that the diagenesis in the deeper Malm differs a little from that in the shallow Malm.

The structure and stress field has been analysed for three 3D seismic data sets from the Bavarian Molasse Basin (Freiham, Unterhaching, Geretsried).  The position of the faults in the recent stress field could be determined and the temporal development of the fault activity has been reconstructed by means of fault throw analysis and horizon flattening, thus allowing for an improved prognosis of the prospectivity of the investigated faults.

Based on the interpretation of synthetic test data applying numerical models, different flow regimes could be identified and their impact on the drawdown behaviour for both simple and complex aquifer systems characterised, e.g., by fault systems and hydraulic boundaries, could be quantified. Thus, it is possible to give recommendations for the necessary duration of a pump test in order to be able to understand the different geological/hydrogeological factors influencing the drawdown behaviour.  

Guidelines for the management of a geothermal project (DE) including the costs and schedules to be expected have been compiled for a project as an example.