In an R&D precursor project (BMU II) ERDWERK already considered the phenomenon of annually decreasing injection pressures under operational conditions. The fact that the IEP (Innovative Energie für Pullach GmbH) intended to reverse the existing injection well, which had been in operation for several years, into a production well was of benefit to us for a geoscientific investigation of the issue (a project description of the Pullach project can be found here).

The BMU (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety) funded the IWC (Institute for Water Chemistry) of the Technical University of Munich and ERDWERK (FKZ 0325469), so that this unique possibility could be used to investigate the injection behaviour by means of a tracer test and the temperature development in more detail, as well as to derive regional reservoir properties accordingly.

The objectives of ERDWERK's work were to determine the forecast reliability for long-term operation and the potential extension of existing plants. The focus was on quantifying the forecast uncertainty. Based on the project history of the Pullach geothermal project, the various development scenarios were mapped and examined. A discovery prognosis for the next geothermal expansion stage was submitted in order to subsequently evaluate it on the basis of the real drilling results.

In summary, it can be said that a prediction is difficult due to the strong heterogeneity of the lithofacies in Malm. Only with the derivation of the thickness of the higher permeable mass facies from the texture of high-quality seismic data was it possible to predict the significantly higher productivity of the Pullach Th 3.

The results of the R&D project have shown that the reason for the improvement in injectability is due to temperature-induced acidification in the area near the well, and that this leads to an improved connection to the reservoir.