Munchen, Germany
Munchen, Germany

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Seithel R.,Karlsruhe Institute of Technology | Steiner U.,ERDWERK GmbH | Muller B.,Karlsruhe Institute of Technology | Hecht C.,Stadtwerke Munich | Kohl T.,Karlsruhe Institute of Technology
Geothermal Energy | Year: 2015

Background: The characterization of fault zones in the Bavarian Molasse Basin plays a major role for further geothermal reservoir development. Hence, their identification, geological origin, and hydraulic characterization are discussed extensively. Methods: Stress indicators and fractures are interpreted from image and caliper logs of three highly deviated wells at the Sauerlach site. We transform the identified stress field into the borehole coordinate system and compare the observed orientation to the modeled stress field which assumes a homogeneous borehole surrounding. Results: High breakout occurrence, cross-cutting fractures, and a fracture orientation from N-S to NNE-SSW are observed in Sauerlach Th1. In Sauerlach Th2 and Th3, fractures strike primarily ENE-WSW and N-S to NNE-SSW. Drilling-enhanced natural fractures and drilling-induced tensile fractures are observed in all three wells and indicate the orientation of tensile stress at the borehole wall. In Sauerlach Th2 and Th3, stress transformation indicates a SH-dir. ~ N 10°E in a strike-slip stress regime. The modeled stress orientations match the observed orientations within the well Sauerlach Th1 if either SH-dir. is N 320°E in a strike-slip regime or SH-dir. is N 10°E in a normal faulting regime. Conclusion: This approach improves the detection of the local stress field especially for non-vertical wells, which has, in combination with the facture pattern, a major impact on the hydraulic system of the geothermal reservoir. © 2015, Seithel et al.; licensee Springer.

The groundwater flow direction in deep inclined aquifers is generally determined from contour maps based on the conversion of the reservoir pressure from deep wells to standardized groundwater levels. The standardizing is done with a representative water column of constant density in which an increasing depth of the aquifer has an increasing influence on the calculated groundwater levels. However, integration of new pressure data from recently drilled geothermal wells in the Malm of the South German Molasse Basin in the greater area of Munich led to a hydrogeologically unrealistic groundwater flow direction below the Alps. The present work demonstrates the applied method for standardization, performs an error analysis, and shows the limits of the applicability of this method. An alternative approach is introduced along with a concrete example where the local flow direction is determined by neighboring wells (cluster method). A sensitivity analysis with respect to the uncertainty in temperature shows that this approach provides realistic results from realistic input scenarios. The presented cluster method is therefore able to provide pilot points for calibration/verification of a basin-scale groundwater flow model. © 2015, Springer-Verlag Berlin Heidelberg.

Bohm F.,ERDWERK GmbH | Savvatis A.,ERDWERK GmbH | Steiner U.,Free University of Berlin | Schneider M.,Free University of Berlin | Koch R.,Friedrich - Alexander - University, Erlangen - Nuremberg
Grundwasser | Year: 2013

The significant increase of geothermal energy production from the Malm reservoir in the greater area of Munich requires better understanding of the associated aquifer system. In this article, a good correlation between lithofacies and hydraulics is found on the basis of lithofacies evaluation of 17 geothermal wells. The main reservoir capacity within the Malm is made up by predominantly dolomitized massive limestones. Well analyses led to a simplified hydrostratigraphic profile, in which the lower Malm units (alpha to gamma) act as aquitards while Malm delta and epsilon units show a two-dimensional widespread and relatively homogeneous aquifer. Malm zeta can develop both aquifer- and aquitard-characteristics due to significant lateral facies changes. Facies changes depend largely on the basin position and subsequent dolomitisation is a crucial factor for the yield of wells drilled in this area. Based on these results, a new exploration strategy should focus more on facies characteristics than on structural features within the Malm Reservoir. © 2012 Springer-Verlag.

Lentsch D.,ERDWERK GmbH | Savvatis A.,ERDWERK GmbH | Schubert A.,ERDWERK GmbH | Schoebel W.,Baker Hughes Inc.
Transactions - Geothermal Resources Council | Year: 2012

Several geothermal wells have been drilled successfully in the Southern German Molasse Basin within the last years. Some of them have reached depths of 4500 m with a horizontal displacement of up to 3000 m. However, as the wellpaths have become deeper and more complex, drilling has emerged as extremely challenging and cost-intensive, which can be critical for geothermal projects due to the high cost pressure. Usually conventional steerable motor systems were used to drill directionally, but the drilling performance was not sufficient. Penetration rates while sliding were typically 50-60% less than those obtained when rotating. Lower than the optimum weight on bit (WOB) was often applied to maintain direction. Poor weight transition, motor stall outs, high bit wear and low penetration rates were getting progressively worse with depth. In addition, weak drilling performance could have been a major factor for severe tectonic breakout in time-sensitive shales causing over gauge hole, stuck pipe and inadequate cementation. In order to avoid these problems, rotary steerable systems (RSS) have been deployed in two recently drilled wells. The result was a step change in well delivery time and reduced drilling cost. Moreover, no borehole stability problems have been encountered since drilling with RSS. This paper presents a case study demonstrating that the change from conventional systems to RSS has been both, technically and commercially successful.

Lentsch D.,ERDWERK GmbH | Schubert A.,ERDWERK GmbH
Oil Gas European Magazine | Year: 2014

To date, cost planning and time schedule forecasting/or the well construction process of deep geothermal wells drilled in the South German Molasse Basin have been based on a deterministic approach. This means the estimate has been based on a historic average time and uncertainties have been taken into account by adding a contingency factor. © 2014 URBAN-VERLAG Hamburg/Wien GmbH.

Lentsch D.,ERDWERK GmbH | Schubert A.,ERDWERK GmbH
Transactions - Geothermal Resources Council | Year: 2013

In the last five years about 30 deep geothermal wells have been drilled in the Southern German Molasse Basin. 16 of them have been planned and/or supervised by ERDWERK GmbH who supports the operator as a consultant throughout the project. One of the main duties of a consultant like ERDWERK GmbH is cost planning and time schedule forecasting for the well construction process. To date, these estimates have been based on a historic average time for the main operations which have been added up to the total well construction time. Uncertainties have been taken into account by adding a contingency factor. This approach has the advantage of being simple, fast and easy to communicate. However, it does not give any idea about the variability of the estimate and the risks involved, which limits its application. Therefore, the aim of the work presented in this paper was to establish a well construction model based on statistical methods to allow probabilistic time and cost estimation. Firstly, a literature review on probabilistic methods in well planning was performed. Then a model to determine the total well construction time was set up. Offset data of 16 wells was gathered and analyzed to determine a probability function for the duration of each process. Morning reports were the main data source for this task but also rig sensor data was used. The model was fed with the gathered data and verified by comparison with real historic results. Trends observed in the offset data were implemented to model the performance mean and its variation over time. Then a multi-well model was established. Finally, the model was extended by adding costs. With the presented approach of well construction modeling, one can deliver risk assessment for geothermal wells to investors, insurance companies and decision makers. This will aid proper budgeting and the calculation of insurance premiums. Moreover, the modeled technical limit or best historic performance can be used as technical performance reference. Based on the results of the sensitivity anaylsis, the key driving forces can be identified. Therefore, optimization strategies can be steered into the right direction.

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