3D Geothermal Reservoir Characterization And Production Optimization Of Intelligent Multi-Well Patterns In The Fractured And Karstified Upper Jurassic Aquifer In The Bavarian Molasse Basin. Case Study: Greater Munich Geothermal Field

Abstract

It has always been challenging to assess the impact of the porosity and permeability distribution of complex geological structures on groundwater flow and heat transport in deep geothermal systems. In particular, understanding the impact of fractures, faults, and karst-related features (collapse or sinkhole structures) on the permeability distribution of different carbonate depositional settings is of paramount importance for a successful geothermal reservoir characterization and modelling. In addition, the proper characterization and implementation of the lateral and vertical distribution of the hydraulic properties of heterogeneous limestone facies is a major focus of this study. This work lies within the framework of the GeoParaMoL-project, which is part of the GRAME-project and concentrates on the estimation of geophysical parameters to determine facies of the Malm, structural and stratigraphic geological features and the numerical modeling of the thermal- hydraulic long-term behavior of the Malm affected by optimized geothermal multi-well arrays. Pioneering geothermal reservoir modelling workflows of complex fractured and karstified carbonate facies essentially combine in this work the use of SKUA-GOCAD, ArcGIS and FEFLOW 7.0 with a fully unstructured mesh. The combination of these modelling softwares proved successful when it comes to realistically modelling complex permeability structures that may result from the intersection of synthetic and antithetic faults typical of the study region. Heterogeneous and anisotropic porosity and permeability distributions that result from geological structures recently interpreted from 3D seismic data (e.g., Horst and Graben structures, relay ramps and horsetail splay faults) are discussed. Apart from fractures and faults, the characterization of carbonate facies plays an important role. The combination of P- and S-waves makes it possible the derivation of geophysical parameters (e.g., Vp/Vs) to support the facies interpretation. The optimization of multi-well-systems in deep geothermal reservoirs is a multi-variable optimization problem. In addition to groundwater and heat transport modelling, this work focuses on several technical and economic parameters that compete against each other in the optimization process. Existing district heating networks and concession fields together with the temperature field and hydraulic properties of the deep geothermal reservoir are key factors. The thermal and hydraulic interference of neighboring geothermal wells also influences decisively the optimized geometric patterns of geothermal doublets and triplets. Ultimately, geothermal reservoir management and performance depend crucially on the minimization of the pressure difference between injection and production wells and the minimization of temperature drop in the production well (Vörös et al. 2007). The thermal breakthrough, which basically depends on the distance between injection and production wells, flow rate and the net reservoir thickness among other factors, fundamentally controls the temperature drop in the production well. Among several methods used to tackle the optimization of multi-variable problems, simulated annealing has proved quite efficient when applied to similar problems in hydrocarbon reservoirs. This work presents first steps towards adapting existing program schemes to geothermal applications. This project has been funded by the Federal Ministry for Economic Affairs and Energy (BMWi).

AAPG Datapages/Search and Discovery Article #90345 © 2018 AAPG European Region, Geothermal Cross Over Technology Workshop, Part II, Utrecht, The Netherlands, April 17-18, 2018