Title: New Concept for the application of Outcrop Analogue Data for Geothermal Probability of Success (POS) Studies – Examples of Projects in the Northern Upper Rhine Graben (Germany)
Abstract: Probability of success (POS) studies for deep geothermal projects are based usually on hydraulic test data of wells located in the same reservoir system in a comparable regional setting. Based on this fact prospective risk insurances ('Fundigkeits'insurance), which are often an important economic prerequisite for geothermal power projects in Germany, are not available for geothermal greenfield projects, where almost no drilling or hydraulic information of the reservoir are available. To bypass this problem, which is partly responsible for the slow progress of the development of geothermal power production in Germany, we propose an alternative form of POS studies based on suitable outcrop analogue data. Based on a vast data base of thermophysical rock properties (more than 9,000 measurements) and hydraulic test data sets (more than 1,500 tests) sampled east and west on the Graben shoulders, borehole temperature measurements (more than 2,500 measurements) and a 3D geological model, a detailed geothermal model of the northern Upper Rhine Graben was established. This regional model, which incorporates important fault systems within the Graben and their influence on the depth and temperature dependent geothermal and hydraulic properties of different reservoir formations, is used for a local calculation of the POS. We demonstrate the usability of this probabilistic model to determine the POS for different actual project locations within the northern Upper Rhine Graben and discuss statistic uncertainties and inferred explorations risks for different locations. Investors usually require POS studies to decide whether an investment for a deep geothermal project is economically viable or not. The same applies for insurance companies that need POS studies to decide whether prospective risk insurance for the success of a geothermal well ('Fundigkeitsversicherung') with attractive conditions for the project developer is possible. Therefore, a POS study is a key for the realization of a deep geothermal project if the equity of the project developer is insufficient. This problem is partly responsible for the slow progress of the development of deep geothermal projects for electricity generation or the utilization of direct heat in the low enthalpy regions of Europe. In Germany, so far POS studies for geothermal projects are generally based on the results of deep wells in the same reservoir in the immediate vicinity of the project to be developed. For regions and reservoirs where no wells have been drilled into the reservoir formation - so called green fields - this classic approach for POS studies is not possible. Based on the example of the federal state of in Germany a new alternative approach for POS studies is proposed, which fully relies on the combination of geothermal rock parameters derived from suitable outcrop analogue studies, geological 3D modelling and temperature modelling. Comprehensive data sets about the potential deep geothermal systems of so far only existed for the underground temperature in the region of the Upper Rhine Graben which is only a small part of the state area (Fig. 1). In addition to temperature, the bulk permeability of the reservoir, the achievable flow rate of thermal water, is the main factor of influence on the deep geothermal potential for open systems. Additionally, matrix permeability, porosity and thermal conductivity are important factors to estimate the conductive and convective heat flows within the reservoir. For assessment of the deep geothermal potential, knowledge of geological structure and geothermal properties of potential reservoir rocks are indispensable. None of the above mentioned parameters were available for the identified reservoir formations and therefore had to be collected state-wide in bibliographic, archive and most importantly in outcrop analogue and drill core investigations. This was performed in the context of the project 3D-modelling of the deep geothermal potentials of Hesse (Sass and Hoppe, 2011; Arndt, 2012 and Bar, 2012) which was initiated in 2008 with the aim to identify and evaluate systematically the deep geothermal potential of Hesse. The established vast database could then be connected with the 3D structural model and the underground temperature model for parameterization with thermophysical and hydraulic properties. The resulting geological-geothermal 3D model allows for a comprehensive evaluation of all deep geothermal potential reservoirs of and is capable to display the potential for open systems like hydrothermal or petrothermal (EGS) systems as well as for closed systems like deep borehole heat exchangers (Bar et al., 2011). Additionally, it provides detailed characteristics of the geothermal reservoir needed for probabilistic modelling which is the basis for POS studies without the need of direct information from deep wells in the reservoir of interest.
Publication Year: 2015
Publication Date: 2015-11-12
Language: en
Type: article
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Cited By Count: 1
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