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Main Title: Reservoir-scale transdimensional fracture network inversion
Author(s): Somogyvári, Márk
Kühn, Michael
Reich, Sebastian
Type: Article
Language Code: en
Abstract: The Waiwera aquifer hosts a structurally complex geothermal groundwater system, where a localized thermal anomaly feeds the thermal reservoir. The temperature anomaly is formed by the mixing of waters from three different sources: fresh cold groundwater, cold seawater and warm geothermal water. The stratified reservoir rock has been tilted, folded, faulted, and fractured by tectonic movement, providing the pathways for the groundwater. Characterization of such systems is challenging, due to the resulting complex hydraulic and thermal conditions which cannot be represented by a continuous porous matrix. By using discrete fracture network models (DFNs) the discrete aquifer features can be modelled, and the main geological structures can be identified. A major limitation of this modelling approach is that the results are strongly dependent on the parametrization of the chosen initial solution. Classic inversion techniques require to define the number of fractures before any interpretation is done. In this research we apply the transdimensional DFN inversion methodology that overcome this limitation by keeping fracture numbers flexible and gives a good estimation on fracture locations. This stochastic inversion method uses the reversible-jump Markov chain Monte Carlo algorithm and was originally developed for tomographic experiments. In contrast to such applications, this study is limited to the use of steady-state borehole temperature profiles – with significantly less data. This is mitigated by using a strongly simplified DFN model of the reservoir, constructed according to available geological information. We present a synthetic example to prove the viability of the concept, then use the algorithm on field observations for the first time. The fit of the reconstructed temperature fields cannot compete yet with complex three-dimensional continuum models, but indicate areas of the aquifer where fracturing plays a big role. This could not be resolved before with continuum modelling. It is for the first time that the transdimensional DFN inversion was used on field data and on borehole temperature logs as input.
Issue Date: 8-Nov-2019
Date Available: 13-Jan-2020
DDC Class: 550 Geowissenschaften
Subject(s): discrete fracture network models
transdimensional DFN inversion
Waiwera aquifer
geothermal groundwater
Sponsor/Funder: DFG, 318763901, SFB 1294, Data Assimilation - The seamless integration of data and models, Assimilating data with different degrees of uncertainty into statistical models for earthquake occurrence (B04)
TU Berlin, Open-Access-Mittel - 2019
Journal Title: Advances in Geosciences
Publisher: Copernicus Publications
Publisher Place: Göttingen
Volume: 49
Publisher DOI: 10.5194/adgeo-49-207-2019
Page Start: 207
Page End: 214
EISSN: 1680-7359
ISSN: 1680-7340
Appears in Collections:FG Hydrogeologie » Publications

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