Improving the temperature predictions of subsurface thermal models by using high-quality input data. Part 2: A case study from the Danish-German border region

Abstract

Highlights 3D steady-state thermal FE model using Feflow  Well-log based parameterization approach  Spatial parameterization of rock thermal conductivity  New heat-flow data  North German Basin (Danish-German border area) ABSTRACT We present a 3D numerical crustal temperature model and analyse the present-day conductive thermal field of the Danish-German border region. The model region covers the northernmost part of the North German Basin, a transition zone between the deep-reaching sedimentary rocks of the Glückstadt Graben (including complex salt structures) and the shallow crystalline basement of the Ringkøbing-Fyn High. The modelling approach is novel as it implements for the first time a comprehensive analysis of well-log data on a regional modelling scale. Those logs were used both to derive the spatial distribution of rock thermal conductivity across the study area, and to calculate heat flow values. New values of terrestrial surface heat flow are reported for eight deep boreholes in the North German Basin ranging from 72 to 84 mW/m² with a mean of 80 ± 5 mW/m². The values are computed from continuous temperature logs, carefully corrected BHT values, drill-stem tests and well-log derived rock thermal properties (thermal conductivity, radiogenic heat production) and were included in the setup of the numerical lower boundary conditions. New surface heat flow is up to 20 mW/m² higher than low values reported in some previous studies for this region. Heat flow from the mantle is 33 to 40 mW/m². The model temperature predictions are validated against 59 temperature observations from 24 wells. The prediction uncertainties between observed and modelled temperatures at deep borehole sites are small (rms = 3.5 °C, ame = 2.1 °C). Pronounced lateral temperature variations are predicted and found to be caused mainly by complex geological structures, including a large amount of salt structures and marked lateral variations in the thickness of basin sediments. The associated variations in rock thermal conductivity generate significant variations in model heat flow and large variations in temperature gradients.With regard to the utilization of geothermal energy, the Rhaetian and the Middle Buntsandstein sandstone reservoirs are found with temperatures within the range of 40-80 °C, suitable for low enthalpy heating purposes, in most of the area and locally also with higher temperatures.Temperatures above 120 °C, of interest for the production of electricity, are observed only in the very southeastern part of the study area.

A three-dimensional lithospheric-scale thermal model of Germany

“…The model is consistent with seismic experiments (e.g. TRANSALP, Gebrande, 2001;ALP2002, Brückl et al, 2007ALPASS, Mitterbauer et al, 2011, well logs, local models and geological atlas data (see Przybycin et al, 2014 for an overview).…”

On the importance of rock thermal conductivity and heat flow density in basin and petroleum system modelling

“…Analyses of previously published heat flow data and comparisons with reliable estimates for the same tectonic units based on results from super‐deep and deep scientific wells (Clauser et al, ; Emmerman & Lauterjung, ; Fuchs & Balling, ; Kukkonen et al, ; Popov et al, ) lead to the conclusion that early HFD data often contain systematic errors of 40%–130%. The reasons for this are twofold: unsatisfactory quality of the thermal conductivity measurements (Pasquale, Chiozzi, Verdoya, & Gola, ; Popov et al, ); and the features of early approaches used for HFD estimation.…”

Improving the temperature predictions of subsurface thermal models by using high-quality input data. Part 1: Uncertainty analysis of the thermal-conductivity parameterization

“…To establish a convenient lower thermal boundary condition, the final geological model was extended to a depth of 20 km, which left place for a minimum of 5 km of crystalline crust below the maximum depth of the Glückstadt Graben. Further details of the local geological settings are given in part 2 (Fuchs and Balling, 2016; this issue)…”

“…This paper includes the description of the background data (Section 2), details of the modelling methods and procedures applied (Section 3) and a numerical uncertainty analysis to identify the most-promising TC parameterization approach (Section 4). A detailed heat-flow study and new detailed subsurface temperature maps of the area of study (Danish-German border region in the NGB) derived based on the outcome of this study (part 1) are presented and discussed in part 2 (Fuchs and Balling, 2016; this issue).…”