Temperature and pressure corrections applied to rock thermal conductivity: impact on subsurface temperature prognosis and heat-flow determination in geothermal exploration

Ben Norden,Andrea Förster,Sven Fuchs,Hans-Jürgen Förster

doi:10.1186/s40517-020-0157-0

Ben Norden, Andrea Förster + Show 2 more

Open Access

https://doi.org/10.1186/s40517-020-0157-0

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Abstract

Precise knowledge of the subsurface thermal field plays a key role in the assessment of geothermal targets. Unfortunately, deep underground temperature data is generally scarce and a matter of research. To achieve first estimates for subsurface temperatures, steady-state conductive thermal modeling is commonly applied. Thereby the rock thermal conductivity is an essential parameter, which is usually determined under ambient laboratory conditions. To arrive with in situ thermal conductivity, the ambient values need to be corrected for in situ temperature and pressure. In this paper, we apply different conversion functions for the correction of thermal conductivity and study the impact on the resultant temperature and heat flow prognoses for a synthetic, upper crustal sedimentary and a magmatic scenario along 2-D geological cross sections. Application of the correction functions results in maximum temperature prognosis uncertainties of about 8 °C and 55 °C at 2 km depth and at 8 km depth, respectively. The effect positively correlates with the magnitude of the basal heat flow used in modeling. In contrast to the heat flow determined at depth, the resulting surface heat flow is only minor affected by the different correction functions applied. In addition, the modeled temperature at depth is strongly dependent on the type and sequence of application of the pressure and temperature correction equations.

Highlights

In geothermal exploration, temperature models are frequently applied, e.g., for estimating the geothermal potential at depth or for studying the thermal evolution of sedimentary basins (e.g., Balling et al 2013; Bédard et al 2018; Békési et al 2018; Förster et al.2018; Fuchs et al 2020; Lemenager et al 2018; Schintgen et al 2015a, b; Sonibare et al.2018; Vélez et al 2018)
The maximum difference between λ(maxp) and λ(maxT) could be used as an indicator for the uncertainty of T prognosis using correction functions. It accounts for about 8 °C at 2 km depth and to about 55 °C at 8 km depth, respectively
Due to the chimney effect of the higher conductive salt, T is increased at the salt diapir by about 5 °C close to the surface

Summary

Introduction

Temperature models are frequently applied, e.g., for estimating the geothermal potential at depth or for studying the thermal evolution of sedimentary basins (e.g., Balling et al 2013; Bédard et al 2018; Békési et al 2018; Förster et al.2018; Fuchs et al 2020; Lemenager et al 2018; Schintgen et al 2015a, b; Sonibare et al.2018; Vélez et al 2018). Norden et al Geotherm Energy (2020) 8:1 commonly used as boundary conditions, and the rock-specific thermal properties of the rocks. Under steady-state conductive conditions, one of the most influential parameter is the thermal conductivity (λ, in W m−1K−1) of the rock, which in turn, largely depends on λ of minerals constituting the rock matrix and on λ of the pore fluid (e.g., Blackwell and Steele 1989). For improving the reliability of thermal models, a proper mapping and parameterization of geological (and thermal) units is necessary, and an understanding of the change of thermal rock properties due to different p/T conditions

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