On the determination of thermal conductivity of sedimentary rocks and the significance for basin temperature history

Abstract

Thermal history is an important control on generation of gas and oil in source rocks. Therefore, a realistic treatment of thermal conductivity in rocks is essential for hydrocarbon generation modelling in sedimentary basins. We present two different techniques for thermal conductivity estimation: (1) upscaling, based on arithmetic, geometrical and harmonic mean values of averaged conductivity from anticipated mineral composition; (2) infometric regression of thermal conductivity and anisotropy from measurements in rocks of known porosity and mineral composition. The accuracy of the estimate depends on the technique and we expect that the most precise way to predict thermal conductivity of sedimentary rocks leads to considerable improvement in the accuracy of basin modelling and hydrocarbon prospect identification.Various thermal conductivity models based on porosity and lithology are used for modelling temperature history for sensitivity purposes. Models where matrix conductivity is determined from measured thermal conductivities based on the mineralogy give considerably lower strata temperatures than models where geometrically averaged matrix conductivity are determined from mineralogy. This is assumed to be caused by deficiency in the mixing laws not taking into account the texture effect of the sediments. The temperature histories estimated by the three mixing law models -arithmetic, geometrical and harmonic mean -are considerably different. We show that the mixing law models give a temperature history and predicted hydrocarbon maturation far off even if we have temperature measurement at the same location. For example the harmonic model predicts the onset of the maturation of the Jurassic formations 20 million years later than does the model based on measured conductivities.

Mudstone compaction curves in basin modelling: a study of Mesozoic and Cenozoic Sediments in the northern North Sea

“…There are several ways to determine the thermal conductivity structure of the sediments in a basin, and the results will vary signi¢cantly depending on which model is applied. Fjeldskaar et al (2009) showed that thermal conductivities based on measured samples from the North Sea show signi¢cantly higher temperatures than mixing law models, and that this may be due to the fact that these models do not take into consideration the e¡ect of the texture of the sediments.…”

“…Fjeldskaar et al (2009) showed that thermal conductivities based on measured samples from the North Sea show significantly higher temperatures than mixing law models, and that this may be due to the fact that these models do not take into consideration the effect of the texture of the sediments. Since the variations between the different mixing law models have been thoroughly described by Fjeldskaar et al (2009), this is not tested in the present study, but this issue should also be considered when evaluating the temperature history of a sedimentary basin.…”

“…The temperatures obtained in this study are all lower than those found when using thermal conductivities found in the northern North Sea (e.g. Fjeldskaar et al , 2009). This is because the thermal conductivities used for the post‐rift sequence are higher than the values observed from the study area.…”

“…Thermal conductivities are controlled by the porosity, the conductivity of the fluid phase and the mineral composition. The thermal conductivity structure used in this study for the pre‐ and syn‐rift sediments (pre‐Cretaceous) is based on laboratory measurements of sedimentary rocks from the Norwegian Continental shelf (TCD ™ ‐database, a trademark of TGS NOPEC) (Fjeldskaar et al , 2009) (Table 3). For the post‐rift sediments (Cretaceous–Cenozoic), thermal conductivities were calculated from the weighted average (Fig.…”

Estimation of the global inventory of methane hydrates in marine sediments using transfer functions

“…Thermal conductivity depends on mineralogy and increases with sediment depth due to compaction and cementation (Wallmann et al, 2012). Considering a thermal conductivity of 0.9-3 W m −1 K −1 for clays (Fjeldskaar et al, 2009), 0.6 W m −1 K −1 for pore water in marine sediments (e.g. Deming et al, 1989), and an average porosity of 0.5 over the sediment column, the thermal conductivity of sediments was estimated at 0.7-1.34 W m −1 K −1 .…”