Abstract

Vertical matrix thermal conductivities of clays and claystones in onshore Denmark decrease with decreasing porosity, probably because of increasing orientation of highly anisotropic clay platelets during compaction. The relationship between vertical matrix conductivity λ_vm and porosity for this dataset can be expressed as either λ_vm=2.544exp(0.943φ) or λ_vm=2.749exp (0.637φ), depending upon the statistical methods used to analyse the data. Using the first equation the vertical matrix conductivity of the Danish clays and claystones is found to be about 4.9 W m⁻¹ K⁻¹ in highly porous sediments, decreasing to 2.54 W m⁻¹ K⁻¹ when porosity reaches zero. Using the second equation the vertical matrix conductivity of the Danish clays and claystones is about 4.3 W m⁻¹ K⁻¹ in highly porous sediments, decreasing to about 2.75 W m⁻¹ K⁻¹ at zero porosity. Anisotropy varies from an assumed value of 1.02 in highly porous clays to 2.44 at zero porosity using the first equation, and 1.87 at zero porosity using the second equation. These values agree well with measured data.

This phenomenon is probably common or universal in fine-grained clay-rich sediments, and this method of data analysis could probably be applied to most or all claystone datasets. However, the equations derived in this study will be most appropriate for shales and claystones with comparatively high quartz contents similar to those of the samples analysed. Other specific relationships will probably exist for clay-rich shales and more-pure claystones.