Feedback between Temperature and Thermal Conductivity

In general, thermal conductivity is regarded as a material constant. However, as a result of strong heating or strong cooling, changes in the state of the materials can occur which also influence their thermal properties. In particular, gases generally have much lower thermal conductivities than liquids (see e.g. here: https://www.thermal-engineering.org/what-is-thermal-conductivity-of-water-and-steam-definition/). Such processes could lead to changes in the thermal properties of gas-bearing sediments in the offshore area as a result of both natural and anthropogenic influences. Reduced thermal conductivity due to increased gas content in the sediment could thereby prove problematic for the installation of offshore energy cables. This project is funded by the state of Bremen within the framework of the state program "Promotion of Research, Development and Innovation" (FEI) of the Senator for Economics, Labor and Europe of the Free Hanseatic City of Bremen.

Heat conductivity and temperature diffusivity

For many years, the thermal conductivities of sediments have been calculated at FIELAX from the data of special temperature measurements. For many applications, however, the thermal diffusivity is also of interest. Together with the University of Bremen it was investigated how the calculation of thermal diffusivity from temperature data in addition to thermal conductivity can be achieved or improved. As a result of this project, which was supported by the European Regional Development Fund (ERDF), a scientific publication was produced, which is available at https://doi.org/10.1007/s13137-021-00183-1.

TRT measurements Off-/Near-/Onshore Holland – cooperation with Next Geosolutions and Marine Sampling Holland

Since December 2020 and ongoing, FIELAX provides thermal conductivity / thermal resistance measurements for cable routes for three wind zones in the Dutch North Sea to be connected by TenneT (offshore-energy.biz/tennet-picks-next-geosolutions-for-route-surveys-fugro-as-backup/). As a subcontractor to Next Geosolutions (nextgeosolutions.com), FIELAX conducts most of the surveys using our systems in combination with Next's Vibrocorer.

At shallow water depths / tidal flats / onshore, the VibroHeat method is not feasible. We are pleased to offer different adapted deployment methods with different geotechnical equipment in close cooperation with Marine Sampling Holland (marinesamplingholland.nl). Some nearshore and - so far - all onshore tests have been performed with the PushHeat system (a combination of a mini-CPT with a coiled thermal test rod; the picture shows one site on the beach on a stormy day). In 2021, we also expect to deploy downhole technology for onshore locations where a high-resolution TRT profile is required to depths greater than 10 meters. To reach these depths, multiple cycles of drilling/probing will be performed. More information on the methods and additional references can be found at www.fielax.de/en/what-is-heat-flow/.

Modelling

FIELAX presents its latest development: 2D and 3D temperature evolution calculations in marine sediments. The models incorporate the geothermal heatflow, measured thermal properties of the sediments as well as temperature variations through seasonal variations of the bottom water temperature. As a result the models determine temperature distributions resulting from superimposition of seasonal, natural temperatures and those induced by internal sources such as power cables, the latter also time-dependent.

  • The Cable Route Model is a full model for the temperature field in and around submarine power cables. The model includes heterogeneous properties of the sediments, seasonal heating and cooling through bottom water temperature variations, and heating thgough time-dependent power loss from the cable. Applications are the 2k-criterion or the dimensioning of subsea power cables (PDF-Flyer).
  • The 3D temperature model has been developed to calculate temperature fields in marine sediments or onshore soil. Given inputs are measured thermal properties and approximated seasonal temperature deviations of the water/air. Thus, the seasonal effects as well as influences from heat sinks- and sources (such as energy cables or heat exchangers) may be modelled.

Read our “Prediction of Sediment Temperatures” (PDF) brochure for detailed information: