The Importance of Thermal Conductivity for Geothermal Research

Written by Igor Oliveira, M. Eng., Marketing Lead.

This post highlights the use of C-Therm’s MTPS sensor/method for testing geological samples.

A group of researchers from the British Geological Survey (BGS) – a world-leading geological survey and global geoscience organisation – published a paper in which C-Therm’s Modified Transient Plane Source (MTPS) method was used to measure the thermal properties of some UK bedrock materials. The results were published in EAGE’s (European Association of Geoscientists and Engineers) 2nd Geoscience & Engineering in Energy Transition Conference.

The publication, Thermal properties of Triassic Sherwood (Bunter) Sandstone Group and Mercia Mudstone Group (Keuper Marl) lithologies [1], includes the test results of 59 samples of Sherwood Sandstone Group (SSG) sandstone and 29 samples of Mercia Mudstone Group (MMG) argillaceous/mudstone facies.

C-Therm’s MTPS sensor being used during the tests. Copyright BGS, UKRI 2021 [1]

As described by the authors, the thermal properties of rocks and soils are extremely important for the design of renewable energy systems including geothermal wells and underground energy storage systems. Additionally, they explore the concept that the correct design of Ground Source Heat Pumps (GSHP) and Underground Thermal Energy Storage (UTES) requires estimation or direct measurement of local thermal properties in the relevant depth interval [2]. The table below presents a sample of the results obtained by Boon et al. [1] in the form of a simplified summary, focusing on Thermal Conductivity and Effusivity measurements using C-Therm’s MTPS method.

The United Kingdom has plans to transition to a Net Zero economy by 2050, something that will require decarbonization of heat according to the UK Government’s strategy, which introduced a target to grow the installation of heat pumps from 30,000 per year to 600,000 per year by 2028 [3]. BGS’s authors responsible for the research – D.P. Boon, G. J. Farr and E. Hough – estimate that GSHP will play an important role in this transition, accounting for 10% to 20% of these heat pumps [1].

Geothermal energy refers to producing renewable energy from underground heat, and it is described by the U.S. Department of Energy as a “vital, clean energy resource” and that it “supplies renewable power around the clock and emits little or no greenhouse gases.” [4]

According to Busby [5], geological mapping in England started over 2 centuries ago and since then there has been extensive onshore exploration for minerals, coal, oil, gas and geothermal resources. The temperatures at depth are determined by the heat flow and the thermal conductivities of the strata, and Busby presented 184 observed heat flow measurements based on equilibrium temperatures and laboratory thermal conductivities, as well as 504 estimated heat flows based on corrected BHTs and estimated thermal conductivities [5].

Measured temperatures at 1km below ground level, the median temperature is 38 °C (left) and estimated temperatures at a depth of 7 km (right) [5] – BGS/NERC

Geothermal heat found in mine water is an example with great potential in the UK. According to the Coal Authority, the government body responsible for former coal-mining assets, one-quarter of the UK’s residential properties sit on coalfields, regions with huge potential to provide a low-carbon energy for homes and businesses in former coal-mining areas in Wales, the Midlands and the north of England [6]. “The mine water is heated by geothermal processes, is constantly replenished and maintains a stable temperature. According to the Coal Authority’s calculations, there’s theoretically enough water to provide all of the heating needs for the populations in the coalfields, as well as being used by local businesses working in areas such as horticulture and manufacturing.”[6]. According to CNBC, energy firm Ecotricity has signed a ten-year deal for electricity which will be produced by a British geothermal power plant, representing another step forward for the country’s fledgling industry [4] and shows that this field’s potential is yet to be explored to its fullest.

When looking at these research and data, thermal conductivity presents itself as a key component of this type of analysis, which can be crucial for future developments in this field. C-Therm’s MTPS, TPS, and TLS methods are great options to study strata.

C-Therm Trident pictured above with MTPS (ASTM 7984), FLEX TPS (ISO 22007-1) and TLS NEEDLE (ASTM D5334 and D5930) configuration

For more information on Trident or its methods applied to different research fields, please contact a subject-matter expert from C-Therm.

You may also be interested to learn of C-Therm’s new TLS-HT300 which has been developed for application of testing the thermal conductivity of geological samples at elevated temperatures (300ºC) and pressures (3000 PSI). Learn more here.

References