GFZ Thermal Petrophysics Lab – Data Report 2024-01: Thermal properties of the shaly Jurassic (Upper Toarcian) formation at the Tournemire underground research lab (Tournemire, France) #

Abstract #

The thermal characterization of the clayey Jurassic (Upper Toarcian, ca. 180 My old) is contributing to the site characterization of the Tournemire Underground Research Lab (URL), located in Southern France. This URL is installed in a former railway tun-nel to better understand the physical processes resulting from thermal and hydrau-lic loading in a small fault zone in a highly consolidated shale formation (Bonnelye et al., 2023). At the Tournemire site, faults and fractures of different sizes extend from the surface (sedimentary cover) to the crystalline basement. At one specific gallery (Gallery East 03) installed in the former tunnel, thermally controlled in-situ fluid injection experiments are scheduled on a strike-slip fault zone outcropping at the URL (Bonnelye et al., 2023). In 2022, we visited the URL for baseline characteri-zation of thermal properties and to study the heterogeneity of the clay-dominated formation. Therefore, we took the chance to collect data and samples for a laborato-ry measurement campaign and to measure thermal conductivity in-situ in the tun-nel wall of Gallery East 03. The thermal data shall provide the baseline for the pa-rameterization of future numerical 3D models to better understand the thermal-hydraulic processes related to the experiment. This data publication provides the results of the investigations and measurements conducted on-site in the field la-boratory and at the Thermal Petrophysics Lab at GFZ.

Methods #

Thermal conductivity and diffusivity of rock samples were measured under both ambient laboratory conditions and elevated reservoir temperatures using three primary methods: the Transient Line Source (TLS), Transient Optical Scanning (TCS), and Transient Plane Source (TPS) methods. TLS measurements involved inserting a heated probe with temperature sensors into drilled holes in rock cores, capturing heat decay data to compute conductivity. For these, the TLS-50 sensor with a Thermtest MP-2 device was used. TCS measurements were performed on oven-dried, black-painted samples scanned under a moving heat source, with conductivity values derived from the resulting infrared temperature profiles. In each case, multiple readings per sample ensured reliable results.

The Hot Disk TPS 1500S method, employing a double-spiral Nickel foil sensor sandwiched between insulating layers, was used to measure thermal conductivity, diffusivity, and specific heat capacity at various elevated temperatures. This approach allowed for testing up to 275°C using a software-controlled convection oven. Seven core samples were tested under ambient conditions, and six were tested across seven temperature steps, with multiple runs per sample.

To account for in situ reservoir conditions, thermal measurements conducted on dry samples were corrected for water saturation using a geometric mean model. This model incorporates the porosity of the samples and known thermal conductivities of air and water. Porosity values, based on Bonnelye et al. (2024), were set at 12% for samples from fault and damaged zones, and 10% for intact non-fault samples. These corrections provided estimates of saturated thermal conductivity that more accurately represent the subsurface thermal behavior of the studied formations.