Nuclear Waste Repository
Geotek Core Logging Services : Case Study
MSCL and X-Ray Radiography of the Boom Clay and Ypresian Clay Stratigraphy
On behalf of ONDRAF/NIRAS, the Belgian organisation in charge of the management of radioactive waste Geotek conducted MSCL and X-ray logging of two target clay formations
AIMS
- To identify small and large scale lithological variations
- To provide geotechnical and geophysical parameters
- To visualise the effect of sample expansion and sample disturbance
Correlation with downhole geophysics links the MSCL data to more regional geological units, providing stratigraphical tie points, and ultimately improves the resolution of the downhole geophysics.
Technique
Geotek mobilised a Standard Multi-Sensor Core Logger (MSCL-S), and a X-ray Computer Tomography machine (MSCL-XCT) within a mobile containerised laboratory. Two Geotek geoscientists accompanied the equipment and logged approximately 500 m of core within a 3.5 week period at 1 cm to 2 cm resolution.
Results
The high resolution MSCL data and 100 micron resolution X-ray images provided Ondraf/Niras with a multi-parameter stratigraphy that can be integrated with imaging of the natural and artificial structure within a core sample. This provided ONDRAF/NIRAS with vital information to help plan and determine laboratory testing, and aid their geological and geotechnical evaluation.
The X-ray images provide visualisation of previously unidentified features within the stratigraphy such as fine-scale cross-bedding. Core disturbance was also identified from the decrease in gamma density (comparable to bulk density) and loss of P-wave signal.
The electrical resistivity and natural gamma data indicates fining and coarsening grain-size sequences, and resolved features that were previously unidentified from the downhole geophysics. Formation boundaries and authigenic precipitates were observed from sharp changes in gamma density and P-wave velocity. Magnetic susceptibility differentiated the two clay formations, and sand due to their relative magnetic mineral contents.
