Geophysics

BGS undertakes research and development in the field of near surface geophysics. This work is supported by temperature controlled laboratory facilities, in which geophysical property measurements and laboratory-scale imaging studies are undertaken. Direct geophysical property measurements of samples are carried out to provide calibration data for field scale geophysical models; testing is carried out using both bulk samples and core imaging. Testing is also undertaken to investigate geophysical-hydrogeological property relationships for calibration of time-lapse geophysical datasets. Tank-scale imaging studies are used to evaluate the performance of geophysical imaging/monitoring methodologies by simulating real-world problems in highly controlled conditions. These highly controlled analogue studies are also used to systematically assess the resolving capabilities of geophysical characterisation and imaging approaches, evaluate the performance of new geophysical modelling code, and test new survey design/data acquisition strategies.

The laboratory based geophysical research and development is integrated with ongoing programmes of geophysical modelling and inversion code development, and the development of field-scale geophysical observatories used for monitoring a range of environmental problems.

Geophysical Capabilities

Acoustics

Ultrasonic research facilities comprise bio-inspired signal processing and transducer technologies for rock property characterisation and imaging using coded acoustic signals. Waterborne precision transducer systems operating between 40 kHz to 250 kHz with a 116 micron reposition repeatability have been developed and deployed in a large experimental tank facility for research and development activities.

High-resolution core resistivity scanning

The laboratory is equipped with the BGS-developed Core Resistivity Imaging System, which can scan the surface of reservoir rocks and produce electrical images of fine sedimentological structures at centimetric scale. Core scanning facilities at BGS are used to study petrophysical properties affecting fluid flow, migration and compartmentalisation, such as, porosity, permeability, grain size distribution, mud/sand ratio and contribution to fault gouge, which are governed by small-scale (mm-to-m scale) structure.

Hydrogeophysical property measurement and imaging

Facilities include electrical imaging systems for the measurement of DC resistivity and induced polarization (IP), self-potential (SP), and spectral-induced polarisation (SIP). A range of sample holders for four-point electrical measurement of unconsolidated samples have been developed, for the direct measurement of individual samples. Experimental tanks and columns, with hydraulic control, are used for hydrogeophysical monitoring experiments, and are equipped with a range of borehole and surface based imaging arrays. The laboratory is also equipped with a range of other sensors for monitoring water depth, moisture content, pore fluid EC and temperature.

Applications

Rock property characterisation

Ultrasonic and core-scale geoelectrical approaches to rock property characterisation are being developed with the aim of determining pore morphology, the size, nature and extent of fractures and fracture networks, surface texture effects and sediment properties.

Multiphase flow imaging

Experiments are undertaken to develop electrical imaging techniques for monitoring contaminant transport in porous media. This work include both aqueous phase and non-aqueous phase contaminants.

Heterogeneity determination

Research is undertaken into the performance of spatial and volumetric imaging techniques for the characterisation of heterogeneous unconsolidated experiments. This work has applications in determining both lithological and hydrogeological heterogeneity.

Slope stability

Calibration measurements are undertaken in temperature controlled conditions to assess the relationships between moisture content and resistivity for samples collected from unstable slopes and structures. This work supports ongoing slope stability monitoring undertaken by BGS at a number of field observatories where slope failure processes are being studied.

Publications

Kuras, O, Pritchard, J, Meldrum, P I, Chambers, J E, Wilkinson, P B, Ogilvy, R D and Wealthall G P. 2008. Monitoring hydraulic processes with Automated time-Lapse Electrical Resistivity Tomography (ALERT). Comptes Rendus Geosciences - Special Issue on Hydrogeophysics, Vol. 341, 868—885.

Loke, M H, Chambers, J E, and Ogilvy, R D. 2006. Inversion of 2-D spectral induced polarization imaging data. Geophysical Prospecting, Vol. 54, 1—15.

Chambers, J E, Loke, M H, Ogilvy, R D and Meldrum, P I. 2004. Non-invasive monitoring of DNAPL migration through a saturated porous medium using electrical impedance tomography. Journal of Contaminant Hydrology, Vol. 68, 1—22.

Chambers, J E, Kuras, O, Meldrum, P I and Ogilvy, R D. 2003. Comparison of fundamental modes of illumination for cross-hole electrical impedance tomography: Part I - sensitivity analysis. 9th European Meeting of Environmental and Engineering Geophysics, European Association of Geoscientists and Engineers, August 31 — September 4, 2003. (Prague, Czech Republic.)

Kuras, O, Chambers, J E, Meldrum, P I and Ogilvy, R D. 2003. Comparison of fundamental modes of illumination for cross-hole electrical impedance tomography: Part II - synthetic modeling. 9th European Meeting of Environmental and Engineering Geophysics, European Association of Geoscientists and Engineers, August 31 — September 4, 2003. (Prague, Czech Republic.)

Chambers, J E and Wilkinson, P B. 2009. CLARET WP3: Laboratory Experiments. British Geological Survey Commissioned Report, CR/08/053.

Contact

Please contact Dr David Gunn for further information