Petrophysics

Laboratory Resistivity Measurements

Laboratory Resistivity Measurements

non-contact resistivity

electrical resistivity measurements

The overall aim of petrophysics studies is the characterisation and prediction of physical properties and ground stability of UK formations, including superficial deposits, using innovative non-invasive geophysical techniques and a newly developed rapid geophysical probing suite.

The project objectives include:

  • improving the correlation between geophysical measurements and key geotechnical parameters
  • development of best practice at the interface between geophysics and geotechnics
  • linking geophysical property data with the National Geotechnical Properties Database
  • providing information for use at the desk-study phase of ground investigations
  • improving the understanding of the control of pore-scale processes on geophysical and geotechnical properties.

This project and has strong links with academia and partners from the civil engineering/construction industry. Additional users and partners are found in the oil industry and defence research agencies, where laboratory studies have been an ongoing theme for a number of years.

Examples of research

A resistivity-moisture content relationship determined from samples of tropical red soil is used to predict the water content distribution of an embankment following resistivity monitoring surveys (Jackson et al., 2000).

The embankment failed at the zone of high water content identified by the red zone on the RH shoulder. Note also the area of high water content (red) below the tarmac pavement across the embankment top.

Determining the relationship in the laboratory enables geophysical survey data to be interpreted in terms of properties more relevant to the user.

[Jackson P D, K J Northmore, P I Meldrum, D A Gunn, J R Hallam, J Wambura, B Wangusi & G Ogutu 2002 Non-invasive moisture monitoring within an earth embankment - a precursor to failure. NDT&E International, vol. 35: 107-115]

A new laboratory technique has been developed using a non-contact resistivity method (Jackson et al., 1997) to determine the resistivity-moisture content relationship for a loessic brickearth deposit at Ospringe, Kent (Jackson et al., 2006)*.

The relationships established in the laboratory were used to calibrate field resistivity measurements undertaken to assess ground conditions of the loessic brickearth during a large-scale field ‘collapse test’, in collaboration with the universities of Birmingham Loughborough and Nottingham Trent.

[* P D Jackson, et al., 2006. Electrical resistivity monitoring of a collapsing metastable soil. Quarterly Journal of Engineering Geology and Hydrogeology, 39, 151–172]

A methodology has been developed for assessing the fine-scale structure of rock and soil cores using electrical resistivity measurements. The technique incorporates a bench-top ‘robot’ that automatically acquires very closely spaced resistivity point data across faces of prepared core samples. The data are processed to create a resistivity image that highlights fine-scale sedimentary, and discontinuity structures across the area of core face, allowing millimetre-scale variability to be assessed. Recognition and assessment of these fine-scale structures are important in understanding the flow paths of fluids, such as water and oil, in reservoir rocks. The assessment of fine-scale structures in rocks and soils is assuming ever more importance as their sensitivity to past climatic change becomes recognised.

Contacts

For further information contact: enquiries@bgs.ac.uk