Advanced laboratory techniques characterising solids, fluids and pores in shales

Shales are of significant interest as reservoirs, seals and overburden in petroleum exploration and production, geological storage of CO2 and in the nuclear waste industry. Their properties and microstructure are difficult to measure and image and as such, there are still considerable gaps in our understanding of shale behaviour. The advent of more advanced and quantitative imaging methods along with novel sample preparation techniques including synchrotron imaging and K-edge subtraction with a contrast fluid, scanning (SEM) and transmission electron microscopy (TEM), have combined to allow the resolution of pores in the matrix and the organic matter in gas shales down to the nanometre scale. Textural quantification methods include neutron diffraction to quantify clay fabric alignment in siliciclastic shales as well as stress-dependent calcite c-axis orientation in carbonate-rich gas shales. The contents of the pores are also critical to the assessment of the preservation state of shales as well as the degree of water/gas saturation in resource shales. Combinations of dielectric analysis and 2 and 23 MHz nuclear magnetic resonance (NMR) measurements in siliciclastic and carbonate-rich gas shales can resolve not only the location of water, but also the interaction between water and mineral/organic surfaces in addition to the water and oil content. The organic content of shales is of particular interest in unconventional resources and this has driven application of Fourier transform infra-red (FTIR), to distinguish both mineral and organic maceral components in gas shales and Raman spectroscopy, which is increasingly used for organic matter characterisation in high maturity shales. Ultimately, shales are extremely complex nano-composite materials which require the application of multiple techniques to help determine their bulk physical and flow properties as well as factors controlling fabric and pore orientations and structure.