'Shale machine' set to crack the clay code

Posted 25 September 2013

Rocks rich in clay minerals can exhibit complex behaviour in response to changes to the physical conditions. Image: Wikimedia Commons.

A new analytical system developed at the UNSW Connected Waters Initiative (CWI) is now poised to tackle measuring the properties of one of the most complex kinds of rock.

Designed and built by Dr Hamid Roshan, the innovative 'Shale Machine' is being brought to bear on some of the most challenging aspects of groundwater research currently undertaken at CWI.

Porous rocks can contain fluid natural resources such as groundwater, oil and gas in the spaces between grains and crystals that comprise them.

Predicting and evaluating the effects of human activities on subsurface rock systems that contain these fluid resources, such as mining, drilling and extraction, requires a detailed understanding of the physical and chemical properties of rocks.

These properties of rocks vary with the structure and composition of the minerals they contain.

"Of the different kinds of minerals present in rocks, clay minerals exhibit the most complex behaviour," says Dr Roshan. "Their physical and chemical properties can change significantly in response to changes to the physical conditions in which they occur."

The properties of clay are determined by the atomic structure of the clay mineral crystals and the "electrostatic double layer" formed by the surface charge they carry. The presence of surface charges can lead to swelling, shrinkage, osmosis or cracking, with potentially significant implications depending on the context in which these changes occur.

"Understanding and characterising the properties of clay-rich rocks is essential but extremely complicated," Dr Roshan says.

Dr Roshan's design uses a unique combination of sensors (pressure, temperature, flow-rate and displacement transducers) that simultaneously feed measurements from a pressurised rock sample injected with fluid to a computer.

The apparatus can measure 4 different key properties of clay-rich rocks, such as shale:

  1. Permeability and porosity;
  2. Chemical and thermal osmotic flow;
  3. Change in permeability due to change in stress;
  4. Multiphase fluid and solute transport.

One of the advantages of the system is that all of these measurements can be taken from a single sample as long as the physico-chemical properties of the sample are unchanged during the test.

"Previously, measurement of these different properties would require multiple samples and different laboratory procedures. This is the first time both solid and fluid attributes of a shale sample can be measured at once," says Dr Roshan.

'Shale machine'The innovative 'Shale machine' can measure both solid and fluid attributes of a shale sample at once.

While in the past is was possible to obtain thermal osmotic flow measurements of low accuracy from unconsolidated samples, the new system is able to provide these measurements at high accuracy from rock and consolidated soil samples.

Micro-scale and chemical analyses involved in the process such as the Electron Microscope Unit (EMU), X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) are performed at the UNSW Mark Wainwright Analytical Centre.

The data can be applied to modelling how clay-rich rocks might respond to changes in the environment in situations where they play an important role in the containment of fluid natural resources. 

The work forms part of the CWI contribution to national research programs investigating surface water-groundwater interactions and the innovative characterisation of aquifers and aquitards, in conjunction with the National Centre for Groundwater Research and Training (NCGRT). The Connected Waters Initiative is a joint research initiative of the UNSW Faculty of Science and Faculty of Engineering.

Links:

Contact:
Dr Hamid Roshan
Email - H.Roshan@wrl.unsw.edu.au; Phone - +61 2 8071 9850

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