Unconventional reservoir characterisation
Unconventional gas and light oil reservoirs are typically associated with very low matrix permeabilities (<0.1 mD). These reservoirs can be clastic or carbonate. Many are composed of shale, which can also serve as the source rock. Because of the low matrix permeabilities, development of these reservoirs relies on horizontal drilling and stimulation by hydraulic fracturing in order to maximise contact of the formation with the well bore. Although unconventional reservoirs are often pattern-drilled and fractured, production on a well-to-well or fracture-stage basis can be extremely variable.
As with all reservoirs, heterogeneities within the unconventional reservoir occur at different scales and thus influence individual fracture stage and well performance in addition to overall field productivity. As a result, reservoir characterisation requires measurements over many length scales, from the microscopic to the seismic scales. Variability in lithology and other petrophysical properties leads to variability in the reservoir’s elastic and geomechanical properties, which have a direct impact on the rock’s response to hydraulic fracturing. In addition, understanding physical property anisotropy and the state of stress in the subsurface is essential in order to properly orient horizontal wells and to predict how induced fractures will interact with the surrounding rock, naturally-occurring fractures, and with each other.
To support the application of unconventional reservoir characterisation at all length scales, CRGC is working in the following areas:
- quantitative microstructure characterisation using micro-CT and nano-indentation
- digital rock modelling based on X-ray microtomographic images acquired under high pressure and temperature conditions
- laboratory measurements of intrinsic and stress-induced elastic property anisotropy
- modelling elastic properties of fractured reservoirs
- modelling stress-dependent properties of rocks
- measurements of seismic anisotropy from VSP and surface seismic data