Visualisation and analysis of pore networks and fluid flow in porous rocks

Paul Boughton
The Department of Petrophysics and Borehole Geophysics at the Leibniz Institute for Applied Geophysics (LIAG) conducts fundamental and applied research in process-focused petrophysical characterisations of natural rocks.

Besides standard petrophysical core analysis (CAL), special rock core investigations (SCAL) are carried out to understand complex petrophysical processes and to improve the assessment and characterization of porous reservoir rocks.

Results are directly linked to improve recent and develop new methodologies, devices and techniques for paleo-climatic research, geochronology, general reservoir characterisation, geothermal energy usage as well as CO2 sequestration and storage (CCS).

A significant strength of this department is the close linkage of in-situ measurements in boreholes with detailed and complex lab scale experiments, which greatly enhances the knowledge of physical processes on different scales.

An important part of modern petrophysical research is recently formed by numerical modelling – so called 'digital rock physics' (DRP) – which is getting an increasing focus of interest. Recent developments of new and versatile imaging techniques and auspicious computational hardware have greatly increased the possibilities for complex and interdisciplinary rock characterization.

The Department of Petrophysics and Borehole Geophysics uses a high resolution micro-CT (nanotom 180, from GE Sensing & Inspection Technologies – phoenix|x-ray) to derive non-destructively high quality 3D imaging data sets of conventional reservoir and highly complex porous rocks. With this compact lab scale imaging device, voxel resolutions within the sub-micron range (600 – 800 nm) are feasible. These high-resolution data sets are used for qualitative and quantitative petrophysical investigations and for numerical modelling purposes at the pore scale.

In this respect, Avizo Fire software offers great functionality and a wide range of possibilities for visualisation and complex rock sample characterisation.

Generally, the workflow starts with basic visualisation and identification of the different mineral phases within the rock sample. Then, pore space can be segmented from this data in different ways: either by means of total porosity evaluation or by segmenting effective – ie interconnected – porosity only.

The so-derived pore network can be further investigated to get access to even smaller scale pore space topology and geometry by using the skeletonisation module of Avizo.

Additionally, a variety of quantification tools allow even more complex research, eg the determination of small-scale porosity inhomogeneities, determination of representative elementary modelling volumes, pore space tortuosity and many more.
Once this image-based rock characterisation is performed, imaging data can be prepared for numerical modeling purposes. Not only computational fluid dynamics (CFD), but also modeling of complex electrical properties and nuclear magnetic resonance effects at the pore scale can be conducted. Avizo’s 'Wind' module offers a versatile toolbox for the visualisation of these results, which greatly increases the knowledge of petrophysical rock properties.

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