Digitalcore has extensive experience in 3D analysis of carbonate core material. The determination of the pore size distribution in carbonate rocks remains challenging; extreme variability in carbonate depositional environments and susceptibility to a range of post-depositional processes results in complex pore structures comprising length scales from tens of nanometers to several centimeters. To increase understanding of the role of pore structure on connectivity, conductivity, permeability and recoveries requires one to probe the pore scale structure in carbonates in a continuous range across more than seven decades of length scales (from 10 nm to 10 cm) and to integrate information at these different scales. Digitalcore has developed innovative technology to probe the pore scale structure in carbonates across many decades of scale.

Integrated Multiscale 3D Imaging
From the nanometer to the plug scales:

• 3D micro-CT imaging of plug scales (up to 2 inch /50 mm)
• 3D micro-CT pore/grain scale imaging (down to 1 micron resolution)
• 3D FIBSEM imaging (from 10nm to – 1 micron resolution)
• 2D optical thin section imaging
• 2D SEM imaging; from 10 nm to 2 micron resolution

Micro-CT systems are utilised to acquire 3D images made up of 2000³ voxels on core plugs up to 6 cm diameter with resolutions down to 1 micron. Complimentary experimental techniques including optical microscopy, petrography, backscattered scanning electron microscopy (BSEM), and Focused Ion Beam SEM (FIBSEM) are used to allow us to probe the pore scale structure in core material in a continuous range across over six decades of length scales (from 5 nm to 5 cm). This allows the 3D pore-space of a rock and fluid distributions within pores to be imaged over several orders of magnitude.

Digitalcore’s patented registration technology enables VoxelPerfect™ integration of 3D micro-CT images to a range of complimentary techniques. These are then used to couple information at different length scales. This leads to better understanding of carbonate pore/grain structure and the static and dynamic properties of different carbonate core.

From micro-CT and FIB Tomography data on carbonate samples we can derive properties at multiple scales:

1. Macro/meso/microporosity, pore volume, porosity connectivity, pore-throat/body size distribution, shape, roughness, heterogeneity.
2. Petrophysical properties including permeability, formation factor.
3. Estimation of drainage capillary pressure, primary drainage relative permeability and visualization of drainage displacement.
4. Estimation of imbibition relative permeability, capillary pressure and residual hydrocarbon saturations In addition Digitalcore can derive petrographic/mineralogical information including fabric orientation. A number of studies have been undertaken: examples of some to date have included:

• Mark Knackstedt, A. Sheppard, S. Latham, M. Madadi, T. Varslot, C. Arns, G. Baechle, G. Eberli, Probing Pore systems in Carbonates, Paper A, Society of Petrophysicists and Well Log Analysts Annual Symposium, May 25-28, 2008, Edinburgh, Scotland. copyrighted – see OnePetro
• M. Knackstedt, M. Madadi, C. Arns, G. Baechle, G. Eberli, Carbonate Petrophysical parameters derived from 3D images, 2008 AAPG Annual Symposium, San Antonio, TX, April 23, 2008. (Awarded George C. Matson Award for best paper at the Annual AAPG convention). copyright AAPG
• A. Ghous, T. Senden, R. Sok, C. Arns, A. Sakellariou and M. Knackstedt, 3D characterization of microporosity in carbonate core, Society of Petrophysicists and Well Log Analysts Middle East Symposium, Paper E, April 16-18, 2007, Abu Dhabi, UAE. copyrighted – see OnePetro
• M. Knackstedt, C. Arns, A. Ghous, A. Sakellariou, T. Senden, A. Sheppard, V. Nguyen, W. V. Pinczewski, 3D imaging and characterization of the pore space of carbonate core; implications to single and two phase flow properties, Society of Petrophysicists and Well Log Analysts Annual Symposium, Paper A, June 5-8, 2006, Veracruz, Mexico. copyrighted – see OnePetro
• C. H. Arns, F. Bauget, A. Limaye, A. Sakellariou, T. J. Senden, A. P. Sheppard, R. M. Sok, W. V. Pinczewski, S. Bakke, L. I. Berge, P. E. Oren and M. A. Knackstedt, Pore scale characterization of carbonates using micro X-ray CT, December 2005 Society of Petroleum Engineers Journal, 475-484, (2005) copyrighted – see OnePetro

 

Streamlines derived from flow simulations in 3D image.

 

3D Visualization of an Oomoldic reservoir carbonate; yellow shows the dry pores. The sample undergoes centrifugal drainage to a pore size of ~3 microns; given in red is the drained pores.