Pore Scale Characterization of Carbonates Using X-Ray Microtomography
- Christoph H. Arns (Australian National U.) | Fabrice Bauget (Australian National U.) | Ajay Limaye (Australian National U.) | Arthur Sakellariou (Australian National U.) | Timothy Senden (Australian National U.) | Adrian Sheppard (Australian National U.) | Robert Martin Sok (Australian National U.) | Val Pinczewski (U. of New South Wales) | Stig Bakke (Statoil) | Lars Inge Berge (Statoil) | Paul E. Oren (Numerical Rock Inc.) | Mark A. Knackstedt (Australian National U.)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 2005
- Document Type
- Journal Paper
- 475 - 484
- 2005. Society of Petroleum Engineers
- 1.8 Formation Damage, 4.3.4 Scale, 5.3.1 Flow in Porous Media, 2.4.3 Sand/Solids Control, 5.6.1 Open hole/cased hole log analysis, 5.3.2 Multiphase Flow, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.5.3 Scaling Methods, 1.6.9 Coring, Fishing, 5.8.7 Carbonate Reservoir, 5.1 Reservoir Characterisation, 1.2.3 Rock properties, 7.5.3 Professional Registration/Cetification
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A reservoir carbonate core plug has been imaged in 3D across a range oflength scales using high-resolution X-ray microtomography. Data from theoriginal 40-mm diameter plug was obtained at the vug scale and allows the size,shape, and spatial distribution of the disconnected vuggy porosity to bemeasured. Within the imaged volume over 32,000 separate vugs are identified anda broad vug size distribution is measured. Higher resolution images on subsetsof the plug exhibit interconnected porosity and allow one to measurecharacteristic, intergranular pore size. Pore scale structure and petrophysicalproperties (permeability, drainage capillary pressure, formation factor, andNMR response) are derived directly on the highest resolution tomographicdataset. We show that data over a range of porosity can be computed from asingle plug fragment. Data for the carbonate core is compared to resultsderived from 3D images of clastic cores and strong differences noted.Computations of permeability are compared to conventional laboratorymeasurements on the same core material with good agreement. This demonstratesthe feasibility of combining digitized images with numerical calculations topredict properties and derive cross-correlations for carbonate lithologies.
Carbonate reservoirs contain more than 50% of the world's hydrocarbonreserves. In carbonate rocks, the processes of sedimentation and diagenesisproduce microporous grains and a wide range of pore sizes, resulting in acomplex spatial distribution of pores and pore connectivity. A reliablepetrophysical interpretation for predicting the transport properties andproducibility of carbonates is lacking.
Much of the poor reliability in estimating carbonate properties is due tothe diverse variety of pore types observed in carbonates. Unlike sandstones,many carbonate sediments have a bi- or tri-modal pore size distribution withorganisms playing an important role in forming the reservoirs. Carbonate rocksare further complicated by the significant diagenesis occurring throughchemical dissolution, reprecipitation, dolomitization, fracturing, etc. Forthese reasons the size and shape of any porous network is expected to be veryheterogeneous and exhibit pore sizes ranging from sub-micron to meters.Excluding fractures, three qualitatively different contributors to porosity canbe identified: Vuggy porosity (r = 100 µm), intergranular (r = 5 µm) andintragranular (r < 5 µm).1 The sizes associated with the three types ofporosity may vary across studies and are given as indicative values only. Thesefeatures distinguish the petrophysical properties and productivity of carbonatefields from other sedimentary rocks including sandstones and shales.
|File Size||2 MB||Number of Pages||10|
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