Download Pore Network Analysis of Carbonate Rocks by Tomographic Images

Pore Network Analysis of Carbonate Rocks by Tomographic Images Taken at Multiple
Spatial Resolutions
Rodrigo Nagataa, Carlos Roberto Appolonia and Paulo José dos Reisb
a
State University of Londrina
Rodovia Celso Garcia Cid | Pr 445 Km 380 | P.O. Box 10.011
Zip code: 86.057-970 - Londrina - PR
b
Midwestern State University
Rua Simeão Camargo Varela de Sá, 03
Zip code: 85040-080 - Guarapuava - PR
Carbonate rocks are sedimentary rocks well known as petroleum reservoir. Since petroleum is
the world’s main energy source, there is a high interest in finding more effective ways to its
extraction. To do that, it is important to know the structural parameters of the reservoir rock,
especially the pore network, once it gives information about the rock’s storage capacity and
how difficult it might be to extract the petroleum. Since carbonate rocks have a large range of
pores sizes, their pore network is highly complex and have been the main object of many
studies.
X-ray computed tomography has arisen in the last 15 years as a powerful alternative to study
petrophysical properties of reservoir rocks, among many other applications. Because of the
features of this technique, it is necessary to have very small samples in order to have high
resolution images. However, many times such small samples are not representative to the
original rock. In order to evaluate the differences that the sample size and spatial resolution
used might have in the pore network results achieved by X-ray computed tomography, two
kinds of carbonate rocks (Desert Pink Limestone and Winterset Limestone) were cut and
resample to be scanned in five different spatial resolutions (90 µm, 13 µm, 5.5 µm, ~1 µm,
65 nm). To perform these measurements, four microtomographs were utilized: V|tome|x
L300 (GE), SkyScan 1172 (Bruker microCT), Versa XRM-500 (Zeiss/Xradia) and Ultra
XRM-L200 (Zeiss/Xradia).
The generated 3D images allowed the qualitative analysis of pore dispersion throughout the
sample. The 2D images were used to calculate the total porosity and the pore size distribution
of the samples. The results showed the importance of many measurements at different spatial
resolutions to measure the whole range of pore sizes. The achieved total porosity results were
ϕ90=0.202%, ϕ13=2.19%, ϕ5.5=11.7%, ϕ1.7=7.43%, ϕ65=9.93% for Desert Pink samples and
ϕ90= 1.38%, ϕ13= 6.23%, ϕ5.5= 20.5%, ϕ1.3= 19.8%, ϕ65= 7.81% for Winterset samples. They
showed that there is a notable variation in the total porosity results when the spatial resolution
changes.