Print this pageTraditional Carbonate Classification Using X-Ray Micro-Ct
Carbonate structures are notoriously challenging to predict and understand. A key to understanding the complexity of carbonates lies not with the old technology, but with new, digital rock analysis.
The principal objectives of this paper are to digitally classify 10 unique carbonate samples according to Folk and Dunham’s classification schemes, and then to determine the important measurements of:
Porosity - effective and isolated,Permeability with respect to the classified rock, Acoustic properties, Elastic properties
Additional objectives include: Documenting and building a 3D digital archive of different kinds of porosity (intergranular, intragranular, moldic, vuggy, fracture, and intercrystalline), and comparing our collected data against industry’s standard knowledge of how each porosity type relates to permeability.
To accomplish these objectives, we performed imaging and calculated measurements at Ingrain’s digital rock analysis laboratory. The Micro CT scanner we used has a maximum resolution of 1 micron and produces a 3D digital volume of the rock in a 0 - 255 grayscale. We digitally measured porosity, permeability, acoustic, and elastic properties on the 3D digital volume that subsequently was segmented into black (pores) and white (grains). We acquired measurements through proprietary flow algorithms using the Lattice Boltzman approach. Images showed a heterogeneous carbonate containing intragranular, intergranular, shelter, and vugular porosity in one 2.55 mm diameter sample. These images further revealed a Bryozoan’s mold in one sample that was hidden within an algal mat, microfossils, Intraclasts, propagating fractures, and multiple modes of porosity; they also revealed calcitic and dolomitic intercrystaline porosity.
Our collected data correlated with the industry’s accepted understanding of how intergranular, intragranular, moldic, vuggy, fracture, and intercrystalline porosity relate to permeability. Intergranular porosity was effective, intragranular porosity was isolated, intercrystalline porosity was extremely effective, and the many modes of porosity dramatically improved permeability.
The strengths of the 3D digital analysis allow for experimental repeatability, measurement of the anisotropy of permeability, analysis of fractures found in the reservoir rock, visualization of complexly heterogeneous carbonates, and detailed images of microfossils that cannot be seen without the use of Micro XCT.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009