REV ANALYSIS FOR CARBONATE ROCKS USING PNM FROM MICRO-CT IMAGES AND NMR T2 DISTRIBUTION

Resumo

Reservoir studies have reached a great advance in the last years with the introduction of
microtomography (micro-CT) images of rocks. This technology is a non-destructive method that allows
the investigation of internal structure of rock in pore scale, and to build representative 3D models of the
rock. With the purpose to retrieve representative petrophysical properties from these digital models, the
objective of this work is to apply a Representative Elementary Volume (REV) analysis for the
heterogeneous carbonates, considering threshold values, image resolution and NMR pore-size
distributions, to estimate porosity and permeability REVs. In this study, carbonate rock samples,
Coquina and Edwards Brown, were submitted to three main laboratory measurements: routine core
analysis, NMR experiments, and microtomography scans. The micro-CT images were processed using
a commercial image processing software. The threshold selection analyzed by applying three methods,
but the NMR pore-size distribution oriented threshold was used to proceed with the entire workflow.
Skeletons were extracted from pore space binarized in the micro-CT image and exported to PoreFlow
for the generation of Pore Network Models (PNM) and permeability estimation. The permeability of the
PNMs were estimated considering Hagen-Poiseuille Law to simulate single-phase flow and Darcy’s
Law. This methodology was applied to three samples of different sizes, their volume was further divided
into smaller sub volumes and their relation with REV were analyzed. The rock samples studied could
be considered, with a high confidence, as REV for porosity, but only the larger samples could be
considered as REV for permeability.