Proceedings of the Second International Energy 2030 Conference,
November 4-5, 2008, Abu Dhabi, U.A.E.

Characterization of the Pore Structure Heterogeneities in Heterogeneous Reservoirs Using CRAI Porosimetry

Dr. Ioannis Chatzis
The Petroleum Institute, UAE & University of Waterloo, Ontario, Canada

Dr. Nima Rezaeii
University of Waterloo, Ontario, Canada

Abstract
This paper elucidates the pore level physics of gas invasion in heterogeneous porous media when a slug of air is injected at constant rate. The porous medium is saturated with a wetting liquid prior to gas injection. When the rate of gas injection is very low and buoyancy forces are minimized in horizontal displacements, the magnitude of capillary pressures at the pore scale determines the pathways selected by the invading gas. As the gas invades a relatively large pore (such as a vug - of mm size pores in carbonate rocks), the gas pressure registered near the face of injection drops suddenly and then builds up again to invade the largest pore throat connecting it to adjacent pores. Constant rate air injection (CRAI) by forcing a known slug of air volume in a porous medium with heterogeneities and monitoring the pressure at the face of injection enables the determination of the volume and size distribution of macroscopic heterogeneities. The heterogeneities were vugs of size greater than 1mm³ or were regions of high permeability surrounded by pore matrix of lower permeability. Flow visualization results obtained by conducting these experiments in sintered glass bead models with heterogeneities validated the rationale of this method that offers an inexpensive way for characterizing the pore structure of heterogeneous porous media. Results of vug size characterization are in very good agreement with the actual vug size made artificially in micromodels. The CRAI porosimetry has applications for routine core analysis for vugs greater than 1mm³ in porous media that become accessible by air during the constant rate injection.