Image Analysis of Pore Geometry: Relationship to Reservoir Engineering and Modeling

Abstract

ABSTRACT Image analysis of thin section and SEM samples from core plugs, sidewall cores and cuttings samples provides rapid, quantitative data concerning the size and geometric complexity of reservoir pore systems. Several distinct classes of porosity (Pore Types) co-exist in many reservoirs. This is particularly true in reservoirs which are shaly or have under-gone diagenesis (sandstones with less than 25% porosity, and all carbonates). Each pore type has 1) a unique size distribution that is independent of other pore types in the same reservoir, and 2) a unique relationship between pore body and pore throat size. Reservoirs with similar values for porosity and permeability can have different production efficiencies due to variations in pore geometry. Regression procedures provide a first order model between measured capillary pressure and image-derived pore types. This relates pore types to measured pore throat size and allows for the direct calculation of permeability and capillary pressure from small samples (sidewall cores). Three dimensionless variables (Tau, Epsilon and Sigma) are calculated from image analysis of pore geometry. These provide quantitative information regarding the relative efficiencies of individual sands within a reservoir and between various reservoirs. Comparisons of efficiency based on Tau and Epsilon, allow for a numerical ranking of reservoir quality based on a uniform, quantitative system of analysis.