Pore Type Analysis Using Bore Hole Electrical Images with New Sonic and Dielectric Measurements

Mohamed Watfa, Roy Nurmi

In carbonates and some complex sandstone reservoirs the determination of pore types is critical for an accurate reservoir analysis (saturation, permeability, effective porosity, producibility). Until recently, it has been necessary to retrieve rock samples of a reservoir formation to determine which types of pores are present. However, a well-log approach has been developed which permits both the recognition and quantitative interpretation of pore types. The approach is an integration of the newly developed electrical bore-hole imagery with dielectric and sonic measurements, geological sequence modeling, and a thorough formation evaluation analysis. This approach permits routine mapping of pore types and their respective volumes within reservoir zones.

The reservoirs studied have included carbonates and sandstones with complex pore systems (mixtures of both primary and secondary pore types) in the San Andres and Smackover Formations in the U.S.A. and the Pre-Khuff, Khuff, Arab, Shuaiba, and Mishrif formations on the Arabian Peninsula.

The analysis of electrical images and Archie equation exponent m variations in common carbonate depositional sequences generally permit the interpretation of both rock and pore types. The electrical images allow a direct analysis of rock fabric, porosity heterogeneity, and large individual pores such as vugs, channels, and fracture. Dielectric measurements, combined with more traditional analysis of porosity and fluid saturations, permit a level-by-level calculation of the exponent m, which is valuable in analyzing the smaller but more abundant pores, whereas the dielectric and sonic (shear, compressional, Stoneley) data provide additional quantification of pore types when related to total pore volume.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.