In recent years, and particularly in the Rocky Mountain and West Texas areas, many commercially productive oil and gas reservoirs have been developed in low-permeability, often non-homogeneous, fractured and vuggy formations. In order to evaluate this non-homogeneous rock, whole core analysis techniques have been developed. The use of the whole core for analysis minimizes sampling errors and allows the inclusion of fractures and solution cavities in the test specimens.
Equipment and procedures used in whole core analysis methods are briefly discussed. Comparisons with conventional analysis methods are made to illustrate the type of formation where whole core analysis is desirable.
The major portion of this paper is devoted to examples of whole core analyses of reservoirs in the Rocky Mountain area and their interpretations. The interpretation of the data and its application are presented in terms of fluid contacts, probable production, and the estimation of oil-in-place and recoverable oil.
During the last ten to fifteen years a large percentage of the oil and gas reservoirs discovered in the Rocky Mountain and West Texas areas have been in carbonate rocks. These carbonate formations are often characterized by erratic porosity and permeability development, and non-uniform lithology. In many cases, the porosity and permeability are due almost entirely to vugs and fractures.
The advent of diamond coring was of great benefit in the evaluation of carbonate reservoirs since it permitted faster penetration and much better recovery of dense, fractured formation. Another tool for the evaluation of these reservoirs which was developed to work hand-in-glove with the improved core recovery is whole core analysis.