Paper: Core Slabbing For Reservoir Analysis

To achieve maximum recovery from an oil field, especially when using supplemental recovery methods, the nature of the reservoir must be known in the greatest detail possible. In the past, several large reservoirs have been subjected to waterflooding under the assumption that they were "blanket" accumulations. When later detailed geologic analyses have been forced by a multitude of operational problems, the reservoirs were found to possess significant lateral discontinuity and/or marked permeability variations, requiring radical changes in the injection patterns. It is therefore important to reinforce the analysis of petrophysical and volumetric parameters of a reservoir with a sound geologic interpretation of the productive interval. This can best be accomplished by detailed examination of cores followed by careful correlation with well logs. Most of the following discussion will center on carbonate areas based partly on the author's experience in the Permian Basin, but also on the fact that carbonate reservoirs exhibit more complex porosity-permeability relationships than do sandstone reservoirs. Cores are slabbed simply by cutting a 3/4-inch thick vertical slice from top to bottom. The remnants are stored for possible special analyses based on interpretation of the slabs. The slabbed core is marked and placed in cardboard boxes which hold up to 18 feet (Fig. 1). The boxes can then be conveniently laid out on the floor or a long table for examination. The slabs are swabbed with mineral oil to bring out the natural features, leaving a strip along one side for observation of porosity and testing with acid.