An Application of Statistical Methods to Core Analysis Data of Dolomitic Limestone

Abstract

Abstract This paper applies the methods of statistical analysis to the interpretation ofcore analysis data of dolomitic limestone from the San Andres formation atWasson and the Clearfork formation at Fullerton. Probability relationships are shown to connect the porosity and thepermeability and the porosity and the fluid saturation. For example, theporosity-permeability relationship expresses the probability that a sample ofporosity, J, will or will not be permeable. The over-all porosity frequency distribution of the reservoir together with thefrequency curves of permeability (one for each class interval of porosity)provide a precise basis for computing the weighted average productive porosityof the reservoir for any assigned value of the minimum productivepermeability. The probability that the permeability of a core specimen from Fullerton willexceed a given value appears to be dependent on the percentage porosity of thespecimen, its void structure type (i.e., porosity in the qualitative sense), and the given value of the permeability. If continuous profiles of voidstructure type and 'porosity are available together with the appropriateporosity-probability of permeability: plots, the, net pay thickness may beestimated. The Invasion Index of a well is defined in terms of the porosity ‘andpermeability data. This -index’ is suggested 'as a basis for comparing- wellsas regards their suitability as fluid-injection wells. Introduction Three problems of importance in the exploitation of limestone reservoirs may'be stated as follows:The determination of the productive porosity of the reservoir.The determination of the number of feet of oil-bearing porous rock that willproduce at a commercial rate into the well bore; i.e., the net paythickness.The choice of fluid-injection wells in a secondary recovery program. The ultimate recovery of the reservoir is proportional to the productiveporosity. The productive capacity of the well is proportional to the net paythickness. The principal purpose of this paper is to show that the methods of statisticalanalysis when applied to core analysis data of dolomitic limestones offer auseful approach to the solution of these three problems, as well as others ofimportance in reservoir engineering. The use of these methods was suggested bythe work of Jan Law. T.P. 2025