Relative Permeability Characteristics of Vugular Cores - Their Measurement and Significance

Abstract

Abstract Carbonate reservoir rock can have a highly developed secondary fracture/vug network in addition to intergranular porosity. Because of this, the multiple phase flow properties are very much different from rocks with wholly intergranular porosity. This paper represents an attempt to characterize the immiscible displacement behavior of fractured and vugular reservoir rock. An apparatus and method for the determination of relative permeabilities in large vugular cores is presented. The errors associated with this method and with vugular core analysis in general are discussed. To test the significance of relative permeability and other data obtained from core measurements, a mathematical model is proposed for the secondary pore network. This model permits the simulation pore network. This model permits the simulation of cores of unlimited size to predict realistic reservoir flow properties. It is concluded that water and gas reservoir displacement efficiencies will be underestimated using core measurements where a substantial secondary pore system exists. Introduction Dolomitized limestone reservoirs can have a highly developed secondary network of fractures and vugs in addition to a primary (intergranular) pore system. Reservoirs with secondary pore pore system. Reservoirs with secondary pore systems are highly productive and have flow properties quite different from those with wholly properties quite different from those with wholly intergranular porosity. This paper represents the beginning of an attempt to characterize the relative permeability and immiscible displacement behavior of fractured and vugular reservoir rocks. It is concerned specifically with reservoirs in the Acheson-Homeglen-Rimbey D-3 Reef Trend in Western Canada, but should be at least qualitatively applicable to similar formations. The D-3 formation is a series of bioherm reefs whose primary biological structure has been obliterated by dissolution and dolomitization processes. The rock contains vugs of various processes. The rock contains vugs of various sizes interconnected by minute shrinkage cracks. There are also larger fractures of mechanical origin. The permeability of the formation ranges from about 100 md to about 3000 md2. The primary porosity is very tight, with only about 0.01 md to porosity is very tight, with only about 0.01 md to 0.1 md permeability.