ABSTRACT

In the previous chapters on porosity and permeability, the storage capacity of a rock and the conductive capacity of a rock were discussed. However, for the reservoir engineer, yet another very important factor needs to be determined, apart from porosity and permeability: the amount of hydrocarbon fluids present in the reservoir rock. While porosity represents the maximum capacity of a reservoir rock to store fluids, fluid saturation or pore space saturation actually quantifies how much of this available capacity actually does contain various fluid phases; in other words, how is that storage capacity, pore volume, or pore space distributed or partitioned among the three typical reservoir fluid phases: gas, oil, and water (usually referred to as brine or formation water). Therefore, initial fluid saturations defined as fractions of the pore space occupied by gas, oil, and water are key factors in the determination of initial hydrocarbons in place.