A Simple Convincing Proto-Saturation Model for Clastics, Carbonate, and Tight Gas Reservoirs

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Abstract The primary goal of this study is to determine the irreducible water saturation in all types of reservoirs and highlight its significance in estimating hydrocarbon initial-in-place. Irreducible water saturation is strongly correlated to permeability and porosity, and it has a significant impact on reservoir characteristics. The irreducible water saturation refers to the quantity of water that is removable from the reservoir and occupies the reduced part of available effective porosity. It acts as a barrier preventing hydrocarbon accumulation. Accurately determining the irreducible water saturation is crucial for consistent and accurate interpretation of well log data, which, in turn, affects the estimation of oil and gas reservoir resources. In conventional petrophysics, resistivity logs are commonly used to identify pay zones based on the resistivity contrast between hydrocarbons and formation water. However, when a pay zone exhibits saturation-dependent Archie exponents or contains conductive minerals, these logs become inadequate for identifying producing zones and providing insights into water mobility. Consequently, many potentially productive zones with high irreducible water saturations are often overlooked in various fields around the world. Laboratory measurements offer accurate data on mobile water and irreducible water saturation, which includes bound water from clay and capillary. In this study, well log data results were utilized to calculate the irreducible water saturation in the reservoir. The analysis focused on the reliance of irreducible water saturation on the detailed pore structure. It was observed that irreducible water saturation decreases with increasing porosity and permeability. Additionally, factors such as pore and throat size, as well as the volume of clay or silt, impact the volume of irreducible water content. In tight gas reservoirs, the microscopic pore arrangement is more complicated, resulting in a higher proportion of micro-pores bound to water. Evaluating the reservoir requires attention to various factors that affects the saturation of irreducible water. Overall, this paper emphasizes the importance of accurately determining the irreducible water saturation in reservoirs and highlights the need to consider multiple factors when evaluating reservoirs to avoid overlooking potentially productive zones with high irreducible water saturations.