AAPG Southwest Section

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Evaluation of the Equational Components used in Petrophysical analysis of the San Andres residual oil zone, tall cotton field, Gaines County, Texas


Hydrocarbon acquisition in the Permian Basin continues to advance, with more operators applying enhanced oil recovery (EOR) techniques. This results in the ability to produce from reservoirs with immobile oil, such as in a Residual Oil Zone (ROZ). Targeting ROZs provides the potential to recover billions of barrels of oil in both new and old fields. A dependable geological analysis is necessary to optimize potential production, and calculating hydrocarbon saturation requires an accurate water saturation (Sw) value. While the theoretical values for the variable components of this equation serve as useful recommendations, small changes in these components yield significant differences in the equation's outcome. Previous investigation has shown methodologies utilized in calculating these components show substantial variation in values. To demonstrate this inconsistency, the constituents used to calculate water saturation will be calculated for the San Andres Reservoir in Tall Cotton Field and compared to the previously determined values in the San Andres Reservoir in Goldsmith Field.