Residual Oil Saturation Estimation Using the Generalized-Archie Parameters, “FAS”-Field, Niger Delta

Background and Objective: The estimation of residual oil saturation (S_or) in shaly sand hydrocarbon reservoirs has been a difficult task due to the non-linearity in reservoir properties. However, the study aimed to identify the deficiencies associated with estimating residual oil saturation from the generalized Archie petrophysical exponents and also provides the procedures for applying the conventional (Archie) method in S_or estimation, thereby facilitating easy automation. Materials and Methods: The study utilized well-log data obtained from the “FAS” Field, Offshore Niger Delta, to estimate S_or using the Archie method. The reliability of the method was tested statistically with Core S_or data from the study area. Results: The S_or ranged from 0.2 (FAS_06 and FAS_08) to 0.47 (FAS_03) in the delineated reservoirs (A and B). The percentage deviation of the estimated S_or concerning the core data varied from 51% (FAS_03) to 86% (FAS_02) within the field. It was inferred that the delineated reservoirs are generally dirty, having a high proportion of shale in them, which made the generalized Archie petrophysical exponents unreliable and inappropriate for the study area. Conclusion: It was therefore suggested that the conventional (Archie) method of computing field-based petrophysical exponents be automated, rather than using the commonly used petrophysical parameters, for an optimal residual oil saturation recovery in the study area.