A non-Archie water saturation method for conventional reservoirs based on generalization of Passey TOC model for unconventional reservoirs

• Main Author: Moustafa Oraby
• Format: Article
• Language: English
• Published: SpringerOpen 2020-07-01
• Series: Journal of Petroleum Exploration and Production Technology
• Subjects: Water saturation; Non-archie water saturation; Unconventional reservoirs; Passey model
• Online Access: https://doi.org/10.1007/s13202-020-00945-x
• ISSN: 2190-0558; 2190-0566

Abstract The determination of the formation water saturation, S w, is a continuous process throughout the life of the fields. Multiple water saturation models are developed to increase the accuracy of calculating this critical parameter for both open-hole and cased-hole wells. All current open-hole water saturation models require prior knowledge of some field parameters namely; formation water resistivity, R w, clay volume, V c and rock electrical properties (m, n). It is normally assumed that those reservoir parameters as either constant for the entire reservoir section or change by zones. This is obviously an impractical assumption especially for the (m) and (n) parameters. Also, when a reservoir is under water injection for enhanced oil recovery, the water salinity may change throughout the reservoir, based on the distribution of the reservoir permeability and the salinity of the injected water, resulting in a variable R w. This case represents a real challenge to the existing water saturation models. In this paper, a methodology to determine water saturation without the need for prior knowledge of the formation water resistivity or the rock electrical properties is developed. This approach is a generalization of the Passey total organic carbon, TOC, model which is developed to determine the organic richness of the unconventional reservoirs. The scientific basis of the method, the modification required to be applied in conventional reservoirs, the proof of concept using forward modeled cases and actual field applications in sandstone and carbonate reservoirs are performed to examine the theoretical and the practical applications of the methodology. Excellent results are obtained and discussed.