A non-Archie water saturation method for conventional reservoirs based on generalization of Passey TOC model for unconve
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A non‑Archie water saturation method for conventional reservoirs based on generalization of Passey TOC model for unconventional reservoirs Moustafa Oraby1 Received: 4 March 2020 / Accepted: 24 June 2020 © The Author(s) 2020
Abstract The determination of the formation water saturation, Sw, 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, Rw, clay volume, Vc 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 Rw. 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. Keywords Water saturation · Non-archie water saturation · Unconventional reservoirs · Passey model
Introduction The determination of water saturation is an essential and continuous process for every well, new or old, throughout the lifetime of a reservoir. Incorrect calculations of this critical parameter result in inaccurate field development decisions that will lead to producing high volume of reservoir water or missing potential hydrocarbon zones. There are multiple water saturation models developed for field applications. All these models are developed to improve the accuracy of determining this critical parameter, Sw. Archie (1942) developed the first water saturation model which took the form
* Moustafa Oraby [email protected] 1
Swn =
aRw �m Rt
(1)
where (m) and (n) are defined as cementation and saturation exponents, respectively. The Rt and Ф represent the resistivity and the porosity of the reservoir rock at each depth. Archie model does not include corrections for the effect of the clay minerals. Clays are conductive minerals that deceas
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