Improved water saturation estimation in shaly sandstone through variable cementation factor
Document Type
Article
Publication Date
5-1-2022
Abstract
Estimation of water saturation, S-w, in shaly sandstone is an intricate process. The surface conduction of clay minerals adds up to the electrolyte conduction in the pore spaces, thus generating high formation conductivity that overshadows the hydrocarbon effect. In each resistivity-based water saturation model, the key parameter is formation factor, F, which is typically derived from Archie's Law. Referring to a log-log plot between formation factor and porosity, cementation factor reflects the slope of the straight line abiding Archie's Law. In the case of shaly sandstone, derivation based on Archie's Law in combination with Waxman-Smits equation leads to higher cementation factor, m*. In the shaly parts of the reservoir, high m* is counterbalanced by clay conductivity. Nonetheless, high m* used in clean parts increases S-w estimation. In this study, the variable cementation factor equation is introduced into the standard correlation of S-w versus Resistivity Index, RI, to develop a water saturation model with shaly sandstone parameters. Data retrieved from two fields that yielded mean arctangent absolute percentage error (MAAPE) were analysed to determine the difference between calculated and measured data within the 0.01-0.15 range for variable cementation factor method. The conventional method yielded maximum MAAPE at 0.46.
Keywords
Shaly sandstone, Formation factor, Variable cementation factor, Water saturation
Divisions
sch_che
Funders
Fundamental Research Grant Scheme by the Ministry of Higher Education, Malaysia (Grant No: FRGS/1/2019/TK07/UITM/03/1)
Publication Title
Journal of Petroleum Exploration and Production Technology
Volume
12
Issue
5
Publisher
Springer Heidelberg
Publisher Location
TIERGARTENSTRASSE 17, D-69121 HEIDELBERG, GERMANY