Abstract
The key to improving reservoir description and exploitation is to describe complex variations in pore geometry within different lithofacies. Variations in shale properties, shale distribution and pore geometrical attributes define the existence of distinct hydraulic (flow) units with similar fluid-flow characteristics in shaly sand reservoirs. This study proposes a new method for identifying hydraulic flow units in shaly sand reservoirs. The proposed method is based on the application of several shaly sand models, including the Coates—Dumanoir, and Waxman and Smits models, the Coates and Denoo, and Morris and Biggs correlations, and the Simandoux model. The developed equations indicate that for any flow unit, a log—log plot of a “reservoir quality index” (RQI) vs. porosity should yield a straight line with a characteristic slope; 1.5 for sand reservoirs, 2.5 for laminated shale and structural shale, and 3.5 for dispersed shale. The intercept of the straight line with φ = 1, designed as the “shale zone indicator” (SZI), is a unique parameter for each flow unit. The proposed technique has been successfully tested in shaly and very shaly sand reservoirs from Texas. The examples show that there are strong relationships between cation-exchange capacity, formation resistivity factor, permeability, and reservoir quality index and shale zone indicator. This paper includes the theoretical development, validates and characterizes the flow units to demonstrate the efficiency of the proposed technique.
Published Version
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