Characterization of the generalized permeability jail in tight reservoirs by analyzing relative-permeability curves and numerical simulation

Abstract

This study comprehensively characterizes the boundary values of generalized permeability jail in tight reservoirs through relative-permeability curve analysis, numerical simulation, and economic evaluation. A total number of 108 relative-permeability curves of rock samples from tight reservoirs were obtained, and the characteristics of relative-permeability curves were analyzed. The irreducible water saturation (Swi) mainly ranges from 20% to 70%, and the residual gas saturation (Sgr) ranges from 5% to 15% for 55% of the samples. The relative-permeability curves are categorized into six types (Category-I to VI) by analyzing the following characteristics: The relative permeability of gas at Swi, the relative permeability of water at Sgr, and the relative permeability corresponding to the isotonic point. The relative permeability curves were normalized to facilitate numerical simulation and evaluate the impact of different types of curves on production performance. The results of simulation show significant difference in production performance for different types of relative-permeability curves: Category-I corresponds to the case with best well performance, whereas Categories-V and VI correspond to the cases with least production volume. The results of economic evaluation show a generalized permeability jail for Categories-IV, V, and VI, and the permeability jail develops when the relative permeability of gas and water is below 0.06. This study further quantifies the range of micro-pore parameters corresponding to the generalized permeability jail for a tight sandstone reservoir.