Compressibility Coefficients in Nonlinear Transport Models in Unconventional Gas Reservoirs

Abstract

Transport models for gas flow in unconventional hydrocarbon reservoirs possess several model parameters such as the density (ρ), the permeability (K), the Knud-sen number (K n), that are strongly dependent upon the pressure p. Each physical parameter, say γ, in the system has an associated compressibility factor ζ γ = ζ γ (p) (which is the relative rate of change of the parameter with respect to changes in the pressure, [1]). Previous models have often assumed that ζ γ = Const, such as Cui [9], and Civan [7]. Here, we investigate the effect of selected compressibility factors (real gas deviation factor (ζ Z), gas density (ζ ρ), gas viscosity (ζ µ), perme-ability (ζ K), and the porosity (ζ φ) of the source rock) as functions of the pressure upon rock properties such as K and φ . We also carry out a sensitivity analysis to esti-mate the importance of each model parameter. The results are compared to available data.