Relative Permeability of Near-Miscible Fluids in Compositional Simulators

Advisor

Hamdi Tchelepi, primary advisor
Denis Voskov, advisor

Abstract

The relative permeability functions are a key parameter in Darcy`s law extension for modeling multiphase flow. They are empirical functions that lump the effects of complex interactions between flowing fluids and the porous medium, but they are usually reported as functions of saturation only. The dependence of the relative permeability on phase identification can lead to significant complications in near-miscible displacements.

We present an analysis of existing methods that aim to account for miscibility effects by including compositional dependence in the relative permeability functions. The solution evolution in compositional space is analyzed, and the impact of compositional changes in the relative permeabilities on simulation results and performance is quantified. We show the sensitivity of different methods to the choice of reference points used, and we provide guidelines to limit the modification of the relative permeabilities to physically reasonable amounts.

We use the Gibbs free energy based strategy with some modifications. The new approach was implemented in a general-purpose simulator (AD-GPRS), and tested on a wide range of compositional displacements. We have found that including any compositional dependence in the relative permeability near the critical point improves the nonlinear convergence significantly. Only slight differences are observed in the final saturation distributions and well production rates. The new approach, which applies a correction to the area above the critical tie line extension, results in smoother transitions between the single and two phase regions.

In summary, we show a clear advantage of incorporating compositional dependence in the relative permeability in terms of nonlinear performance. This is especially clear in displacements near the critical point (near-miscible). The differences between different models are sensitive to the reference points used, which can only be validated with experimental evidence and a more solid physical foundation. We provide a basic framework in the AD-GPRS simulator for possible further investigation into this topic.