Investigation on the Importance of the Diffusion Process During Lean Gas Injection Into a Simple Synthetic Depleted Naturally Fractured Gas Condensate Reservoir

Abstract

A depleted naturally fractured gas condensate reservoir with extremely tight matrix permeability in the center of Iran is used for gas storage. Due to the tightness of the matrix, simulation of this process may present a unique challenge in terms of the importance of diffusion process in flow behavior of the injected gas in matrix blocks. This article presents a multimechanistic (Darcian-type flow and Fickian-type flow) mathematical model to investigate the importance of diffusion process as a function of important rock and fluid parameters. The authors' approach consists of the following steps: (a) development of a 1-D governing equations for a single matrix block consists of a gas condensate mixture considering multimechanistic approach and (b) numerical solution of the highly nonlinear governing equations using Newton-Raphson technique in conjunction with Broyden updating approach. The model developed is validated against an analytical model applying the simplifying assumptions behind the analytical model. To investigate the importance the diffusion process a sensitivity study is done using typical values of rock and fluid properties for a tight gas condensate reservoir. In general, the results show that the diffusion is an effective process at permeabilities less than about 0.01 md and ignoring this process may create a drastic error in performance prediction of the reservoir.