Gas-Condensate Pseudopressure in Layered Reservoirs

Abstract

Summary This paper presents verification of the Fevang and Whitson (1996) gas-condensate pseudopressure method for layered reservoirs. Layers may be characterized by widely varying permeability and composition, and they may be communicating or noncommunicating. The pseudopressure method is used in well calculations for coarse-grid models with relatively large areal grid dimensions (>50 m), capturing near-well condensate blockage without local grid refinement, thereby reducing run time and model size. The paper presents examples from several field studies and from two synthetic systems using a commercial reservoir simulator. The field studies include rich- and lean-condensate reservoirs. The study was conducted using a commercial compositional reservoir simulator. Three-dimensional multilayer, fine-grid (radial and Cartesian) models and equivalent coarse-grid models were used. Both depletion and gas-injection cases were simulated for a wide range of reservoir fluids. Reservoir performance of fine-grid models and coarse-grid models was compared using the gas-condensate pseudopressure method and showed comparable results in all cases studied, including relative permeabilities with capillary-number dependence and high-velocity (β) flow treatment. The coarse-grid model with pseudopressure is somewhat dependent on coarse-grid size, generally requiring Δx=Δy≈50-100 m for lean gas condensates and Δx=Δy≈100-200 m for rich gas condensates. The paper verifies for the first time that the gas-condensate pseudopressure method as proposed by Fevang and Whitson (1996) is valid and accurate for layered systems with significant heterogeneity (permeability variation), with and without crossflow, with and without capillary-number modification of relative permeabilities, and for widely ranging fluid compositions in each layer.