Compositional upscaling in fractured reservoirs during gas recycling

Compositional simulation of fractured reservoirs with explicit fracture representation is computationally prohibitive. This paper studies the upscaling of component transport by the alpha factor method that can be used in single-porosity, coarse-grid models to make compositional simulation feasible at the reservoir scale. Primary production of a gas-condensate reservoir followed by lean gas recycling is considered. A reservoir segment with a single fracture is modeled by 2D and 3D fine-grid compositional simulation. Alpha factors are computed and the effect of fracture orientation, gravity, capillary pressure, and diffusion on alpha factors are studied. Results show that horizontal fractures have lower alpha factors than vertical fractures. Down dip injection, capillary pressure and diffusion increase alpha factors. Alpha factors calculated from three-dimensional models are larger than those calculated with two-dimensional models. Use of alpha factors in coarse-grid 3D models reduces computational time by factors of thousands (over fine-grid models) and makes full-field compositional simulation a practical tool for reservoir engineers.