Compositional upscaling in heterogeneous reservoirs

Reservoir heterogeneities vary from the pore-scale to the reservoir-scale. Geologic reservoir models containing millions of grids are able to incorporate the fine-scale heterogeneities present in oil or gas reservoirs. Because reservoir simulation flow models are limited to only thousands of grids due to the high computational expense, these models are not able to incorporate all the fine-scale heterogeneities. To this end, algorithms to take the fine scale geologic models and produce effective flow properties which still represent the key fine scale features have been developed.; While extensive work has been done in upscaling absolute and relative permeability, upscaling compositional flows has not been studied in depth. In this work, an in depth study of alpha factors, a method developed by Barker and Fayers (1991) for upscaling compositional flows, is undertaken. Physical phenomena which affect alpha factors are studied during lean gas recycling in a gas condensate reservoir. The reservoir is modeled at a fine-scale using a single porosity model with explicit fracture representation. Fracture orientation, gravity, capillarity, and diffusion affect alpha factors. Horizontal fractures have lower alpha factors than vertical fractures. Gravity effect must be taken into account in alpha factor calculation.; Parametric study of alpha factors is conducted to determine the robustness of alpha factors. Parameters which affect the phase velocities and the component compositions are studied. Results show that increasing fractured zone permeability and increasing vertical to horizontal permeability ratio reduce alpha factors. Increasing reservoir dip angle and reducing bottom hole pressure increase alpha factors. Fracture-fracture spacing does not have a large impact on the alpha factors. Fracture orientation, reservoir fluid composition and production strategy also affect alpha factors. Finally, alpha factors are applied in the upscaling of three fictitious reservoirs: a vertically fractured reservoir, a horizontally fractured reservoir and a heterogeneous reservoir. Incorporation of alpha factors improves the results obtained for all the reservoirs. Alpha factors are shown to differ in different regions, layers, and geologies. Use of coarse grid models reduces the computation time by factors of thousands and makes field-scale compositional simulation feasible.