Effect of Mixing on Gas Floods Above the MME Using Slug and WAG Injection

by
Leonardo Bermúdez, MSE

University of Texas at Austin, 2002
Supervisor: Russell T. Johns

This thesis examines the different parameters that affect oil recovery in miscible gas floods that undergo slug and WAG injection with gas enriched above the MME. Numerical simulations of x-z cross-sections are used to quantify the effects of numerical dispersion, physical dispersion, heterogeneity, level of enrichment, and injection boundary conditions on the interaction of local displacement and sweep efficiency. The results obtained are used to investigate the interaction of local displacement and sweep efficiency and to evaluate the mixing mechanisms and their relation to the final oil recovery.

This research shows that the grid-block size is closely related to the local displacement and sweep efficiency; consequently, adequate grid-block size that represents the correct amount of mixing in the reservoir remains unclear. It was found that for slug injection in homogeneous reservoirs, recovery difference between different gas enrichment levels are insensitive to typical grid-block sizes. Another significant observation made in this thesis is that contrary to 1-D models, where the addition of physical dispersivity reduces the final recovery, recovery in 2-D simulations can increase when physical dispersivity is added due to improved sweep efficiency. Finally, slug and WAG injection processes are complex because they involve local displacement and sweep efficiencies that result from gas injection and water. The complexity of slug and WAG injection processes and the heterogeneous nature of reservoirs can lead to a combination of factors where additional enrichment may or may not result in additional recovered reserves.

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