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45175-AC9
Unstable Miscible Displacements: Influence of Non-Vertical Wells, Reservoir Inclination, and Permeability Anisotropy and Stratification

Eckart H. Meiburg, University of California (Santa Barbara)

High-resolution simulations are employed to identify and analyze the mechanisms dominating miscible porous media displacements generated by inclined injection wells. Compared to vertical injection wells, significant differences are observed that strongly influence breakthrough times and recovery rates. Constant density and viscosity displacements, for which the velocity field is potential in nature, demonstrate the existence of pronounced flow nonuniformities, due to the interaction of the inclined well with the reservoir boundaries. These nonuniformities deform the fronts during the initial displacement stages.

In the presence of a viscosity difference, the nonuniformities of the potential flow field result in a focusing of the fingering instability. If the fluids also have different densities, a gravity tongue will reinforce the dominant finger along one front, while a gravitational instability leads to the disintegration of the dominant finger along the other front. Hence, the two fronts emerging from the inclined injection well usually evolve very differently from each other for variable density and viscosity displacements.

For inclined injection wells and sufficiently large mobility ratios, gravity tongues are seen to evolve dendritically for an intermediate range of density contrasts. While mild gravitational forces are necessary to create the gravity tongue in the first place, large density differences will suppress the growth of the dendritic side branches. Since the dendritic branches appear along the side of the gravity tongue that should be stable according to traditional stability criteria, it can be concluded that the tip region plays a crucial role in their formation.

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