Miscibility is an important parameter to optimize oil recovery in the gas drives. Additionally 2-D effects such as channeling, gravity tonguing, and crossflow can impact the level of miscibility and both local displacement and sweep efficiency. The adverse fingering or channeling tendencies will be mitigated to varying degrees by crossflow effects induced by the following physical mechanisms: (i) mass diffusion, (ii) dispersive mixing, (iii) viscous forces, and (iv) gravity forces [10]. All these factors are rate and process dependent, so that the effectiveness of a nearly miscible displacement needs to be analyzed in a manner which takes quantitative account of these interacting mechanisms. When mixing between layers of fast and slow flow occurs, the composition paths occurred in one dimensional flow change, and hence the development of miscibility is altered, to some extent at least in heterogeneous flow systems where crossflow occurs. In any real miscible floods the flow will be anything other than one-dimensional, as reservoir heterogeneity and viscous instability produce faster flow in some zones than in others. Therefore better understanding of the scaling of those interactions is an important part of improved accuracy of performance predictions for reservoir scale flows. Furthermore as numerical dispersion can cloud the interpretation of the results by artificially increasing the level of mixing in the reservoir, the effects of numerical dispersion should be clearly analyzed for each fluid displacement at the beginning of simulations. This has been done by selecting both the appropriate grid details and the compositional representation to achieve a solution which is not overcome by numerical functional errors.

The objective of this study is to understand each individual key dispersion mechanisms induced by reservoir parameters. The second step is to identify the parameters that have strong influence on the displacement process. The numerical simulations of x-y and x-z cross sections are used to quantify the effects of various mixing factors and reservoir heterogeneity.

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