Abstract

Normally, when analyzing Driving Forces to determine the Displacement Efficiency (ED) during flooding, only Viscous Forces (vμ), which are proportional to the Macro Pressure Gradient (dp/dl), are considered. Micro Forces in pores are not considered. The micro forces considered in this paper are: First, the Normal Force caused by the change in shape of the flow lines in pores; second, the kinetic force caused by the change in momentum, which is due to the change in flow lines in pores also. Both these two micro forces are caused by the change in flow lines, the larger the change in flow lines, the larger the two micro forces.

Analysis, calculations and experiments show that the Flow Lines in pores are different between Visco-Elastic Fluids and Newtonian Fluids. Flow lines in pores of visco-elastic fluids, compared to Newtonian fluids, look more like and “expanding” and “contracting” Piston Flow. The change in flow lines changes the micro Forces, these Micro forces act on locations that caused the flow lines to change, mainly the Protruding Portions of residual “oil blobs”. This enhanced Micro force causes the protruding portions of the “oil blobs’ to change shape and mobilize. The results of the calculated magnitude of the enhanced micro forces are shown in this paper. For visco-elastic fluids, micro forces in pores are much larger that that for Newtonian fluids and must be considered when analyzing the “Displacement Efficiency”.

Results on “Visualization Core Models” confirm the above calculations and analysis. The affect of ED by core flooding using visco-elastic fluids is shown. Due to this mechanism, “Very High Concentration Polymer Flooding” is being implemented in the field, the incremental recovery is nearly twice that of conventional polymer flooding.

Tests show that only the “First Normal Force Differential” (N1) and its corresponding “Weisenberg Number” (We) affect the shape of the flow lines, other elastic properties and the viscosity of the driving fluid do not affect flow lines, therefore they do not affect the ED either.

The above analysis of the affect of visco-elasticity on flow lines, micro forces and ED is new in the study of flow of fluids in porous media and in Reservoir engineering; It is of significant value to further understand the mechanism of increasing ED in porous media; Useful in designing, screening, developing and evaluating better chemical products, chemical floods and methods to further increase oil recovery; “High Concentration Polymer Flooding” that utilizes the high visco-elasticity of the driving fluid to increase ED is field trailed in a large scale (4 large field tests) and shows a very much higher incremental recovery over water flood and conventional polymer flood, this is a “New Flooding Method” that has high potentials.

The above also shows that this is a new mechanism for displacement by flooding in porous media with multiple phases in its pores.

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