Effect of flow instabilities on oil displacement in regular and irregular porous network

Date

2017-08

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Abstract

This study documents the effect of viscoelastic instabilities, that occurs at a high Mach Number (Ma), on oil displacement technique through porous medium. Polymer flooding is a common practice in Enhanced Oil recovery techniques that can recover almost 30-60% oil from the reservoir after primary and secondary methods. Primarily, it is believed that the increased viscosity and excess pressure drop was the mechanism of enhancement, but recent studies showed that the change in the flow pattern of Non-Newtonian fluid is the reason of improvement in oil displacement. In this study, we have demonstrated the improvement of displacement by polymer flooding compared to Newtonian fluids at different flow rates. Using 2D arrays of cylinders in a microchannel the high viscosity oil is displaced by low viscosity Newtonian solution and Non-Newtonian solution, which were analyzed in ImageJ and MATLAB. The Non-Newtonian fluid creates an elastic instability on flowing past a cylinder at higher Mach Number (Ma) which primarily has the ability to overcome the capillary pressure in locally trapped oil bridges between the solid surfaces and to better penetrate trapped regions of oil through normal velocities than Newtonian fluid. Thus, the argument of excess pressure drop in driving away the fluid better does not hold good where the change in flow pattern is observed to have greater influence in displacing the oil. The comparison of higher pressure drop in case of Newtonian fluid and lower pressure drop for Non-Newtonian fluid is also demonstrated where the polymer solution is observed to have higher efficacy. However, we have also demonstrated about the nature of the porous network on displacing the oil which has pronounced effect on increasing the efficacy. Using irregular geometries, it is observed that polymer flooding is benefited by non-regular porous network which allow normal velocities created by instabilities to better displace flow. Thus, above the critical Mach Number, polymer flooding is able to better penetrate denser networks than Newtonian fluids due to normal flow velocities that develop. This work will help to better understand about improved oil recovery technique which is one if the ongoing research in microfluidics.

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Keywords

Instability, Newtonian, Displacement

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