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Microfluidic study of end-point relative permeability change after polymer injections
Kenzhekhanov, Shaken
Kenzhekhanov, Shaken
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2025
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Abstract
Polymer solutions see broad applications in hydraulic fracturing, enhanced oil recovery, conformance control, and groundwater remediation. Due to the high viscosity of polymer solutions, flows after polymer injection are often subjected to significant permeability impairment. The permeability loss is attributed to polymer trapped inside porous medium that traditionally has been characterized by effluent fluid analysis and pressure drops in core flooding measurements. Although these measurements provide a thorough characterization of post-polymer flows in porous medium, due to the opaque nature of the medium, how polymer is trapped on the pore-level and contributes to permeability reduction is not well understood. This study investigates polymer trapping and permeability impairment (end-point relative permeability change) using transparent microfluidic micromodels. Microfluidic micromodels are simplified porous media that can be used to visualize many pore-scale processes. The objectives of this work are: (a) to measure end-point relative permeability change in post-polymer flows; (b) to correlate end-point relative permeability change to pore-scale fluid distribution.
Fluid flow sequences that typically occur in hydraulic fracturing and polymer flooding applications were conducted in micromodel experiments. Unsteady- and end-point relative permeabilities were successfully measured at constant flow rates. We observed that the end points of relative permeabilities of water and oil after polymer flows were disproportionally low, consistent with core flooding experiments reported in literature. Visualization of fluid distributions showed that polymer solution occupied aligned-to-flow channels and tended to stay in aligned-to-flow channels even in post-polymer flows. Due to polymer’s blockage of aligned-to-flow channels, flow of water and oil after polymer injection had to occur in not-aligned-to-flow channels. These flow paths are therefore more tortuous, leading to disproportionally low end-point permeabilities. In order to support the correlation between increased tortuosity of flow pathways and reduced end-point relative permeability, a mathematical model was developed. End-point relative permeability estimations from the model are in good agreement with the majority of experimental data. This agreement supports that there is a correlation between pore-scale fluid distribution and the end-point relative permeability, and the form of the developed mathematical model provides a useful basis for understanding and enhancing oil/water flows during/after polymer injections as well as in any multiphase flows.
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