Alkaline Surfactant Polymer Flooding: What Happens at the Pore Scale?

Abstract

Abstract Alkaline-surfactant-polymer (ASP) flooding is a Chemical Enhanced Oil Recovery (CEOR) method whereby alkali, surfactant and polymer are injected as the same slug. It is one of the most promising world-wide focus of CEOR research and field trials, due to the unique synergy of the three chemical components. Polymers increase the viscosity of injected water, which improves macroscopic sweep efficiency by stabilizing the displacing front and counteracting heterogeneity effects. Surfactants, on the other hand, decrease the interfacial tension between the injected water and crude oil, which improves microscopic displacement efficiency by mobilizing trapped oil. Alkaline chemicals generate soap when reacting with crude oil, which reduces surfactant adsorption to grain surfaces. To fully understand the flow mechanisms in oil reservoirs and develop efficient recovery methods, it is essential to recognize the physics at the pore scale since this is the length scale at which capillary-trapped oil is mobilized. We developed an experimental micro-scale approach in which oil recovery is analyzed using microfluidics. The micromodels are fabricated based on: (1) a pore network generated via a Delaunay triangulation with an average pore size of 60 µm, (2) X-ray micro-Computed Tomography images of Bentheimer sandstone with resolution of 4.95 µm, and (3) a fractured network with a porosity of 10%. The networks are etched into silicon wafers and used to fabricate polydimethylsiloxane (PDMS) microfluidic devices. We compare not only oil recovery with ASP flooding between different porous networks but we also study displacement mechanisms and pore scale emulsion formation for ASP formulations that exhibit Winsor Type II+, II- and III behaviour. Our studies elucidate micro-scale oil recovery mechanisms for different ASP flooding scenarios. Our results provide direct visualization of the micro-scale phenomena occurring during ASP flooding and will guide further studies to target effective ASP flooding scenarios.