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Better Understanding of Polymer Behaviour in Porous Media Allowing Reducing OPEX of EOR Projects
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IOR+ 2023, Oct 2023, Volume 2023, p.1 - 22
Abstract
Polymer Enhanced Oil Recovery (EOR) is a globally deployed technology in over 350 projects that has shown to be highly effective in sustainably recovering more oil. Over the last decade, several polymer pilot demonstrated to be highly efficient in increasing and accelerated oil recovery. They resulted in larger field deployments.
Historically, most of the projects were conducted in reservoir of relative high permeability, from 500 mD and above. The technology is now considered for reservoir with lower permeability reservoir where we usually observed quite high resistance factor (RF) in regard to the injected viscosity of the polymer solution measured in solution despite good injectivity.
Over the years, many researchers have considered that resistance factor is the product of viscosity and residual resistance factor (RRF), and reservoir simulators have been built accordingly. In a recent paper, Seright et al. pointed out the importance of having reliable RRF data, which is usually not the case, leading to underestimation of the apparent viscosity of the polymer solution in porous media. The depleted layer theory has been developed to explain this apparent reduction in viscosity in porous media. Some research even recommends increasing polymer concentration to compensate for this apparent lower viscosity. As very well explained by Seright et al., depletion layer does not apply to the flow of polymer solution in porous media, since polymer adsorbed onto the rock surface.
Going further in the implication of this assertion, the effective concentration in porous media is higher than the injected concentration because the adsorbed polymer brings extra-concentration. In high permeability cores (> 1 Darcy) this effect is limited however, for lower permeability cores, increase in effective concentration can be as high as 80% having a much more significant impact on apparent viscosity versus injected viscosity, up to one order of magnitude.
In this paper, we will present in detail this mechanism supported by extensive laboratory data covering a broad range of reservoir conditions and polymer type. We propose another definition of the effective viscosity in porous media, has being the product of the resistance factor and the water viscosity. Depending on permeability, it can allow reducing polymer concentration by several tenth of percent. In reservoirs, having permeability lower than 500 mD, polymer consumption could be reduced by up to 50% to achieve the targeted level of mobility ratio, significantly reducing OPEX of EOR project.