Abstract
Polymer flooding most commonly uses partially hydrolyzed polyacrylamides (HPAM) injected to increase the declining oil production from mature fields. Apart from the improved mobility ratio, also the viscoelasticity-associated flow effects yield additional oil recovery. Viscoelasticity is defined as the ability of particular polymer solutions to behave as a solid and liquid simultaneously if certain flow conditions, e.g., shear rates, are present. The viscoelasticity related flow phenomena as well as their recovery mechanisms are not fully understood and, hence, require additional and more advanced research. Whereas literature reasonably agreed on the presence of these viscoelastic flow effects in porous media, there is a significant lack and discord regarding the viscoelasticity effects in oil recovery. This work combines the information encountered in the literature, private reports and field applications. Self-gathered laboratory data is used in this work to support or refuse observations. An extensive review is generated by combining experimental observations and field applications with critical insights of the authors. The focus of the work is to understand and clarify the claims associated with polymer viscoelasticity in oil recovery by improvement of sweep efficiency, oil ganglia mobilization by flow instabilities, among others.
Highlights
We present data that cover the areas of shear thinning, shear thickening and elastic turbulence, all associated to the interpretations of the possible existence of viscoelastic properties/behaviour
In order to increase the viscoelasticity of a PAM, the amide groups hydrolyzed to a certain degree, forming a partially hydrolyzed polyacrylamide (HPAM)
In this work the role of polymer viscoelasticity was discussed in detail
Summary
Oil production is currently assumed to be higher than the actual demand, the future of oil and gas production will have to tackle severe challenges: fewer new fields are found and major producing fields show declining production. Polymer EOR applications have to consider reservoir depth, reservoir temperature, reservoir thickness, porosity, permeability, oil gravity, oil viscosity and water chemistry (especially salinity and hardness) [35] All these factors can decrease the quality of the injected polymer solutions which potentially results in an unfavorable polymer solution viscosity. Polymers with high elasticity change the stability of the laminar flow causing elastic instabilities This means the elastic turbulence is likely to occur at the pore level and represents a more recent interpretation on the effects in porous media. Overall, this shows the necessity of polymer solution optimization and especially, the requirement for a viscoelasticity-focused optimization approach. In order to account for the latter, it is imperative to understand the EOR polymers’ viscoelastic behavior in all its different shades
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