Polymer Injectivity: Investigation of Mechanical Degradation of Enhanced Oil Recovery Polymers Using In-Situ Rheology

Abstract

Water soluble polymers have attracted increasing interest in enhanced oil recovery (EOR) processes, especially polymer flooding. Despite the fact that the flow of polymer in porous medium has been a research subject for many decades with numerous publications, there are still some research areas that need progress. The prediction of polymer injectivity remains elusive. Polymers with similar shear viscosity might have different in-situ rheological behaviors and may be exposed to different degrees of mechanical degradation. Hence, determining polymer in-situ rheological behavior is of great significance for defining its utility. In this study, an investigation of rheological properties and mechanical degradation of different partially hydrolyzed polyacrylamide (HPAM) polymers was performed using Bentheimer sandstone outcrop cores. The results show that HPAM in-situ rheology is different from bulk rheology measured by a rheometer. Specifically, shear thickening behavior occurs at high rates, and near-Newtonian behavior is measured at low rates in porous media. This deviates strongly from the rheometer measurements. Polymer molecular weight and concentration influence its viscoelasticity and subsequently its flow characteristics in porous media. Exposure to mechanical degradation by flow at high rate through porous media leads to significant reduction in shear thickening and thereby improved injectivity. More importantly, the degraded polymer maintained in-situ viscosity at low flow rates indicating that improved injectivity can be achieved without compromising viscosity at reservoir flow rates. This is explained by a reduction in viscoelasticity. Mechanical degradation also leads to reduced residual resistance factor (RRF), especially for high polymer concentrations. For some of the polymer injections, successive degradation (increased degradation with transport length in porous media) was observed. The results presented here may be used to optimize polymer injectivity.

Effect of microscopic aggregation behavior on polymer shear resistance

“… HPAM, an industrial product, has a molecular weight of 24 million g/mol, hydrolysis degree of 26.3%, and solid content of 88.9%. DHAP has a molecular weight of 6 million g/mol, hydrolysis degree of 25%, hydrophobic monomer content of 0.6 mol %, and a branching degree of 1. The molecular formula of DHAP is shown in Figure .…”

Adsorption behavior and shear degradation of ultrahigh‐molecular‐weight hydrolyzed polyacrylamide in a capillary flow

“…found that HPAM solution showed predominant shear thickening behavior at high flow velocities, which was due to successive contraction/expansion flowed in pores. It was also found that in situ rheological behavior of HPAM in porous media was different from bulk rheology observed in the rheometer . Experimental results showed that mechanical degradation occurred when the apparent viscosity increased.…”

On the Role of Polymer Viscoelasticity in Enhanced Oil Recovery: Extensive Laboratory Data and Review

“…Because of this stretching and the high shear rate, the polymer molecule has no sufficient time to re-coil itself. By that, the polymer flow is dominated by elongational forces and the viscosity increase is referred to as elongational viscosity or extensional viscosity [ 14 , 58 , 62 , 70 , 71 , 72 ].…”

“…Mechanical degradation can be understood as the break-up of polymer chains or rather molecules due to mechanical forces caused by the high shear stress [ 13 , 17 , 43 , 70 , 71 ]. Usually those conditions are encountered in the near-wellbore region and in the equipment such as pumps and valves.…”