Polymer Injectivity: Investigation of Mechanical Degradation of EOR Polymers Using In-Situ Rheology

Abstract

Water soluble polymers have gained an increasing interest in enhanced oil recovery (EOR) processes, especially as 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 extent 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 HPAM (partially hydrolyzed polyacrylamide) polymers was performed using Bentheimer sandstone outcrop cores. Results show that, HPAM in-situ rheology is different from bulk rheology measured in 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 measurements in the rheometer. 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 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.

Critical Review of Polymer Flooding in Daqing Field and Pelican Field: Case Studies of the World’s Largest Polymer Flooding in Light and Heavy Oil Reservoirs, Respectively

“…Amongst the chemical enhanced oil recovery (cEOR) methods, polymer flooding is a proven chemical enhanced oil recovery (cEOR) method used to recover residual oil, especially in heavy oil where waterflooding is not effective due to viscous fingering [13][14][15]. In the oil and gas industry, two types of polymers are mostly used: synthetic polymers like hydrolyzed polyacrylamide (HPAM) and its derivatives, and biologically produced biopolymers like xanthan gum (XG) and cellulose [15,16,17].…”

Comparative Analysis of the Effects of Monovalent and Divalent Ions on Imported Biopolymer-Xanthan Gum and Locally Formulated Biopolymers-Gum Arabic and Terminalia Mantaly

“…Polymer flooding is a promising Chemical Enhanced Oil Recovery (cEOR) method used to recover residual oil, especially in heavy oil where waterflooding is not efficient due to viscous fingering [1][2][3][4][5][6]. In the oil and gas industry, two types of polymers are mostly used: synthetic polymers like hydrolyzed polyacrylamide (HPAM) and its derivatives, and biologically produced biopolymers like Xanthan Gum (XG) and cellulose [7][8][9][10].…”