Rheology of a New Sulfonic Associative Polymer in Porous Media

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 141355, ’Rheology of a New Sulfonic Associative Polymer in Porous Media,’ by R.S. Seright, SPE, Tianguang Fan, SPE, Kathryn Wavrik, SPE, and Hao Wan, SPE, New Mexico Tech, and Nicolas Gaillard, SPE, and Cedrick Favero, SPE, SNF Floerger, prepared for the 2011 SPE International Symposium on Oilfield Chemistry, The Woodlands, Texas, 11-13 April. The paper has been peer reviewed. See SPE Reservoir Evaluation & Engineering December 2011. For hydrophobic associative polymers (APs), incorporating a small fraction of hydrophobic monomer into a partially hydrolyzed polyacrylamide (HPAM) polymer can promote intermolecular associations and, thereby, enhance viscosities and resistance factors. The behavior of a new AP in porous media was investigated. Introduction In polymer or chemical floods that use polymer for mobility control, the cost effectiveness of the polymer is a major concern. Resistance factor is the effective viscosity of the polymer solution in porous media, relative to water (i.e., water mobility divided by polymer-solution mobility). HPAM and xanthan polysaccharides have been the dominant polymers used for enhanced oil recovery (EOR). If polymers that are more cost effective than these traditional EOR polymers can be identified, field applications of chemical floods could become much more widespread. For hydrophobic APs, incorporating a small fraction of hydrophobic monomer into an HPAM polymer is intended to promote intermolecular associations to enhance viscosities and resistance factors. At moderate concentrations (e.g., 0.05 to 0.5%), these polymers (with 0.1 to 7% hydrophobic monomer) can provide substantially higher viscosities than equivalent-molecular-weight polymers without hydrophobic groups. In some cases, the increase in viscosity with increasing polymer concentration is abrupt—leading to concerns about controlling the performance of the polymer during flooding operations. If small changes in concentration cause large changes in viscosity, small operational errors could accentuate injectivity problems if polymer concentrations are higher than the target and could provide insufficient mobility control if polymer concentrations are low. Another concern is the ability of APs to penetrate deep into a reservoir. Within a certain range of shear rates, the polymer becomes sufficiently extended to promote intermolecular interactions over intramolecular interactions. Polymer complexes formed by APs enhance viscosity and can provide high resistance to flow for a short distance in porous media. However, an important unresolved issue with many APs is whether the enhanced-viscosity characteristics can be propagated deep into a reservoir. Most previous studies of these polymers used short cores with no internal pressure taps to evaluate behavior in the porous media. As a result, resistance factors that appear high may actually reflect plugging. This study examined the rheology (both in a viscometer and in porous media) for a new sulfonic hydrophobic AP. This sulfonated polymer has lower hydrophobe content (and higher molecular weight) than most APs investigated for EOR previously. This sulfonated polymer exhibits viscosities that are not noticeably higher than those for the HPAM analog. It provides significantly higher resistance factors in porous media than HPAM, and the associative proper-ties allow polymer propagation through porous media.