Flow of Hydrophobically Modified Water-Soluble-Polymer Solutions in Porous Media: New Experimental Insights in the Diluted Regime

Abstract

The specific molecular structure of hydrophobically modified water-soluble polymers (HMWSPs), also called hydrophobically associative polymers, gives them interesting thickening and surface-adsorption abilities compared with classical water-soluble polymers (WSPs), which could be useful in polymer-flooding and well-treatment operations. However, their strong adsorption obviously can impair their injectivity, and, conversely, the shear sensitivity of their gels can be detrimental to well treatments. Determining for which improved-oil-recovery (IOR) application HMWSPs are best suited, therefore, remains difficult. The aim of this work is to bring new insight regarding the interaction mechanisms between HMWSPs and rock matrix and the consequences concerning their propagation in reservoirs.A consistent set of HMWSPs with sulfonated polyacrylamide backbones and alkyl hydrophobic side chains together with an equivalent WSP was synthesized and fully characterized. HMWSP and WSP solutions were then injected in model granular packs. As expected, with HMWSPs, high resistance factors (or mobility reductions, R m ) were observed. Yet, within the limit of the injected volumes, the effluent showed the same viscosity and polymer concentration as the injected solutions.A first significant outcome concerns the specificities of the R m curves during HMWSP injections. R m increases took place in two steps. The first corresponded to the propagation of the viscous front, as observed with WSP, whereas the second was markedly delayed, occurring several pore volumes (PV) after the breakthrough. This result is not compatible with the classical picture of multilayer adsorption of HMWSPs but suggests that injectivity is controlled solely by the adsorption of minor polymeric species. This hypothesis was confirmed by reinjecting the collected effluents into fresh cores; no second-step R m increases were observed.Brine injections in HMWSP-treated cores revealed high residual resistance factors (or irreversible permeability reductions, R k ), which can be attributed to the presence of thick polymer-adsorbed layers on the pore surface. Nevertheless, R k values strongly decreased when increasing the brine-flow rate. This second significant outcome shows that the adsorbed-layer thickness is shear-controlled.These new results should lead to proposing new adapted filtration and injection procedures for HMWSPs, aimed, in particular, at improving their injectivity. IntroductionSpecific attention currently is devoted to the development of innovative polymeric systems for IOR applications. The corresponding goals are, in particular, to lower the costs by reducing the quantities of chemicals needed; to broaden the range of suitable application cases (wells or reservoirs) for polymer technologies and, specifically,

Use of Polymers to Recover Viscous Oil From Unconventional Reservoirs

“…10. Consistent with previous research (Dupuis et al 2010), the associative polymer appears to contain a species that propagates through porous rock at rates comparable to those for HPAM and a second species (or perhaps multiple species) that moves much slower and creates much higher resistance factors.…”

“…Examination of the curves suggests that two species of polymer propagated through the core-a fast species that arrived at the end of the first core section after 0.23 PV and a much slower species that caused resistance favors to steadily increase for many PV. This concept is consistent with that proposed by Dupuis et al (2010). The first polymer species provided a resistance factor plateau of 7-8 after 1 PV.…”

“…Either way, the species was not expected to propagate deep into a reservoir to provide low-flux resistance factors that were substantially higher than expectations from viscosity measurements. During a study of a hydrophobically associative polymer, Dupuis et al (2010) concluded that it contained a low-mobility (high-resistance-factor), high-Mw species that propagated significantly slower than other components of the polymer. We wondered whether mechanical degradation would reduce the high resistance factors that we observed.…”

“…If polymers are identified that are more cost-effective than these traditional EOR polymers, field applications of chemical floods could become much more widespread. Associative polymers have been investigated as a possible substitute for HPAM polymers in EOR applications (Evani 1984, Bock et al 1988, Taylor and Nasr-El-Din 1998, Buchgraber et al 2009, Dupuis et al 2010). In particular, Nasr-El-Din (1998, 2007) extensively reviewed the literature for synthesis and performance of associative polymers.…”

“…Several authors (Eoff et al 2005, Zhao et al 2006 proposed utilizing highly adsorbing associating polymers to reduce rock permeability for acid diversion and conformance improvement. During a study of associative polymers in 10-cm-long cores with two internal pressure taps, Dupuis et al (2010) noted a "minority polymeric species" that provided high resistance factors but that propagated very slowly through the cores. They felt that their observations were inconsistent with the classic view of multilayer adsorption of a polymer.…”