Low molecular weight hydrophobic associating polymer: Heterogeneity regulation performance and mechanisms

Hydrophobic associating polymers demonstrate exceptional heterogeneity regulation capabilities and extensive application potential in oilfields. Nonetheless, the regulation performance and mechanisms of low molecular weight hydrophobic associating (LMWHA) polymers require further investigation. This work presents a novel LMWHA polymer poly(N-Vinyl-2-Pyrrolidinone-co-Double hexadecyldimethylallyl ammonium chloride), referred to as NDC16, and measured its fundamental properties. Its heterogeneity regulation performance was comparatively evaluated against conventional HPAM in both core groups and three-dimensional models. Subsequently, its regulation mechanisms were explored by rheological analysis and molecular dynamic simulation. The results indicated that the NDC16 polymer functioned as a salt-thickening polymer, possessing a low molecular weight of 3.45 x 105 and a viscosity exceeding that of HPAM at salinities above 5000 mg/L. The flooding experiments demonstrated that the NDC16 polymer exhibited superior heterogeneity regulation performance compared to HPAM in both in-layer and interlayer dimensions. It could enhance oil recovery in low-permeability layers by 10 % more than HPAM, and the disparity in interlayer oil recovery diminished as permeability differences reduced. Concerning in-layer characteristics, it exhibited a more consistent oil saturation front edge compared to HPAM. The results of rheological analysis and molecular simulation demonstrated that the spatial structure of NDC16 mostly consisted of hydrophobic associating microdomains, which led to the strong intermolecular interactions, systematic molecular organization, and resistance to aggregation breakdown. The special molecular structural characteristics enabled the LMWHA polymer to exhibit higher thickening, elasticity, and recovery capabilities throughout the flow process. Therefore, its heterogeneity regulation mechanism could be encapsulated as the synthesis of the elevated elasticity to enhance oil washing efficiency and superior recovery ability to increase permeability resistance in high permeability areas. This research enhances the comprehensive of the heterogeneity regulation mechanism of LMWHA polymer solutions and establishes the foundation for further investigations aimed at improving heterogeneity in polymer flooding in the future.