Associative Polymer Propagation, Pressure Response, and Recovery

Abstract

Hydrophobically modified polyacrylamides, commonly referred to as associative polymers (aP), present a promising alternative to conventional hydrolyzed polyacrylamides (HPAM) used in enhanced oil recovery (EOR). The bulk rheological properties of associative polymers have been studied in the literature and are believed to be well understood. However, debate continues over the underlying mechanisms that govern the observed behaviors of aP in porous media testing. In this study, a mechanistic single-phase coreflood test was conducted to investigate aP behaviors in porous media at shear rates representative of deep-reservoir flow. Additionally, a series of two-phase coreflood tests were performed to study potential application advantages of aP over HPAM. The resulting observations support a hypothesis that high resistance factors (RF) generated by aP are caused by formation in the porous media of an associative network which modifies permeability. This study also provides support for proposals from literature that the formation of the permeability-modifying associative network is dependent upon specific surface characteristics in which the hydrophobic groups of aP adsorbed on the pore surface can functionally anchor an associative network in the pore space. Building upon these concepts and study of previous observations, we propose a mechanism that certain processes can affect these associative anchor points to allow for the mobilization and removal of the retained associative network out of the porous media. This observed behavior may function by either removing these anchor points or by masking their attraction to the non-adsorbed associative polymer. In addition to these studies of flow mechanisms, the two-phase testing demonstrated superior RF generation and incremental oil recovery when utilizing aP compared to HPAM of similar molecular weight, showing potential for aP to improve incremental recovery with reduced concentration versus conventional HPAM.