Determination of a critical separation concentration for associative polymers in porous media based on quantification of dilute and semi-dilute concentration regimes

Abstract

Hydrophobic interactions are an inherent property of associative polymers which results in the formation of molecular aggregates. The loss of hydrophobic interactions under reservoir conditions have been reported, and this results in increased fluid – rock interaction effect such as adsorption. However, existing adsorption studies only reports the interaction of individual molecules with rock surface without taking into account mechanically retained molecular aggregates in narrow pores. The implication of this is a reduction in associative effect between polymer molecules during transport in a porous media. In this work, the minimization of this phenomenon and sustenance of the interaction network was studied through a theoretically defined dimensionless parameter for the quantification of molecular interactions in the various polymer concentration regimes. It was established in this work that associative polymers exhibit a critical separation concentration during propagation in a porous media under given reservoir conditions. This critical separation concentration marks the concentration beyond which large molecular aggregates constituting the hydrophobic network is sterically excluded and retained in narrow pore spaces. This separation phenomenon was predicted to occur when the proportion of molecular interactions arising from hydrophobic and intramolecular interactions are equal. Thus, the balance in the molecular interactions in the semi – dilute concentration regime was identified as key in minimizing the loss of hydrophobic interactions to aggregate retention and optimizing its sustainability in a porous media. Consequently, a novel approach was developed based on this knowledge for the transport of associative polymers at which these hydrophobic interactions are sustained. It was demonstrated that propagating associative polymers using this approach ensured the sustainability at concentrations below the critical separation concentration tend to maximize the hydrophobic interaction network with minimal loss of polymer chains retention mechanisms.