Polymeric Wax Inhibitors and Pour Point Depressants for Waxy Crude Oils: A Critical Review

Paraffin precipitation during pipeline transport of waxy crude oils gives rise to several challenges, including wax deposition, flow reduction, and gel formation, which adversely impacts pipeline performance. Small dosages of polymeric wax inhibitors or pour point depressants comprise an effective preventative measure. In this article, the structural character, functionality, and mechanisms of the polymeric additives targeting paraffin wax are reviewed, and factors influencing product efficacy are summarized. Most polymeric additives contain a nonpolar moiety as well as a polar moiety, with the exception of crystalline-amorphous copolymers. Via nucleation, adsorption, co-crystallization and solubilization interactions, polymeric additives alter the morphology and interface of precipitated wax crystals, inhibiting wax deposition, improving flow, and impeding gel formation. The presence of asphaltenes significantly impacts wax crystal morphology and interfaces, thus influencing the mechanism of polymeric additives. Most polymeric additives fall into the categories of crystalline-amorphous copolymers, ethylene-vinyl acetate copolymers, comb polymers and nanohybrids. Factors influencing polymeric efficacy include molecular structure, fluid composition, and pipeline transport conditions.