Chemical Additives as Flow Improvers for Waxy Crude Oil and Model Oil: A Critical Review Analyzing Structure–Efficacy Relationships

Waxy crude oil has become a crucial unconventional oil alternative owing to the depleting conventional oil resources. However, ascertaining flow assurance in a waxy crude oil pipeline at low temperatures is challenging due to the high viscosity and gelation properties of waxy crude oil and wax deposition on the pipeline wall. Researchers and industries use different classes of chemical additives to resolve the flow assurance issues. The current review aims to build a relationship between the structural properties of chemical additives and their flow improvement efficacy. A wide array of compounds reported in the past decade has been critically examined to understand the progress in the field. Polymers form a bulk of these compounds. However, there is a shift toward polymer nanocomposites owing to their better effect compared to pure polymers. Surfactants, organic solvents, and other molecules have also been utilized as additives to ensure flow during waxy crude oil transportation. The presence of different structural properties such as alkyl chain length, aromatic rings, size of aromatic rings, polar groups, and others have been related to their effect on the flowability of waxy crude oil. Moreover, the factors related to scaling of lab-scale results to industry level have been enumerated. The future directions and perspectives related to utilizing structure–efficacy relationships of chemical additives have been discussed. In contrast to the existing literature, special importance has been given to the chemical structures of additives and their molecular interactions with waxy oils. The perspective of the structure–efficacy relationship will help in designing novel additives with greater efficacy and suitability for waxy crude oil.