Wax crystallization in crude oil is a main concern in flow assurance. Paraffin inhibitors (PIs) are commonly employed as additives to reduce the wax appearance temperature (WAT), thereby mitigating oil gelation, deposit formation, and pipeline blockage. The efficiency of the PI is a function of chemical structure, wax properties, and other components of the crude that may stabilize or destabilize wax in the composition. The efficacy of a family of maleic anhydride−α olefin comb copolymer-based PIs having alkyl side chains was examined by rheological and crystal morphology means in a simple wax-containing, dodecane-based synthetic crude oil model in the presence and absence of asphaltenes. PIs possessing different ranges and breadths of the alkyl chain side-chain length distributions, densities of said chains, and chemistries of their attachment to the backbone were chosen for study. PIs possessing ester attachment of the alkyl side chains to the backbone are more effective in reducing the WAT and oil viscosity than that with analogous amide/imide attachment in this model crude. Differences in the side-chain densities appeared to have the greatest effect, to the exclusion of differences in chain length distribution range or breadth, belaying the commonly held philosophy that matching the carbon distribution of the wax present in the crude with that of the alkyl side chains in the PI is an effective strategy. In small amounts, asphaltenes appear to act as a natural PI with an efficacy that is comparable with that of the aforementioned ester-functional PIs. While the addition of asphaltenes in the concentration studied appears to render the various crystal assemblies more amorphous, a molecular model describing these interactions is lacking. Further studies involving PIs that vary in their structural features in more incremental, systematic ways is needed, as are additional methods for evaluating the PI efficacy.

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The effect of wax molecular weight distribution on the efficacy of two alpha olefin-maleic anhydride paraffin inhibitors (PIs) having different densities of alkyl side-chains were examined in light West Texas crude in the absence and presence of asphaltenes. Interpretation of the data was aided by cross-polarization microscopy. Primary differences in wax crystal morphology appear to be driven by the composition of the wax, with secondary differences being associated with the choice of PI. In the absence of asphaltenes, the effect of wax composition on PI performance (i.e., reducing oil viscosity and wax appearance temperature) is greater for the PI having the higher chain density, with the one having the lower chain density being generally more effective regardless of the wax composition. These differences are diminished in the presence of asphaltenes such that the PI having the higher chain density is somewhat more effective. Trends in both morphology and viscosity suggest a steric effect associated with wax composition that is lessened on interaction of the PIs with asphaltenes.