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.

The present study proposes a new nonoscillatory nonrotary (NONR) method to measure gelation temperature based on a temperature-dependent normal force. A variation in the normal force signal is observed due to the combined effect of volume shrinkage and wax crystal network. The sample retains fluidity above the gelation temperature, in the absence of a gel network. The proposed method shows good repeatability for a model waxy oil and real crude oils. The results of the NONR method are consistent with the results from earlier methods. Gelation temperature measurement using the NONR method does not require gel movement. However, all of the existing rheological methods use either shear stress or shear rate, which participates in the gelation process. The gelation temperatures of 15% macrocrystalline wax in the dodecane sample measured using constant shear stress, constant shear rate, oscillatory, and NONR methods are 26.6, 27.5, 26.8, and 27.0 °C, respectively.

Flow assurance challenges associated with waxy crude oil precipitation at low ambient conditions are significant concerns for oil industries during production, transportation, and storage. Numerous methods have been employed to mitigate wax deposition and gelation issues. Since wax precipitation is temperature-sensitive, heating has emerged as a promising method to enhance oil flowability. The present work intends to examine the degelation behavior of waxy oil using rheometry, differential scanning calorimetry, and microscopy techniques. In addition, a non-isothermal flow restart simulation is performed using an in-house numerical simulator consisting of a rheological model of sol–gel transition developed in the current work. A numerical simulation of a preheated gelled pipeline demonstrates the significance of the degelation temperature. The effects of the wax concentration, initial gel temperature, and aging period on the degelation temperature are examined. The observed degelation temperature is higher than the gelation temperature, leading to thermal hysteresis. The extent of thermal hysteresis reduces with a decrease in the heating rate. The numerical simulation uses the finite volume method with variables placed on a staggered grid. The gel heated above and below the degelation temperature shows a significant variation in axial velocity profiles. However, further heating does not affect the velocity profiles. A shear banding type of effect is observed in the axial velocity profile above the degelation temperature. Heating the gelled oil to the degelation temperature instead of the wax disappearance temperature saves excessive heating energy during storage and transport operations.