Study On Flow Improvers For Heavy Crude Oils With High Content Of Asphaltenes

Asphaltene and wax are two important components of crude oils. As the temperature, pressure and composition of crude oils change, the asphaltenes are ready to aggregrate, precipitate, and subsequently deposit on the pipeline wall, whereas the waxes tend to crystallize and form compact three-dimensional network structure. These problems will lower the flow ability of crude oils and even lead to the blockage of the pipelines, causing significantly adverse effects and great losses on the oil production. Poly (styrene-co-N-octadecyl maleimide) (SNODMI) is comnsidered as an effective flow improver for waxes. Its octadecyl chain can interact with waxes while its aromatic benzene rings and polar groups, which are incompatible with waxes, can inhibit the growth of wax crystals, resulting in flow improvement for crude oils. The asphaltene stabilizers need to possess polar or aromatic groups, which can associate with asphaltenes, and long alkyl chains, which are compatible with hydrocarbon matrix in crude oils. Fortunaly, SNODMI have both characteristics and thus can also be applied as an asphaltene stabilizer.In this work, poly (styrene-co-maleic anhydride) (SMA) with different maleic anhydride (MAh) molar contents and molecular weights (Mn) were synthesized via RAFT polymerization technique. Then, the SMAs were reacted with octadecyl amine through amidation and subsequent imidization to obtain SNODMIs with various imidization degrees. Finally, the SNODMIs were utilized as an asphaltene stabilizer and an flow improver for waxes simultaneously. The influences of molecular structures of SNODMI on its ability to stabilize asphaltenes and its effectiveness of flow improvement were studied elaborately.Turbiscan LA6Expert was used to investigate the effects of the MAh content in SMA, the molecular weight, and the imidization degree of SNODMI on the ability of SNODMI to stabilize asphaltenes in model crude oil with high content of asphaltenes. The results indicate that the higher the MAh content, also the higher the content of octadecyl chains in SNODMI, the better the asphaltene stabilization. Therefore, SNODMI with an alternative structure is the best asphaltene stabilizer. An appropriate molecular weight (Mn= 3500 Da) was most conducive to stabilize asphaltenes in model crude oils. Too low or too high molecular weight will deteriorate the ability of SNODMI to stabilize asphaltenes. In addition, (a/t)SNODMI with an appropriate imidization degree (66.10%) was able to stabilize asphaltenes most effectively. The optimal imidization degree of SNODMI decreases with decreasing the MAh content. The most effective imidization degrees of (ran)SNODMI-2 (MAh%= 20.92 mol%) and (raw)SNODMI-1 (MAh%=10.37 mol%) were 64.31% and 0%, respectively.Second, the influences of the molecular structures of SNODMI as a flow improver on the cold flow ability, asphaltene morphology, and crystallization temperature of model crude oil with high content of asphaltenes were thoroughly investigated. It is found that with increasing the MAh content the rheological properties of model crude oil was bettered, that is, the complex viscosity and yield stress were decreased, and the asphaltene particle size was reduced and the particles were better dispersed. An appropriate molecular weight (Mn= 3500 Da) was most beneficial for SNODMI to decrease the complex viscosity and yield stress, to improve the rheological properties of model crude oil, and to reduce the size of the asphaltene particles and disperse the particles better. After the addition of (alt)SNODMI-4 and (ran)SNODMI-2, the rheological properties of model crude oil were improved with increasing their imidization degrees.100% imidized (alt)SNODMI-4 and (ran)SNODMI-2 both achieved the lowest complex viscosity and yield stress of model crude oil and the smallest size of asphaltene particles as well as the best dispersion of the particles.