Effect of oil dispersible polymethylsilsesquioxane microspheres on the formation and breakage of model waxy oil gels

Abstract

It has been reported that the oil dispersible polymethylsilsesquioxane (PMSQ) microsphere can effectively improve the flow behavior of the waxy crude oil through the spacial hindrance effect. Because of the complex composition of the crude oil, in this work, model waxy oil is used to further investigate the effects and mechanisms of PMSQ microspheres on influencing the rheology of the waxy oil. The effects of PMSQ microspheres with sizes from 200nm to 10μm on the formation and breakage of the waxy oil gel are first studied based on the rheological measurements. Results show that adding PMSQ microsphere effectively inhibits the formation of the waxy oil gel and weakens the gel structure of the waxy oil formed at 20°C under static cooling condition. The gelation point, the G′, G″ value at 20°C/25°C and the yield stress at 20°C of the doped waxy oil are found to first decrease and then increase with the increase of the PMSQ microsphere size, and the PMSQ-3 (2μm) has the best improving performance. Under static isothermal condition, the formation of waxy oil gel is delayed after adding the PMSQ microsphere. However, under dynamic cooling condition, adding PMSQ microsphere slightly increases the losing flow point and apparent viscosity of the waxy oil. DSC results show that PMSQ microsphere can act as the heterogeneous nucleation sites favoring slight increase of the WAT but have no apparent influence on the precipitated wax crystals’ amount of the waxy oil at each temperature. Associated with the microstructure observation, the mechanism of the PMSQ microsphere influencing the formation and breakage of waxy oil gel is deduced. Under static cooling condition and static isothermal condition, PMSQ microsphere occupies a certain space in oil phase and impedes the interactions of the precipitated wax crystals around the microsphere through spacial hindrance effect, thus effectively inhibiting the formation of wax crystal network under static cooling and weakening the strength of the formed waxy oil gel. Under dynamic cooling condition, the interactions among the precipitated wax crystals are greatly weakened by shearing, the PMSQ microsphere cannot further weaken the interactions among the precipitated wax crystals, but act as a dispersed phase in the waxy oil to increase the concentration of the dispersed phases (wax crystals and PMSQ) at each temperature, resulting in the slightly higher losing flow point and apparent viscosity for the doped waxy oil.