Effect Of Comb-polymers On Asphaltene Aggregation Behavior And The Rheological Property Of Heavy Oil Under High Pressure

Asphaltene,consisting of aromatic structures with complex assembly behavior,can easily aggregate and deposit from solution and block the pipeline.It is the main reason for the high viscosity and low mobility of heavy oil,which make it be a huge challenge in mining or transport process.Adding polymer viscosity reducer,which can improve the aggregation state of asphatene,in oil reserves is an economical and feasible method to improve the flow ability of oil.Development of effective viscosity reducers aiming at heavy oil,it should be investigated that the interaction form and strength between the dispersant and asphaltene.So,from the micro and macro perspective,the aggregation behavior of asphaltene in model oil at low concentration influenced by both MACs and PMV series were studied,and meanwhile with their effect on the rheological properties of heavy oil with high asphaltene concentration.By means of radical polymerization,poly（maleic anhydride-vinyl acetate）（PMV）intermediates were synthesized.Then comb-type polymer（PMV）were grafted with different side chains by amination,which were divided into two series:one were grafted with alkane varying in chain length of PMV-8,PMV-14 and PMV-18;the others were grafted with aniline,naphthylamine and 2-amino benzimidazole respectively,called PMV-A,PMV-N and PMV-B.’H NMR was used to characterize the structure and grafting ratio of the newly synthesized polymers.At room temperature and atmospheric pressure,MACs and PMV series about their effect on dispersion and stability of asphaltene（the "onset of precipitation"）in model oil were investigated by UV-Vis spectra,turbidity measurement and dynamic light scattering,and the aggregation behavior by fluorescence microscopy.The results showed that:Among MACs,NMAC（grafted with naphthalene）show the best effect on asphaltene dispersion which delay the onset of precipitation by 20%;and within PMV Series,PMV-18 give a good performance in delay the onset of asphaltene precipitation.Microscope characterized the transformation of asphaltene from flocculation to the ellipsoidal gel particle when added polymers.The DLS results showed that several polymer additives could make the average size of asphaltene aggregates decrease while the distribution be narrow,which testified that the comb-polymer can boost asphaltene particle to keep stability and dispersion.The effect of temperature,static pressure and high CO₂ pressure on the rheological properties of heavy oil,were investigated by rotary rheometer with a high pressure test system.The rise of temperature can significantly reduce the zero shear viscosity of heavy oil,and the static pressure make the viscosity increase slowly while high CO₂ pressure can evidently reduce the complex viscosity.The modulus corresponding to gel point,keep nearly constant before supercritical pressure,whereas it decreased rapidly when surmount supercritical pressure.It means that the heavy oil is incline to a Newtonian fluid.By testing the combined effect of comb-polymer with high CO₂ pressure,it was found that they had somewhat synergistic effect,which convinced the feasibility of polymer viscosity reducer assisting CO₂ flooding.