The Study And Application Of Demulsifier For Breaking Crude Oil Emulsions Formed By Polymer Flooding

To explore more crude oil from underground,polymer flooding technology are widely used in the world especially in China.During the exploring,the water-in-crude-oil(W/O)emulsions are innevitably formed.The existing of polymer in emulsions makes the emulsions more stable.The demulsifier current used becomes more and more difficult to meet the needs of oilfields,therefore,upgrading is imperative.In addition,due to the small processing space of offshore platform,a demulsifier which can break the emulsions fast and efficiently is required more urgently.This paper is to study the demulsification of breaking the W/O emulsions formed from polymer flooding,and to develop a demulsifier which can be used in offshore platform,especially to provide a reference to break the emulsions for offshore platform.The work of this paper is divided into the following sections:(1)The relevant literature on the demulsification were summarized and classified,and the results to break emulsions were described.The mechanism of breaking emulsions and the characteristics of W/O emulsions formed by polymer flooding were discussed in detail.Factors affecting demulsification performance were analyzed.(2)The highly branched polyether BPA was synthesized based on phenol amine resin.The structure was tested by 1H-NMR and dynamic light scattering which showed that the actual PO/EO ratio was consistent with the designed ratio.This phenominon indicated that this reaction technology was very stable.Aggregation behavior showed that the increasing hydrophobic PPO groups reduced the cmc and promoted the formation of micelles.Salting-out effect of inorganic salts can reduce the surface tension and improve the surface activity as well as increasing temperature.(3)Demulsification of BPA demulsifier showed that dehydration rate of triblock,tetra-block demulsifier was very slow and only diblock demulsifier had higher dewatering rate.Among which,BPA6927 had the highest dehydration rate and was even higher than the current used demulsifier in offshore platform.Benzene was found to play an active role in the process of demulsification.The modifier containing aromatic rings can improve the demulsification.The greater the numbers of aromatic rings in modifier,the higher the dehydration rate.Both bottle test and Turbiscan Lab analysis confirmed this conclusion.(4)A novel polyether demulsifier with four aromatic rings and four branches was synthesized by using innovative technology which used PO as a solvent to polymerize with PO and EO.The aggregation behavior at pure water and minerialized water was studied by surface tension respectively.As expected,the demulsification performance is very poor due to their small branches though the aromatic rings improved the affinity with the crude oil.After modification,the demulsification performance was improved,but the effect was still poor for polymer flooding.(5)A novel polyether named TPEA was synthesized based on novel phenolic amine resins prepared by 1,1,2,2-tetrakis(p-hydroxyphenyl)ethane,formaldehyde,and tetraethylenepentamine.The increasing in hydrophobic PPO chain length decreased cmc and improved the surface activity as well as BPA polyether.Compared with the less branched poiyetner,higniy branched polyether had higher efficiency to reduce the surface tension and lower effectiveness to reduce the surface tension,indicating that the more polyether branches,the more carbon atoms in the hydrophobic core,the higher efficiency to reduce the surface tension,but the effectiveness to reduce the surface tension is not proportional to the molecular weight or the number of branches.The addition of inorganic salts had an obvious impact on surface tension before cmc and a negligible effect after cmc.Increasing temperature was significantly lower the surface tension and cmc of the polyether,improved the surface activity of the polyether molecules whether with or without inorganic salts.(6)Demulsification showed that this kind of demulsification had powerful demulsification performance,and even higher than BPA demulsifier.The demulsification order obtained from Turbiscan Lab was the similar with the bottle test demulsification.The demulsification mechanism was studied according to microscope and partition coefficient.It is observed that the water droplets grows by merging other water droplets with closed diameter or "eating" the smaller water droplets in W/O emulsions.During the demulsification,demulsifier molecules more and more aggregated in the water phase.When the concentration of added demulsifier was below 200 mg·L-1,the content of demulsifier in oil phase can be neglected.Demulsifier molecules were hindered during the diffusion process from oil phase to water phase,resulting in the increase of demulsifier in oil phase with further increasing in concentration.(7)According to the method of TPE polyether preparation,a novel kind of block consisting of a 1,3,5-tri(p-oxaphenyl)benzene(TPB)core,hydrophobic poly(propylene oxide)(PPO)and hydrophilic peripheral poly(ethylene oxide)(PEO)in the structure of TPB-PPO-PEO was prepared.1H-NMR and GPC measurements confirmed the mature technology of preparation.Cloud point and critical micelle concentration(cmc)were affected by their hydrophobicity and hydrophilicity.Inorganic salts decreaseed the cloud point by salting-out effect depending on their valence of either anions or cations.It was found that fluorescence quenching was observed in good solvent such as water,whereas,another opposite fluorescence phenomenon,fluorescence enhancement appears in poor solvent like hexane.Whether a good or poor solvent was determined by the PEO groups.It meaned that the appearance of these two contradictory fluorescence properties can be controlled by the polarity of solvent.Their fluorescence showed a strong selective quenching to Fe3+.Not only polyether with terminated hydroxyl but also polyether with terminated methoxyl can cause this fluorescence quenching indicating that the key role was oxygen atom.This sensitivity to detect Fe3+ was both interrelated to PPO chains and TPB content.The partition coefficient performed in mixed heptane/water showed that most of polyethers were still in the water,just as in the crude oil.The effect of concentration on partition coefficient was contratry to the effect in the crude oil indicating that a large gap exited between simulated and real situation.Though this polyether had large conjugate benzene ring,a poor demulsification performance was observed due to its small number of branches.