高剪切流场和含水率对驱油剂产出高峰期三元复合驱采出液油水分离特性的影响(二)

Effects of strong shearing flow field and water-cut of ASP flooding produced fluid on its oil/water separation performances during peak production of injected chemicals(Ⅱ)

以大庆油田北一区二排区块现场三元复合驱采出液为介质,研究了采出液含水率和离心泵中的高剪切流场对石油磺酸盐表面活性剂弱碱体系三元复合驱采出液油水分离特性的影响及其影响机制。驱油剂产出高峰期三元复合驱采出液的最主要特征为含水率和驱油剂含量高,油水界面张力低,油水乳化程度高,在离心泵等高剪切湍流场内易发生二次乳化而油水分离难度显著增大。水包油(O/W)型三元复合驱采出液的油水分离难度随其含水率增大而增大。含水率大于等于93.7%的高表面活性剂含量石油磺酸盐表面活性剂弱碱体系三元复合驱采出液单位体积内的油滴数量少,油滴间发生相互碰撞和接触的机会少,加上油滴在Marangoni效应作用下聚并缓慢,其在上浮进入三相分离器和游离水脱除器油水界面下方的油珠聚集体之前难以充分聚并,粒径过小,使得油珠聚并后被圈闭在油连续相中的水滴粒径过小,所形成的油包水(W/O)型原油乳状液中含有大量直径小于4μm的细小水滴,这些细小的水滴受Brown运动影响严重,沉降和聚并困难,造成驱油剂产出高峰期三元复合驱采出液脱水达标困难。离心泵对含水率小于60%的三元复合驱采出液总体上有显著的二次乳化作用,使其油水分离特性变差,而对含水率为77.3%的三元复合驱采出液的油水分离特性则没有显著的不利影响。离心泵对三元复合驱采出液的乳化机理为离心泵内存在高强度的湍流场,其中尺寸与分散相液滴相近的漩涡与液滴发生碰撞而使后者发生破裂,粒径变小,其影响程度随油水界面张力和分散相体积分数下降而增大。转油放水站外输液为含水率为60%~80%的O/W型乳状液时其后续脱水难度较低。

Effects of strong shearing flow field in centrifugal pumps and water-cut of produced fluid by ASP flooding injecting Na;CO;,petroleum sulfonate and partially hydrolyzed polyacrylamide on its oil/water separation performances,as well as the governing mechanisms,were investigated on the ASP flooding produced fluid by an ASP flooding project implemented at N1-2 block of Daqing fields.The most important characteristics of ASP flooding produced fluid during peak production of injected chemicals are high water-cut and high contents of injected chemicals,low oil/water interfacial tension,high degree of emulsification,as well as susceptibility to the secondary emulsification by high shearing turbulent flow in centrifugal pumps which tends to significantly downgrade its oil/water separation performances.The oil/water separation performances of o/w ASP flooding produced fluid worsen with the increase of its water-cut.For ASP flooding produced fluid with water-cuts over 93.7%,it is difficult for the oil droplets in it to coalesce and merge into larger droplets during the creaming process in 3 phase separators and free water knockouts(FWKO)due to the low collision frequencies between the sparsely dispersed oil droplets and Marangoni effects,leading to small oil droplets entering the concentrate oil droplet layer beneath the oil/water interface in 3 phase separators and FWKOs,which in turn results in a large number of water droplets with diameters below 4μm in the w/o crude oil emulsion formed by the coalescence of oil droplets in the concentrate oil droplet layer(phase reversal).It is difficult to remove the tiny water droplets with diameters below 4μm from the w/o crude oil emulsion by gravity settling and static electro-coalescence due to the effects of Brown motion,making it extremely difficult to dehydrate ASP flooding produced fluid to meet the oil export specification during peak production of injected chemicals.Centrifugal pumps generally enhanced the emulsification of ASP flooding produced fluid with water-cut below 60%,downgrading its oil/water separation performances.However,centrifugal pumps did not show significant effects on the oil/water separation performances of ASP flooding produced fluid with a water-cut of 77.3%.The mechanism governing the secondary emulsification of ASP flooding in centrifugal pumps involves collision between a droplet and an eddy of similar size in the high shearing turbulent flow inside centrifugal pumps,which results in deformation of the droplet and finally its breakup into smaller droplets.The effects of centrifugal pumps on the emulsification of ASP flooding produced fluid intensify with the lowering of oil/water interfacial tension and volume ratio of the dispersed phase.The oil/water separation performances of the oil export of an oil gathering station are above the ordinary when the oil export is o/w emulsion with water-cuts between 60%and 80%.