碳酸盐岩油藏智能水驱规律与机制

Effects and mechanisms of smart water-flooding in carbonate reservoir

基于伊拉克Missan油田Mishrif组孔隙型碳酸盐岩油藏开展长岩心驱替试验、润湿角测定和界面张力测定试验,研究碳酸盐岩油藏智能水驱作用规律与机制。结果表明碳酸盐岩油藏智能水驱中岩石表面润湿性改善与油水相互作用改变协同作用提高采收率,其中润湿性改善影响较大。关键离子类型及质量浓度对润湿性及界面张力影响明显。其中Mg^(2+)和Ca^(2+)促进润湿性和界面张力的改变,随着其质量浓度增加,润湿角和界面张力均先减小后增大,存在最优质量浓度使得润湿角和界面张力最小;Mg^(2+)作用效果强于Ca^(2+)。SO^(2-)_(4)促进关键阳离子对润湿性的影响,抑制其对界面张力的影响,质量浓度越高作用效果越明显。碳酸盐岩油藏智能水驱中SO^(2-)_(4)优先吸附于方解石表面,促进关键阳离子发生多离子交换反应,造成润湿性的转变;随着溶液中离子类型及质量浓度的改变,吸附于油水界面的极性原油分子发生盐溶和盐析作用,影响油水相互作用。

On the basis of the long core flooding experiment,contact angle and interfacial tension measurements of the porous carbonate reservoir in Mishrif formation,Missan oil field,Iraq,the effects and mechanisms of smart water-flooding in carbonate reservoir were investigated.It is shown that the wettability improvement and the fluid-fluid interaction change act synergistically to enhance oil recovery in smart water-flooding of the carbonate reservoir,in which the influence of the wettability is more significant.The type and amount of potential determining ions have great influence on wettability and interfacial tension.Herein,Mg^(2+) and Ca^(2+) can effectively promote the change of wettability and interfacial tension.With the concentration increasing,the contact angle and interfacial tension decrease first and then increase afterward.There is an optimal concentration corresponding to the minimum contact angle and interfacial tension.It is also found that the effect of Mg^(2+) is greater than that of Ca^(2+).SO^(2-)_(4) promotes the potential determining cations effect on wettability,meanwhile,hinders their effect on interfacial tension.The higher concentration of SO^(2-)_(4) means greater effect.SO^(2-)_(4) is preferentially adsorbed on the calcite surface,and promotes the multiphase ion exchange reaction between cations and oil-wet calcite surface,which causes the wettability alteration.With the ionic composition of the solution changing the adsorbed polar crude oil molecules on the oil-water interface undergo salting-in and salting-out processes,resulting in the fluid-fluid interaction change.