Study On Displacement Mechanism Of PPG Dispersed In Heterogeneous Combination Flooding System

In recent years,polymer flooding is widely used in oil fields of China,and the technology is already quite mature.But there are still amount of residual oil in reservoir after polymer flooding,and many polymer flooding blocks are in the water recovery stage,further methods should be taken to reduce residual oil saturation.Therefore,the combination of PPG and polymer was proposed to improve oil recovery.The stability and rheological property of heterogeneous combination flooding system were studied.Then,the displacement efficiency of the heterogeneous combination system was evaluated.Finally,the microscopic EOR mechanisms of PPG in heterogeneous combination system were proposed.Rheological method,weight method and screen mesh filtering method were respectively used to study rheological property,swelling property and plugging property of PPG with different elasticity and to select proper PPG.Then temperature resistance,salt tolerance and pH resistance of the chosen PPG were researched.PPG with high elasticity is fragile;in contrast,PPG with low elasticity cannot plug the microporous membrane effectively.So considering swelling ratio,elasticity and plugging property,so 2#PPG that with moderate elasticity was selected.that with moderate elasticity is selected.And the chosen one has a certain temperature resistance,salt tolerance and p H resistance.The chosen PPG was dispersed in polymer solution to form a heterogeneous combination flooding system,and its stability and rheological property were studied by turbiscan and rheometer.The system stability is enhanced with the increase of polymer concentration,and weakened by the increasing PPG concentration.The best formula of heterogeneous combination flooding system is 1000mg/L PPG dispersed in 1000mg/L polymer.The heterogeneous combination system has a good performance of temperature resistance,salt tolerance and pH resistance.Its storage modulus decreases with the increase of temperature and ion concentration.And it decreases slightly with the increase of pH,but overall is not too much.The displacement characteristics of heterogeneous combination system were evaluated by chemical flooding simulation experiments.PPG dispersed in polymer solution can decrease polymer consumption;in the meantime,it can enhance the displacement efficiency.PPG can plug high permeability zone effectively,and it can enhance oil recovery on the basis of polymer flooding no matter in homogeneous or heterogeneous reservoir.The transport behavior of the PPG through a porous medium was studied by visual microscopic flooding model and microscopic EOR mechanisms of PPG dispersed in heterogeneous combination system were proposed.The transport behaviors of PPG through a porous medium and residual oil distribution were studied by visual microscopic flooding experiments.The main effects of reducing residual oil saturation are deformable passing through throats,snap-off and passing through throats,and trapped by throats,and effects of adsorbed onto rock surface and directly passing through throats are less important.The main kinds of residual oil distributing in the reservoir after polymer flooding are oil segment,cluster type residual oil,columnar residual oil,and residual oil at dead-end.Because of selective plugging mechanism and elastically deformable displacement mechanism,PPG in heterogeneous combination system can reduce oil segment,cluster type residual oil and columnar residual oil effectively,but it produces little effect on residual oil at dead-end.