Research On Plug Removal And Injection Stimulation System On Water Injection Well In Offshore Oilfiled

In the waterflood development of the offshore oilfield B,the production wastewater is usually used for reinjection after treatment.Due to the site limitation of the offshore platform and insufficient sewage treatment capacity,the injection water quality has not reached the standard for a long time,and the injection water contains a large amount of suspended solids and dirty oil,which will cause serious plugging in injection well and affect the flooding development effect of the oilfield.In order to solve the plugging problem in water injection well,the acidification and plugging removal measures have been adopted in offshore oilfields.Although good injection effect has been achieved,there are also many problems.On the one hand,the acid liquid cannot penetrate the oil film on the surface of the solid plugs formed by the adsorption of dirty oil,and the acidification effect is poor.On the other hand,the oil content in the injected water exceeds the standard,the acidification period is short,and the acidizing operation needs to be repeated,and the plugging removal effect is getting worse.First,the analysis of the plugs from the on-site water injection wells shows that the plugs are mainly composed of oxidative corrosion products of iron and a small amount of carbonate scale wrapped in dirty oil.Adsorption of dirty oil on the surface of the plugs will not only increase the plugging degree,but also not conducive to the acid dissolution.The impact of suspended solids and oil content in the injected water on the reservoir was analyzed through the core damage evaluation experiments,which provides a basis for the research on the plug removal and injection simulation system.Then,for solving the problem of the impossibility of acid penetrating plugs with high oil content,0.8% DAB/TAB was selected as the sludge dispersant through the sludge ball dispersion experiments,and the compounded mass ratio of DAB and TAB was 2:1.The DAB/TAB compound system can quickly disperse the oil in the plug and open the channel for acid solution corrosion.For solving the problem of the short period of plug removal after acidification,0.5% FZC was selected as the wetting reversal agent through the wetting performance tests.After acidizing and plug removal,FZC can reverse the wettability of the rock from hydrophilic to weakly oleophilic,and the emulsified oil droplets in injection water will spread into an oil film on the surface of the rock,eliminating the blocking effect of oil droplets and prolonging the effective period of plugging removal.According to the screening evaluation results,a plug removal and injection simulation system for offshore oilfield injection wells was finally formed and composed of 0.8% DAB/TAB and 0.5% FZC.Finally,through the core flow experiments,the permeability recovery rate of the plug removal and injection simulation system combined with earth acid,fluoroboric acid and polyhydrogen acid on the cores polluted by injected water was evaluated,which was 94.6%,113.4% and 188.4%,respectively.The results show that the plug removal and injection simulation system has a better removal effect on plug induced by the injection water pollution.Through oil pollution and solid suspension pollution experiments,the effective period of plugging removal of the plug removal and injection simulation system was evaluated.The results show that the core treated with the plug removal and injection simulation system has better resistance to oil pollution,indicating that the plug removal and injection simulation system can extend the effective period of plugging removal.