| ChangQing oilfield is located in the northern part of Shaanxi province where water resources is seriously insufficient and the permeability of the formation is rather low.The No.2 oil Production factory is main oil-producing region of Changqing oil field.At present,the factory has entered the stage of water-flooding development,moisture content is nearly about 70%in produced fluid,a large amount of oil production sewage is formed after oil and water separation.It leads to a huge water consumption for underground water injection in order to keeping continuous development of oilfield.At the same time,with the recovery of crude oil,formation water and injected water come out to the ground,because oil field produced water contains high concentration of oil,salt and other impurities,so it can’t be direct discharged.Oil field produced water has severe corrosion since the characteristics as follows:high saltness and bacteria amount and low pH value and also containment of sulfur ion,iron ion which lead to the occurrence of corrosion phenomena in many different parts of water treatment system such as valves,pipelines,processing facilities and reinjection well and cause perforation,broken leakage and damage as well as significant economic losses.With the increase of corrosion even the whole oil field production could be affected.Therefore,it is significant to analyse main factors that causes the corrosion of oil field produced water system and put forward the anti-corrosion measures to make sure the stability of the oil field work.Hualian joint station is the center station of oil-gas-water treating in the No.2 plant of Changqing oil field.the station has been put into operation in1995,with an area of 80 Chinese acres and an investment about 70000000 yuan.With the scale of crude oil production of the No.2 plant increasing sharply,Hualian station overloads operation of water treatment device which causes the problem that produced water is not up to the standard,the ground system corrosion caused by low quality of produced water seriously restricts the crude oil production and water injection development level of Changqing oil field.This paper uses SY/T 5523-2000 standard,taking Hualian station as the center.the injection water system corrosion factors was studied through the static and dynamic and grey relational analysis method as well as on-site tank hanging metal plate method in Hualian station.The influence of inorganic ion,ion interaction,dissolved oxygen,pH value and temperature of wastewater on corrosion rate were discussed in this research.It shows that the corrosion rate order of per unit cationic ions is Na+<Ca2+<Mg2+<Fe2+<Fe3+;The anion ion is SO42<HCO3-<S2-;Corrosion rate will increase with the higher of dissolved oxygen concentration;the major influence factors of corrosion rate are Fe3+and S2-in considering of dissolved oxygen,pH value and temperature of produced-water.The produced water conveying line measured in each site around Hualian station are highly corroded,mainly uniform corrosion,besides,there are local corrosion such as pitting corrosion.From well 78-2/well 78-7,Hua-5 oil transfer station,Hualian station settlement tank outlet to Hualian station feed water pump outlet,static corrosion rate respectively is:0.0822,0.0916,0.0964,0.1204 and 0.1254 which are all more than 0.076 mm/a of petroleum industry standards and showing a gradually increasing trend.Research also shows that:the results of grey relation analysis is in accordance with indoor simulation experiment results,main factors affecting Hualian station produced water delivery system corrosion is S2-,Fe3+ and pH value,through the implementation of the corrosion prevention measures,the average corrosion rate is reduced from 0.1204mm/a to less than 0.0616 mm/a,the corrosion has been effectively controlled. |
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