Study On Effects Of Chemical Workover On Treatment Of Produced Fluid By ASP Flooding

Since carrying out of pre-experiment of weak alkali ASP flooding in Daqing oilfield,fracturing and pickling operation are needed which increase production and solve the problem that the alkali may often result in serious wellbore scaling.As it is difficult to backflow thoroughly for the acid liquid the early-stage produced fluid of producers usually have an effect on the treatment of the produced liquid and water,such as the increase of the difficulties of the Oil/water separation,the increased concentration of the suspended solid and oil of the water treatment system,the failure to up to standard of the treated water and so on.In this paper,the influence of the fracturing operation,the pickling operation assistant of the early-stage produced fluid of producers,the large size solid particles,the water soluble inorganic pollutants to the ASP flooding produced liquid and produced water in N2W block in Daqing oilfield were investaged.The results were shown as follows:The influences of the early-stage produced fluid of fracturing operation to the weak alkali ASP flooding produced liquid and produced water weren't the principal factor.The main reasons of the abrupt increase of the suspended solid content(SS)in ASP flooding produced water after restart of producers gone through acidic downhole scale removal were determined by the formation of mineral particles such as FeS,CaCO3,CaF2,FeCO3 and Fe(OH)2 by the reactions between Ca2+,F-and Fe2+ in the initial produced fluid of producers which put back into production and S2-and CO3-present in the topside blending water after the mixing of the two streams at wellheads.In addition,the destabilization and precipitation of partially hydrolyzed polyacrylamide(HPAM)in the topside blend water by Al3+ in the initial produced fluid of producers which was put back into production also contributed to the increase of SS in ASP flooding produced water.The early-stage produced fluid of producers put back into production after downhole acidic scale removal service,resulted in significant deterioration of the oil/water separation of produced liquid and water by a weak alkaline ASP flooding project conducted at the N2W block of Daqing Oilfield.Effects of additives used in oil well acidic scale removal service and the precipitate forming ions in the early-stage produced fluid of producers put back into production after downhole acidic scale removal service,on the oil/water separation properties of produced liquid and water by N2W block ASP flooding project,were investigated.The major reason that the early-stage produced fluid of producers put back into production after downhole acidic scale removal service,leads to deterioration of oil/water separation of ASP flooding produced liquid and water was found to be the Fe2+ in produced fluid of producers,which reacts with S2-in the hot water blended into the produced fluid of producers at well sites to form ferrous sulfide particles.The black particles tend to adsorb on the surface of oil droplets and present steric hindrance to the oil droplet coalesce.Before the early-stage produced fluid of ASP flooding mixed with the ground water,dose of water quality stabilizing medicament and sulfide scavenger was added to the ground water.It can effectively reduce the influence of the produced fluid on weak alkali ASP flooding on oil/water separation properties.