Research On Scale Inhibitor Of Reinjection System In An Offshore Drilling Platform

To reduce deficit of formation pressure,water is injected into stratum in the process of oil and gas well running.On the one hand,reinjection water comes from formation water,which has been purification treatment;on the other hand,it is from surface water.The injected water quality should meet related standards.During water operation,water injection scaled due to the effects of temperature,pressure,water quality and pH.Adding proper scale inhibitors can solve the problem.In this paper,injected water quality and working condition of drilling platform in CNOOC was studied.Based on PASP,IDS,and tenary copolymer(arcrylic acid/methyl acrylate/maleic anhydride),a kind of phosphorus-free compound scale inhibitor was developed.According to corresponding national standard and industrial standard,the properties of the resistance of calcium carbonate was evaluated in laboratory.Results were as follows:(1)Under the.same condition,adding signal component(PASP,IDS,ternary copolymer),its antiscaling performance was not as good as complex products.(2)The order of the scale inhibition performance of complex product was that PASP/ternary copolymer>PASP/IDS/ternary copolymer>IDS/ternary copolymer.The inhibition rate of all samples were over 85%.(3)The composited rate of PASP/ternary copolymer was 1:3;addition was 100-150mg/L,the range of pH was 6-7,temperature range was 60-80?,time was 6-8h.The inhibition rate were over 90%.(4)Based on two field water quality,under certain conditions,for example,the rate of PASP/ternary copolymer was 1:3,addition was 150mg/L,the temperature was 60°C,the pH was 7.0,calcium ion concentration was 500-900mg/L,bicarbonate ion concentration was 700-1400mg/L.The inhibition rate were over 90%.Mixed scale inhibitor can meet field requirements.(5)By XRD and SEM,scale inhibition mechanism of composited antisludging agent was that functional groups of antisludging and metal ions combined with chelation.It resulted in distorting lattice,changed the morplology of CaCO3,produced the decomposition of calcite and made vaterite and aragonite stable.