延长油田长2储层采出水回注结垢研究

A study on produced water scaling during reinjection from Chang 2 reservoir in Yanchang Oilfield

关键词:  采油污水  絮凝  回注  结垢预测 

Key words:  oil wastewater  flocculation  reinjection  scale prediction

摘要:

以延长油田长2储层采油厂的采出水为研究对象,采用Scalechem软件对采出水及其与地表水、地层水的配伍进行了结垢预测。结果 表明,在地面管线中,ρ(BaSO₄垢)为176 mg/L,ρ(CaCO₃垢)为540 mg/L；在井筒水平段,ρ(BaSO₄垢)为168 mg/L,ρ(CaCO₃垢)为526 mg/L,不符合油田回注水要求。需进行絮凝复配工艺处理,ρ(PAC)为60 mg/L,ρ(CPAM)为1.2 mg/L,最佳加药间隔为30 s,搅拌时间为5 min,处理后采出水透光率为88.1%,配伍性较好。采用Scalechem软件进行结垢预测,BaSO₄结垢率降低超过75%,CaCO₃结垢率降低甚至达到99%,降低了采水负荷,符合油田回注水要求。 

Abstract:

In this study, taking produced water from oil production plant of Chang 2 reservoir, Yanchang Oilfield as a research object, scaling potential of the produced water, as well as the compatibility of produced water with surface water or formation water, were determined by the simulation tool Scalechem. The results showed that mass fraction of BaSO₄ and CaCO₃ scales in produced water would be 176 mg/L and 540 mg/L respectively in surface pipelines, while 168 mg/L of the BaSO₄ and 526 mg/L of the CaCO₃ was predicted to generate in horizontal section downhole, failing to meet the requirements of water reinjection in oil fields. Thus, it was necessary to treat the water with coagulation/flocculation process. The optimum operation parameters were identified to be with PAC dosage at 60 mg/L, CPAM dosage at 1.2 mg/L, the interval time between the above two chemicals was 30 s, and mixing time for flocculation was 5 min. Light transmittance of the treated produced water was 88.1% with better compatibility. According to Scalechem simulation, mass fraction of BaSO₄ scaling was reduced more than 75%, while CaCO₃ scaling was reduced almost 99% in reconciled water after treatment. The proposed treatment was proved to decrease the water production load and satisfy with the water reinjection requirements in oilfield.