基于改性壳聚糖螯合的新型除钙技术

Novel calcium removal technology based on modified chitosan chelation

目的以长庆油田某区块钻井污水为例,解决钻井污水产量大、组分复杂和Ca^(2+)等多价离子含量高,且经常规工艺处理后污水仍难以满足压裂液回配性能要求的问题。方法基于以上难解工艺特征,提出多官能团壳聚糖改性螯合Ca^(2+)新型除钙工艺,并对其除钙效果、除钙机理、适用条件(温度、pH)、环境影响(产泥量)及回配性能进行了评价。结果以高脱乙酰度壳聚糖为原料,过硫酸钾作引发剂接枝丙烯酸,在温度为70℃,m(壳聚糖)∶m(过硫酸钾)∶m(丙烯酸)=1.0∶1.2∶25.0的条件下反应2 h可制得高水溶性多官能团SZ-1螯合剂,采用质量浓度为600 mg/L的SZ-1可将Ca^(2+)质量浓度螯合去除至500 mg/L以下;SZ-1在10~40℃、pH为6~14条件下均适用,产泥量低(0.016 g/L),回配压裂液基液黏度较优(30.9~31.2 mPa·s),满足SY/T 7627—2021《水基压裂液技术要求》的基液黏度范围要求(10~40 mPa∙s)。结论该药剂绿色清洁、性能优异、制备简单,有望为油气田高含钙钻井污水处理提供新方法。

Objective The drilling wastewater in a block of Changqing Oilfield is large in volume,complex in composition,and high in Ca^(2+)and other multivalent ions,which makes it challenging to meet the requirements of fracking fluid blending performance after conventional treatment.Methods Based on the above difficult process characteristics,a new type of calcium removal process was proposed by modifying chitosan with multifunctional groups to chelate Ca^(2+),and its effect on calcium removal,calcium removal mechanism,applicable conditions(temperature,pH),environmental impact(mud production)and back-mixing performance were evaluated.Results The results showed that chitosan with a high degree of deacetylation was used as raw material,potassium persulfate was used as initiator to graft acrylic acid,and chitosan:potassium persulfate:acrylic acid=1.0:1.2:25.0 was reacted under the conditions of temperature of 70℃for 2 h to produce highly water-soluble multifunctional chelating agent,and the Ca^(2+)could be chelated and removed to less than 500 mg/L by using 600 mg/L SZ-1.SZ-1 could be applied under the conditions of 10-40℃,pH=6-14,with low sludge production(0.016 g/L)and suitable viscosity of base fluid(30.9~31.2 mPa∙s),which satisfied the requirements of base fluid viscosity range(10-40 mPa∙s)in SY/T 7627—2021 Technical requirements of water-based fracturing fluid.Conclusion It is expected to provide a new solution for the treatment of drilling wastewater with high calcium content in oil and gas fields,with its green and clean color,excellent performance,and simple preparation.