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

关键词:  钻井污水  壳聚糖  螯合剂  除钙  压裂液

Key words:  drilling wastewater  chitosan  chelating agent  calcium removal  fracturing fluid

摘要:

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Ca²⁺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Ca²⁺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Ca²⁺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。

Abstract:

Objective The drilling wastewater in a block of Changqing Oilfield is large in volume, complex in composition, and high in Ca²⁺ 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 Ca²⁺, 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 Ca²⁺ 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.