用于钻井堵漏的特种凝胶屈服应力研究

A study of the yield stress of a viscoelastic gel applied in severe lost circulation control

特种凝胶是一种处理钻井恶性漏失的堵漏剂,其屈服应力与凝胶的可泵性、施工管线的安全性和在地层的堵漏效果等密切相关。为此,采用先进的HAKKE RS6000流变性锥板系统及锯齿板系统研究了特种凝胶(ZND-2)的屈服应力,分析了稳态方法和动态方法测试之间的关系,并与钻井液常用屈服应力评价方法的结果进行了对比,还分析研究了屈服应力恢复与时间的关系。结果表明,选用控制应力模式的应变—应力双对数曲线拐点和应力扫描测试的线性黏弹区与非线性黏弹区界限能够准确的获取凝胶的屈服应力,凝胶屈服应力在温度低于50℃时随温度增加而小幅增加,屈服应力在剪切作用停止后恢复速度快,是有利于堵漏成功的因素。

This special gel is a plugging agent for serious lost circulation control during drilling. Its yield stress is closely related to the pumping property of the gel, the safety of the pipelines, and the plugging property in formations. The yield stress is tested by using cone plate system and serrated plate system of high precision rheometre (HAKKE RS6000 Rheometre). The results of yield stress tested by stable tests and dynamic tests are analyzed and compared with the data obtained by conventional drilling fluid yield stress evaluation method. And the rule of yield stress recovery with time is studied. The analysis results show that the yield stress of the gel can be exactly obtained by the inflexion of strain-stress log-log plot curve under stress control test and the crossover of the linear viscoelastic range and nonlinear viscoelastic range of stress scan test at a fixed frequency. The yield stress of the gel increases slightly with the increasing temperature below 50℃, and it recovers very fast after the shearing is stopped. They are both helpful for plugging.