深水油气井新型膨胀导管力学特性

喷射法下入表层导管在行业内已经成为一种广受欢迎的导管安装方式,若导管承载能力不足,可能造成井口失稳、建井失败等巨大损失。为提高表层导管的承载能力,采用了新型可膨胀导管技术,此技术能有效增大导管外表面积,加强导管承载力,降低井口失稳风险,是一种既经济又安全的高效方法。首先对遇水延迟膨胀材料进行了评价和优选,通过实验测试了不同温度和压载情况下膨胀材料随时间的体积变化率。根据表层导管极限承载力变化规律,分析了膨胀导管在吸水延迟膨胀阶段的力学行为特征,利用实验数据线性回归得到了材料体积膨胀系数,建立了涵盖体积膨胀效应的膨胀导管极限承载力计算模型,并进行现场应用实验。实验结果表明：膨胀材料的膨胀率随温度的下降略有减小,随围压的增大缓慢降低,起始膨胀时刻可通过技术手段进行控制。试验井实际应用结果表明：理论预测结果符合实际情况,新型膨胀表层导管可使导管表面积增加20 % 以上,承载力提升30 % 以上。膨胀导管既能满足现场施工要求,减少表层导管下入深度和使用数量,又能显著提升水下井口承载力,可为深水钻井降本增效提供技术支撑。

Mechanical properties of a new type of expandable surface conductor in deepwater oil and gas wells

The jetting method is widely used to install the surface conductor within the industry. However, if the surface conductor cannot provide sufficient bearing capacity, it may cause huge losses such as non-stable wellhead and failure in well construction. A new type of expandable casing technology is adopted to improve the bearing capacity of surface conductor. This technology can effectively increase the external surface area of surface conductor to strengthen its bearing capacity, and reduce the risk of wellhead instability. It has proved to be an efficient, economical and safe method. The study first evaluates and selects the delayed expandable material in the presence of water; An experiment-based test is performed on the volume change rate of expandable material under different conditions of pressure loading, temperature and material ratio. According to the changing law of the ultimate bearing capacity of surface conductor, this paper analyzes the mechanical behavior characteristics of the expandable surface conductor during the stage of delayed expansion caused by water. The volume expansion coefficient of the material is obtained through the linear regression of experimental data. The calculation model has been established for the ultimate bearing capacity of the expandable surface conductor as considering the volume expansion effect, and experiments of field application have also been performed. The experimental results show that the expansion rate of expandable material decreases slightly with the decrease of temperature, decreases slowly with the increase of confining pressure, and the initial expansion moment can be controlled by technical means. When the filling ratio of cross-linking agent is less than 25 % , the expandable characteristic curve of the material can be significantly divided into the water resistance phase and the expansion phase. The application practice shows that the theoretical predictions are consistent with the actual situation. Using the new type of expandable surface conductor, the surface area of surface conductor can be increased by over 20 % and the bearing capacity by more than 30 % . The expandable surface conductor can meet the requirements of field construction, reduce the setting depth and number of surface conductor, and can significantly increase the bearing capacity of underwater wellheads, thus providing technical support for increasing the efficiency of deepwater drilling while reducing costs.