基于气固两相流的气体钻井套管冲蚀数值模拟研究

Numerical Simulation on Casing Erosion Wear Based on Gas-cuttings Flow in Gas Drilling

气体钻井过程中携岩速度较高,岩屑对套管冲蚀较为严重,冲蚀磨损导致套管含缺陷,降低套管强度,缩短服役寿命。基于气固两相流和冲蚀理论,建立了气体钻井环空岩屑运移模型,采用Grant和Tabakoff半经验公式求解岩屑粒子冲蚀速率。计算了钻柱关键点处套管冲蚀情况及携岩速度、岩屑直径和岩屑数量对套管冲蚀的影响情况。通过数值模拟计算得出钻柱接头位置套管的冲蚀速率明显高于其他位置的冲蚀速率。为有效控制套管的冲蚀速率,建议在气体钻井中有效的控制携岩气流速度;建议在由冲蚀较严重而造成套管失效几率高的气体钻井中使用牙轮钻头钻进。

The velocity of gas-cuttings flow is very high in gas drilling. The erosion wear of casing is severe in gas drilling. There are some severe damages for the casing due to erosion wear, such as the casing containing defect, lower casing strength, then, the service life of the casing reduces. Based on the gas-cuttings flow theory and the erosion theory, the model of cuttings transport in wellbore is established. The erosion rate of casing is calculated by using Grant and Tabakoff formula. The erosion rate is calculated at critical points of drill string. The effects of gas-cuttings velocity, diameter of cuttings and number of cuttings on the erosion rate were studied. The calculated results show that the erosion rate of casing for drill string joint position is significantly higher than that of the other locations.