气体钻井上返岩屑对井斜影响的分析

气体钻井井眼环空的气固流动状态给固体岩石颗粒冲击井壁提供了条件。高速气流携带的岩屑与井壁碰撞的频率和剪切应力较大,因而井壁岩石更易破碎,井径扩大更为严重。井径的扩大导致底部钻具组合(BHA)受力状态发生变化,从而造成控制井眼轨迹的难度增加,引起井斜。同时,井壁岩石颗粒碰撞剥落在下井壁形成岩屑垫层,同样影响底部钻具组合力学特性,造成增斜力,从而影响井斜。为分析气体钻井上返岩屑对井斜的影响,根据气体钻井环空流动模型与颗粒碰撞的能量关系,建立了气体钻井条件下的井径扩大判别模型。实例计算表明该模型准确、有效,可以为气体钻井设计和井径分析提供依据。

Study of the impacts of cuttings on well deviation in gas drilling

The gas-solid flow characteristics in the annular space of gas drilling provide favorable conditions to well bore erosion by cutting particles. Collision frequency and shear stress between cuttings entrained in high velocity gas flow and well bore are high. So, sidewall rock is easily crashed, well hole enlargement is obvious. Well hole enlargement results in the variation in the stress state of BHA. The difficulty of well trajectory control is increased, thus causes the well deviation. On the other hand, cuttings cushion is formed with the results of particles detached, impacting the mechanical properties of BHA, forming buildup force, and causing hole deviation. To study the impacts of cuttings on gas drilling well deviation, using the annulus flow model and the particle collision model, distinguishing model of well hole enlargement was established. Case calculation shows that the model has high predicting accuracy, can be used to provide foundation for the optimization design and the formation rock stability analysis in gas drilling.