【作者】 李军； 陈勉； 柳贡慧；

【Author】 LI Jun, CHEN Mian, LIU Gong-hui (Institute of Petroleum and Gas Engineering, China University of Petroleum, Beijing 102249, China)

【机构】 中国石油大学石油天然气工程学院；

【摘要】 套管损坏是制约油气生产的瓶颈问题,而套管外挤载荷设计合理与否对套管寿命具有决定性的作用。前人在研究套管外挤载荷时,都将地层考虑为正交各向异性、横观各向同性材料,没有考虑在垂直井眼轴线平面上岩石力学性质各向异性的问题。在考虑这一特点的基础上,建立了套管应力计算的力学及有限元模型。计算结果表明,在均匀水平地应力条件下,若地层为横观各向同性,则套管应力为均匀分布;若地层力学性质在垂直井轴平面上为各向异性,则套管应力由均匀分布转化为非均匀分布,且应力极值增大。这一结论说明:在均匀水平地应力条件下,地层各向异性对套管受力有着较为明显的影响,在设计套管外挤载荷时,应该给予充分考虑:同时这也有助于解释套管所受外挤载荷超过上覆岩层压力的问题。在非均匀水平地应力条件下,无论地层为各向同性或各向异性,套管应力均呈现非均匀分布态势,其套管应力极值变化不大。因此,在非均匀水平地应力条件下,地层各向异性对套管受力影响不大,在设计套管外挤载荷时,可简化省略。更多还原

【Abstract】 Casing damage is the bottleneck problem for oil and gas production. Reasonable design of collapse load is vital to the life of casing. Former researchers considered the formation to be orthotropic and transverse isotropic. But the rock mechanics orthotropy in the plane perpendicular to well axis is not taken into account. Based on this point, the mechanics and finite element models for casing stress calculation are established. The results show that casing stress presents uniform distribution situation if the formation is transverse isotropic with the uniform horizontal in-situ stress. If the formation is orthotropic, however, the casing stress becomes non-uniform distribution. At the same time, the maximum casing stress is larger than the former. So it is obvious that the formation orthotropy has great effect on the casing stress, which should be considered in casing design process. This conclusion is also helpful for explaining the question that casing collapse load maybe larger than the overburden stress some times. When the horizontal in-situ stress is non-uniform, the casing stress is non-uniform at all times not only in the isotropic formation but also the orthotropic ones. At the same time, the maximum casing stress is almost same to each other. Therefore, under this condition, the rock mechanics orthotropy problems can be overlooked during the casing design process.更多还原