深井岩盐层套管外载的三维有限元分析

深埋于地下的岩盐在一定地应力和温度作用下发生蠕变,对井中的套管产生随时间而变化的外载,致使套管变形甚至挤毁,为此,针对塔里木油田羊塔地区岩盐层的温度、应力状态及其蠕变特性,建立了岩盐层、水泥环和套管耦合的三维有限元力学模型,研究了地应力状态及其大小、井内液体支撑压力对岩盐层套管受力的影响规律。研究表明,非均匀地应力作用下,盐岩蠕变产生的套管外载是非均匀的,在最小地应力方向的套管外载最大,此时若按上覆地层压力计算套管外挤载荷局限性较大。应用新模型对深井、超深井封固岩盐层的?250.83 mm套管、?177.8 mm套管和?206.38 mm 3种技术套管的强度进行了分析,计算结果与该油田技术套管挤毁的情况吻合,可见新建模型是合理的,可为深井岩盐层套管强度设计提供理论依据。

3-D finite element analysis of casing loads in salt rocks of deep wells

The oilfield has suffered huge economic losses due to the creep of the salt rock deeply buried underground under the effect of certain earth stress and temperature, which causes the casing load to change with time and results in the casing deformation and shear. So a 3-D finite element analysis (FEA) mechanical model concerning salt rocks and cement mantles as well as casing couples is established in this paper to research the conditions and dimension of the earth stress and the effect of the abutment pressure of fluid in a borehole on the forces exerting on casing in salt rocks. The research shows that the casing load caused by the creep the salt rocks are inhomogeneous, which is the highest in the direction of the minimum earth stress. Therefore, it is greatly limited to calculate the casing external collapse load based on using overlying formation pressure. So in this paper, the new 3-D FEA model is applied to calculate the strength of the three kinds of intermediate casing in deep wells, ultra deep cementing wells and salt rocks. The calculating result is in agreement with the intermediate casing collapse of the oilfield, which proves that the newly established model is reasonable and will lay a solid theoretical basis for the strength design of casing in salt rocks of deep wells.