注蒸汽热采井套管损坏机理研究

考虑环空水泥环在轴向和径向给予套管柱的弹性约束和摩擦约束，对注汽期间套管柱产生的轴对称热胀应力进行了近似分析．分析发现，在封隔器附近靠近接箍端面的地方，套管柱可能产生严重的缩颈变形，其变形值和套管柱受热膨胀时接箍端面对水泥环台肩的推力有关系．研究结果表明，大部分注蒸汽热采井的套管损坏位置都集中于油藏盖层内，其原因是存在着和局部缩颈变形相对应的恶性局部应力，必须设法控制这种局部应力才能延长套管柱的使用寿命．

NEW DEVELOPMENT OF THE STUDY ON CASING FAILURE MECHANISM FOR THE PRODUCTION WELLS STIMULATED WITH STEAM INJECTION

An approximate theoretical analysis of axisymetrically thermal stresses of the casing string during steam injection period is given with consideration of reaction forces produced by the annulus cement sheet. Nearby the thermal packer close to the joints of casing string, the severe local neck down deformations may occur in concerning with the thrusts given by the joints to the annulus cement shoulders when the casing string tends to extension under the height heeting temperature. A series of approximate formulas for the calculation of these thermal stresses and local neck down deformations are derived. The casing failure positions in steam injection wells are mainly concentrated in the cap formation of oil reservoir, which results in malignant local stresses corresponding the local neck down deformations. So, the positions of casing failures should be controled by any way to increase the safe life of the casing string.