地层和水泥环弹性模量对套管强度的影响分析

以地层-水泥环-套管组合系统为研究对象,根据弹性力学理论,推导了热应力和非均匀地应力作用下套管壁上的三轴应力计算公式,并研究了热采井和常规非热采井中不同地层、水泥环弹性模量对套管强度的影响规律。研究结果表明,随着水泥环弹性模量的增加,套管内壁Mises应力先急剧增加,后呈缓慢下降趋势;在套管Mises应力达到最大值之前,降低水泥环的弹性模量,可以对套管起到明显的保护作用,这一点对于热采井注汽期间的套管保护效果更加显著;地层弹性模量越大,常规井中套管内壁的Mises应力值越小,而热采井注汽过程中套管内壁的Mi-ses应力值则越大。

Effect of elastic modulus of stratum and cement sheath on casing strength

Based on elastic mechanics, a formula is derived to calculate the triaxial stress of casing under the effect of thermal stress and non-uniform in-situ stress. Studies have been done on the effects of different elastic modulus of stratum and cement sheath on casing strength in conventional wells and thermal recovery wells. Findings show a rapid increase first and a steady decline later in Mises stress of casing in conventional wells with a rise in elastic modulus of cement sheath. The casing is to be protected with a drop in elastic modulus of cement sheath prior to the maximum of Mises stress, which is more obvious with thermal recovery wells. With an increase in elastic modulus of stratum, Mises stress becomes smaller in conventional wells, but much greater in thermal recovery wells.