气井环空带压对水泥环力学完整性的影响

受井下作业、油套管或封隔器泄漏等因素产生的井口环空带压，使高温高压气井水泥环密封完整性面临巨大 挑战。为此，基于弹性力学多层厚壁圆筒理论和摩尔库仑失效准则，建立了水泥环应力和失效计算模型，研究了环空 带压对水泥环胶结面应力和失效的影响。结果表明，环空带压将增大水泥环胶结面的切向拉应力，过大的切向拉应力 将导致水泥环失效。与此同时，井筒温度增加产生的切向拉应力也会增大水泥环失效风险。环空带压越大，水泥环安 全系数越低，且温度效应对安全系数的影响较小。对高温高压气井，可根据井身结构（地层水泥环套管）参数建立 水泥环安全系数图版，从而为确定合理的最大允许环空带压值提供依据，研究结果对提高气井井筒安全性、延长开采 寿命具有重要意义。

The Effect of Sustained Casing Pressure on the Mechanical Integrity of#br# Cement Sheath in Gas Wells

Sustained casing pressure（SCP），resulted from downhole operations，the leakage of casing and oil tube or packer poses great challenges to the sealing integrity of cement sheath in HTHP gas wells. Thus，we estasblished the failure calculation model and the stresses of cement sheath，and studied the influences of SCP on the stresses and failure of cement sheath，based on the multi-layer thick wall cylinder theory of elastic mechanics and Mohr-Coulomb failure criterion. Results show that the SCP problem will make cement sheath sustain overlarge tangential tensile stress which is the principal factor for its failure. Besides， the tangential tensile stress that is resulted from the increasing temperature in wellbore will increase the risk of the failure of cement sheath. The larger the SCP value，the lower the safety factor of cement sheath，and the influence of temperature effect on the safety factor is not clear. For high temperature and high pressure gas wells，a safety factor diagram of cement sheath can be drawn according to parameters of well construction（formation-cement sheath-casing），which gives the basis for determining proper allowable maximum SCP value and is of great guiding significance to increase the wellbore safety and to extend the working life of gas well production.