井筒载荷-腐蚀耦合作用对碳钢套管服役寿命的影响

Influence of shaft load-corrosion coupling on the service life of carbon steel casing pipe

基于应力-腐蚀介质协同作用原理,结合化学力学效应理论,对高温高压超深井碳钢油、套管在使用过程中面临着CO2、H2S等腐蚀介质以及拉、压等复杂载荷建立了结合热应力影响套管腐蚀速率的解析模型,给出了计算应力影响管柱寿命衰减的解析公式,研究了碳钢油井管服役寿命,并对内压力、挂片实验实测腐蚀速率以及壁厚对碳钢套管服役寿命的影响进行了研究。结果表明,解析模型所得结果与文献报道的应力对腐蚀速率的影响结果相符。在井筒载荷及腐蚀工况下,增加壁厚相对于减小套管内压力,增加套管使用寿命效果不明显。初始腐蚀速率对套管的服役寿命影响较大,当管柱所受应力越大,管柱实际寿命衰减得越快。

Considering the corrosion media such as CO2,H2 S and the complex load（e.g.,pulling,pressing,etc.）suffered by carbon steel casing pipe in high temperature pressure super-deep wells,as well as the influence of thermal stress on casing corrosion rate,an analytical model was built based on stress-corrosion medium synergy principle and mechanochemical effect,and an analytical formula was presented for calculating the influence of stress on the attenuated lifetime of tubular column so as to study the service life of carbon steel oil well pipe.Moreover,this paper studied the influence of internal pressure,corrosion rate actually measured during coupon test and wall thickness on the serve life of carbon steel casing pipe.The result from analytical model was accord well with that from experimental research on the influence of stress on corrosion rate（reported in literatures）.Under the influence of shaft load and corrosion,increasing wall thickness cannot significantly prolong the service life of casing pipe compared with reducing internal pressure inside casing pipe.Furthermore,initial corrosion rate exhibits great impact on the service life of casing pipe;the larger the stress on pipe column is,the quicker the actual lifetime of pipe column will be attenuated.