摘要
介质渗透是固井水泥发生各种腐蚀的必要条件,也是套管外壁发生腐蚀的首要条件。模拟固井水泥的实际应用环境,将套管钢嵌入G级固井水泥中,采用开路电位法和动电位扫描极化法,研究了含饱和CO2地层水介质在水泥中的渗透和套管的腐蚀。结果表明,动电位扫描极化法和半电位法都便于测定介质在固井水泥中的渗透时间。由极化曲线特征可知氯离子发生了优先渗透,水泥包覆下套管的腐蚀受阳极过程的电化学和扩散步骤共同控制。介质在水泥中渗透初期,钢的腐蚀速率很低,CO2的渗入起到了阳极去极化的作用,使钢的腐蚀逐渐增大,并最终形成较严重的局部腐蚀。固井水泥的渗透深度与时间呈幂函数关系,指前因子和幂指数分别为0.85和0.62,故随着水泥环厚度增大,渗透时间缓慢增加。
The penetration of corrosive medium would result in various corrosion of bond cement and outer surface of casing in oil well.A simulation experiment was carried out to embed casing steel into grade G cement under the real environment of bond cement.The penetration of formation water with carbon dioxide in the cement and its corrosion to casing were investigated using the open-circuit potential measurement and electrochemical potentiodynamic polarization methods.The results show that both methods are favorable to determine penetration time by detecting the potential and polarization curves of casing steel inlayed in cement ring.The polarization curve characteristics show that the penetration of Cl-is preferential.The corrosion rate of steel can be controlled synchronously by anodic electrochemical reaction and diffusion processes.The delaying penetration of carbon dioxide after Cl-can accelerate the anodic depolarization.Therefore,the corrosion rate of formation water to casing can be enhanced,which results in the marked local corrosion on the surface of steel.The penetration depth depended on the time as a power function.The fitted pre-exponential factor and power exponent are 0.85 and 0.62,respectively.Thus,the penetration time can increase slowly with the increasing thickness of cement ring.
出处
《石油学报》
EI
CAS
CSCD
北大核心
2010年第2期322-332,共11页
Acta Petrolei Sinica
基金
四川省教育厅青年基金(07ZB097)资助
关键词
固井水泥
渗透性
二氧化碳
地层水
套管腐蚀
bond cement penetration carbon dioxide formation water casing corrosion
