二氧化碳对油井水泥石的腐蚀及其防护措施

在湿环境下,油气构造中富含的CO_2对水泥石产生碳化腐蚀,碳化结果使水泥石渗透率变大、抗压强度减小,诱发流体窜流、塑性地层井壁垮塌等事故,造成巨大的经济损失。介绍了在不同温度下的水泥水化产物及其碳化产物。从化学角度分析了CO_2在不同温度下对油井水泥环碳化腐蚀的机理、影响因素及防护措施。在低于110℃的温室下,CO_2的腐蚀速度受扩散控制,其影响因素包括水泥浆密度和水泥石渗透率及水泥石孔隙液中Ca(OH)_2的含量,在水泥中掺加活性硅灰或提高水泥浆密度可预防碳化腐蚀。在大于110℃的高温下,碳化腐蚀速度受水泥水化产物中Ca(OH)_2含量和水泥石碳化后渗透率大小的影响。正确的防腐工艺是在水泥石中加入10％—15％的石英砂,或者在纯水泥中加3％—8％的膨润土。

Carbon dioxide corrosion in oilwell cement and its prevention measures

Oilwell cement hydration products and cement carbonization products at different temperature conditions are introduced. The corrosion mechanism, influence factors of corrosion and prevention measures at different temperature are analyzed. At the temperature helow 110 C , corrosion influence factors include cement slurry density, cement permeability and calcium hydroxide existing in the cement pore fluid. Carbon dioxide corrosion can be prevented by adding activated grammite or increasing cement slurry density. At the temperature of 110 Cto 250 C, carbon dioxide corrosion rate is dependent on calcium hydroxide existing in cement hydration products and cement permeability; and the prevention measures is adding silica sand (the dosage is 10%-15%) or adding ben-tonite(the dosage is 3%-8%) to cement.