高酸性气体对硫铝酸盐水泥石腐蚀作用机理

Corrosion mechanisms of sulfoaluminate cement by highly sour gas

为了研究硫铝酸盐水泥石在含有H_(2)S的高酸性环境的性能变化及腐蚀机理,采用氮吸附比表面积及孔径分析测试仪(BET和BJH方法)测试了腐蚀前后水泥石比表面积和孔隙结构变化,利用X射线衍射仪(XRD)和热分析仪(TG/DTG)分析了腐蚀前后水泥石水化产物的变化,采用扫描电子显微镜(SEM)观察对比了腐蚀前后水泥石水化产物微观形貌的变化。结果表明:SAC在60℃时强度发展较好,60℃腐蚀14 d后水泥石主要产物为AFt,90℃腐蚀14 d后主要生成物是CaSO_(4)·2H_(2)O;水泥石被H_(2)S腐蚀后会产生明显的分层现象,外层最先被腐蚀,内层会由于膨胀作用出现短期内的强度提高;H_(2)S的腐蚀机理为水泥水化产物中的C−S−H和CH分别与H_(2)S发生反应,生成具有膨胀性的AFt和CaSO_(4)·2H_(2)O,进而使水泥石产生裂纹,导致抗压强度下降。研究结果为硫铝酸盐水泥在高含硫油气井的固井应用提供了一定的实验及理论基础。

This research investigated the property variation and corrosion mechanisms of sulfoaluminate cement in highly sour services.The variations of the specific area and pore structure of the cement after corrosion were measured by cryogenic nitrogen adsorption tests(the BET and BJH methods).The changes in hydration products after corrosion were tested using the X-ray diffractometer(XRD)and thermal analyser(TG/DTG).Finally,the micro-scale morphological variations of hydration products of cement after corrosion were observed using the scanning electron microscope(SEM).The results showed that SAC presents a desirable strength at 60℃.The hydration products are mainly Aft after 14-day corrosion at 60℃and CaSO_(4)·2H_(2)O after 14-day corrosion at 90℃.Notable stratification of the set cement is observed after corrosion by H_(2)S.The outer layer is first corroded,while the inner layer presents short-term strength growth due to swelling.The mechanism of H_(2)S corrosion is that C−S−H and CH in the hydration products of cement react with H_(2)S respectively and produce swelling Aft and CaSO_(4)·2H_(2)O,which results in cracking of cement and reduction in compressive strengths.The findings of this research provide the experimental and theoretical basis for applications of sulfoaluminate cement in cementing of oil and gas wells with highly sour gas.