CO_2环境下磷铝酸盐-硅酸盐复合水泥石耐腐蚀机理研究

Corrosion resistance mechanism of phosphoaluminate-portland cement in CO_2 condition

为解决油气井中较高含量的CO_2给油井水泥环带来的严重腐蚀问题,试验研究了1种耐CO_2腐蚀复合材料(磷铝酸盐(硅酸盐复合水泥石)。通过对磷铝酸盐(硅酸盐复合水泥石在CO_2腐蚀前后水泥石抗压强度、孔隙率、渗透率等性能和结构的变化评价这种水泥石的耐腐蚀性能。同时,利用扫描电子显微镜(scanning electron microscope,SEM)、X射线衍射(X-ray diffraction,XRD)等分析水泥石腐蚀前后微观结构和物相的变化,探讨复合水泥石耐腐蚀的机理。室内研究表明,CO_2分压为7 MPa,总压力为10MPa,温度为90℃条件下腐蚀3、7、14、28d后这种复合水泥石的抗压强度比腐蚀相同时间的硅酸盐水泥石高;且孔隙率和渗透率比硅酸盐水泥石低。在试验加量范围内(5%、10%、15%、20%),磷铝酸盐水泥加量为15%时复合水泥石腐蚀后各项性能最好。腐蚀28d后含15%磷铝酸盐复合水泥石的强度为22 MPa,比硅酸盐水泥石高46%,孔隙率、渗透率为21%和0.012 8mD,分别比硅酸盐水泥石低40%和18%。

To solve the serious CO2 corrosion problems in oil and gas wells cement, a new kind of CO2 corrosion-resistant compos- ite material （aluminophosphate-silicate composite cement） was developed in the researches. To evaluate the corrosion resistance of composite cement stone before and after CO2 corrosion, the changes of compressive strength,porosity, permeability and structure of cement stones were examined. Moreover, SEM and XRD analysis of cement microstructure and phase change before and after corrosion were carried out to discuss the mechanism of corrosion resistance of composite cement. After corrosion in the CO2 partial pressure of 7 MPa and the total pressure of 10 MPa condition at the temperature of 90℃ for 3 days, 7 days, 14 days, 28 days, the results have shown that the compressive strength of composite cement is higher than that of the Portland cement with the same time of corrosion. In addition, the porosity and permeability of composite cement is lower than that of Portland cement. Within the ranges of quantity （5%, 10%, 15%, 20%） in experiment, the corrosion resistance of composite cement is best when the aluminophosphate cement is 15 %. After 28 days corrosion the strength of cement with 15% aluminophosphate is still 22 MPa which is 46% higher than that of the Portland cement stone. The porosity is 21% and the permeability is of 0. 012 8 mD, which are 40% and 18% lower than those of the Portland cement, respectively.