二氧化碳埋存条件下油井水泥石腐蚀的热力学分析

Thermodynamic Analysis of Oilwell Set-cement Degradation under Carbon Dioxide Sequestration Condition

利用热力学平衡常数理论计算了CO2埋存条件下的油井水泥石水化产物相关纯矿物受腐蚀的热力学条件,并比较了其耐腐蚀性能。利用Gibbs自由能最小化原理计算和分析了水泥石受腐蚀过程中水化产物的变化。结果表明:水化产物相关纯矿物或端元组分的耐腐蚀性能不同,优劣次序为4Mg(OH)2·2Al(OH)3·3H2O、0.83CaO·0.67SiO2·1.83H2O、0.67CaO·SiO2·1.5H2O、6CaO·Al2O3·3SO4·32H2O、6CaO·Al2O3·3SO4·30H2O、1.33CaO·SiO2·2.17H2O、3CaO·0.5Al2O3·0.5Fe2O3·0.84SiO2·4.32H2O、3CaO·Fe2O3·0.84SiO2·4.32H2O、1.5CaO·0.67SiO2·2.5H2O、Ca(OH)2;水泥石腐蚀时各水化产物被腐蚀的次序不同,先后次序为Ca(OH)2、水化硅酸钙固溶体、硅水榴石固溶体、钙矾石固溶体、4Mg(OH)2·2Al(OH)3·3H2O;固溶体被腐蚀时不但质量减少,端元组分的摩尔数和比例也发生变化,但变化不完全受端元组分相对耐腐蚀性能控制。

For the degradation of oil well set-cement under CO2 sequestration condition,the thermodynamic conditions of pure minerals related to hydration products degradation were determined based on the equilibrium constant theory,and the resistance difference was investigated.The mass change of hydration products was simulated based on the Gibbs free energy minimization principle.The results show that the order of degradation resistance of related pure minerals or end members is 4Mg(OH)2·2 Al(OH)3·3 H2 O,0.83 CaO·0.67SiO2·1.83H2 O,0.67CaO·SiO2·1.5H2O,6CaO·Al2O3·3SO4·32H2 O,6CaO·Al2O3·3SO4·30 H2O,1.33CaO·SiO2·2.17 H2 O,3 CaO·0.5 Al2 O3·0.5Fe2 O3·0.84SiO2·4.32H2 O,3CaO·Fe2O3·0.84SiO2.4.32H2 O,1.5CaO·0.67SiO2·2.5H2O,Ca(OH)2.The order of mass decrease in set-cement degradation process is Ca(OH)2,calcium silicate hydrate solid solution,Si-hydrogarnet solid solution,ettringite solid solution,and M4 AH10.The number of moles and the proportion of end member minerals changes and the quality of solid solution decreases,but the change is inconsistent with its relative degradation resistance.