二氧化碳埋存条件下油井水泥石腐蚀的热力学模拟

Thermodynamic simulation of oilwell cement degradation under carbon dioxide sequestration condition

水泥石腐蚀问题是导致CO2埋存失效的关键因素之一。基于热力学吉布斯能最小化方法,模拟CO2埋存条件下水泥石的腐蚀,研究腐蚀过程中水泥石矿物组成与矿物质量的变化、矿物体积的变化和孔隙溶液pH值的变化,分析温度和压力对腐蚀的影响。结果表明水泥石矿物中羟钙石最先受到腐蚀,方解石的耐腐蚀性能最好,其他矿物的耐腐蚀性能相似;在羟钙石被完全腐蚀之前,水泥石矿物总体积不会缩小,孔隙溶液pH值基本维持不变,完全腐蚀之后总体积减小、pH值会降低,其他矿物陆续受到腐蚀。温度和压力对水泥石矿物种类的影响较小,温度越高时腐蚀水泥石所消耗的CO2质量越大;压力主要影响方解石的腐蚀,压力越高方解石的腐蚀程度越严重。研究结果可为水泥石CO2腐蚀的防治提供指导和依据。

Set-cement degradation is one of the key factors leading to the failure of CO2 sequestration.Based on the thermodynamic Gibbs energy minimization method,the degradation of set-cement under CO2 sequestration condition was simulated.The changes of minerals composition and mass,minerals volume and pH of pore solution were studied.The influence of temperature and pressure on degradation was analyzed.The results show that the portlandite is the first to be degraded.The degradation resistance of calcite is the best,and the degradation resistance of other minerals is similar.Before the portlandite is completely degraded,the total volume of minerals in set-cement does not decrease,and the pH of the pore solution remains unchanged.The total volume of minerals decreases after the complete degradation of portlandite,then the pH decreases,and other minerals are degraded one after another.Temperature and pressure have little effect on the mineral species of set-cement.The higher the temperature,the greater the mass of CO2 consumed by set-cement degradation.The pressure mainly affects the degradation of calcite.The higher the pressure,the more serious the degradation degree of the calcite it is.The research results can provide guidance and basis for the prevention and control of set-cement degradation by CO2.