粒径对油井水泥水化热及力学性能的影响

油井水泥的粒径与其性能和用途密切相关，考察了3种粉磨方式下不同粒径分布油井水泥浆的性能。利用等温量热仪（ICC）、X射线衍射分析仪（XRD）、压汞仪（MIP）和扫描电镜（SEM）分别测试了不同粒径水泥颗粒早期水化放热速率、水泥石水化产物、孔结构及颗粒微观形貌。结果表明，物理粉磨方法只能将颗粒超细化，不能纳米化；相同水灰比的水泥浆，其原料颗粒粒径分布对浆体密度、水化产物无明显影响。但随水泥颗粒粒径的减小，浆体稠化时间缩短、流变性变差、析水率降低，稳定性增加。同时，超细水泥颗粒反应活性增强，水化放热量及放热速率增加，水灰比为0.5的0.013mm超细水泥（MC1000-0.5）24 h累积水化放热量较水灰比为0.5的普通G级水泥（G-0.5）提高了91.03%。在短期内生成了更多的水化产物，提高了水泥石早期强度及抗渗性能，且降低了水泥石的总孔隙率，水灰比为0.7的0.013 mm超细水泥（MC1000-0.7）水泥石的1 d龄期抗压、抗折强度较水灰比为0.7的普通G级水泥（G-0.7）分别提高了226.32%、153.13%，其28 d龄期总孔隙率及渗透率较G-0.7水泥石分别降低了10.1%及41.7%，但后期抗压强度增长幅度不大。 

Effects of Particle Size on Hydration Heat and Mechanical Performance of Cement

The particle sizes of oil well cement are closely related to its performance and use. Oil well cements of different particle size distribution obtained with three grinding methods have been studied for their early hydration exothermic rate (rate of hydration heat liberation), hydration product of set cement, pore structure and the micro-morphology of particles using ICC, XRD MIP and SEM experiments. It was shown that physical grinding cannot produce nano particles; it can only produce ultra-fine particles. Particles size distributions of cement slurries with the same water/cement ratio had no appreciable effect on the density of the slurries and the hydration products. On the other hand, cement slurries with smaller particle sizes had shortened thickening time, poor rheology, reduced percentage of free water, and better stability. Meanwhile, ultra-fine cement particles had enhanced hydration reactivity and higher hydration heat and hydration exothermic rate. The cumulative hydration heat released in 24 hours of a 0.013 mm ultra-fine cement (MC1000-0.5) was 91.03% higher than that of conventional class G cement (G-0.5) at the same water/cement ratio of 0.5. The ultra-fine particle cement produced more hydration products in a short period, and the set cement had improved early strength and impervious performance, and reduced total porosity. The set cement of a 0.013-mm ultra-fine cement (MC1000-0.7) had 1-d compressive strength and flexural strength that were 226.32% and 153.13% higher than those of the class G cement (G-0.7) respectively at the same water/cement ratio of 0.7. The MC1000-0.7set cement had 28-d total porosity and permeability that were 10.1% and 41.7% lower respectively than those of the G-0.7 set cement, while the late-stage compressive strength of the MC1000-0.7 set cement only slightly increased.