固井水泥浆水化早期阶段水状态与电导率关系

油气井固井早期气窜现象常发生于固井水泥浆液固态转变阶段，准确掌握该阶段水泥浆的组织结构是探究固井早期气窜机理的关键。电导率方法是评价水泥浆水化进程及微观结构的有效方法之一。为此，利用电感式电导率仪研究了固井水泥浆沉降稳定性、水化速率对其电导率的影响；结合质量守恒定理和低场核磁共振技术，探究了水化早期阶段水泥浆中水状态与其电导率的关系。实验发现，在新配水泥浆中，孔溶液离子浓度和孔隙结构分布决定了水泥浆的初始电导率；随着水泥浆沉降稳定性的增加，水泥浆中孔结构分布更均匀，使其初始电导率由16.8 mS/cm增加至19.4 mS/cm；随水泥浆水化进程增加，水泥颗粒表面及孔隙中水化产物的形成改变了水泥浆的固相微观结构及孔隙结构，使分布于大孔隙中的自由水转变为小孔隙中的毛细水、凝胶水。实验结果表明，在水化早期阶段水泥浆的电导率与蒸发水、自由水含量呈线性关系。

Relationship Between Water States and Electrical Conductivity of Cement Slurry in Early Hydration

In the cementing of oil and natural gas wells "short-term gas migration" is usually happened during the liquid-solid transition stage of the cement slurry. Understanding the process of cement hydration during this stage is the key to study the mechanism of "short-term gas migration". And electrical conductivity is one of effective method to investigate the hydration degree and microstructure of cement slurry. Therefore, the conductivity measurement instrument was applied to investigate the effects of the stability, hydration rate of the cement slurry on its electrical conductivity. Meanwhile, combining the principle of mass conservation and low-field nuclear magnetic resonance (LF-NMR), the relationship between the water states and electrical conductivity of the cement slurry was investigated. The experimental results showed that the initial electrical conductivity of the cement slurry was determined by the concentration of the pore solution and pore structure in the cement slurry. And the pore structure distribution was more uniformed with increasing stability of the cement slurry, which increases the initial electrical conductivity of the cement slurry from 16.8 mS/cm to 19.4 mS/cm. Moreover, with hydration degree increases a large amount of hydration products form on the surface of cement particles and in pores to change the solid-phase microstructure and pore structure of the cement slurry. It made the free water distributed in large pores change to capillary water or gel water in small pores. Finally, the experimental results show that it can be seen that the electrical conductivity is proportional to the content of free water, evaporable water in the cement slurry.