比表面积氮气吸附法在蒙脱石碱性溶蚀表征中的应用

Application of Specific Surface Area Nitrogen Adsorption Method to Characterize the Alkaline Dissolution of Montmorillonite

蒙脱石矿物颗粒粒径小、比表面积大、水敏性强,易堵塞储层孔隙和喉道,是影响油田储层质量的主要黏土矿物,碱性条件下蒙脱石的溶蚀特征是油田开发中普遍关注的问题。对于蒙脱石溶蚀特征的表征,前人常用的方法有反应前后质量对比法、X射线衍射法、溶液离子浓度分析法及pH值分析法,质量对比法操作复杂,X射线衍射图谱计算人为误差大,溶液离子浓度法对难熔元素的检测误差大,pH值法受温度变化的影响。本文应用比表面积氮气吸附法测量蒙脱石在不同氢氧化钠浓度条件下的比表面积、孔容、孔径变化及吸附脱附曲线来表征其碱性溶蚀特征,优选出适合油田开发的氢氧化钠溶液浓度及充注时间(反应时间)等实验条件,确定了最佳溶蚀浓度为0.05 mol/L氢氧化钠溶液,最佳反应时间为3 h。实验表明,比表面积氮气吸附法测得的比表面积、孔容、孔径及吸附脱附曲线表征的蒙脱石溶蚀特征,与反应后溶液pH值及离子(如Si4+)浓度变化所得的结论相同,验证了该方法的正确性,且具有直观、准确、可靠的特点,可应用于比表面积较大的多孔矿物溶蚀研究。

Montmorillonite is characterized by small particle size,large specific surface area and strong water sensitivity,which results in blocking the pore and throat of the reservoir and in turn affecting its quality. Dissolution characteristics of montmorillonite under alkaline conditions are common concerns in the development of oil fields.Mass contrast,X-ray Diffraction,solution concentration analysis and value analysis of pH methods are commonly used to characterize dissolution of montmorillonite. However, the quality comparison method is complex.Calculation of diffraction pattern by the X-ray Diffraction involves large manual operation errors. The ion concentration analysis method shows a large detection error for infusible elements. Value analysis of the pH method is influenced by temperature changes. The specific surface area,pore volume,pore diameter change,adsorptiondesorption curve measured by nitrogen adsorption method was used to characterize the dissolution of montmorillonite under alkaline conditions and is reported in this paper. The experimental conditions were optimized,including the concentration of NaOH solution and filling time（ reaction time）. The best concentration of NaOH solution was 0. 05 mol / L and the best reaction time was 3 h. Results show that the dissolved results of montmorillonite by the nitrogen adsorption method characterized by specific surface area,pore volume,pore diameter and adsorption desorption curve are consistent with the results by the change of the pH value and the concentration of the solution（ such as Si^4 ＋）. Therefore,the method is feasible and can be used to characterize the dissolution of minerals with multiple pores and large specific surface area.