砂地层孔径分析及其对泥浆在地层中渗透性的影响

为明确砂地层孔径分布特征及其对泥浆在地层中渗透的影响，采用压汞试验对5组均一粒径的砂地层孔径进行实测，并参考谢拉德等计算砂砾料滤层孔径的方法，基于等直圆管对砂地层孔径计算方法进行改进。同时配制9组不同性质的泥浆在不同孔径的砂地层中开展泥浆渗透试验，依据渗透试验结果讨论地层平均孔径与泥浆颗粒粒径之间的对应关系。以泥浆在砂地层中形成泥皮+渗透带的渗透试验为例，通过测试泥浆在地层中渗透流量的变化，并计算地层渗透系数的变化分析砂地层孔径对泥浆在地层中渗透的影响。研究结果表明：基于等直圆管进行计算的地层平均孔径与压汞法实测的孔径结果相符，即为地层中频率最大的孔隙的孔径；该计算方法考虑了对达西定律中渗透流速和渗径的调整，适用于颗粒粒径较为均匀，孔径较为单一的砂地层；泥浆在高渗透性地层发生渗透时，地层孔径越大，形成泥皮或泥皮+渗透带所需泥浆颗粒的粒径越大，地层孔径大小直接决定了通过孔隙的泥浆颗粒的粒径大小；渗入地层孔隙中的泥浆颗粒在地层中形成稳定淤堵，改变了地层的物理结构，降低了地层的渗透性，阻碍了泥浆的渗透过程；地层孔径与泥浆颗粒粒径之间的对应关系是影响泥浆渗透结果的关键因素。

Pore Size Analysis and Its Influence on Slurry Infiltration in Sandy Layers

To determine the pore size distribution characteristics of sand formation and its influence on slurry penetration in the formation, the sand formation pore sizes of five groups of uniformly sized particles were measured using the mercury injection test. The calculation method for the formation pore size was improved based on the straight pipe method with reference to the calculation method for the sand gravel filter pore size by Sherad et al. Simultaneously, nine groups of slurries with different properties were prepared to conduct the slurry permeability test on the sand formations with different pore sizes. According to the results of the permeability test, the relationship between formation pore size and slurry particle size was discussed. Taking as an example the forming filter cake with an infiltrated zone in the slurry permeability test, the influence of sand formation pore size on the permeability of the slurry in the formation is analyzed using the change in the permeability flow of the slurry in the formation and by calculating the change of the formation permeability coefficient. The results show that the average pore size calculated based on the straight pipe method is consistent with the pore size measured using the mercury injection method; that is, the pore size of the most frequent pore in the formation. The calculation method considering the adjustment of seepage velocity and seepage diameter as per Darcy's law, is suitable for a sand formation with a uniform particle and pore sizes. When slurry penetrates a high-permeability formation, the larger the pore size of the formation, the larger the particle size of the slurry required to form a filter cake or a filter cake with an infiltrated zone. The pore size of the formation directly determines the particle size of the slurry particles passing through the pores. The slurry particles infiltrating the formation pores form a stable silting, which changes the physical structure, reduces the permeability of the formation, and hinders the penetration of the slurry. The corresponding relationship between formation pore size and slurry particle size is the key factor affecting slurry permeability.