Study on the Dispersion Stability and Sealing Performance of Nanoscale Plugging Materials for Shale Formations

Abstract

Summary Nanoscale plugging materials are commonly used in the petroleum industry to seal microfractures and pores within shale formations, thereby maintaining wellbore stability and preventing drilling accidents caused by formation collapse. However, the influence of inorganic salts present in the formation and drilling fluids on the dispersion properties of nanoscale plugging materials often affects their sealing performance. In this study, we focus on investigating the influence of three commonly encountered inorganic salts in the drilling process—sodium chloride (NaCl), potassium chloride (KCl), and calcium chloride (CaCl2)—on the dispersibility and sealing performance of commonly used nanoscale plugging materials such as nanosilica and nanoemulsions in shale formations, exploring the dispersion and sealing mechanisms. Zeta potential is used as a characterization parameter, and molecular dynamics simulations are used to study the effects and mechanisms of inorganic salt ions on the dispersion of plugging materials. Filtration and pressure transmission experiments are conducted to investigate changes in their sealing performance. Scanning electron microscopy (SEM) is used to observe the microstructure of the formed filter cake, providing insights into the dispersion and sealing mechanisms. The results reveal that nanosilica agglomerates at zeta potentials ranging from −18 mV to −15.5 mV, resulting in an increase in filtration volume from 93.3 mL to 171.1 mL and downstream stable pressure transmission rising from 330.98 psi to 551.98 psi. Nanosilica (modified with KH570) agglomerates at zeta potentials of −10.3 mV to −9.9 mV, leading to an increase in filtration volume from 93.1 mL to 171 mL and downstream stable pressure transmission rising from 326.98 psi to 553.35 psi. The average gyration radius of the KH570 molecule decreases from 0.347 nm to 0.337 nm under the influence of inorganic salts. In contrast, the dispersion stability of nanoscale emulsions is independent of zeta potential; however, under the influence of inorganic salts, the filtration volume increases from 92.2 mL to 170.9 mL and downstream stable pressure transmission rises from 293.03 psi to 550.98 psi. The average gyration radius of nanoscale emulsion monomer molecules decreases from 0.340 nm to 0.336 nm under the influence of inorganic salts. Microscopic examination of filter-cake morphology shows that inorganic salts not only affect dispersion stability, leading to the aggregation of nanomaterials and influencing sealing performance, but also reduce the deformability of organic particles, thereby affecting sealing performance. The properties obtained in this study provide theoretical references for the sealing performance of nanomaterials in drilling fluids, offering significant value for researchers and field engineers in selecting nanoscale plugging materials for shale formations.