Abstract: To address the critical challenge of wellbore instability characterized by "collapse induced by lost circulation" in fractured formations spanning the Liujiagou to Shiqianfeng Groups within the northern Ordos Basin, this study systematically investigated the petrophysical properties and microstructural characteristics of formation cores. The analytical results demonstrated that high clay mineral content coupled with extensive micro-fracture networks constitutes the primary mechanism driving wellbore destabilization. Building on these findings, an innovative technical strategy termed "rigid-flexible synergistic instant sealing with sustained clay inhibition" was developed, which integrates multi-scale rigid sealing materials and nano-flexible sealing agents into a tailored water-based drilling fluid system.Laboratory evaluations revealed that the optimized fluid system achieves rapid formation of effective sealing layers, exhibiting a pressure-bearing capacity of 10.6 MPa. Furthermore, it enhances cuttings recovery rate to 85% while reducing hydration-induced swelling by 52.1%. To validate field performance, the system was implemented in Well A, where a 69.7% reduction in fluid loss was recorded in the Liujiagou Formation compared to offset Well B. Significantly, comparative analysis of borehole enlargement rates within the same stratigraphic interval confirmed superior wellbore stability in Well A, with the enlargement rate decreasing from 7.61% to 4.52% without inducing downhole complications.These outcomes collectively underscore the system's efficacy in mitigating instability risks in fracture-dominated formations. By establishing a theoretical framework for sealing-inhibition synergy, this research provides actionable solutions for safe and efficient drilling operations in the northern Ordos Basin, thereby advancing the economic exploitation of tight gas reservoirs.