Abstract: Severe mud losses, coexistence of blowout and mud loss and difficulty of drilling are problems associated with narrow safe drilling windows found in Moxigaoshiti and Xiadongchuan, Sichuan, and were all overcome thanks to the use of precisely managed pressure control drilling technology. In managed pressure control drilling, lack of effective and safe process control techniques during tripping and well completion also resulted in severe mud losses and high risk of well control. To resolve these problems, a brittle and drillable gel slug separating technology has been presented based on inorganic hydraulic cementing theory, close packing theory and strengthening through solidification theory. By selecting the best additives and optimizing, a gel slug-forming working fluid was prepared. Evaluation of the working fluid showed that it has good initial mobility and stability. The 40 Bc thickening time of the working fluid is manageable in 0.5-4.0 h. It functions normally at 150℃, and is resistant to contamination from drilling fluid. The gel slug, after becoming hardened, has compressive strength of 8.02 MPa. When bonded with the surfaces of the casing, the bond strength can be 1.45 MPa/m². The hardened slug itself has good cementing performance, with gas containment capacity of no less than 2.69 MPa/m under pressure. Thus gel slug, after hardening, has drillability of grade 1, and can be drilled out with drill bit.