Abstract: To clarify the feasibility of Φ149.2 mm solid expandable liner (SEL) used in directional well sections of Daniudi Gas Field to isolate fragile formations, the finite-element simulation and laboratory tests have been conducted to analyze the impact of borehole conditions and expansion pressures on outside diameter, maximum equivalent stress and maximum equivalent the plastic strain of SEL. The indoor testing results showed that a Φ149.2 mm SEL could meet the requirements of directional well sections in the Daniudi Gas Field, which has been successfully deployed in two wells, Well PG22 and Well DPT-112. To effectively isolate the sloughing formation that interbedded with coal and mudstone, in which the Well PG22 possesses a total isolating section of 109.00 m and inclinations from 59.72° to 73.69°. The successful application of SEL in the directional section of Daniudi Gas Field indicated that the technology would have the ability to isolate long complex sections in high angle wells, and to provide a new technical means for improving downhole operation safely.