Abstract: A mudstone interlayer is difficult to be dissolved and is left inside the cavity after the cavity construction. For the operation
period of gas storage, the problem of collapse of non-corroded mudstone interlayers due to strong rock rheology threatens the safe
operation of gas storage. In this study, an interlayer stability evaluation method based on collapse time is proposed. First, an interlayer
mechanic model was established based on the elastic mechanics theory and the threshold strain, when an interlayer partially collapsed,
was solved. Second, according to the creep test results of mudstone interlayers in Pingdingshan region, a creep constitutive model was
built up. Finally, the interlayer mechanic model and the creep constitutive model are combined to derive the model of the interlayer
collapse time. Using Matlab program based on the PSO algorithm, the model can calculate the collapse time value of different preset
thicknesses of the interlayer and compute for the critical collapse thickness. The result shows that the calculated collapse time
increases with the increase in interlayer thickness and the interlayer stability is higher. For the mudstone interlayer of the same
thickness, the greater its span, the shorter collapse time, the greater the calculated critical thickness, the worse the stability.
Meanwhile, for an interlayer with less than critical collapse thickness, the risk of an interlayer collapse is higher within its service life;
and vice versa.

Key words: mudstoneinterlayer, mechanicmodel, creepconstitutivemodel, collapsetime, criticalcollapsethickness, stabilityevaluation