Abstract: Weak contact between layers with different properties is one key factor affecting the stability of engineering structures, e. g., slopes, underground roadways, and chambers. The movement of overlying strata induced by coal mining is the main reason for the damage of vertical shale gas wells drilled within the mining affected areas. By using two-dimensional geological model, predictions have been made about various well deformations, e.g., shear slippage, bed separation, tension and compression, and the effect of weak contacts between layered strata on the stability of gas wells piercing a coal seam has been analyzed. The axial heights at which the gas well is prone to failure has been acquired through the analysis of the axial distribution characteristics and various deformation of well holes in the different positions of coal pillars, according to which the position of the well has been optimized thereafter. Results indicate that the “interface” element in FLAC is excellent in realizing the possible deformation responses occurring at weak interfaces caused by coal mining, and it is very commendable in characterizing the shear failure mode, which is the major mode of well instability.

Key words: alternating layers, weak contacts, mining influence, gas well stability