Abstract: There are great differences in damage mechanism between coal-beds and conventional reservoirs owing to the unique char-acteristics of pore structure, gas storage and production process-es in coal-beds. Coal-beds at the national test site for coal-bed methane development in Liupanshui are selected. Mercury in-jection and SEM are applied to analyze pore types, size and dis-
tribution of pore throats of coal-beds. The parameters of pore structure of coal-bed are computed. On this basis of anthropo-logical features, pore structure, sensitivity and damage evalua-tion test from working fluids, damage mechanisms of coal seams have been analyzed. Results indicate that microprobes occurred in plant tissues, pores resulted from gas generation, and frac-tures are well developed in coal seams, so the reservoirs belong
to dual-porous medium. Therefore coal-beds can easily be invad-ed and damaged by working fluids. The study shows that solid invasion, stress sensitivity, aqueous trapping and adsorption of high molecular polymers are major damage factors.

Key words: coal-bed methane, pore structure, fracture, cleat, reservoir damage