Experimental investigation of methane adsorption/desorption behavior in coals with different coal-body structure and its revelation

KANG Zhiqin; LI Xiang; LI Wei; ZHAO Jing

doi:10.13225/j.cnki.jccs.2017.1326

Abstract：The adsorption/desorption experiment of bulk coal sample can be more effective to characterize the flow state of methane (CH4) in coal seams compared to powder coal sample,since CH4 flow through a coal seam consists of fluid flow,diffusion and adsorption/desorption process.Thus,the low-pressure CH4 adsorption/desorption properties of bulk primary coal (PC),cataclastic coal (CC) and mylonitic coal (MC) with identical volume collected from Hancheng Mine,Weibei coalfield were analyzed using self-designed adsorption/desorption apparatus of bulk coal.In combination with micro-focus CT and scanning electron microscope images,the influence of coal-body structure on CH4 adsorption/desorption behavior was discussed.The results indicate that the obvious difference can be observed in coals with different coal-body structures.Long CH4 adsorption/desorption equilibrium time,small adsorption capacity and low desorption rate were recorded in PC due to its dense structure and low porosity.In comparison with PC,a shorter adsorption/desorption equilibrium time,higher adsorption capacity and faster desorption rate were occurred owing to developed and connected fracture system and increased porosity in CC under brittle tectonic stress.Under ductile deformation,the coal composition of MC was folded and concomitant with increased pore number and closed fracture,which induced isolated pore structure and poor permeability.These characteristics result in the shortest adsorption/desorption equilibrium time and the fastest desorption rate,indicating most of CH4 in bulk MC may merely adsorb on inter-granular pores formed during deformation process.Therefore,the CC reservoir is a favorable area for CBM development.Nonetheless,for both PC and MC reservoirs,the increase in the well yield and efficiency can be achieved through reservoir reformation by means of multi-scale fracturing,heat injection and other techniques which can increase the channels within coal fracture.