Origin of coalbed methane and its influence in Linfen,Southeastern Ordos Basin

To study the origin type of coalbed methane in Linfen block,based on the previous achievements,the de- sorption gas of coal core,wellhead gas,carbon isotopes characteristics,coalbed water hydrogeochemical characteristics and hydrodynamic conditions were studied and analyzed. The preservation conditions of coalbed methane were consid- ered to be good,but the methane carbon isotope values were obviously lighter and the heavy hydrocarbon component were less,which show the gas were influenced by some factors and secondary transformation. After the contrastive anal- ysis of factors causing methane carbon isotope values lighter and the heavy hydrocarbon component less,the desorp- tion-diffusion process effect was considered to be the biggest,and the forming conditions of secondary biogenic gas were found in the eastern edge and Xueguan of Linfen block. With the Whiticar Chart Board,it is believed that the ori- gin type of coalbed methane is mostly thermal gas,the No. 5 and No. 8 coalbed methane of J81 well and the No. 8 coal- bed methane of J25 well are secondary biogenic gas,the J60,J62,J11,J80 well and the No. 5 coal seam of J25 well have mixture gas of thermal and biogenic origin. Although the supplement of secondary biogenic gas in Xueguan and Diaokou to the east of Puxian of block eastern edge,the gas preservation on later time is poor,causing low gas content. Thermal gas preservation is good in the structural slope to the west of Xueguan Fracture,and the gas content is high.