鄂尔多斯盆地东南缘临汾区块煤层气成因及其影响

为研究临汾地区煤层气成因类型,在综合前人研究成果的基础上,研究分析了煤芯解吸气成分、井口气成分、碳同位素特征、煤层水地球化学特征及水动力等条件,认为研究区煤层气保存条件整体良好,但甲烷碳同位素偏轻、重烃组分偏少,表明受到了一定因素或次生作用的影响。对比分析导致甲烷碳同位素偏轻、重烃组分偏少的次生改造作用,认为扩散-运移的影响作用最大,还认为临汾区块东缘和薛关一带具备形成次生生物成因气的条件。结合Whiticar图版,认为临汾区块煤层气主要为受到运移-扩散次生作用影响的热成因气,J81井5号和8号煤、J25井8号煤层气为次生生物成因气,J25井5号煤和J60,J62,J11,J80井煤层气为热成因气和次生生物气的混合气。薛关一带和东缘刁口—蒲县东一带虽有次生生物气的补充,但后期保存条件较差,含气量普遍偏低。薛关断裂以西的构造斜坡带,热成因气保存条件良好,含气量高。

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 desorption 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 considered 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 analysis of factors causing methane carbon isotope values lighter and the heavy hydrocarbon component less，the desorption-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 origin type of coalbed methane is mostly thermal gas，the No.5 and No.8 coalbed methane of J81 well and the No.8 coalbed 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.