桂中坳陷下石炭统岩关阶页岩气成藏条件及资源潜力分析OA

A study was conducted on the shale gas accumulation conditions of Yanguan Stage(C1y)of Lower Carboniferous in Guizhong Depression,focusing on aspects such as the thickness of mudstone,total organic carbon content w(TOC),and reservoir characteristics.The results indicate that Yanguan Stage of Lower Carboniferous in Guizhong Depression represents a set of dark mudstone deposits in a platform basin setting,with individual layer thickness commonly ranging from 20 to 30 meters and cumulative thickness typically falling between 50 and 250 meters.The main body of the depression shows w(TOC)values exceeding 1.0％,with type Ⅱ organic matter,vitrinite reflectance values ranging from 1.75％to 2.93％,indicating a thermal evolution stage from mature to overmature.The average content of brittle minerals such as quartz,feldspar,pyrite,and carbonate rock reaches as high as 67％,with methane adsorption capacities ranging from 0.93 to 1.25 m3/t.The average porosity and permeability are 6.69％and 0.144 mD,respectively,meeting the criteria for reservoir conditions.Various types of storage spaces are developed in the mudstones,predominantly flat and slit-shaped pores,with macro-pores and meso-pores contributing over 80％to the pore volume.The specific surface area is predominantly attributed to micropores.Larger pores exhibit higher fractal dimensions and more complex structures compared to smaller ones.Considering factors such as the thickness of dark mudstone,burial depth,w(TOC),and degree of thermal evolution,the favorable areas for shale gas in Yanguan Stage of Lower Carboniferous in Guizhong Depression are predicted to be mainly distributed in Libo area in the north of the depression,and Luocheng-Yizhou-Laibin-Shanglin region in the central and southwestern parts of the depression.Utilizing geological resource abundance analogy methodology,the estimated geological resources of shale gas in Yanguan Stage of Lower Carboniferous in Guizhong Depression amount to(0.36～0.53)×1012 m3.