柴达木盆地鸭湖地区生物气形成条件分析

有利的生物生气条件是生物气形成的必要前提,源岩的规模、组成、有机质类型、丰度控制了甲烷生产菌的生气能力和生气强度。柴达木盆地北缘鸭湖地区钻井(鸭深1井)显示该地区上第三系生气岩厚度近1 600 m,其暗色泥岩有机碳含量平均为0.36%,含有明显的三环萜烷和孕甾烷,为偏腐殖的混合型母质,表明源岩为咸水的弱还原—弱氧化沉积环境;R_o一般在0.4%～0.5%,处于有机质演化早期阶段。剖面岩性一般为泥岩、泥质粉砂岩、粉砂岩和少量砂岩,为较松散的细粒沉积,孔隙度较大,处于成岩阶段早期。这些特征有利于微生物的生存和繁殖,指示出该地区上第三系(N₂2—N₂3)暗色泥岩已经具备了形成生物气的条件,可以形成一定规模的生物气,具有一定生物气的勘探前景。 

ANALYSIS ON THE FORMATION CONDITIONS OF THE BIOGENIC GAS IN YAHU AREA, THE QAIDAM BASIN

The favourable gas-generating condition is the indispensable precondition of biogenic gas formation.The size and composition of source rock as well as the type and abundance of organic matter control the gas-generating ability and intensity of methane bacteria.Yahu area is located in the north of Qaidam Basin.The Well Yashen 1 shows that the thickness of the Upper Tertiary gas source rock is(about) 1 600 meters.The average value of total organic carbon of the dark mudstone is 0.36% and obviously contains tricyclic terpane and pregnane.The kerogen is humic mixed organic type and the source rocks form in weak preducing to weak oxidizing environments with salt water.The R_o value is between 0.4% and(0.5%,) showing in the early stage of thermal evolution.Lithologies of mudstone,pelitic siltstone,siltstone and a little sandstone exist in the cross section.The loose fine grain sediments have relatively larger porosity and is in eogenetic stage.These are favorable for bacteria's living and breeding and indicate that the Upper Tertiary dark mudstone in this region have conditions of biogenic gas formation.The biogenic gas exploration in Yahu area have good future.