沁水盆地石炭—二叠系煤层气成藏期研究

Carboniferous-Permian coalbed methane-accumulating stages in the Qinshui basin Shanxi

根据储层的成岩序次、油气包裹体特征及含烃盐水包裹体均一温度,自生伊利石K-Ar同位素年龄,结合构造热演化史及裂变径迹资料,对沁水盆地石炭—二叠系煤层及顶板砂岩煤层气成藏期次进行了综合研究。认为该气藏主要有两大油气充注过程:第一期发生在三叠纪末—早侏罗世,山西组、太原组主力煤层普遍处于成熟阶段,主要生成液烃、气液烃包裹体;第二期发生在晚侏罗世—早白垩世,对应于干酪根裂解气阶段,为煤层气大量生成阶段,是石炭—二叠系煤层气的主要成藏期。山西组顶板砂岩样品自生伊利石年龄约为191Ma,表明早侏罗世,伴随盆地抬升,从煤层中解吸附的油气向砂岩储层充注的最早时间。

According to the diagenetic sequence of the reservoir, characteristics of oil-gas inclusions and homogenization temperatures of hydrocarbon-bearing saline inclusions and isotope dating of authigenic illite, combined with the tectonothermal evolution history and fission-track path data, an integrated study has been performed on the stages of coalbed methane accumulation in Permo-Carboniferous coalbeds and roof sandstone in the Qinshui basin. The authors think that two stages of hydrocarbon injection occurred in the methane accumulation. The first stage occurred in the terminal Shanxi and Taiyuan formations were in a mature stage Triassic to Early Jurassic, when the main coal seams of the and liquid hydrocarbon and gas-liquid hydrogen inclusions formed; and the second stage took place in the Late Jurassic to Early Cretaceous, corresponding to the phase of thermal cracking of kerogen, when large amounts of coalbed methane were produced, so the stage is the main accumulation stage of Permo-Carboniferous coalbed methane. The age of authigenic illite in roof sandstone, Shanxi Formation, is ～191 Ma, which implies that the Early Jurassic was the earliest time for filling of oil/gas desorbed from coalbeds methane in the sandstone reservoir with basin uplift and erosion.