鄂尔多斯盆地中奥陶统平凉组烃源岩地球化学特征及勘探潜力

鄂尔多斯盆地西、南缘中奥陶统台缘深水斜坡相平凉组烃源岩包括泥页岩和泥灰岩,厚度80~200 m,在西缘桌子山—刘庆7井—苦深1井—石板构—环14井—平凉—陇县等地和南缘旬邑以南、耀县以北的广大地区呈"L"形连片分布。干酪根碳同位素平均值为-29.95‰,有机质类型指数约为100%,氯仿沥青"A"中饱/芳比大于3,以Ⅰ型有机质类型为主。有机碳含量大于0.2%,西缘露头和岩心的氯仿沥青"A"平均值分别高达232×10-6和380×10-6,生烃潜力(S₁+S₂)平均值分别高达0.42,0.37mg/g,烃源岩有机质丰度高。除了西缘逆冲带成熟度较低(生油窗)外,天环坳陷和南缘渭北隆起R_o值在1.60%~2.60%之间,处于高—过成熟阶段。生烃模拟实验证实平凉组在达到R_o值2.1%演化程度时产烃率即可高达224.33 kg/t,地质历史上已累计生成资源量约4.323 8×108t油气当量。中央古隆起不但长期控制了平凉组烃源岩的油气运聚,而且提供了马家沟组马四段溶蚀白云岩有利储集空间,天环坳陷东缘和鄂南渭北隆起北部下古生界都具有较大勘探潜力。 

GEOCHEMICAL CHARACTERISTICS AND EXPLORATION POTENTIAL OF MIDDLE ORDOVICIAN PINGLIANG FOMATION IN THE ORDOS BASIN

Pingliang Fomation source rocks of Middle Ordovician include 80 to 200 meters mudshale and marlstone,which distributed in Zhuozishan,Well Liuqing 7,Well Kushen 1,Shibangou,Well Huan 14,Pingliang,Longxian,Xunyi and Yaoxian,formed in platform slope facies around the western and southern margin of Ordos Basin.The organic matter of Pingliang Fomation source rocks is mainly typeⅠkerogen with-29.95‰ δ13C value,neary 100% Ity value,and greater than 3 saturated to aromatic hydrocarbon rate of "A".TOC value is more than 0.2%.The mean contents of "A"and hydrocarbon generation potential(S₁+S₂) are up to 232×10-6,380×10-6 and 0.42,0.37 mg/g respectively,corresponding to outcrop and drill core samples from the western margin of Ordos Basin.The organic matter is at stage of high to post maturity with Ro value between 1.60% and 2.60%,except samples from the western thrust zone.Pyrolysis simulating experiment results show that hydrocarbon resource amount of Pingliang Fomation source rocks is 0.433 8 billion tons oil equivalent in history.The central paleouplift supplied not only the oil and gas convergence belt,but also accumulation reservoir.The eastern part of Tianhuan Depression and northern part of Weibei Uplift are prospective exploration regions in future.