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.