ORDOVICIAN SEQUENCE PALEOGEOGRAPHY AND RESERVIOR QUALITY IN JIZHONG DEPRESSION

In the Ordovician, the Jizhong depression was one part of the Huabei epicontinental sea, in which a set of carbonate formations deposited. The Lower Ordovician consists of the Yeli Formation and Liangjiashan Formation, and the Middle Ordovician only contains the Majiagou Formation, which is further divided into six members. The Upper Ordovician is missing. In the early Ordovician, the study area was mainly occupied by tidal flats and restricted platforms. During the middle Ordovician, however, the area was characterized by open platforms and restricted platforms. The formation of reservoirs depends upon various factors, such as lithology, facies, diagenesis, faults and fractures. They are classified into three main types, i.e. fracture type, karst cave type and the type of intercrystal pores of dolomite, with relatively higher or lower capacities. Relatively good reservoirs are distributed in Raoyang, Wenan, Langgu, Wuqing and Jindong regions.