Formation And Evolution Of Hefei Basin And Geologic Characteristic Of Oil And Gas

The Hefei basin, located in east China, is a terrestrial basin with multi-cycle stacked features, which was experienced stable terrestrial edge basin and back-arc fore-land basin in pre-Mesozoic, rebuilt fore-land basin in Mesozoic and Cenozoic and the subsequent composite fore-land basin, and stages above are clearly of features exhibiting multi-period stack and multi-tectonic influence.Although it is supposed to be of abundant hydrocarbon resource, it is so far still in a primitive stage due to the lack of effective methods and complex surface conditions even after more than 40 years exploration and great efforts. In this thesis, multi-discipline combined with reversal development of gravitation, magnetic, electrical, seismic and theories, such as sedimentology, tectonics, geophysics and geochemistry and so on, are first applied in the systematic and comprehensive research on the Hefei basin, and such achievements are achieved as: (1) two-layer tectonic system vertically, and north-south partitioning laterally in the Hefei basin; the bottom tectonic layer, in the central and northern basin and part of north China plate, is composed of metamorphic rock traced back to Archean and old Proterozoic, and sedimentary rocks existed in the upper Proterozoic and Palaeozoic; whereas, the southern part is comprised of Proterozoic and Paleozoic metamorphic rocks coming from Dabieshan orogen; in addition, the upper tectonic layer contains mainly Jurassic, Cretaceous and Cenozoic terrestrial clastic rocks acting as the cap of the basin. (2) the Hefei basin is divided by the Feizhong fracture into two tectonic units, that is, Feibei slop area and Feinan fracturing compression area. (3) the tectonic evolution of Hefei basin is characterized by such stages as front basin stage of pre-Jurassic, foreland basin stage in Jurassic, compression and slip stage in early Cretaceous, extension stage in late Cretaceous and Paleogene, and compression stage formed in Neogene and Quaternary, that forced by the Dabei orogen and Tanlu slip fracture. (4) Rich in organic matter but over matured in Cambrian; coal system is well developed in Carboniferous-Permian northern of Feizhong fracture; Fanghushan formation is conspicuous for better hydrocarbon resource rock developed in lower Jurassic, whereas, Qiuzhuangformation of upper Ciriaccous for mid-poor resource rock, and Dingyuan formation of Paeogene for mid-better resource rock. The basin is variant in the combination of generation, migration, and sealing. The central area is favorable for hydrocarbon exploration, in which the Muchangbu fracture anticline and Zhuxiang nose structure is preferential in the selection of structure trap. The east part of the basin is relatively favorable, whereas the south part is inferior to those above and may be potential exploration area.