Superimposed-Composite Characteristics of Micro-Craton Basins and Its Bearing Petroleum Systems, Central-Western China

There are rich hydrocarbon resources in the basins located in western and central China. They are many micro-craton basins surrounded by large orogenic belts of Hercynian-Indosinian and Himalayan, which are characterized by small structurally stable in the kernel craton and structurally active in margin foreland thrust belts. Compared with large petroliferous basins in North America and Europe continent etc. the petroliferous basins in China are small in scale and structurlly more active. These basins commonly underwent four tectonic evolution stages:①Micro-craton plates floating in the ocean separately during Cambrian to Silurian; ②Terrane accreting along south flank of the Eurasian plate during Devonian to Permian;③Tethys ocean closing and continental depression (or rift) basins during Triassic to Paleogene;④Rejuvenation foreland basins since Neogene. Accordingly there formed and superposed four structural sequences, the lower Paleozoic marine craton basins, the upper Paleozoic paralic craton basins, intra-continental depression (or rift) basins and rejuvenation foreland basins. Tectonic movements of Paleozoic craton basins are relatively stable; while multiphase unconformable contacts and large palaeohighs developed during Paleozoic; and forland basins compositing and superimposing on their margin and formed structures distributing in rows and zones during Mesozoic-Cenozoic. The superimposed-composite petroleum system, determined by the nature of composition-superimposition of petroliferous basins in China, comprises multiple petroleum systems and several source layers, experienced multiple stages of hydrocarbon generation and multiple periods of hydrocarbon accumulation, consequently there are multi-layers bearing oil and gas. There are two major fields in petroleum exploration in central and western China basins: the Paleozoic micro-craton sequence and the Mesozoic-Cenozoic foreland sequence. The factors controlling the hydrocarbon accumulation and enrichment include palaeohighs and slopes in the lower Paleozoic craton sequence, large-area lithological reservoirs in the upper Paleozoic craton sequence and large scale thrust belts in the Mesozoic-Cenozoic foreland basins.