中国中西部小型克拉通盆地群的叠合复合性质及其含油气系统

中国中西部盆地油气资源潜力巨大,是晚古生代一早中生代一新生代大型造山带环绕的小型克拉通盆地,盆地核心为构造相对稳定的小型克拉通,边缘环绕构造活跃的前陆冲断带。与北美、欧洲等大型含油气盆地相比,中国含油气盆地规模小、构造活动性强。盆地普遍经历：（1）寒武—志留纪,各自漂离于大洋中的小型克拉通盆地；（2）泥盆—二叠纪,亚欧板块南缘地体增生；（3）三叠—古近纪,特提斯洋关闭,陆相断（坳）陷盆地；（4）新近纪以来,再生前陆盆地等四个构造演化阶段。从下而上叠合了早古生代海相克拉通盆地、晚古生代海陆交互相克拉通盆地、早中生代陆相断（坳）陷盆地和新生代再生前陆盆地四个构造层序。古生界克拉通盆地构造相对稳定,古生代发育多期不整合界面和大型古隆起；中新生代前陆盆地叠置复合在其边缘,发育成排成带的构造。中国含油气盆地的叠合-复合性质决定了其叠合-复合含油气系统的特征：具有多油气系统、多源多阶段生烃、多期成藏、多层系含油气。中国中西部盆地的油气勘探主要包括古生界小型克拉通层序和中新生代前陆层序两大领域,其中早古生代克拉通层序以古隆起及其斜坡、晚古生代克拉通层序以大面积岩性储集体、中新生代前陆盆地以大型冲断带控制着油气的成藏与富集。

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 characteriied 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 strncturlly 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 superimposedcomposite 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 microcraton 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.