塔里木盆地中—下奥陶统台缘结构特征及油气指示意义

Structural Characteristics of Carbonate Platform Margins in Lower-Middle Ordovician of Tarim Basin and Related Hydrocarbon Implication

塔里木盆地下古生界台缘是一个油气富集区,根据地震、测井、岩心和露头等资料,揭示塔里木盆地中—下奥陶统不同地区台缘特征差异大:塔北地区为退积陡坡弱镶边型;塔中地区为加积陡坡镶边型;塔西南和阿瓦提地区为弱加积—进积缓坡型;塔南地区为弱加积—进积型,陡坡缓坡均有分布,并在其间发育继承性台间斜坡。综合构造、沉积、古环境以及成岩作用等方面的研究发现,塔北、塔中地区在早—中奥陶世处于古迎风面,台缘坡度陡;塔西南、阿瓦提地区处于古背风面,台缘坡度缓;塔北地区同沉积时自台地向盆地构造沉降速率变化快,台缘结构为退积型;塔中地区变化慢,台缘结构为加积型。由此认为,古气候和构造沉降速率变化快慢对台缘类型影响较大。台缘结构特征对比有利于岩相古地理恢复以及滩体等有利储集区的纵、横向展布预测,对塔里木盆地中—下奥陶统的油气勘探由台缘带向台内区拓展具有重要意义。

The carbonate platform margins of Lower Paleozoic are an oil-gas enriched region.The seismic,logging,core and outcrop datafrom this area reveal that the structural types of the platform margins of Middle-Lower Ordovician in different areas in Tarim basin are bigdifferent.Tabei area（the northern Tarim） occurs in steep retrogradation rimmed margin type,Tazhong area（the central Tarim） in steep ag-gradation rimmed margin type,Taxi＇nan area（the southwestern Tarim） and Awati area in weak aggradation-progradation ramp types,and Ta＇nan are（the southern Tarim） is in weak aggradation-progradation steep-ramp type,with inheritance inter-platform slope facies.The compre-hensive study of structure,deposition,paleo-environment and diagenesis,shows that：1） Tabei and Tazhong areas were located in the wind-ward side with steep slope gradient of margins in Early-Middle Ordovician,and Taxi＇nan and Awati areas were located in the leeward sidewith ramp slope gradient; 2） Tectonic subsidence rate from platform to basin in Tabei area was fast when the synsedimentary occurred,thestructures of platform margin were on style of retrogradation; while Tazhong area changed slowly,the structures on style of aggradation.It issuggested that the structures of platform margins are affected by paleoclimate and tectonic subsidence rate.The comparisons of carbonateplatform margins are in favor of the reconstruction of lithofacies palaeogeography and the prediction of vertical-lateral distribution of favor-able shoal reservoirs,and it is meaningful for petroleum exploration extension from platform margins to inner platform of Lower-Middle Or-dovician in Tarim basin.