用自生伊利石定年确定鄂尔多斯盆地东北部二叠系油气成藏期次

Authigenic illite dating for the timing of oil- gas accumulation of the Permian reservoirs in northeastern Ordos Basin

运用含油气砂岩自生伊利石K-Ar定年方法,探讨分析了鄂尔多斯盆地东北部上古生界二叠系油气成藏的期次和时间。结果表明,二叠系不同含油气层段均不同程度地经历了与烃源岩两次主生烃作用相应的(175～155 Ma和145～115 Ma)原生油气成藏事件,峰值年龄主要集中在中侏罗世晚期的165 Ma和早白垩世早期的130 Ma。其中,下二叠统油气成藏期以较宽的时域分布(178～110 Ma),中、上二叠统则相对较晚地分布在(160～108 Ma),且上二叠统的起止时限主要集中在(160～125 Ma);二叠系样品年龄的空间分布总体呈现其油气成藏过程具有自南(178～122 Ma)向北(131～108 Ma)年龄逐渐减小的渐次运聚成藏特点。因此,包括上二叠统在内的二叠系不同层段均不同程度地经历了早-中侏罗世和早白垩世的两期原生油气成藏作用,上二叠统气藏现今显示的次生成藏特点很可能是在原生油气成藏基础上后期叠加改造或次生成藏的结果。

The K-Ar dating method with authigenic illite（AI）is applied to oil-gas-bearing sandstone core-samples to determine the stages and timing of the Permian oil-gas accumulation in northeastern Ordos Basin.Results show that the Permian oil-gas-bearing intervals all experienced two events of original oil-gas accumulation during the periods of 175-155 Ma and 145-115 Ma,respectively corresponding to two age-peaks at 165 Ma of the Middle Jurassic and 130 Ma of the Early Cretaceous in coincidence with the generation stages of the permian hydrocarbon source rocks in the Early and Middle Mesozoic.Specifically,oil-gas accumulation in the Lower Permian features in a relatively wide time range from 178 Ma to 110 Ma,while that in the Middle and Upper Permian is characterized by a narrow time range from 160 Ma to 108 Ma.The AI dating of（160-125）Ma of the Upper Permian samples indicates a relatively earlier ending time of its oil-gas accumulation.Also,the spatial and temporal distribution of the AI ages shows that the sequence of oil-gas migration to accumulation in the Permian is mainly from south（178-122 Ma）to north（131-108 Ma）.Accordingly,it could be speculated that reservoirs in the Permian almost unanimously experienced two stages of original oil-gas accumulation during the Early to Middle Jurassic and the Early Cretaceous;and the current secondary accumulation features of the Upper Permian reservoirs should be mainly caused by the later reformation and adjustment of the original oil-gas accumulation during the Late Mesozoic to Cenozoic uplifting of the basin.