Analysis Of Differential Uplift Process During Mesozoic-Cenozoic The Northeast Of Ordos Basin

The relation between Differential uplift and the mechanism of gas accumulation,gas dissipation is the main problem of dynamics reaserch and gas exploring. Starting with the regional tectonic research of the Northeast Slope and adjacent active area of Ordos Basin, through integrated use of field geological survey, seismic profile interpretation, we did the research mainly on the spatial and tempora unconformity distribution in Cenozoic and the tectonic sequence, the structure characteristics and tectonic margin system; Based on basin modeling and tectonic thermochronology, we realized the characteristic of different Uplift in the northeast of the basin in Mesozoic-Cenozoic, And ultimately we discussed the relation between the process of differential Uplift and the gas accumulation in the Upper Paleozoic.(1)Based on the fractures of Unconformity's temporal and spatial distribution in Mesozoic- Cenozoic, dividing it into three primary tectonic sequces:Indo-tectonic layer,Yanshan tectonic layer,Himalayan tectonic layer and 9 secondary layers.(2) Based on the combination of Gravitic and Magnetic abnormality and marginal fracture zone features, concluding that: Shihalagou fracture is the significant boundary of Ordos Terrane and Hetao Basin, Lishi strike-slip fault belt is the significant boundary of Ordos Terrane and Shanxi Terrane; the reaserch area is divided into three main units, repectivly shenmu-mizhi slop,yimeng moletrack and Western Shanxi Torsion fold belt.(3) Basin subsidence modeling indicating that: four stages of differential subsidence which consist of relative rapid sedimentation in Early-Mid Triassic,wavy slow sedimentation in the Late Triassic-Early and Mid Jurassic,rapid sedimentation in Early Cretaceous and slow sedimentation in Quaternary; And four stages of differential uplift, respectively in the Late Triassic,Late Yan'an in Early-Mid Jurassic,Late An ding in Mid Jurassic and the stage since the Late Cretaceous; Tectonothermal chronology analysis indicates that our research area has experienced the slow uplift-cooling stage during the late of the Early-Cretaceous to Paleocene and the rapid uplift-cooling stage since the Neogene; the uplift in the north was earlier than the south; the east edge uplifted earlier than the inner-basin, and Gaojiabu S8 - West Jiaxian M8 uplifted even later.(4) Tectonothermal chronology analysis and Basin subsidence modeling indicate that: the source rocks persist in its gas generation in the Late Cretaceous, even before the end of Paleogene; Based on the combination of Differential Uplift process and source rocks'mature differentiation, conluding that: Gas generation and accumulation stages consist of hydrocarbon source rocks'massive gas generation and primary gas pools'rapid accumulation in the end of Ealy Cretaceous,local hydrocarbon source rocks'limited gas generation and primary gas pools'slender accumulation and stable conservation during the Late Cretaceous-Paleogene,gas generation pause and secondary gas pools'accumulation and dissipation since Neogene.(5) The features of pressure coefficient'distribution indicates that The Upper Paleozoic gas reservoir is divided into the lower primary gas pools and the upper secondary gas pools by peach mudstone, The pressure decreases from bottom to top, and decreased gradually from south to north within the same system. The pressures in primary gas pools were differential from north to south because of the shortage of hydrocarbons in the late of Early-Cretaceous, The rapid uplift since Neogene caused the Shenmu original gas pools'vertical leakage to form the Q5 secondary gas pools, which had ultra-low pressure, and caused the gas dissipation. The primary gas pools'differential pressure between Shenmu and Mizhi increased since the Shenmu original gas pools became the gas source of the Q5 gas pools.