焉耆盆地博湖坳陷古地温与油气形成关系

Relationship between paleogeothermal and hydrocarbon formation in the Yanqi Basin, Northwest China

采用磷灰石裂变径迹、包裹体测温、自生伊利石同位素年代测定等方法恢复焉耆盆地博湖坳陷古地温。磷灰石裂变径迹显示,北部凹陷为增温型,最大古地温与现今地温一致;南部凹陷和种马场断裂构造带属于冷却型,古地温高于今地温。包裹体均一温度研究显示,北部凹陷包裹体均一温度明显分为两组(101～110℃和121～130℃),南部凹陷只有一组(101～110℃)。自生伊利石同位素测年表明,油气生成及成藏有晚白垩世(燕山期)和始新世以来(喜马拉雅期)两期。根据古地温恢复结果,北部凹陷有晚侏罗世—早白垩世早期和第三纪以来两期生油过程,燕山期古构造和喜马拉雅期新构造均是有利构造;南部凹陷主要生油期仅为晚侏罗世—早白垩世早期,燕山期及其前形成的古构造是有利构造。

The AFTA (Apatite Fission Track Analysis), inclusion thermometry, determination of isotopic age of authigenous chilkinite, etc. have been used to reconstruct the paleogeothermal in the Yanqi Basin, Northwest China. The AFTA results suggest a heating paleogeothermal in north sag that means the highest paleogeothermal of strata was consistent with present geothermal; the inclusion thermometry(101-110℃ and 121-130℃) suggests a cooling geothermal that means paleo-geothermal is higher than present geothermal in south sag and Zhongmachang faults belt; the isotopic age of authigenous chilkinite shows that hydrocarbon generation and accumulation existed two periods in the depression, Late Cretaceous the Yanshan period, the one is after Eocene, Himalaya period. The research on paleogeothermal shows that there are two periods of hydrocarbon generation in Jurassic strata in north sag: Late Jurassic-Early Cretaceous and the one after Tertiary, respectively. In south sag and Zhongmachang faults belt, the main hydrocarbon formation existed merely in Late Jurassic and Early Cretaceous. The Yanshan period sediment and the structures of Himalaya are favorable regions for exploration in north sag, but in south sag, the ancient structures formed before Himalaya period are the favorable play target.