阿尔金西段侏罗系沉积特征及石油地质条件分析

阿尔金西段侏罗系由中、下侏罗统大煤沟组和上侏罗统采石岭组组成,出露于格斯沟至黑水沟一带以及祁曼塔格西北缘,呈NEE方向展布。钻井和地震资料表明,阿尔金西段侏罗系在盆地内部新生界覆盖之下也有大面积分布。大煤沟组是以冲积扇-河流-滨湖相沉积为主的含煤建造,暗色泥岩发育;采石岭组是以洪-冲积扇相沉积为特征的碎屑岩建造。其沉积特征与柴达木盆地北缘、西部以及塔里木盆地极为相似,表明侏罗系沉积时柴达木盆地与塔里木盆地是连通的,属于同一侏罗纪原型盆地,此时阿尔金断裂并不存在。直至渐新世伴随阿尔金断裂的大规模走滑,阿尔金山快速隆升,才分割为两个盆地。有机质化学分析表明大煤沟组中暗色泥岩有机质丰度高,为中等-好的烃源岩,干酪根类型为II2-III型,热演化处于成熟-高熟阶段,具有生油潜力。此外该区域生储盖匹配良好,圈闭发育,具有较好的石油地质条件和油气勘探前景。

Jurassic sedimentary characteristics and its petroleum geological conditions in western Altyn area

The Jurassic strata are composed mainly of Lower- - Middle Jurassic Dameigou Formation and Upper Jurassic Caishiling Formation，exposed along the Gesigou to Heishuigou in western Altyn area as well as northwest- ern Qimantagh Mountain，showing NEE- trending distribution． Based on the borehole and seismic data，the Jurassic strata are widely discovered under the Cenozoic strata in western Altyn area． The Dameigou Formation is character- ized by alluvial fan facies- fluvial facies- coastal lake facies，with abundant dark mudstone and minor amounts of coals，whereas the Caishiling Formation is represented by the pluvial- alluvial fan facies sedimentary conditions， with development of clastic rocks． The sedimentary characteristics in western Altyn area are consistent with those in western and northern Qaidam Basin and the Tarim Basin，indicating that the Qaidam and Tarim were probably con- nected with each other at the time when Jurassic deposited，forming a huge Jurassic prototype basin． At that time， the Altyn Fault is not exist． Subsequent to the Oligocene，the rapid uplift of the Altyn Mountain corresponding to the strike- slip activities of the Altyn Fault resulted separation of former Jurassic prototype basin into the present Qai- dam and Tarim basins． On the other hand，the analyses of organic geochemistry on dark mudstone in the Lower- - Middle Jurassic Dameigou Formation are carried out in this study． The presented results show that the mudstones are rich in organic matters，belonging to medium- good hydrocarbon source rocks． The kerogen types of organic mat- ters are mainly type II 2 and type III，with the thermal evolution history in mature to high- mature stage，implying a good hydrocarbon generative potential． In addition，the source rocks，reservoir beds and cap rocks match well，to- gether with the well developed traps，suggesting that the Jurassic in western Altyn area possesses relatively better petroleum geological conditions and oil exploration prospect．