准噶尔盆地腹部侏罗系层序地层特征

准噶尔盆地腹部地区主要目的层侏罗系埋藏深,构造形态简单,岩性油气藏是主要的油气藏类型。综合利用腹部地区钻井和地震资料,建立起了该地区侏罗系三级层序地层格架,把侏罗系划分为6个三级层序(Sq1—Sq6)。研究认为,与具坡折带陆相断陷湖盆层序模型相比,准噶尔盆地腹部地区侏罗系层序形成于坡折带不发育或异常平缓的古地理背景下,因而其形成的层序特征也表现出独有的平缓地形特点,且突出表现为不整合面全盆范围内分布,无法依据坡折带划分低水位体系域,水进体系域厚度薄等特点。受古地形起伏、古气候条件等古地理因素不同的影响,该6个层序形成于3种不同的古地理沉积背景中:潮湿气候平缓斜坡背景(Sq1、Sq2、Sq4)、潮湿气候缓斜斜坡背景(Sq3)、干旱气候平缓斜坡背景(Sq5、Sq6),相应地表现出不同的层序特征。

FEATURES OF THE JURASSIC SEQUENCE STRATIGRAPHY IN THE CENTER OF JUNGGAR BASIN,XINJIANG

In the Central Junggar Basin the Jurassic strata is deeply buried, with poorly developed positive elements, and lithologic reservoirs are the favorable exploration targets. Based on the well and seismic data,sequence stratigraphic theory and techniques are used to build the Jurassic sequence stratigraphic frame, which consists of six 3rd-order sequences(Sq1—Sq6). Compared with the standard sequence models in faulted basins with breaks, the sequences in the Central Junggar Basin were formed in gently dipped slopes with no or gentle breaks and show corresponding characteristics: widely distributied unconformities, untraceable lowstand systems tracts only by gently dipped breaks, thin transgressive systems tracts, etc. All the 6 Jurassic 3rd-order sequences were formed in the gently dipped slopes. However, due to the difference in land forms and palaeoclimate,their depositional environments can be divided into three palaeogeographic groups:flat dipped slope in a humid climate(Sq1,Sq2,Sq4); gentle dipped slope in a humid climate (Sq3); flat dipped slope in an arid climate (Sq5,Sq6)). Accordingly, each group has different stratigraphic characteristics.