内蒙古查干凹陷下白垩统层序地层格架与沉积体系分布

充分利用岩性组合、岩心、测井、地球化学及古生物等响应,结合构造演化及地震反射特征,在查干凹陷下白垩统识别出7个三级层序界面,将其划分为6个三级层序和16个体系域。层序展布早期具有北薄南厚、东薄西厚的特征,晚期沉积中心北移,呈西厚东薄、北厚南薄的格局。在层序格架内,早期由于毛敦次凸的分割作用,凹陷东西两侧的沉积格局存在差异,总体以水下扇、扇三角洲和辫状河三角洲沉积为主;晚期毛敦次凸逐渐接受沉积,沉积了一套冲积平原、泛滥平原及河流相沉积。下白垩统由下而上发育3套生储盖组合,下部SQ1的低位体系域储层与水进域的泥岩盖层形成自生自储的生储盖组合;中部生储盖组合以SQ2的高位域及SQ3的低位域储层为主;上部组合储层主要为SQ4—SQ6碎屑岩及火山岩储层。

Sequence Stratigraphic Framework and Sedimentary Facies Distribution of the Lower Cretaceous in Chagan Depression, Inner Mongolia

Comprehensively using the lithologic association, drilling core, logging, geochemistry and palaeontology data, combining structural evolution and seismic reflection feature, 7 third-order sequence boundaries are identified and 6 sequences，16 system tracts are classified in Lower Cretaceous of Chagan depression. In the early phase, sequences in the south and west were thicker. Lately, the depocencer migrated to the north, and the sequences of the west and north were thicker. The sedimentary framework was different between the west and east in early phase because of the Maodun sub-arch, but subsea apron, fan delta and braid river delta were the main depositional system totally. Lately, Maodun sub-arch deposited to alluvial plain, bet lands, and fluvial facies. Three source rock-reservoir-cap rock assemblages in Lower Cretaceous were developed. In the lower part, the reservoir of the LST was covered by the mudstone of the TST and the self-generation; self-reservation source rock-reservoir-cap rock assemblage was formed. In the middle part, the reservoir developed in the HST of the SQ2 and the LST of the SQ3. The reservoir in the upper part consists of clastic rock of SQ4-SQ6 and volcanic rocks.