内蒙古钱家店凹陷侏罗系层序地层与岩性圈闭

在层序地层学基础理论指导下 ,综合运用大量的地质、测井、地震及室内分析化验资料 ,对内蒙古钱家店凹陷侏罗系进行层序地层学研究。依据地震反射终止关系、古土壤的位置及分布、古生物化石断代位置、地震反射剖面上滨岸上超位置及迁移规律、沉积相、地层叠置型式等一系列特征识别层序边界、最大湖泛面和首次湖泛面。将上侏罗统划分为 4个层序 ,确定层序周期为 5～ 8Ma ,指出层序地层构型主要受盆地断裂活动和物源供给多少的影响。根据盆地西断东超的箕状特征 ,以“地形变化带”为界 ,确定首次湖泛面 ,以最远滨岸上超点确定最大湖泛面 ,进而将断陷湖盆沉积层序划分成低位体系域、湖侵体系域和高位体系域。详细描述了低位、湖侵和高位体系域中发育的近岸水下扇、辫状河三角洲、深水浊积扇及湖泊沉积特征和分布规律 ,结合石油地质综合评价和油气勘探实践 ,指出层序B(九佛堂组 )湖侵体系域盆地缓坡辫状河三角洲前缘砂体和盆地中央深水浊积扇砂体是寻找地层岩性圈闭的有利部位。

Jurassic sequence stratigraphy and lithologic traps in Qianjiadian depression, Inner Mongolia

Under the guidance of the theory of sequence stratigraphy, sequence stratigraphic analysis of the Jurassic has been made by the integrated use of extensive geological, well-logging and seismic data in Qianjiadian depression. On the basis of seismic reflection terminal relations, the recognition of occurrence of palaeosoil, the abrupt change of sedimentary facies and the change of strata stacking pattern of parasequences, 5 sequence boundaries have been recognized and the upper Jurassic can be classified into 4 sequences. Each sequence deposited within a cycle of 5-8Ma. The configuration of these sequences is controlled by fault activity and sediment flux rate. According to the half-graben characteristics of Qianjiadian depression, the first and the largest lacustrine flooding surfaces have been determined respectively by the changed zone of relief and the maximum landward shore onlap. Therefore a sequence of faulted-depression is made up of lowstand system tracts (LST), transgressive system tracts (TST) and highstand system tracts (HST) in which nearshore subaqueous fan, braided delta, deep water turbidite fan developed. Finally two favorable lithologic traps, which are in the delta front to the north of Kundouhua and turbidite fan encased in shale in Liujiazi area respectively, have been prospected by the combination of comprehensive evaluation of petroleum geology and practice of oil-gas exploration in the study area.