渤中坳陷青东凹陷古近系沙三下亚段构造-古地貌对沉积的控制

Control of structure-paleogeomorphology on the deposition of the lower part of the third member of the Paleogene Shahejie Formation in the Qingdong Sag of the Bozhong Depression

李桂范 李建平 王根照 程建春 宫诲婕

Li Guifan Li Jianping Wang Genzhao Cheng Jianchun Gong Huijie

利用地震、测井及录井资料,采用回剥技术及断失量的趋势分析方法,恢复了古近系沙河街组三段下亚段沉积时期青东凹陷的构造-古地貌,并阐明了构造-古地貌对沉积体系的控制.受郯庐断裂及其派生断裂的控制,沙三下亚段沉积时期青东凹陷呈现整体沉陷,为一东断西超的箕状断陷.凹中发育3个近东西向的次隆,将青东凹陷分隔为4个次洼,由南至北,次洼的规模逐渐扩大.受构造-古地貌的控制,沙三下亚段青东凹陷的东部发育扇三角洲,西部和南部发育辫状河三角洲,三角洲沉积体系的主体发育部位明显受次洼的控制.由于凹陷规模小,物源供应充分,扇三角洲和辫状河三角洲的砂质沉积不同程度超覆于次隆之上,次隆地带水浅浪强,形成规模不等的砂质滩坝.发育于东部断坡带的三角洲砂体,发育于西部缓坡带的辫状河三角洲砂体,以及发育于次隆地带的砂质滩坝砂体均具有较好的储集条件和较好的圈闭背景,是油气勘探的重要目标.

Based on seismic and log data,we used back-stripping technology and trend analysis method to restore structure-paleogeomorphology of the Qingdong sag during the sedimentation of the lower part of third member of the Paleogene Shahejie Formation (E3s).We also explained the control of structure-paleogeomorphology on sedimentary systems.Controlled by the Tan-Lu fault and its induced faults,the Qingdong sag subsided as a whole during the sedimentation of the lower part of E3s.It was a dustpan-shaped rift which was faulted in its eastern part and overlapped in its western part.Within the sag,there were three near east-west-trending sub-uplifts which separated the Qingdong sag into four sub-sags.From south to north,the size of these sub-sags became larger gradually.Controlled by structure-geomorphology,fan deltas were developed in the east of the Qingdong sag,while braided deltas were developed in the west and in the south during the deposition of the lower part of E3s.The major part of the delta sedimentary system was obviously controlled by the sub-sags.Arenaceous sediments of fan delta and braided delta facies overlapped,in various degrees,the sub-uplifts because of the small size of the sag and sufficient supply of deposits.The shallow water and strong energy resulted in the arenaceous beach-bar facies of different scales on the sub-uplifts.Favorable reservoir conditions and traps are found in delta sandbodies developed on the eastern ramp,braided delta sandbodies developed on the western gentle slope and arenaceous bench bar deposits developed on the sub-uplifts.These sandbodies should be the major exploration targets.

10.11743/ogg20090406