Classification And Characteristic Analysis Of The Paleo-Lacustrine Shore Belt In The Lower Minghuazhen Formation,Neogene,in The Southeastern Of South Bohai

With the exploration and development of oil and gas in bohai sea,more and more researches show that the extremely shallow water delta sand body of MinhuazhenFormation is the main reservoir type.This has led to extensive covered by shallow water deltas in subsequent studies of new blocks.However,in recent years,the there are both lacustrine facies and fluvial faciesmay discovered in MinghuazenFormation,Neogene in the southeastern of South Bohai.Therefore,there may be a paleo-lacustrine shore belt(river-lake transition belt)with a certain width between the continental and lacustrine sedimentary areas.Its sedimentary characteristics and evolution patterns may be significantly different from those of shallow water deltas and may have different significance in reservoir formation characteristics.This paper takes the southeast of Laizhouwan Sagand eastern of east depression of HuanghekouSag as the study area and the lower MinghuazhenFormation,Neogene is taken as the main target stratigraphy.Integrated application of a large number of data,the high resolution sequence stratigraphy(quasi sequence group)framework,using mathematical statistical methods,to restore the plane of the paleo-water depthin south Bohai,on the basis of analyzing the lacustrine shoreline migration patterns in the paleo-lacustrine shore belt division and sedimentary characteristics analysis,and discusses the paleo-lacustrine shore zone control factors of sedimentary evolution.In combination with log and seismic,the lower submember(SQmL2)and upper submember(SQmL1)of MinghuazhanFormation were divided into 10 quasi sequences and 7 quasi sequences respectively.The study found that the study area belongs to extremely shallow water environment,with the deepest water depth no more than 6m.During the period of transgressive systemtract,the shorelines moved to the shore and the basin expanded.During the period ofhigh system tract,the shorelines migrated to the lake and the basin contracted.Based on the restoration of paleo-water depth in each quasi-sequence,the concept of paleo-lacustrine shore belt is put forward for the first time,it is the range of lake plane fluctuation and shoreline migration is controlled by many factorsduring a certain period of shallow lake basin deposition.The paleo-lacustrine shore belt whose water depthis between 0~1m mainly developed interlacustrine and extremely shallow water delta.Most of the paleo-lacustrine shore belts are purplish-red and grey to greyish-green rock colors,the lithology of the pebbly coarse-grained sandstones and fine-grained sandstones and logs representing fluvial and delta facies,respectively,interacted,and the seismic reflection characteristics of alternating good and bad continuity and alternating strong and weak amplitude vertically.The sand bodies in the paleo-lacustrine shore belt were crossing distributed on the plane under the controling of fluvial action and longshore current.In addition,the sedimentary evolution of the paleo-lacustrine shore belt is controlled by the factors of topography,paleoclimate,paleo-water depth and sediment supply.