Research On The Control Of Base Level Cycles On The Configuration Of Finger-shaped Sand Bars In Shallow Water Deltas

The shoal-water delta deposit is a profitable target for hydrocarbon accumulation,and now it becomes the main point for further research on deltaic sedimentology.However,the correlation between the architectural characters of bar-finger deposits in shoal-water delta deposits and the base-level changes is not clear.As a result,the paper is about barfinger deposits in Lower Ming Huazhen Fm.,Neogene in BZ25-1S oilfield,Bohai Bay Basin.Based on the integrated analysis on core,loggings and seismic,the architectural characters of bar-finger deposits in BZ25-1S oilfield have been put forward.What is more,with the aim of sedimentary numerical simulations,the paper also clarifies the controlling mechanism of base-level changes on the architecture of bar-finger deposits.The research shows that:(1)The lower Ming Huazhen Fm.,Neogene can be divided into one long-term base-level cycle,5 medium-term base-level cycles and 26 short-term baselevel semi-cycles.(2)The planar-type of bar-finger deposits in BZ25-1S oilfield is isolated-type and interweaved-type,while its stack-pattern can be divided into 3 types:isolated,slightly-piled and totally-piled.What is more,the width of bar-finger deposits is between 150 m and 1200 m,while its thickness is between 8m and 9.5m and aspect ratio is between 23 and 133.Besides,there is a positive correlation between the width and thickness of bar-finger deposits.(3)The architectural characters of bar-finger deposits are controlled by the changes of base-level cycles.If the base-level keeps on rising,the barfinger deposits will have smaller size,less distributaries and sinuosity.On the contrary,the bar-finger deposits will become larger size,more distributaries and sinuosity as the base-level falling.(4)In a certain geological history,while A/S value is high,the barfinger deposits tend to be less distributaries and smaller size.Besides,the bar-finger deposits tend to be higher sinuosity while the accommodation space increasing.On the other hand,while A/S value is low,the bar-finger deposits tend to be more distributaries and larger size.Besides,the bar-finger deposits tend to be lower sinuosity while the accommodation space decreasing.