Palaeogene Stratigraphic Characteristics And Main Factors Analysis Of Hydrocabon Accumulation In West Damintun Sag

Damintun Sag is regarded as one of hydrocarbon-rich sags in Liaohe basin.Oil and gas exploration in Damintun Sag demonstrated that hydrocarbon accumulation in Palaeogene is primarily controlled by the stratigraphic.To better understand hydrocarbon accumulation and improve hydrocarbon exploration in West Damintun Sag,this work classified Palaeogene stratigraphic in West Damintun Sag,and performed stratigraphic correlation with well log data.Based on the stratigraphic of West Damintun Sag,we used oil source correlation,sedimentary facies analysis and sonic log to study the geology conditions for oil accumulation and discuss the relationship between stratigraphic classification and hydrocarbon accumulation.The Palaeogene in West Damintun Sag of Liaohe basin includes Fangshenpao Formation,Shahejie Formation and Dongying Formation,which were deposited with fluvial and lake faices.Further study suggested that two sequences can be found in Paleogene of Damintun Sag.Sequence ? is compose of S33 and S34,while Sequence ? includes S31 and Dongying Formation.Sequence ? can be further divided into transgressive system and highstand system that comprises the upper section and the lower section.Es34 is dominated by interbedded sand-shale intervals with wide extension of sandstone.Es33,Es32 and Es31 is interbeds of glutenite,sandstone and mudstone in different thickness.However,governed by the deposition environment,sandstone and mudstone content varies between the south and the north with high sandstone content in the north and high mudstone in the south.The comparison between system tract and source rocks,reservoir and cop rocks suggests that source rocks were deposited in transgressive system tract,reservoirs developed in the lower section of the highstand systems tract with alluvial fan-fan delta-shallow coastal lake deposits and meandering river-delta-shore shallow lake deposits.Also,source rocks developed in the transgressive system also an important regional caprock for Palaeozoic hill pools.While the bottom of the upper part in highstand system is other regional caprock for corresponding reservoir.Low sandstone content in high-waxy-oil source system and thick mudstone in upper Es41 lead to two main oil migration patterns,including source to buried hill and source-faults-Es3 sandstone.Normal-oil source systems are characterized by interbeded mudstone and sandstone,which results in short migration of hydrocarbon from source rocks to sandstone through fault,fractures and accumulation in corresponding reservoirs.