Differential Accumulation Of Oil And Gas Reservoirs In Mesozoic And Paleozoic Buried Hills Of Huanghua Depression

This paper focuses on the the Mesozoic and Paleozoic buried hill reservoirs in Huanghua Depression,and the representative reservoirs in Huanghua Depression were analyzed with the utilization of geology,geophysics,geochemistry data,combining with thin section and physical simulation experiment of hydrocarbon migration and accumulation.On the basis of summarizing the combined features of hydrocarbon accumulation elements,the law of hydrocarbon enrichment and its main controlling factors were analyzed,and the favorable areas for oil and gas exploration were predicted.The buried hill hydrocarbon reservoirs of the Mesozoic and Paleozoic in the Huanghua Depression can be divided into “new generation and old accumulation” reservoir and “old generation and old accumulation” reservoir.The “new generation and old accumulation” reservoir is the reservoir that oil generated in young strata and accumulated in old strata,while the “old generation and old accumulation” reservoir is the reservoir that oil generated in old strata and accumulated in old strata.The “new generation and old accumulation” reservoirs mostly distributed in the north of Huanghua Depression and mainly consisted of ancient landform buried hills and fault block landform buried hills.To this kind of hill,Paleogene source rocks served as the main source of oil and gas.Crude oil migrated laterally through basement faults,sand bodies,and the unconformities at the top of the weathering crust reservoirs,then accumulated in the top of Ordovician.The “old generation and old accumulation” reservoirs are mostly distributed in the south of Huanghua Depression and mainly consist of anticlinal buried hills and thrust fault buried hills.To this kind of hill,Carboniferous-Permian coal served as the main source of hydrocarbon,and oil and gas migrated to Ordovician or Permian through overthrust faults.The Mesozoic formations were dominated by oil and mostly distributed in the south of the depression.The upper Paleozoic formations were dominated by oil and mostly distributed in Kongdian and Koucun areas.The Lower Paleozoic formations were dominated by gas and distributed in the whole depression.The distribution of oil and gas in the Mesozoic and Paleozoic of Huanghua Depression shows up partitioning delamination,and that oil is mainly in the south and gas is mainly in the north,while oil is mainly in the upper fomations and gas in lower.The main controlling factors of hydrocarbon accumulation in the “new generation and old accumulation” buried hill reservoirs were the “ancient high and current low” negative reversal and the fractures.The negative reversal was favorable to the development and preservation of middle and low order buried hill karst reservoirs in the north of Huanghua Depression,and the fractures provided a good migration path and excellent source storage configuration for oil and gas.The main controlling factors of hydrocarbon accumulation in the “old generation and old accumulation” buried hill reservoirs were high-mature coal-bearing source rocks in Carboniferous-Permian determine the enrichment of primary reservoirs,and the existence of an overpressure layer in the coal-bearing source rocks provided favorable conditions for the migration and preservation of oil and gas.The favorable exploration direction of “new generation and old accumulation” buried hill reservoirs is mainly in karst and fracture developmental areas in Qikou and Cangdong Depression.The favorable exploration direction of “old generation and old accumulation” buried hill reservoirs is mainly in areas where the coal-bearing source rock is highly mature,the buried time is late and the reform strength is weak.