Physical property distribution law and main controlling factors of shallow crude oil in Bohai Sea
The lower member of the Minghuazhen Formation and the Guantao Formation(shallow formations)are the primary oil-bearing formations in the Bohai Sea.The physical properties of these formations exhibit rapid planar variations.However,there is a shortage of systematic research on the regional planar distribution law of physical properties of crude oil,which impedes the understanding of the distribution law of shallow oil and gas.Regional geological insights and extensive drilling and crude oil analysis data were used to analyze the physical property characteristics of shallow crude oil and investigate the main controlling factors of its distribution law.The research gave some suggestions:①The physical properties of shallow crude oil in the Bohai Sea are markedly different between the uplifted and the depressed areas.The crude oil in the depressed areas is characterized by low density,low viscosity,low content of resins and asphaltene,low sulfur content,and high wax content.Conversely,the crude oil in the uplifted areas exhibits the opposite traits of high density,high viscosity,high content of resins and asphaltene,high sulfur content,and low wax content.②The burial depth,preservation conditions,and migration distance govern the variable distribution of physical properties of the shallow crude oil.Large burial depth,good preservation,and short migration distance weaken the degradation and chromatographic effects on crude oil,which is beneficial for the formation of oil reservoirs with superior physical properties of crude oil.③The conditions of the hydrocarbon source rock significantly affect the physical properties of the shallow crude oil in the marginal depressions of the eastern Bohai Bay Basin.When the hydrocarbon source rock has undergone a high degree of thermal maturation,and the aquatic environment is less saline,it favors the formation of high-quality oil reservoirs characterized by low crude oil density,low viscosity,and low sulfur content.The research results summarize the planar distribution law and controlling factors of physical properties of crude oil in the lower member of the Minghuazhen Formation and the Guantao Formation in the Bohai Sea,which has guiding significance for finding potential zones of shallow high-quality oil reservoirs.
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