Study on the period and time of oil and gas accumulation in the Shiwu fault depression of the southern Songliao Basin,China

The time of petroleum accumulation in the Shiwu fault depression of the southern Songliao basin is determined according to the studies of structural evolution,hydrocarbon-generating history of source rocks and homogenization temperature of fluid inclusions.The Shiwu fault depression went through five structural movements in all.The most important structural movements are at the end of the Denglouku Formation and Nengjiang Formation.Local traps formed in the two periods. Deep source rocks started to generate oil in the Yingcheng Formation period,reaching the peak in the Quantou formation period.Source rocks started to generate gas in the Denglouku Formation period,reaching the peak in the Qingshankou-Nengjiang Formation period.The homogenization temperature of the organic fluid inclusions in the fissures of sandstone reservoir is 70～80℃, 90～110℃ and 120～140℃.Integrated with the geothermal history and burial history,the formation time of inclusions is about 120 Ma,85 Ma and 72 Ma,respectively.Through analysing the results,the formation of petroleum accumulation in the Shiwu fault depression is divided into three peroids——the end of the Denglouku Formation,Quantou Formation-Nengjiang Formation period and the end of the Nengjiang Formation,respectively.