The Accumulation Process Of Primary Oil And Gas In The Meso-neoproterozoic Sedimentary Strata,Jibei-Liaoxi Area

In this paper,the geochemical characteristics of the oil seepages/asphalts from Jibei-Liaoxi area were systematically studied using organic geochemical analysis methods,and the oil-source correlation was subsquently carried out.Atfer that,the hydrocarbon generation history of the Mesoproteroic source rcoks and the hydrocarbon accumulation history of the primary paleo-reservoirs were studied,based on the reconstruction of regional sedimentary burial-thermal history and the homogenization temperature measurement of fluid inclusions in reservoirs.According to the composition characteristics of molecular markers,the oil seepages/asphalts can be divided into two types:Type I includes the solid bitumen from Xiamaling Formation(Fm)of Longtangou area and the oil seepages from Tieling Fm of Shuangdong area,Tieling-Wumishan Fm of Jiqian 1 Well and Tieling Fm of Jiqian 2Well,as well as the oil sands from the lower part of Luotuoling Fm in Han 1 Well;Type II oil sands includes Wumishan Fm of Xinglong 1 Well and the upper part of Luotuoling Fm in Han 1 well.The type I oil seepages/asphalts are characterized by extremely low relative contents of Pristane(Pr)and phytane(Ph),moderate content of C₂₀ regular tricyclic terpanes(C₂₀TT)and C₁₉TT,and high abundance of tetracyclic terpanes(C₂₄Te T),norneohopanes(Ts and C₂₉Ts)and rearranged hopanes(C₃₀Dia),with an absence of steranes.Compared to Type I,Type II oil seepages/asphalts have moderated abundance of pristane,phytane and sterane.The distribtion of tetracyclic terpanes and hopanes in Type II seepages/asphalts is similar with typical marine carbonate rocks,such as low content of C₂₄Te T and rearranged hopanes,high content of regular hopane(C₂₉H and C₃₀H),and absence of 13?NATT and drimane series.Oil-rock correlation shows that Type I oil seepages and asphalts should mainly come from Hongshuizhuang Fm source rocks,while the organic geochemical composition characteristics of Type II asphalt sandstone are very similar to Gaoyuzhuang Fm carbonate rocks.The evolution of heat flow history can be divided into four stages:gently declining period(Jxg-Qnj),rising period((?)-T),peak period(J-K)and declining period(E-Q).The analysis results of burial and thermal history showed that the sourced rocks of Gaoyuzhuang Fm entered the hydrocarbon generation threshold at the sedimentary period of Wumishan Fm,and reached the hydrocarbon generation peak at Xiamaling sedimentary period,and entered the gas generation stage in the early Paleozoic with the geothermal flow rising rapidly.The sourced rocks of Hongshuizhuang Fm began to generate large amounts of hydrocarbon in Triassic and ended after Yanshanian period due to the decrease of temperature.The results of fluid inclusions analysis showed that the sandstone reservoir of Luotuoling Fm in Han 1 Well undergone two stages of hydrocarbon accumulation.The corresponded temperature are 100?110?and 140?160?,respectively.The results showed that the Liaoxi Depression has experienced two stages of hydrocarbon generation and three stages of hydrocarbon accumulation.The first stage of hydrocarbon generation occurred at the depostional period of Xiamaling Fm and was contributed from Gaoyuzhuang Fm source rocks,forming paleo-reservoirs of Xiamaling Fm,Tieling Fm and Wumishan Fm.To early Paleozoic,tectonic movement destroyed the paleo-reservoirs formed and resulted in hydrocarbons migrating from Wumishan and Xiamaling Fm up to Luotuoling Fm along faults;The second stage of hydrocarbon generation occurred from Triassic to Jurassic and was contributed from Hongshuizhuang Fm rocks.,and oil and gas were charged into the Xiamaling Fm,Tieling Fm,Wumishan Fm and lower part of Luotuoling Fm.Since then,The formed oil reservoir experienced Yanshanian movement II and thus was adjusted,reformed or even destroyed,whereas some of them may be preserved in traps before Yanshanian period.