Deep Hydrocarbon Generation Mechanism And Petroleum System In Bozhong Sag

Deep series of strata,deep water area,and unconventional area are the development trends of oil and gas ex Doration in the wor E.With the deepening of oil and gas ex Doration in the Bozhong Sag of the Bohai Bay Basin,the deep oil and gas ex Doration becomes an irresistible trend.As the deepest hydrocarbon-generating sag in the Bohai Bay Basin,there are multi De hydrocarbon-generating sub-sags and hydrocarbon-bearing u Difts in the Bozhong Sag,which are characterized by the superior hydrocarbon-generating conditions,large resource potential,and low ex Doration degree.Especially in recent years,with the discovery of the B19-6 large gas fie E in a typical continental lacustrine oil-bearing basin,which shows the significance of studying deep hydrocarbon generation mechanism and resource potential in the Bozhong Sag.Therefore,based on the study of the difference of hydrocarbon source rocks in different sub-sags of the Bozhong Sag,the hydrocarbon generation mechanism under the background of high temperature and overpressure in deep strata is discussed,and the petroleum system is analyzed,which is of great theoretical and practical value for deepening the deep petroleum geology and ex Doration.In this paper,the differences of source rocks in different sub-sags is comprehensively evaluated based on the geological and geochemical characteristics;the mechanism of deep hydrocarbon generation and expulsion mechanism is discussed by combining the analysis of natural evolution profile,hydrogenation thermal simulation experiment and the kinetic model of hydrocarbon generation remodified based on the thermal evolution simulation experiment of hydrocarbon generation;the characteristics of temperature fie E and pressure fie E evolution and its influence on hydrocarbon formation are analyzed by means of petroleum system simulation restoring the thermal evolution history;the com Dex petroleum system in Bozhong Sag is classified and described according to the characteristics of multi-source,multi-kitchen,multi-period and mixed-source accumulation;the hydrocarbon migration and accumulation units are divided by means of fluid potential analysis,the resource quantity is evaluated according to the basin simulation results,and the favorable areas are finally predicted.The study shows that there are some differences in terms of strata and sub-sags of the source rocks in the Bozhong Sag.The quality of source rocks of Shahejie formation(Fm.)is better than that of Dongying Fm.vertically.High quality source rocks are mainly developed in the third member of Shahejie Fm.(E₂s₃),the first and second member of Shahejie Fm.(E₃s₁₊₂),and the third member of Dongying Fm.(E₃d₃),and the quality of source rock in the lower second member of Dongying Fm.(E₃d₂^L)is the worst.While on the Dane,the source rocks in the main sub-sag are obviously better than those in the other sub-sags.The thermal evolution simulation of the source rocks shows that the organic matter of the source rocks in the center of Bozhong Sag matures early and has a high maturity,and it is generally in the gas generation stage;while the maturity of source rocks in the high part of the structure around Bozhong Sag is low,and mostly in the oil generation stage.High temperature in deep strata is beneficial to hydrocarbon generation and cracking of organic matter,and overpressure is beneficial to hydrocarbon expulsion and migration.The cracking conversion rate of the crude oil is affected by high temperature and decreases with the decrease of temperature from E₂s₃ to E₃d₂^L.Overpressure generally exists in the deep mudstone,which shows a decreasing trend from the center of the depression to the periphery,which cou E promote the migration of oil and gas from the hydrocarbon generation center of the depression to the peripheral bulge.At present,there is a high excess pressure in the deep strata,which is the driving force for the continuous migration and accumulation of oil and gas.The hydrogenation thermal simulation experiment and previous studies show that there is hydrogenation effect in the high heat flow area(>70m W/m²)near the deep and large fault zone,which significantly increases the hydrocarbon generation potential of source rocks(up to 2.8 times).The com Dex petroleum system in Bozhong Sag is divided into four petroleum systems according to the number of mature source rocks.On the Dane,each petroleum system can be further divided into main sag to north sag sub-petroleum system,west sag sub-petroleum system and southwest sag sub-petroleum system according to the distribution of fluid potential.The accumulation condition of lateral migration and expulsion is better than that of vertical migration and expulsion.There is a huge resource potential and favorable ex Doration prospect in the Bozhong Sag,and the main sub-sag is the main hydrocarbon sup Dy area.The dominant accumulation areas of deep oil and gas are concentrated in B13/19,B21-22,D7-1,427 buried hill and 428 buried hill structures.