Geochemical Characteristics Of Meso-proterozoic Source Rocks And Evaluation Of Hydrocarbon Generation Potential In Liaoxi Depression

Liaoxi Depression,with wide occurrence of Mesoproterozoic marine carbonate successions,belongs to the north China craton.It is one of the potential hydrocarbon prolific depressions in this region.Based on detailed geochemical analyses and basin modeling,this study systematically described the geochemical characteristics of source rocks and the history of hydrocarbon generation.The results show that the potential source rocks of Meso-Proterozoic in the Liaoxi Depression are Hongshuizhuang Formation and Gaoyuzhuang Formation,which are characterized by the dominance of type I-II₁ kerogen,as well as in the stage of maturity-high maturity.Due to the limited areal distribution range and relatively low maturity(Ro?0.6%),the Neo-Proterozoic Xiamaling Formation in this region is not active source rocks.The Tieling Formation and Wumishan Formation are not effective source beds in the study area due to their low TOC content.According to the compositions of molecular markers of the rock,the source rocks can be divided into two types.The type I is the source rock of Xiamaling Formation-Hongshuizhuang Formation,which has high content of secohopane,high content of Ts,C₂₉Ts and C₃₀ rearrangement hopanes,high content of drimanes,entire series of 13?-n-alkyl tricyclic terpenes and low or non-regular steranes.The type II is the source rock of Gaoyuzhuang Formation,which has low content of secohopane,low content of Ts,C₂₉Ts and C₃₀ rearrangement hopanes,low content of drimanes,no 13?-n-alkyl tricyclic terpenes and low or entire series regular steranes.In addition,the sedimentary environment of meso-proterozoic source rocks in this area is mainly marine reductive sedimentary environment,and the organic matters were composed of lower aquatic organisms mainly algae and bacteria.Furthermore,the basin modelling was used to reconstruct the stratiggraphic-burial history,heat flow history and hydrocarbon generation history in this area to determine the hydrocarbon generation potential of source rocks.The result shows that there are two phases of hydrocarbon generation in this area.The source rocks of the Gaoyuzhuang Formation entered the hydrocarbon generation threshold in the middle of the deposition period of the Wumishan Formation,and reached the peak of hydrocarbon generation rapidly in the sedimentary period of Xiamaling Formation.The heat flow rose in the early Paleozoic and quickly entered the gas generation stage.The source rocks of the Hongshuizhuang Formation began to generate a large amount of hydrocarbons in the Triassic period.After the Yanshanian erogeny,due to the lower formation temperature experienced by the Hongshuizhuang Formation,the hydrocarbon generation process ceased and the ultimate maximum cumulative oil generation intensity was greater than that of the Gaoyuzhuang Formation,which is the main source of current liquid hydrocarbon accumulations.