Characteristics Of Paleozoic Source Rocks In The Lower Yangtze And Its Inspirations To Oil And Gas Exploration In South Yellow Sea

Based on the analysis of predecessors' data and the test of new collected samples,the study of source rocks in marine Paleozoic of continental Lower Yangtze is carried out.From the test results,similar to the previous study is that there are four sets of source rocks in the Paleozoic of the continental Lower Yangtze,which are Lower Cambrian,Lower Silurian,Upper Permian and Lower Permian.Among them,the TOC of the Lower Cambrian source rock is between 0.51% and 11.06%,with an average of 3.76%.And the type?kerogen was the main factor,and the maturity was 1.36%-2.07% and the mean value was 1.77%.The comprehensive analysis shows that the Cambrian source rocks belong to the good to very good source rocks.The TOC of Lower Silurian(not conclude the drill samples from Nanjing University)is between 0.02 and 1%,with an average of 0.8%.The type?kerogen is the main factor,and the maturity is 1.12% ~ 1.9%,the mean is 1.56%.Comprehensive analysis that it belongs to the general source rock.The TOC of the Lower Triassic Qixia Formation mudstone sample is between 0.23% and 5.83%.The Lower Permian is mainly type? kerogen;the Upper Permian is dominated by type ? and type ? kerogen;the maturity of Permian hydrocarbon source rocks is between 1.53% and 1.81%,with a mean of 1.71%.It is concluded that the Permian shale source rocks are medium to good source rocks.The difference with the previous study is that the evaluation level of the Lower Silurian source rock may be higher than that of the previous ones.The reason is that Nanjing University in Tangshan drilled three wells,among them the thickness of black mud shale is 52 m in Gaojiabian Formation in Tangshan 2 drilling well,TOC between 1.2-2.5%,maturity between 2.0-2.5%.The thickness of dark gray shale is 80 m in Gaojiabian Formation in Tangshan 3 drilling well,and the TOC is between 1.5-3.0% and the maturity is 1.7-2.6%.It can be seen that the evaluation level of the source rocks of the Lower Yangtze Gaojiabian Formation should be higher than the evaluation level in the past,and the hydrocarbon generation potential may be higher.At present,there are only two drills which drilled Paleozoic source rock in South Yellow Sea,and only drilled Permian.From the TOC,S1 + S2,HI and other indicators of CZ35-2-1 drilling well,Qixia Formation,Longtan Formation and Dalong Formation belongs to the medium to good source rock.Through land and sea contrast and connect the interpretation of the South Yellow Sea seismic data and the analysis and speculation of the South Yellow Sea drilling wells data,the marine Paleozoic in the South Yellow Sea should have four sets of source rocks similar to those of the continental Lower Yangtze,The Lower Cambrian Hetang Formation,the Lower Silurian Gaojiabian Formation,the Lower Permian Qixia Formation,the Upper Permian Longtan Formation and Dalong Formation.Among them,the maturity of the source rocks in the Lower Silurian Gaojiabian Formation is lower than that from the land to the sea,and the reservoir formation conditions have a good trend,which may be an important stratum of oil and gas breakthrough in the South Yellow Sea.