Development And Distribution Of The Main Neoproterozoic Source-reservoir Strata In The Yangtze Block

Neoproterozoic petroleum first made breakthroughs in the Sinian Dengying Formation in the Yangtze block.However,there are few studies on the Neoproterozoic source-reservoir strata in the entire Yangtze plate.Through the study of the developmental characteristics and distribution law of Neoproterozoic source-reservoir strata,it can provide useful reference for the exploration of deep oil and gas in the Yangtze block.In this thesis,through the field exploration and sampling of Neoproterozoic stratigraphic sections in the Yangtze plate,analysis of source rock and casting of reservoir thin sections.Then the organic geochemical characteristics of source rock,reservoir characteristics and the distribution law of the main source-reservoir strata,finally,the typical Neoproterozoic oil and gas reservoirs were dissected,and the favorable areas were further predicted.There are three sets of main source rocks in the Neoproterozoic strata of the Yangtze block:the Datangpo Formation,the Doushantuo Formation and the third member of Dengying Formation.The source rocks of the third member of Dengying Formation are poor source rocks grade,and the source rocks of the Doushantuo Formation and Datangpo Formation are good source rocks grade.Third member of Dengying Formation and Doushantuo Formations source rock type is sapropelic?;the Datangpo Formation is saprolite II₁;Source rock of Third member of Dengying Formation have reached the stage of over-maturation,the Doushantuo Formation and Datangpo Formation entered the stage of thermal metamorphism.From top to bottom,the thermal evolution of the three sets of source rocks increases in turn.The distribution of n-alkanes and its parameters in the three sets of source rocks of the Neoproterozoic are mainly affected by thermal evolution,which can not reflect the original hydrocarbon-generating parent materials.third member of Dengying Formation,the Doushantuo Formation and the Datangpo Formation source rocks are all formed in the reducing environment;and the original hydrocarbon-generating parent materials are mainly lower aquatic organisms such as algae,and the age was more new,the algae are more dominant.It may suggest the gradual growth of the blue-green algae in the Neoproterozoic.The thickness of the source rock of the Datangpo Formation is located in the Xiushan area of Chongqing and the Tongren area of Guizhou,the thickness is rapidly thickened from50m,and the thickness of the extension center is rapidly thinned outward.One thickness center of the source rocks of the Doushantuo Formation is located in the northern part of the Upper Yangtze,in the southern part of Shaanxi,another thickness center is located in the middle Yangtze,in the west part of Hunan and Hubei,the thickness is greater than 50m,and the center of the thickness is gradually thinned outward.The main reservoir types of the Dengying Formation are microbes dolomite,grain dolomite and granular dolomite,microbial dolomite is a favorable rock type for the Dengying Formation reservoir;the Dengying Formation reservoir space is mainly caves,dissolved pores and cracks;microbial carbonate structure during sedimentation and epigenetic karstification during diagenesis are key factors in reservoir formation.The formation thickness center of Dengying Formation is mainly located in the eastern part of the Sichuan Basin,the Mianyang-Changning rift trough edge and the eastern part of Shennongjia,and the thickness is thinner in the southeast direction.At the same time,the lithology is dominated by dolomite and transitions to siliceous rocks.The reservoir thickness of the lower and upper reservoirs is similar to that of the formation thickness of Dengying Formation,but it is affected by the Tongwan movement,in the western part of the Sichuan Basin,the upper part of the Dengying Formation is abruptly extinct,and the reservoir is gradually progressive to the southeast due to changes in the lithofacies.The JinshaYankong ancient reservoir and the Weiyuan-Gaomo gas reservoir are all based on the Dengying Group dolomite as the reservoir,and the Lower Cambrian is the main source rock.The Weiyuan-Gaomo gas reservoir has the contribution of Sinian Doushantuo and third member of Dengying Formation;the hydrocarbon generation center adjacent to the rift trough or the passive continental margin and the karst hilly reservoir are the key elements of hydrocarbon accumulation.The later tectonic evolution has decided the preservation,adjustment and destruction of the reservoir.According to the proximity of the rift trough or the passive continental margin hydrocarbon generation center,adjacent to the Dengying Formation karst hilly reservoir,and the late structural stability,the northeastern Sichuan region is predicted to be a favorable area for the conventional oil and gas of the Dengying Formation;According to the principle of thickness of the shale single layer is more than 50m,the thickness of the shale single layer is above 50m,the thermal evolution degree is below2.5%,and reservoir conditions is good,the western part of Hunan and Hubei is a favorable area for shale gas in the Doushantuo Formation.