Sedimentary Characteristics And Petroleum Geological Significance Of Carboniferous In The Eastern Qaidam Basin

In order to research Carboniferous strata sedimentation and petroleum geology basic features in the eastern Qaidam basin,the article apply the theory knowledge of sedimentology,reservoir geology and petroleum geochemistry,integrating field reconnaissance and measurement,describing lithology and indoor experimental analysis,and then,it established Carboniferous strata sedimentation mode in the eastern Qaidam basin,discussed the facies' longitudinal evolution discipline and plane distribution feature,restored Carboniferous palaeogeographic environment,divided source-reservoir-cap rock association relation,and revealed source,reservoir and cap rock plane distributive characteristics.Carboniferous system in the eastern Qaidam basin including lower Carboniferous chengqianggou formation,Huaitoutala formation,and upper Carboniferous Keluke formation,Zhabusagaxiu formation.In lower Carboniferous,there have two obvious sedimentary cycles of transgressive detrital shore-carbonate platform,it main develop gritty detrital shore at the bottom of the cycle,while forming large sets of carbonate platform and bioclastic beach at the upper.Upper Carboniferous is the epicontinental sea sedimentary environment,the sea level changes frequently,the lithology is composed by limestone and mudstone,including a small amount of lamina coal streak.Five kinds of sedimentation types are divided in the eastern Qaidam basin.Alluvial fan,gritty high-energy detrital shore,mixed product low-energy argillaceous detrital shore and neritic continental shelf.It is composed by a variety of sedimentary facies,including alluvial fan facies,platform facies,platform edge reef facies,littoral facies,tidal flat-lagoon-barrier island and fan-delta facies.Early Carboniferous epoch,the south of eastern Qaidam basin Amunike mountain-Guanjiaoya develop Continental alluvial fan-littoral facies.The areas of Shihuigou-Chengqianggou-Wanggaxiu develop tidal flat,platform and Platform edge shoal facies.After transgression in late Carboniferous epoch,research area shift to shallow oceanic carbonate platform-platform edge shoal facies,and in some special areas like Shihuigou,Wanggaxiu,it develop tidal flat-lagoon-barrier island marine-continental transitional facies.In Huobuxun depression of the south of the basin,it hardly occurs.Research areas Carboniferous source rock mainly located in Ounan depression's Shihuigou and Delingha depression's Wanggaxiu,the lithology is dark mudstone which develop tidal flat-lagoon facies,the organic carbon content is abundant.Carbonate reservoir is composed by bioclastic limestone,it has good porosity and permeability,most of them located in Chengqianggou-Gahainanshan,Huaitoutala formation.Clastic rocks reservoir is composed by fine siltstone-sandy conglomerate which develop Upper Carboniferous tidal-flat facies,fan deltaic facies,it located in Shihuigou-Chengqianggou-Wanggaxiu areas.Shale cap rocks mainly develop in Ounan-Delingha depression.However,upper strata of Carboniferous have a large thickness,so it may be an effective cap rocks.