Sedimentary Environment And Organic Matter Enrichment Of Shale In Upper Jiufotang Formation,ludong Sag,Kailu Basin

Ludong Sag is a secondary negative tectonic unit located in the east of Lujiapu Depression in Kailu Basin in Chifeng City and Tongliao City,Inner Mongolia Autonomous Region.It is also the first breakthrough area for oil and gas exploration in many sags in Mesozoic basins around the Liaohe.Previous studies on the Jiudongtang Formation in Ludong Sag were very limited.The only studies were from the perspective of source rocks,and they were not regarded as shale reservoir research objects,and the researc Research on its sedimentary paleoenvironment is also very scarce.In this thesis,the shale in the upper member of Jiufotang Formation in Ludong Sag is selected as the research object to study the sedimentary environment organic matter enrichment model based on the geochemistry,rock mineral composition and organic microscopic components,etc.The main understandings are as follows:?1?Five lithofacies of the upper member of Jiufotang Formation in Ludong depression have been divided:Organic rich laminar shale facies,organic rich layered shale facies,organic rich massive mudstone facies,organic siltstone facies and organic rich marlstone facie;The shale in the upper member of the Jiufotang Formation is mainly enriched in three major elements,P₂O₅,Fe₂O₃ and Ca O,as well as three trace elements Mo,Sr and Rb.The enrichment of P₂O₅ and Mo indicates that the life activities of shale during the sedimentary period were very prosperous.?2?The paleoenvironmental conditions of the upper member of the Jiufotang Formation of the shale has been restored.The climate was dry and hot when the shale was deposited.The salinity of the water was high,which was a semi saline-saline water environment.The oxygen content in the water was low which was a reduction condition.The deposition rate was high and the water body was deep,which was a deep lake environment,and the productivity is higher in the sedimentary period.?3?The source and enrichment conditions of organic matter in shale has been analyzed.The organic matter in shale mainly comes from low aquatic organisms,and a small part comes from terrestrial higher plants.The types of organic matter are mainly type?and type?1,and a small part of type?2 and type?.The abundance of organic matter in shale is generally high,which is medium to good source rock,and the organic matter has reached the mature stage entered into the oil window.?4?Paleoproductivity is the main controlling factor of organic matter enrichment.Paleoclimatic conditions and paleosalinity of water body also have a certain impact on the enrichment of organic matter.Dry and hot climate has a certain inhibitory effect on life activities,but it also accelerates the evaporation of water body,making the salinity of water body increase,and high salinity environment leads to the accumulation of organic matter.The formation of salinity stratification interface leads to the oxygen poor condition in the bottom water.At the same time,high salinity water may make some organic matters with osmotic activity formed in some algae and bacteria,and accelerate the growth rate of some algae cells,thus promoting the enrichment of organic matter.The faster deposition rate avoids excessive consumption of organic matter in the sedimentation process.The oxygen poor environment of water body is also conducive to the preservation of organic matter.The conditions finally contributed to the formation of high-quality organic rich shale in the upper member of Jiufotang Formation in Ludong sag.