Sedimentary Characteristics And Evaluation Of Hydrocarbon Potential Of Upper Jurassic Shamuluo Formation In The Nima Area,Tibet

The Nima area is located in the middle of the Qinghai-Tibet Plateau.The north is the Qiangtang Basin,south is the Cuoqin Basin,east is the Lunpola basin,west is the Dongcuo Basin.The formation of the Cenozoic strata in the Nima basin is mainly continental facies,and the basement is Jurassic marine strata.The marine strata of the Shamuluo formation are widely distributed in the study area.This paper starts from the perspective of sedimentology,First,We Through field investigation,the purpose is to find out the sedimentary facies and environmental evolution characteristics of the shamuluo formation.Next,Through indoor analysis of samples,we can solve the problem of oil generating potential of the upper Jurassic Shamuluo formation.The main content of this study is the division of sedimentary facies and evaluation of hydrocarbon generation potential of the Shamuluo formation.On the basis of the existing data collection,combined with field survey,rock slice identification and sample analysis,the sedimentary environment and source rock grade of the shamuluo formation are synthetically analyzed.We have obtained the following achievements and understanding:?1?According to the characteristics of lithology,color and structure of outcrop,and then combined with thin slice microscopic identification.We divide the Shamuluo formation into four sedimentary facies,They are lagoon facies,foreshore facies,nearshore facies and far shore facies.The foreshore facies can be divided into bioclastic shoal,oolitic shoal and sandy shoal facies according to the assemblage of sediments.?2?According to the geochemical analysis of dark mudstone,the types of organic matter in the formation are mainly I ₂ kerogen and II ₁ kerogen,but the abundance of organic matter varies greatly.Compared with the profile,the source rock abundance on the route point is high,and most of them reach the standard of good source rocks.The peak temperature of rock pyrolysis is mostly between 440⁵40 degrees,indicating that most of the source rocks of the Shamuluo formation reach maturity stage.It is predicted that the Shamuluo formation in the Nima area has good potential for oil generation and is worthy of further exploration.?3?sedimentary environment,sea level rise and decline,paleo basin topography and tectonics play an important role in controlling the development of source rocks.The dark mudstone and carbonaceous shale in the Shamuluo formation are located in two different sedimentary environments,one in the lagoon phase and mostly in cinereus or black;the other is in the far shore and mainly with gray or celadon.The study shows that the source rocks of the lagoon have high organic abundance,good type and high hydrocarbon generation potential,while the source rocks of the far shore are relatively poor.Therefore,in the late study,the source rocks of the lagoon facies should be used as the preferred area for oil and gas exploration except the Paleogene.