Characteristics Of The Source Rocks In Nangqian-Qamdo Area,Eastern Tibet:Implications For Unconventional Oil And Gas Resources

The Tibetan Plateau is the largest under-explored regions of hydrocarbon resources in China,and there are a large number of marine and continental petroliferous basins.The Nangqian-Qamdo area in eastern Tibetan has proven to be of promising prospects,however,the hydrocarbon potential is still remain to explore.In this study,we aim to fill the gap and determine the potential of source rocks in this area by using a variety of methods.Based on the previous research,several sections were measured for the most potential strata and the source rock samples were collected systematically during the field work.According to facies analysis,the Qamdo area is a result of multi-stage evolution from Late Permian to Cenozoic,and the sea level change play a significant role in the formation of sick and widespred black shales in the Qamdo Basin.The organic petrological and organic geochemical methods were used to determine the kerogen type,organic matter richness and thermal maturity of the collected samples.Consequently,we draws the following results: 1)Tuoba Formation with highest total carbon content followed by Adula Formation and Duogala Formation,these three Formations are considered to be good-mid hydrocarbon source rocks according to evaluation criterion;the source of organic matter in terrestrial plants;the organic matter thermal evolution of hydrocarbon source rocks is higher,and it is in the stage of high maturity and over maturity;the maceral composition and elemental analysis of kerogen indicate the organic matter in the samples from the Qamdo Basin are belong to Type?2-?;Vitrinite reflectance(Ro)results suggest that the samples are at a stage of high to over maturity.Samples from the Gongjue Formation in the Nangqian Basin show a high abundance of organic matter with an average TOC of 5.22%.The kerogen are belong to ? or ? 1,suggesting that the source of organic matter is mainly derived from lacustrine algae or bacteria.The samples are thermally immature or at the early stage of maturity.The biomarker indicators reveal that the Gongjue oil shale was deposit under anoxic,reducing and saline paleoenvironment.We put forward that the Qamdo basin has reached basic requirements for shale gas exploration on the basis of its considerable thickness,high maturity and widely distribution black shale in the Tuoba,Adula and Duogaila Formations.Isothermal adsorption experiments reveals that the rock sample had better adsorption performance,and the mineral composition are also in favor of the development of shale gas in the process of hydraulic fracturing.Therefore,unconventional gas resources exploration is the future research goal and direction of the Qamdo Basin.Finally,this paper also aims to estimate the amount of resources of the shale gas in Qamdo Basin by using Probability Volume method.The Qamdo Basin turn out to be of good prospects with considerable reserves and exploitable reserves,approximately136.74×108m~3 and 17.51×10~8m~3,respectively.