| This paper mainly study on the petroleum geological conditions of the Hoh Xil Basin. Based on the field work and sample-analysis data, this study analyses the geological features of Hoh Xil Basin, as sedimentary strata, construction, source-reservoir-cap combination, etc., and focus on the evaluation of hydrocarbon source rocks in the basin. By the oil route investigating and the section measuring, the different stratigraphic units section are measured, and the basin stratigraphic framework are established. Combining with pre-knowledge and efford, we identify the time-space distribution of sedimentary and construction of the basin preliminarily, analyse and evaluate the conditions of oil and gas of the basin. The main conclusions drawn from this paper are as follows:(1) The study on stratigraphic correlation and sedimentary facies of Hoh Xil Basin shown that Tuotuohe Depression in the south of basin have a great thickness of sedimentary strata, and sustained the longest, deposition started from the Conglomerate fan-delta of lower part of Fenghuoshan Group in the early Eocene to deposited of sandstone and mudstone of lacustrine facies of Yaxicuo Group in the early Oligocene and then to deposited of carbonate of lacustrine facies of Wudaoliang Group in the early Miocene. The Cuorendejia Depression in the central basin which's main sedimentary strata is Yaxicuo Formation. The strata of Yaxicuo Formation deposited in the early Oligocene, which conclude sandy conglomerate of fan-delta facies, sand-shale of fluvial and lacustrine facies, and intercalated by carbonate; th??wer part contains a small amount of the lacustrine facies sand-shale strata of Fenghuoshan Group in the late Eocene, the upper part contains more deposition of lacustrine facies carbonate of Wudaoliang Formation in early Miocene. The upper part of Haidingnuoer Depression in the north of basin is consisted mainly of Wudaoliang Group which's deposition is lacustrine facies carbonate in early Miocenes; the middle part is carbonate of Yaxicuo Group, local contain sandstone and lime clay rock; the lower part is lacustrine facies sand-shale in early Oligocene.(2) Organic matter abundance of source rock of Paleocene-Eocene Fenghuoshan Group in Hoh Xil Basin is low, main type of organic matter isâ…¡1 -â…¡2, the main source rock is in high-mature stage. Organic matter abundance of source rock of Mionece Wudaoliang Formation is low, the main type of organic matter isâ…¡1, the main source rock is in the immature stage. The source rock of Oligocene Yaxicuo Formation, especially grey limestone, charcoal grey oil shale and shale, is belonged to the middle-good range; the type of organic matter is better, mainly in typeâ…¡1, and the main source rock is in the mature stage; so the source rock of Oligocene Yaxicuo Formation is the main strata of source rock in Hoh Xil Basin.(3) During the geological survery of Hoh Xil Basin in the ground, we use the formation or group of Lithostratigraphic unit as the basic scale of classification scheme, based on the data of measure section, to establish there sets of source-reservoir-cap combination from bottom to top.Combinationâ… is located in the middle and lower part of Yaxicuo Formation, the main source bed is thin-middle layer of mudstone and marl which are grey black, reservoir is thin-middle layer medium-fine sandstone, cover is mudstone and gypsum layer. The thickness of source bed of this combination is thin, the grade of source rock is relatively poor, reservoir is thin and sand body is dispersed, we evaluate that it is a poor configuration of source-reservoir-cap.Combinationâ…¡is located in the middle and upper part of Yaxicuo Formation, the source bed is thin-middle layer of grey black mudstone, grey black marl and grey limestone, reservoir is thin-middle layer medium-fine sandstone, cover is mudstone and gypsum layer, forming the combination of source-reservoir-cap is source rocks in the lower part and reservoirs in the upper part. This combination has a certain thickness of source bed, the grade of source rock is common, sand body of reservoir is dispersed, we evaluate that it is a medium-poor configuration of source-reservoir-cap.Combinationâ…¢is located in the top of Yaxicuo Formation and Wudaoliang??mation, the main source bed is the middle layer limestone and oil shale, which are grey black, reservoir is thin-middle layer medium grain sandstone, cover is mudstone and gypsum layer of Yaxicuo formation, regional seal is mudstone-marl of Wudaoliang Formation, forming interbedded source-reservoir-cap combination. The thickness of source bed of this combination is thick, the grade of source rock is better, the thickness of reservoir is thick and the sand body is consecutive, the sealing of the upper gypsum layer is trusted, we evaluate that it is a good configuration of source-reservoir-cap.(4) In the study of geological survey for Hoh Xil Basin, we found a certain scale source rock and the process of hydrocarbon generation and expulsion in Hoh Xil Basin. In addition, we found new oil-soaked limestone of Yaxicuo Formation in Wulanwulahu Depression in the western of basin, the source rock of Tuotuohe Depression which is in the south-eastern of basin is better; through Basin Analysis and Prototype Basin Restoration, we propose that Haidingnuoer Depression of the northern basin have lime source rock of Yaxicuo Formation. Through the comprehensive study on petroleum geology in Hoh Xil Basin, we known that Hoh Xil Basin is one of the important targets of hydrocarbon resource exploration for continental basin of Tibetan Plateau.
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