Geochemistry and charge history of oils from the Yuqi area of Tarim Basin, NW China. (January 2017)

• Record Type: Journal Article
• Authors: Song, Daofu; Wang, T.-G.; Li, Meijun; Zhang, Jianfeng; Ou, Guangxi; Ni, Zhiyong; Yang, Fulin; Yang, Chengyu
• Is Part Of: Marine and petroleum geology. Volume 79(2017)
• Page Start: 81
• Page End: 98
• Publication Date: 2017-01
• Subjects: Tarim basin -- Tabei uplift -- Yuqi area -- Crude oils -- Geochemistry -- Oil charge history; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2016.11.004
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: The geochemistry, origin and charge history of oils from the Yuqi area of Tarim Basin have been investigated, through GC, GC-MS and fluid inclusion microthermometry analysis. The Yuqi oils accumulated mainly in three intervals: (1) in the Lower-Middle Ordovician Yingshan Formation (O1-2 y ) carbonate reservoirs; (2) in the overlying Upper Triassic Halahatang Formation (T3 h ); and (3) in the Lower Cretaceous Yageliemu Formation (K1 y ) sandstones. Oils from different reservoirs have distinct physical properties, varying from extra-heavy (O1-2 y), heavy (T3 h ), to light oils (T3 h and K1 y ). However, their geochemical compositions show a high degree of similarity, which indicates that they derive from the same source rock. Abundant tricyclic terpanes, gammacerane, dibenzothiophene and C21 C22 steranes, together with a low level of diasteranes, indicate an anoxic marine source rock for oils in the Yuqi area. Oil-oil correlation shows that Yuqi oils derive from the same source bed as Tahe oils. The co-occurrence of intact n -alkanes and 25-norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil. In this study, charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1D burial-thermal history models. Two episodes of oil charging are identified in the O1-2 y reservoir (well YQX1-1) at around 436-420 Ma (Middle-Late Silurian) and 10-3 Ma (Miocene to Pliocene), respectively. For the samples from the T3 h and K1 y intervals, only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10-3 Ma. The T3 h heavy oil reservoir is assumed to be a secondary hydrocarbon pool, which accumulated by re-migration and re-distribution of hydrocarbons from O1-2 y hydrocarbon pools. The few early biodegraded oils in the K1 y light oils were probably picked up along the migration pathway during the late fresh oil charging. Highlights: Yuqi oils derive from the same source bed as Tahe oils. Geochemical compositions indicate an anoxic marine source rock. Yuqi oils are a mixture of early filled biodegraded oil and late filled fresh oil. Different oil accumulation processes resulted in the different physical properties.