Abstract
Sampled from the Gangxi oil field in the Huanghua depression, Bohaiwan Basin, the crude oil He and Ar isotopic compositions and their geochemical significance were investigated. The result shows that i) the 3He/4He values of the six oil samples free from air contamination indicate a mantle helium contribution ranging between 13.9% and 32.8% and averaging 24.1%, which means that the Gangxi oil field once had a tectonic background of the mantle-derived helium input and higher geothermal flow with an average of 75.0 mWm-2; ii) deduced from the 40Ar/36Ar aging effect the Gangxi oil should be derived from the Tertiary; iii) water injection is the main reason for the air contamination for the Gangxi oil noble gases and the relations between 3He/4He and 4He/20Ne as well as 40Ar/36Ar and 4He/20Ne are of an applicative potential in estimating the water injection effect and the connectivity of producing formations. The search for the crude oil He and Ar isotopes provides a new approach to inferring natural gas and oil sources, tectonic backgrounds, geothermal flow and water injection effect.
Highlights
Noble gases in natural gas have been widely applied in identifying natural gas genesis (Jenden et al, 1989; Xu Yongchang et al, 1996a), migration (Torgersen and Kennedy, 1999; Bat-Zhang Xiaobao, Ma Liyuan, Chen Jianping, Sun Mingliang, Tu Jianqi, Li Xiufen and Song Chenpeng which greatly changed the Pre-Mesozoic tectonic framework of China by subduction of the Pacific plate under the Asia-Euro plate (Tao Mingxing et al, 1996; Xu Yongchang et al, 1998)
The purpose of this paper is to report He and Ar isotopic values of the oil-dissolved gases and to discuss their application in tracing natural gas source, tectonics, geothermal flow and oil
The research shows that: i) The 3He/ 4He ratio of the six crude oils from the Gangxi oil field is characteristic of a mantle contribution
Summary
Noble gases in natural gas have been widely applied in identifying natural gas genesis (Jenden et al, 1989; Xu Yongchang et al, 1996a), migration (Torgersen and Kennedy, 1999; Bat-Zhang Xiaobao, Ma Liyuan, Chen Jianping, Sun Mingliang, Tu Jianqi, Li Xiufen and Song Chenpeng which greatly changed the Pre-Mesozoic tectonic framework of China by subduction of the Pacific plate under the Asia-Euro plate (Tao Mingxing et al, 1996; Xu Yongchang et al, 1998). Noble gases in natural gas have been widely applied in identifying natural gas genesis (Jenden et al, 1989; Xu Yongchang et al, 1996a), migration After the movement China could be tectonically classified into the Eastern Rift Tectonically Active Area, the Middle Craton Tectonically Stable Area, the Western Tectonically Substable Area, and the Qinghai-Tibet Plate Collision Compression Area (Tao Mingxing et al, 1996; Xu Yongchang et al, 1998), of these areas the Eastern Rift Tectonically Active Area could be further separated into the Near-shore Rift System and the Cathaysion Rift System by the Tancheng-Lujiang deep fault belt (Tao Mingxing et al, 1996; Xu Yongchang et al, 1998) The Near-shore Rift System is located to the east of the Tancheng-Lujiang deep fault belt and the Cathaysion Rift System to the west.
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