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Tufa character and its oil gas significance of Ordovician outcrops in the northwest margin of Tarim Basin
NIU Yong bin1,2, ZHONG Jian hua1, WANG Pei jun1, CHEN Xin1, LI Jia1
(1. College of Geo Resources and Information in China University of Petroleum, Qingdao 266555,China;2.Key Laboratory of Biology Trace and Mining Process of Henan Province, Jiaozuo 454003,China)
Abstract:
By using methods of rock slice, thin section analysis and porosity and permeability testing, the tufa sedimentary characteristics were studied, and the origin of tufa were analyzed through the analysis of geomorphology and karst dynamics. The samples were collected from Ordovician outcrops in the fifth track of Bachu county and Keping sulfur gulch based on field observation. The results show that the tufa deposition is a good kind of reservoir with high porosity and permeability. The origin of tufa of Ordovician in the fifth track of Bachu county is that the fresh water which was rich in CO2 corroded limestone, then the underground river produced. When the karst water flowed out of the underground river, CO2 escaped and CaCO3 deposited largely in the marsh of epicontinental margin with the pressure declining and the temperature rising. The origin of tufa sedimentation of Ordovician in Keping sulfur gulch is that fracture corroded to enlarge into karat cave, then tufa formed as CaCO3 deposited by stage.
Key words:  Tarim Basin  Ordovician  tufa sedimentation  carbonate rock  karst