Author: ZHAO Difei GUO Yinghai Geoff Wang BAI Wanbei ZENG Chunlin JIAO Weiwei LIU Jing | Time: 2020-01-10 | Counts: |
doi:10.16186/j.cnki.1673-9787.2020.1.4
Received:2019/06/01
Revised:2019/07/15
Published:2020/01/15
Sedimentary characteristics of shales graptololite and its implications for high-quality shale gas reservoirs in the Wufeng-Longmaxi formation insoutheast Chongqing
ZHAO Difei1,2,3,4, GUO Yinghai1,2, Geoff Wang5, BAI Wanbei1,2,6, ZENG Chunlin3,4, JIAO Weiwei3,4, LIU Jing1
1.School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116 , Jiangsu, China;2.Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221008 , Jiangsu, China;3.Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120 , China;4.National and Local Joint Engineering Research Center of Shale Gas Exploration and Development, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120 , China;5.School of Chemical Engineering, University of Queensland, Brisbane 4072 .Australia;6.Institute of Resounces and Environment, Henan Polytechnic University. Jiaoz'uo 454000 ,Henan, China
Abstract:Graptolites are the major fossil types of paleontology in the Wufeng-Longmaxi formation shale in China. Taking YC-4, QQ-1 , YC-6 and YC-8 wells in southeastern Chongqing area as examples, combined with hand specimen observation, core research and reservoir laboratory test, comprehensive study of sedimentary characteristics of graptololite, the sequence of graptolite zone, significance of the sedimentary environment of graptolite and its reservoir significance were conducted in the Wufeng-Longmaxi formation shale reservoirs. The results showed that the shale graptolites of the Wufeng Longmaxi formation in southeastern Chongqing were mainly preserved between bedding planes in the form of thin-film organic matter. The shale graptolites fauna of the Wufeng formation transited from the dicellograptus-diplograptus fauna to the late didymograptus fauna. It was a monograptolithic fauna during the sedimentary period of the Longmaxi formation. The sequence of graptolite zone in southeastern Chongqing was established through the drilling study ,3 and 6~8 graptolite zones were identified in the Wufeng formation and Longmaxi formation respectively, which provided a time frame for reservoir fine comparison and evaluation prediction. Controlled by sedimentary environment and sedimentary conditions ,graptolites of Wufeng-Longmaxi formation experienced evolutionary characteristics of extinction , re-evolution and structural complexity during sedimentary period, in which its graptolithic structure, evolution, abundance ,occurrence state and sedimentary mode had changed. The orientation of upward graptolites increased, its abundance decreased, and structural preservation integrity declined, which had the significance of environmental indication. Graptolithic organic matter not only developed abundant organic pore, but also had the function of shale gas seepage channels as a part of sedimentary structure of horizontal bedding of grapholite-rich shales. In conclusion, sedimentary and structural characteristics of graptolites in marine shales could be used as an indicator to predict the distribution of high-quality shale reservoirs, which had geological significance of shale gas.
Key words:southeast Chongqing;Wufeng-Longmaxi formation;shale gas reservoir;graptolite sedimentation;graptolite sequence;sedimentary environment