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The Genetic Mechanism and Evolution Process of Overpressure in the Upper Ordovician–Lower Silurian Black Shale Formation in the Southern Sichuan Basin

by Xiaoqi Wang 1,2,3 and Yanming Zhu 1,2,*
1
Key Laboratory of Coal Bed Methane Resource & Reservoir Formation Process of the Ministry of Education, China University of Mining & Technology, Xuzhou 221116, China
2
School of resources and earth science, China University of Mining & Technology, Xuzhou 221116, China
3
The EMS Energy Institute and Leone Family Department of Energy and Mineral Engineering, The Pennsylvania State University, University Park, State College, PA 16802, USA
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(3), 238; https://doi.org/10.3390/min10030238
Received: 25 January 2020 / Revised: 2 March 2020 / Accepted: 3 March 2020 / Published: 6 March 2020
The overpressure phenomenon is a widespread occurrence in unconventional shale gas reservoirs. Multiple overpressure shale gas fields were discovered in southern China, and there is no doubt that the gas production per well increases with increasing pressure coefficient (the ratio of the reservoir fluid pressure to the corresponding normal hydrostatic pressure). Thus, successful evaluation and production strategies of organic-rich shale deposits require an understanding of the evolution of the pressure coefficient and its controlling factors in these deposits. In this paper, drilling engineering data of a typical well were collected, and clay mineral tests and overburden diffusion coefficient experiments were conducted. Based on multiphysics simulations, this paper analyzes the overpressure characteristics and formation mechanisms of overpressure in the Longmaxi Formation shale, as well as its geological evolution and controlling factors. The results show that the large amount of shale gas is the cause of overpressure formation rather than disequilibrium compaction. The simulation results show that pressure coefficients of the typical well range from 0.84 to 1.49. The current pressure coefficient increases with increasing pressure coefficient after the last hydrocarbon generation. A large initial pressure coefficient (>1.9), short lifting time (<100 Ma) and small lifting amplitude (<4000 m) are favorable for the preservation of shale gas. View Full-Text
Keywords: gas shale; stress sensitivity; genetic mechanism of overpressure; diagenesis of shale; overpressure evolution; southern Sichuan Basin gas shale; stress sensitivity; genetic mechanism of overpressure; diagenesis of shale; overpressure evolution; southern Sichuan Basin
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Wang, X.; Zhu, Y. The Genetic Mechanism and Evolution Process of Overpressure in the Upper Ordovician–Lower Silurian Black Shale Formation in the Southern Sichuan Basin. Minerals 2020, 10, 238.

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