Water Distribution in the Ultra-Deep Shale of the Wufeng–Longmaxi Formations from the Sichuan Basin

Ping Gao, Xianming Xiao, Dongfeng Hu, Ruobing Liu, Yidong Cai, Tao Yuan and Guangming Meng
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Ping Gao: School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
Xianming Xiao: School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
Dongfeng Hu: Sinopec Exploration Branch Company, Chengdu 610041, China
Ruobing Liu: Sinopec Exploration Branch Company, Chengdu 610041, China
Yidong Cai: School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
Tao Yuan: Sinopec Exploration Branch Company, Chengdu 610041, China
Guangming Meng: School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

Energies, 2022, vol. 15, issue 6, 1-17

Abstract: Recently, deep and ultra-deep shales (depth >3500 m) of the Lower Paleozoic Wufeng–Longmaxi formations (WF–LMX) have become attractive targets for shale gas exploration and development in China, and their gas contents may be influenced by the occurrence of water to some extent. However, the water content and its distribution in the different nanopores of the deep and ultra-deep shales have rarely been reported. In this study, a suite of the WF–LMX ultra-deep shale samples (5910–5965 m depth) from the Well PS1 was collected for water content measurements, and low-pressure CO 2 and N 2 adsorption experiments of both as-received and experimentally dried shale samples were carried out to investigate the distribution of water in the different nanopores. Since the studied ultra-deep shales are characterized by higher thermal maturity (equivalent vitrinite reflectance (EqVRo) > 2.5 %) and ultra-low water saturation, the pore water is generally dominated by irreducible water. The content of irreducible water of the studied shales varies from 1.57 to 13.66 mg/g, averaging 6.74 mg/g. Irreducible water may mainly occur in the clay-hosted pores, while it could also be hosted in parts of organic pores of organic-rich shales. Irreducible water is primarily distributed in non-micropores rather than in micropores of the studied shales, which mainly occurs in micopores with a diameter of 0.4–0.6 nm and mesopores with a diameter of 2–10 nm. Very low contents of irreducible water could reduce the specific surface area and volume of non-micropores of the shales to some extent, but the effect of irreducible water on the specific surface area of non-micropores was more significant than the volume of non-micropores, especially for organic-rich shale samples. The ultra-deep shale gas may be predominately composed of free gas, so low contents of irreducible water may play a limited role in its total gas contents. Overall, our findings can be helpful for a better understanding of water distribution in the highly-matured shales, and provide a scientific basis for ultra-deep shale gas exploration.

Keywords: shale gas; irreducible water; pore structure; water distribution (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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