Pore structure variations across structural deformation of Silurian Longmaxi Shale

an example from the Chuandong Thrust-Fold Belt

Hongjian Zhu, Yiwen Ju*, Cheng Huang, Kui Han, Yu Qi, Mengyan Shi, Kun Yu, Hongye Feng, Wuyang Li, Liting Ju, Jin Qian

*Corresponding author for this work

    Research output: Contribution to journalArticle

    21 Citations (Scopus)

    Abstract

    Pore types and pore size vary systematically across structural deformation in the shale gas reservoirs but lack a comprehensive study. Twelve Longmaxi Shale samples spanning a tectonism range from undeformed to deformed were formed in the structural deformation zone located in a field section of the Chuandong Thrust-Fold Belt, South China. Herein, pore structure investigations are performed using three types of organic-rich shale (undeformed shale, fault-related shale, and fold-related shale) with vitrinite reflectance (Ro value) ranging between 1.90 and 2.57% and total organic carbon (TOC) content ranging between 2.25 and 4.40%. Compared to the undeformed shales, deformed samples are quartz rich and carbonate poor. Total porosity from mercury intrusion porosimetry (MIP) ranges between 3.74 and 5.62% in undeformed shales, 2.66–6.83% in fold-related shales, and 2.55–13.92% in fault-related shales. Scanning electron microscopy (SEM) study of the pore type evolution reveals organic matter (OM) pores are dominant in undeformed shales whereas the interparticle (interP) pores, intraparticle (intraP) pores, micro-channels, and micro-fractures are more developed in both fold- and fault-related shales. A combination of low-pressure gas (N2 and CO2) adsorption and MIP techniques suggests that with increasing structural deformation, micropore volumes relatively increase in fold-related samples, while macropore volumes significantly increase in fault-related shales. These observations and experiments confirm that tectonism produces an open and interconnected pore network within organic-rich shale, which is not related to OM pores. The role of structural deformation during ductile folding and brittle sliding, both in changing the mineral composition and in the producing process of the new pore networks, may be critical to understanding tectonism on organic-rich shales. These data could provide important theoretical guidance and scientific basis for the exploration and development of shale gas and resources assessment in the complex tectonic area of South China.

    Original languageEnglish
    Pages (from-to)914-932
    Number of pages19
    JournalFuel
    Volume241
    DOIs
    Publication statusPublished - 1 Apr 2019

    Keywords

    • Longmaxi Shale
    • OM pore
    • Micro-fracture
    • Structural deformation
    • Reservoir quality

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