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TitlePossible pore structure deformation effects on the shale gas enrichment: an example from the Lower Cambrian shales of the eastern Upper Yangtze Platform, south China
AuthorMa, Y; Ardakani, O HORCID logo; Zhong, N; Liu, H; Huang, H; Larter, S; Zhang, C
SourceInternational Journal of Coal Geology vol. 217, 103349, 2019 p. 1-22,
Alt SeriesNatural Resources Canada, Contribution Series 20180450
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
AreaChongqing; Chong; Guizhou; Shanxi; Sichuan; Hubei; China
Lat/Long WENS 105.5000 110.0000 33.2500 27.7500
Lat/Long WENS 105.5000 110.0000 33.2500 27.7500
Subjectsfossil fuels; sedimentology; tectonics; geochemistry; mineralogy; Science and Technology; Nature and Environment; Lower Cambrian; petroleum resources; petroleum exploration; hydrocarbons; gas; reservoir rocks; pore size; pore structure; bedrock geology; lithology; sedimentary rocks; shales; structural features; faults; scanning electron microscopy; capillary pressure; depositional environment; carbonate; geological history; tectonic history; thermal history; thermal maturation; crustal uplift; rifts; hydrocarbon migration; wells; petrography; x-ray diffraction analyses; organic geochemistry; mineralogical analyses; Yangtze Platform; Dabashan Fold Belt; Sichuan Basin; Hubei-Hunan-Guizhou Fold Belt; Longmenshan Fold Belt; Phanerozoic; Mesozoic; Triassic; Paleozoic; Cambrian
Illustrationslocation maps; geoscientific sketch maps; cross-sections; photographs; profiles; lithologic sections; tables; photomicrographs; bar graphs; plots; schematic representations
ProgramGeoscience for New Energy Supply (GNES) Shale Reservoir Characterization
Released2019 11 21
AbstractShale gas reservoir performance and canister desorption experiments of the Lower Cambrian organic-rich shales in the eastern Upper Yangtze Platform reveal a significant difference in shale gas content between the Dabashan arc-like fold-thrust belt in northeastern Chongqing (Deformed Zone) and the slightly folded area in southeastern Chong (Non-deformed Zone). Integrated pore characterization methods including scanning electron microscopy (SEM), low-temperature N2 and CO2 adsorption, and mercury injection capillary pressure (MICP) analyses were comparatively conducted in both areas in order to examine shale gas reservoir pore size variations and thus the possible microscopic pore structure controls on shale gas enrichment.
The Lower Cambrian shales in both Deformed Zone (DZ) and Non-deformed Zone (NDZ) were deposited in the deep-water shelf and show similar organic matter richness and thermal maturity. The majority of organic matter (OM)-hosted pores in DZ samples are in nanoscale size range with the dominance of micro-fractures within the OM or at the interface of OM and minerals. In contrast, OM-hosted meso- (2-50 nm) to macropores (> 50 nm) are the dominant pore types in the NDZ samples. OM-hosted micropores (< 2 nm) are abundant in both zones. Helium ion microscopy observations further confirm the presence of OM-hosted micropores in the studied samples. Mineral-hosted pores in carbonate minerals are abundant in both zones, while dissolution rims around carbonate minerals are more abundant in NDZ samples.
The Dabashan arc-like fold-thrust belt took place by the end of the Late Triassic, while the Lower Cambrian shales have reached thermal maturity peak. OM-hosted meso- (2-50 nm) to macropores (> 50 nm) in DZ samples are most probably collapsed during structural deformation related to tectonic compression, while micropores due to their smaller size survived the tectonic stress. The OM-hosted micropores are the main storage space for adsorbed gas in the DZ area. The dominance of micro-pores in DZ and lack of connection between those pores and matrix pores led to higher gas content in DZ samples. On the contrary, the well-connected OM-hosted pore network in NDZ allows easier gas flow in the rock matrix that eventually led to significant gas leakage during uplift and exhumation and lower gas content in this zone. The results of this study suggest that structural deformation can potentially change the pore structure of shales and thus shale gas content which has major significance for shale gas exploration and development in south China where had experienced complex tectonic movements.
Summary(Plain Language Summary, not published)
This study investigate the possible effects of structural deformation on pore characteristics of shale gas reservoirs.

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