Evaluation of Nanoscale Accessible Pore Structures
for Improved Prediction of Gas Production Potential in Chinese Marine
Shales
Version 2 2018-12-07, 20:08
Version 1 2018-12-07, 20:04
Posted on 2018-12-07 - 20:08
The Lower Cambrian
Niutitang and Lower Silurian Longmaxi shales
in the Upper Yangtze Platform (UYP) are the most promising strata
for shale gas exploration in China. Knowledge of the nanoscale pore
structure may improve the prediction of the gas production potential
in Chinese marine shales. A systematic investigation of the pore accessibility
and its impact on methane adsorption capacity has been conducted on
shale samples using various techniques including geochemical and mineralogical
analyses, field-emission scanning electron microscopy (FE-SEM), small-angle
neutron scattering (SANS), helium porosimetry, and methane adsorption.
The results show that organic matter (OM) pores with various shapes
dominate the pore systems of these shales. OM tended to mix with clay
minerals and converted to organoclay complexes, developing plentiful
micro- and mesopores. A unified fit model with two pore structures,
fractal pores and finite pores, was used to model the SANS data to
characterize the pore structure of the shales. Both mass and surface
fractals are identified for each pore structure. The total porosity
estimated by the Porod invariant method ranges between 2.35 and 16.40%,
of which the porosity for finite pores ranges between 0.35 and 6.36%,
and the porosity for the fractal pores ranges between 2.07 and 8.51%.
The fraction of open pores was evaluated by comparing the porosities
estimated by He porosimetry and SANS. We find that the fraction of
open pores is higher than 64% for most of these shales. Correlation
analyses suggest that clay and total organic carbon (TOC) have opposite
effects on pore structure and methane adsorption capacity. Samples
with higher clay contents have higher pore accessibility and lower
total porosity, surface area, and maximum methane adsorption, whereas
samples with higher TOC content show the inverse relationships. The
high percentage of open pores may reduce methane adsorption capacity
in these shales, whereas low pore accessibility may reduce methane
production at specific pressure differences. Thus, both TOC and pore
accessibility may be essential controlling factors in methane production
from shale gas reservoirs.
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Wang, Yang; Qin, Yong; Zhang, Rui; He, Lilin; Anovitz, Lawrence M.; Bleuel, Markus; et al. (2018). Evaluation of Nanoscale Accessible Pore Structures
for Improved Prediction of Gas Production Potential in Chinese Marine
Shales. ACS Publications. Collection. https://doi.org/10.1021/acs.energyfuels.8b03437
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AUTHORS (9)
YW
Yang Wang
YQ
Yong Qin
RZ
Rui Zhang
LH
Lilin He
LA
Lawrence M. Anovitz
MB
Markus Bleuel
DM
David F. R. Mildner
SL
Shimin Liu
YZ
Yanming Zhu
KEYWORDS
fractal pores rangesChinese Marine ShalesUYPOMmethane productionUpper Yangtze Platformnanoscale pore structuremethane adsorption capacitypore structureshale gas explorationFE-SEMChinese marine shalesshale gas reservoirsmethane adsorptionfield-emission scanning electron microscopySilurian Longmaxi shalesSANSNanoscale Accessible Pore Structurespore accessibilityTOC content show