Evaluation of Nanoscale Accessible Pore Structures for Improved Prediction of Gas Production Potential in Chinese Marine Shales

Journal Article · Wed Nov 28 00:00:00 EST 2018 · Energy and Fuels

DOI:https://doi.org/10.1021/acs.energyfuels.8b03437· OSTI ID:1560485

Wang, Yang ^[1]; Qin, Yong ^[1]; Zhang, Rui ^[2]; He, Lilin ^[3]; Anovitz, Lawrence M. ^[3]; Bleuel, Markus ^[4]; Mildner, David F. R. ^[5]; Liu, Shimin ^[6]; Zhu, Yanming ^[1]

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1. China Univ. of Mining and Technology, Jiangsu (China)
2. The Pennsylvania State Univ., University Park, PA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
6. The Pennsylvania State Univ., University Park, PA (United States)

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. Furthermore, both TOC and pore accessibility may be essential controlling factors in methane production from shale gas reservoirs.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1560485
• Journal Information: Energy and Fuels, Journal Name: Energy and Fuels Journal Issue: 12 Vol. 32; ISSN 0887-0624
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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