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Title: Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water

Abstract

High-volatile bituminous coal samples were reacted in deionized water with supercritical CO{sub 2} (ScCO{sub 2}–water) under simulated in situ pressure and temperature conditions (8 MPa and 40 °C) in unconfined stress state for 14 days, in order to characterize potential CO{sub 2}–water–coal reactions. Micro-structural changes were identified pre- and post-experiment using X-ray powder diffraction (XRD) analysis for powdered coal (mineralogical changes), optical microscopy and scanning electron microscopy (SEM) for polished thin sections (surface feature changes) and micro-CT scanning for a small core (porosity and permeability changes). XRD analysis revealed that carbonic acid leaches out mineral matters in coal, including carbonates (calcite) and silicate minerals (albite, illite and kaolinite). Optical microscopy, SEM and CT images confirmed that the interaction of coal with ScCO{sub 2}–water causes an abundance of micro-cracks to open or propagate in unconfined coal samples. Most micro-cracks preferably propagated along maceral–mineral and maceral–maceral interfaces, which demonstrates that the micro-cracking was caused by differential swelling of different coal lithotypes. Wormhole formation was observed in coal caused by mineral dissolution and hydrocarbon mobilization, which significantly increases coal porosity compared with swelling-induced cracking. 3-D pore network models extracted from CT images show that ScCO{sub 2}–water treatment enlarges the pore and throat size, increases the numbersmore » of pores and throats and improves pore network connectivity. Overall, CO{sub 2}–water–coal interactions under unconfined conditions enhance coal porosity, connectivity and permeability, which can be attributed to the combined effect of micro-cracking, mineral dissolution and hydrocarbon mobilization.« less

Authors:
;  [1];  [2];  [1]
  1. Monash University, Deep Earth Energy Laboratory, Department of Civil Engineering (Australia)
  2. Chongqing University, State Key Laboratory of Coal Mine Disaster Dynamics and Control (China)
Publication Date:
OSTI Identifier:
22943114
Resource Type:
Journal Article
Journal Name:
Natural Resources Research (New York, N.Y.)
Additional Journal Information:
Journal Volume: 28; Journal Issue: 4; Other Information: Copyright (c) 2019 International Association for Mathematical Geosciences; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1520-7439
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; BITUMINOUS COAL; CALCITE; CARBON DIOXIDE; CARBONATES; CARBONIC ACID; COMPUTERIZED TOMOGRAPHY; CRACKING; CRACKS; FELDSPARS; HYDROCARBONS; ILLITE; KAOLINITE; LEACHING; LITHOTYPES; MACERALS; PERMEABILITY; POROSITY; POWDERS; SCANNING ELECTRON MICROSCOPY; WATER; WATER TREATMENT; X-RAY DIFFRACTION

Citation Formats

Zhang, Guanglei, Ranjith, P. G., E-mail: ranjith.pg@monash.edu, Perera, M. S. A., Lu, Yiyu, and Choi, Xavier. Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water. United States: N. p., 2019. Web. doi:10.1007/S11053-019-09463-Y.
Zhang, Guanglei, Ranjith, P. G., E-mail: ranjith.pg@monash.edu, Perera, M. S. A., Lu, Yiyu, & Choi, Xavier. Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water. United States. https://doi.org/10.1007/S11053-019-09463-Y
Zhang, Guanglei, Ranjith, P. G., E-mail: ranjith.pg@monash.edu, Perera, M. S. A., Lu, Yiyu, and Choi, Xavier. 2019. "Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water". United States. https://doi.org/10.1007/S11053-019-09463-Y.
@article{osti_22943114,
title = {Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water},
author = {Zhang, Guanglei and Ranjith, P. G., E-mail: ranjith.pg@monash.edu and Perera, M. S. A. and Lu, Yiyu and Choi, Xavier},
abstractNote = {High-volatile bituminous coal samples were reacted in deionized water with supercritical CO{sub 2} (ScCO{sub 2}–water) under simulated in situ pressure and temperature conditions (8 MPa and 40 °C) in unconfined stress state for 14 days, in order to characterize potential CO{sub 2}–water–coal reactions. Micro-structural changes were identified pre- and post-experiment using X-ray powder diffraction (XRD) analysis for powdered coal (mineralogical changes), optical microscopy and scanning electron microscopy (SEM) for polished thin sections (surface feature changes) and micro-CT scanning for a small core (porosity and permeability changes). XRD analysis revealed that carbonic acid leaches out mineral matters in coal, including carbonates (calcite) and silicate minerals (albite, illite and kaolinite). Optical microscopy, SEM and CT images confirmed that the interaction of coal with ScCO{sub 2}–water causes an abundance of micro-cracks to open or propagate in unconfined coal samples. Most micro-cracks preferably propagated along maceral–mineral and maceral–maceral interfaces, which demonstrates that the micro-cracking was caused by differential swelling of different coal lithotypes. Wormhole formation was observed in coal caused by mineral dissolution and hydrocarbon mobilization, which significantly increases coal porosity compared with swelling-induced cracking. 3-D pore network models extracted from CT images show that ScCO{sub 2}–water treatment enlarges the pore and throat size, increases the numbers of pores and throats and improves pore network connectivity. Overall, CO{sub 2}–water–coal interactions under unconfined conditions enhance coal porosity, connectivity and permeability, which can be attributed to the combined effect of micro-cracking, mineral dissolution and hydrocarbon mobilization.},
doi = {10.1007/S11053-019-09463-Y},
url = {https://www.osti.gov/biblio/22943114}, journal = {Natural Resources Research (New York, N.Y.)},
issn = {1520-7439},
number = 4,
volume = 28,
place = {United States},
year = {2019},
month = {10}
}