Abstract
Low porosity of Marcellus shale often limits the hydrocarbon recovery. To increase shale porosity, hydrothermal deformation (HTD) of Marcellus shale was performed and the effects of subcritical water temperature and reaction time on porosity were evaluated. HTD was performed at 200, 250 and 300 °C for one, three and 6 h of residence time. Low-temperature N2 adsorption was used for porosity measurement. Furthermore, the morphology of raw and HTD shale samples was analyzed with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction analyzer (XRD). It was observed that shale porosity was significantly enhanced by HTD conditions. For instance, HTD at 300 °C for 6 h of residence time, shale porosity increased more than four times compared to raw shale. This porosity was attributed to leaching of calcite, clay and quartz, which is confirmed by analyzing HTD process liquids by Induced Coupled Plasma-Optical Emission Spectroscopy (ICP-OES).
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•Marcellus shale was treated with subcritical water at 200–300 °C for 1–6 h•Higher temperature and longer residence time resulted in lower mass yield and higher porosity.•Porosity of the shale was increased up to four times compared to raw shale at 300 °C for 6 h•Numerous meso and micropores were formed due to calcium-based mineral leaching.