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Energies 2018, 11(11), 3033; https://doi.org/10.3390/en11113033

Permeability Evolution of Pyrolytically-Fractured Oil Shale under In Situ Conditions

1
Key Laboratory of In-Situ Property-Improving Mining of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China
2
Department of Geology, Hebei Vocational College of Geology, Shijiazhuang 050081, Hebei, China
3
Department of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China
4
Energy and Mineral Engineering & Geosciences, EMS Energy Institute and G3 Center, The Pennsylvania State University, University Park, Pennsylvania, PA 16802, USA
*
Author to whom correspondence should be addressed.
Received: 9 September 2018 / Revised: 16 October 2018 / Accepted: 24 October 2018 / Published: 5 November 2018
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Abstract

In-situ injection of steam for heating of the subsurface is an efficient method for the recovery of oil and gas from oil shale where permeability typically evolves with temperature. We report measurements on Jimusar oil shales (Xinjiang, China) at stepped temperatures to 600 °C and under recreated in situ triaxial stresses (15 MPa) and recover permeability evolution with temperature and stress. Initial very low permeability evolves with the temperature above an initial threshold temperature at high rate before reaching a plateau in permeability above a peak temperature. The threshold temperature triggering the initial rapid rise in permeability is a function of triaxial stresses. For Jimusar oil shale, this threshold temperature ranges from 200 °C to 250 °C for burial depths of 500 m and from 350 °C to 400 °C for burial depths of 1000 m. This rapid rise in permeability correlates with the vigor of pyrolysis and directly scales with the production rate of pyrolysis-derived gas production. The permeability increases with temperature to a plateau in peak permeability that occurs at a peak-permeability temperature. This peak temperature is insensitive to stress and is in the range 450 °C to 500 °C for all Jimusar samples. Pyrolysis plays an important role in the stage of rapid permeability evolution with this effect stopping once pyrolysis is essentially complete. At these ultimate high temperatures, permeability exhibits little reduction due to stress and remains elevated due to the vigor of the pyrolysis. These results effectively demonstrate that oil shale may be transformed by pyrolysis from a tight porous medium into highly permeable medium and that oil and gas may be readily recovered from it. View Full-Text
Keywords: oil shale; permeability; pyrolysis; high temperature and high pressure oil shale; permeability; pyrolysis; high temperature and high pressure
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Dong, F.; Feng, Z.; Yang, D.; Zhao, Y.; Elsworth, D. Permeability Evolution of Pyrolytically-Fractured Oil Shale under In Situ Conditions. Energies 2018, 11, 3033.

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