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| Experimental study on the variation of pore and fracture structure of oil shale under different temperatures and pressures |
| GENG Yide1,2,LIANG Weiguo1,2,LIU Jian1,2,KANG Zhiqin1,2,WU Pengfei1,2,JIANG Yulong1,2 |
| (1. College of Mining Engineering,Taiyuan University of Technology,Taiyuan,Shanxi 030024,China;2. Key Laboratory of In-situ Modified Mining Ministry of Education,Taiyuan University of Technology,Taiyuan,Shanxi 030024,China) |
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Abstract In order to study the effect of temperature and pressure on the pyrolysis characteristics of oil shale,12 hours of pyrolytic reaction experiments were conducted on cylindrical oil shale samples of 14 mm in length and 7 mm in diameter under the temperature from 300 ℃–600 ℃ and pressure 5–15 MPa. The X-ray micro computed tomography,mercury intrusion porosimetry and scanning electron microscope were used to investigate the variation of pore and fracture structures. The results show that temperature is the most important factor in changing the structures of oil shale. With the increasing of temperature,the pyrolytic cracking intensifies progressively. The total pore volume and porosity both increase gradually,especially in the range of 300 ℃ to 400 ℃. With the increasing in temperature,the transition pores expand and interconnect to each other,forming larger pores. As a result,the proportions of transition pore and mesopore increases gradually. The fractures of different scales are generated,and the number of fractures increases continuously. The fracture area density of big fracture at 600 ℃ is 8.1 times as high as that at 300 ℃. To a certain extent,the increasing of the external pressure and thermal stress caused by pyrolysis act together to promote the expansion of the original crack and the birth of new cracks,which results in the increasing in the total pore volume and the number of fractures. The porosity and fracture area density reach the maximum at the pressure of 15 MPa,and the maximum porosity is 51.6%. The pyrolytic cracking of oil shale is affected by the thermal stress due to the expansion of mineral particles and pyrolysis of kerogen. The coupling of temperature and pressure increases the degree of pyrolytic cracking and also promotes the generation,expansion and development of pore and fractures.
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