The pores in oil shale, which act as channels for the migration of products of cracking of organic matter and the place for heat transfer in the rock mass, directly influence pyrolysis efficiency. In this paper, the pore characteristics of oil shale during pyrolysis under the convection and conduction modes of heating were determined by mercury intrusion porosimetry (MIP). Results show that in case of both the heating modes, the threshold temperatures for transformation of pore structure from simple to complex are 382 °C and 452 °C, respectively. The porosity of oil shale subjected to convection heating is generally higher than that subjected to conduction heating. By the convection heating mode, the high-temperature fluid can extract the shale oil attached to the pore wall and increase the porosity. As the pyrolysis temperature increases from 314 °C to 555 °C, the average pore size of oil shale increases from 23.70 to 218.15 nm in convection heating and from 21.68 to 145.60 nm in conduction heating. During the pyrolysis of organic matter and extraction of oil and gas, high-temperature steam continuously widens the pores. Finally, when the pyrolysis temperature is above 314 °C, pores with a smaller size gradually change into mesopores and macropores with a larger size. It is proved that under the convection heating mode, oil shale changes from a dense rock to a porous medium with an obviously higher amount of pores.
1. Dyni, J. R. Geology and resources of some world oil-shale deposits. Oil Shale, 2003, 20(3), 193–252.
2. Yu, X. D., Luo, Z. F., Li, H. B., Gan, D. Q. Effect of vibration on the separation efficiency of oil shale in a compound dry separator. Fuel, 2018, 214, 242–253.
3. Wang, L., Zhao, Y. S., Yang, D., Kang, Z. Q., Zhao, J. Effect of pyrolysis on oil shale using superheated steam: A case study on the Fushun oil shale, China. Fuel, 2019, 253, 1490–1498.
4. Yang, L. S., Yang, D., Zhao, J., Liu, Z. H., Kang, Z. Q. Changes of oil shale pore structure and permeability at different temperatures. Oil Shale, 2016, 33(2), 101–110.
5. Kang, Z. Q., Zhao, Y. S., Yang, D., Tian, L. J., Li, X. A pilot investigation of pyrolysis from oil and gas extraction from oil shale by in-situ superheated steam injection. J. Petrol. Sci. Eng., 2020, 186, 106785.
6. Sun, Y. H., Bai, F. T., Lü, X. S., Jia, C. X., Wang, Q., Guo, M. G., Li, Q., Guo, W. Kinetic study of Huadian oil shale combustion using a multi-stage parallel reaction model. Energy, 2015, 82, 705–713.
7. Bai, F. T., Sun, Y. H., Liu, Y. M., Guo, M. G. Evaluation of the porous structure of Huadian oil shale during pyrolysis using multiple approaches. Fuel, 2017, 187, 1–8.
8. Han, J., Sun, Y. H., Guo, W., Li, Q., Deng, S. H. Characterization of pyrolysis of Nong’an oil shale at different temperatures and analysis of pyrolysate. Oil Shale, 2019, 36(2S), 151–170.
9. Ribas, L., Dos Reis Neto, J. M., França, A. B., Porto Alegre, H. K. The behavior of Irati oil shale before and after the pyrolysis process. J. Petrol. Sci. Eng., 2017, 152,156–164.
10. Zhao, Y. S., Feng, Z. C., Yang. D., Liu, S. Y., Sun, K. M., Zhao, J. Z., Guan, K. W., Duan, K. L. The Method for Mining Oil & Gas from Oil Shale by Convection Heating. China Invent Patent, CN200510012473, April 20, 2005.
11. Kang, Z. Q., Zhao, Y. S., Yang, D. Physical principle and numerical analysis of oil shale development using in situ conversion process technology. Acta Petrolei Sinica, 2008, 29(4), 592–595 (in Chinese).
12. Chang, Z. B., Chu, M., Zhang, C., Bai, S. X., Lin, H., Ma, L. B. Influence of inherent mineral matrix on the product yield and characterization from Huadian oil shale pyrolysis. J. Anal. Appl. Pyrol., 2018, 130, 269–276.
13. Wang, L., Yang, D., Li, X., Zhao, J., Wang, G.Y., Zhao, Y. S. Macro and meso characteristics of in-situ oil shale pyrolysis using superheated steam. Energies, 2018, 11(9), 2297.
14. Maes, J., Muggeridge, A. H., Jackson, M. D., Quintard, M., Lapene, A. Scaling analysis of the in-situ upgrading of heavy oil and oil shale. Fuel, 2017, 195, 299–313.
15. Geng, Y. D., Liang, W. G., Liu, J., Cao, M. T., Kang, Z. Q. Evolution of pore and fracture structure of oil shale under high temperature and high pressure. Energ. Fuel., 2017, 31(10), 10404–10413.