Based on a sample of oil shale from the Lucaogou Formation in Shichanggou, Xinjiang, China, the mechanism of changes in the physical and mechanical properties of oil shale during in-situ pyrolysis was systematically analyzed, and combined with the kinetics of the pyrolysis reaction, a constitutive model of permeability change during the in-situ pyrolysis of oil shale was established. By leaching experiments, the changes in the physicochemical parameters and pollutant concentration of oil shale immersion solution under different pyrolysis temperatures were studied. Basing on the theoretical permeability value and pollutant concentration under in-situ pyrolysis conditions, a hydrogeological model was established to simulate groundwater pollution caused by the in-situ pyrolysis of oil shale. The results showed that the permeability of oil shale after in-situ pyrolysis increased by three orders of magnitude, changing from a water-proof layer before pyrolysis to a weakly permeable layer after pyrolysis. However, the permeability of oil shale after complete pyrolysis at 600 °C was only 2.062 mD and still very low, and the pollutants had low concentration and were mainly concentrated in the pyrolyzed oil shale layer. The in-situ pyrolysis of oil shale would not pollute the groundwater in the mining area, but the pH of groundwater would gradually increase with rising pyrolysis temperatures. At 600 °C, pH even increased to 11.68, which is strongly alkaline. It is suggested that the pyrolysis temperature should be 400–500 °C.
1. Kang, Z., Yang, D., Zhao, Y., Hu, Y. Thermal cracking and corresponding permeability of Fushun oil shale. Oil Shale, 2011, 28(2), 273–283.
https://doi.org/10.3176/oil.2011.2.02
2. Eseme, E., Krooss, B. M., Littke, R. Evolution of petrophysical properties of oil shales during high-temperature compaction tests: Implications for petroleum expulsion. Mar. Petrol. Geol., 2012, 31(1), 110–124.
https://doi.org/10.1016/j.marpetgeo.2011.11.005
3. Bai, F., Sun, Y., Liu, Y., Guo, M. Evaluation of the porous structure of Huadian oil shale during pyrolysis using multiple approaches. Fuel, 2017, 187(1), 1–8.
https://doi.org/10.1016/j.fuel.2016.09.012
4. Tang, H., Zhao, Y., Kang, Z., Lv, Z., Yang, D., Wang, K. Investigation on the fracture-pore evolution and percolation characteristics of oil shale under different temperatures. Energies, 2022, 15(10), 1–14.
https://doi.org/10.3390/en15103572
5. Zhao, J., Yang, L., Yang, D., Kang, Z., Wang, L. Study on pore and fracture evolution characteristics of oil shale pyrolysed by high-temperature water vapour. Oil Shale, 2022, 39(1), 79–95.
https://doi.org/10.3176/oil.2022.1.05
6. Geng, Y., Liang, W., Liu, J., Cao, M., Kang, Z. Evolution of pore and fracture structure of oil shale under high temperature and high pressure. Energy Fuels, 2017, 31(10), 10404–10413.
https://doi.org/10.1021/acs.energyfuels.7b01071
7. Geng, Y., Liang, W., Liu, J., Kang, Z., Wu, P., Jiang, Y. Experimental study on the variation of pore and fracture structure of oil shale under different temperatures and pressures. Chin. J. Rock Mech. Eng., 2018, 37(11), 2510–2519 (in Chinese with English abstract).
https://doi.org/10.13722/j.cnki.jrme.2018.0623
8. Geng, Y., Liang, W., Liu, J., Wu, P., Zhao, J. Experimental study on the law with permeability of Fushun oil shale under high temperature and triaxial stresses. J. Taiyuan Univ. Tech., 2019, 50(3), 272–278 (in Chinese with English abstract).
https://doi.org/10.16355/j.cnki.issn1007-9432tyut.2019.03.002
9. Yang, D., Wang, G., Kang, Z., Zhao, J., Lv, Y. Experimental investigation of anisotropic thermal deformation of oil shale under high temperature and triaxial stress based on mineral and micro-fracture characteristics. Nat. Res. Res., 2020, 29(1), 3987–4002.
https://doi.org/10.1007/s11053-020-09663-x
10. He, W., Meng, Q., Lin, T., Wang, R., Liu, X., Ma, S., Li, X., Yang, F., Sun, G. Evolution of in-situ permeability of low-maturity shale with the increasing temperature, Cretaceous Nenjiang Formation, northern Songliao Basin, NE China. Petrol. Explor. Dev., 2022, 49(3), 453–464 (in Chinese with English abstract).
https://doi.org/10.11698/PED.20210881
11. Zhao, L., Cheng, Y., Zhang, Y. Pore and fracture scale characterization of oil shale at different microwave temperatures. Oil Shale, 2023, 40(2), 91–114.
https://doi.org/10.3176/oil.2023.2.01
12. Brandt, A. R. Converting oil shale to liquid fuels: Energy inputs and greenhouse gas emissions of the shell in situ conversion process. Environ. Sci. Technol., 2008, 42(19), 7489–7495.
https://doi.org/10.1021/es800531f
13. Zhang, F., Liu, Z., Li, C., Tao, Y., Lü, C. Risk assessment of the atmospheric environment during in-situ oil shale exploitation. Sci. Tech. Rev., 2013, 31(26), 44–47 (in Chinese with English abstract).
https://doi.org/10.3981/j.issn.1000-7857.2013.26.006
14. Hu, S., Wu, H., Liang, X., Xiao, C., Zhao, Q., Cao, Y., Han, X. A preliminary study on the eco-environmental geological issue of in-situ oil shale mining by a physical model. Chemosphere, 2022, 287(1), 131987.
https://doi.org/10.1016/j.chemosphere.2021.131987
15. Cai, M. Rock Mechanics and Engineering. Science Press, Beijing, 2002 (in Chinese).
16. Porter, L. B., Ritzi, R. W., Mastera, L. J. The Kozeny-Carman equation with a percolation threshold. Groundwater, 2013, 51(1), 92–99.
https://doi.org/10.1111/j.1745-6584.2012.00930.x
17. Liu, J., Liang, W., Kang, Z., Lian, H., Geng, Y. Study on the quantitative model of oil shale porosity in the pyrolysis process based on pyrolysis kinetics. Oil Shale, 2018, 35(2), 128–143.
https://doi.org/10.3176/oil.2018.2.03
18. Coats, A. W., Redfern, J. P. Kinetic parameters from thermogravimetric data. Nature, 1964, 201, 68–69.
https://doi.org/10.1038/201068A0
19. Braun, R. L., Rothman, A. J. Oil-shale pyrolysis: Kinetics and mechanism of oil production. Fuel, 1975, 54(2), 129–131.
https://doi.org/10.1016/0016-2361(75)90069-1
20. Liu, J., Liang, W., Lian, H., Li, L. Study on the quantitative model of the elastic modulus of oil shale during pyrolysis. Oil Shale, 2018, 35(4), 327–338.
https://doi.org/10.3176/oil.2018.4.03
21. Li, L., Liu, J., Geng, Y. Study on the permeability of oil shale during in situ pyrolysis. Oil Shale, 2021, 38(2), 119–136.
https://doi.org/10.3176/oil.2021.2.02
