Study on pore and fracture evolution characteristics of oil shale pyrolysed by high-temperature water vapour

In this study, a self-designed test system for injecting water vapour was used to pyrolyse oil shale from Barkol, Xinjiang, China. The internal structure of oil shale samples after water vapour pyrolysis at different temperatures was characterised using micro-computed tomography (micro-CT). The results showed that under the action of high-temperature water vapour, oil shale underwent evident thermal cracking and pyrolysis, and the porosity increased from 0.08% of the original state to 16.73% at 550 [degrees]C. At 300 [degrees]C, the maximum pore group was distributed along the bedding plane due to the influence of thermal cracking, and the equivalent diameter was 1201.73 [micro]m. When the water vapour temperature increased from 300 [degrees]C to 400 [degrees]C, the organic matter at a low boiling point in oil shale began to pyrolyse, forming several pores. These pores were gradually connected with adjacent fractures. The pores with an equivalent diameter of approximately100-500 [micro]m in oil shale accounted for > 60% of the total pore volume. The maximum pore cluster expanded perpendicular to the bedding plane, but there was still no effective seepage channel. With an increase in the water vapour temperature, the large-scale pyrolysis of organic matter began and the pores and fractures in oil shale were continuously generated and gradually connected; at 450 [degrees]C, the seepage channel connecting the entire digital core area began to form. At 550 [degrees]C, the equivalent diameter of the maximum pore group reached 5756.72 [micro]m, accounting for 69.65% of the total pore volume. Keywords: water vapour, Chinese Barkol oil shale, pore structure, micro-computed tomography, temperature.