In-situ conversion is essential for the development of oil shale resources. Reservoir blockage has been confirmed to be a technological bottleneck via laboratory-scale experiments and field tests. This issue arises from the precipitated asphaltene and its thickening effect on the pyrolysis oil. Promoting in-situ secondary cracking of asphaltene has the potential to mitigate blockage. However, the secondary cracking characteristics of asphaltene have not yet been determined. In this study, asphaltenes were obtained under different pyrolysis temperatures, atmospheres and duration times, their secondary cracking mechanisms were investigated. These findings demonstrate considerable mass loss and discrepant reaction processes across different asphaltenes. Firstly, the mass loss of asphaltenes exceeds 80% at 500 ◦C for all the samples, and the released space can restore reservoir permeability. Second, based on the evolution of the activation energies and pyrolysis gas components, the asphaltenes obtained under severe conversion conditions undergo pyrolysis defined by synchronous two-stage reactions, whereas the asphaltenes obtained under mild conversion conditions undergo pyrolysis defined by sequential three-stage reactions. Finally, a method for eliminating reservoir blockage was proposed based on the above theories, involving inhibiting asphaltene migration and promoting its in-situ secondary cracking by controlling the parameters of the heat-carrying fluid, thereby achieving an unaffected reservoir or reservoir self-unblocking. The obtained results can provide valuable references for the in-situ exploitation of oil shale. Document Type: Original article Cited as: Guo, W., Fan, C., Deng, S., Shui, H., Liu, Z. Secondary cracking characteristics of asphaltenes and insights into the reservoir unblocking during oil shale in-situ exploitation. 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In order to weaken the influence of external groundwater on in situ pyrolysis exploitation, the flow characteristics of groundwater were studied according to the oil shale reservoir characteristics of Qingshankou Formation in Songliao Basin, China. In addition, the parameters of marginal gas flooding for water-stopping were optimized. Taking a one-to-one pattern and a five-spot pattern as examples, the characteristics of groundwater flow under the in situ process were studied. Under the one-to-one pattern, the external groundwater flows into the production well from the low-pressure side, and the water yield was basically stable at 1000 kg/d. In the five-spot pattern, the groundwater can flow into the production wells directly from the windward side, and the water yield of the production well on the leeward side mainly comes from the desaturated zone; the water yield of each production well remains at a high level. By setting water-stopping wells around the production well and keeping the gas flooding pressure slightly higher than the production well, the water yield of the production well can be reduced and stabilized within 100 kg/d under gas flooding pressures of 3 and 5 MPa. However, the gas yield of the production well slightly decreased when the gas flooding pressure reduced from 5 to 3 MPa. Therefore, the gas flooding pressure of water-stopping wells shall be determined in combination with the water yield and gas yield, so as to achieve the best process effect. It is expected that the results will provide technical support for large-scale oil shale in situ pyrolysis exploitation.