Secondary cracking characteristics of asphaltenes and insightsinto the reservoir unblocking during oil shalein-situexploitation

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. Advances in Geo-Energy Research, 2025, 15(1): 13-26. https://doi.org/10.46690/ager.2025.01.03