Contrasting mechanical evolution of bakken shale under hydrous and anhydrous pyrolysis: A nanoindentation-based assessment

作者：Mengdi Sun, Jiajun Fu, Yeping Ji, Yiquan Ma, Bo Liu, Qiuli Huo, Aydin Larestani, Abdolhossein Hemmati-Sarapardeh, Mehdi Ostadhassan · 发表于：International Journal of Rock Mechanics and Mining Sciences · 年份：2026 · DOI：10.1016/j.ijrmms.2026.106526 · 被引用次数：3 · 研究领域：Hydrocarbon exploration and reservoir analysis、Drilling and Well Engineering、Rock Mechanics and Modeling

The Bakken Formation is one of the largest unconventional shale oil reserves, where hydraulic fracturing and horizontal drilling are key methods for enhancing recovery. A thorough understanding of its mechanical properties is crucial for designing these processes, especially since kerogen within the shale undergoes chemical changes during thermal evolution that alter its mechanical behavior. This communication primarily concentrates on evaluating how the mechanical behavior of Bakken shale, rich in Type II kerogen, evolves during controlled thermal maturation under anhydrous and hydrous pyrolysis conditions. The immature samples are pyrolyzed at 300, 325, 350, 365, 400, and 450 °C. To extensively investigate the mechanical characteristics of shale samples, a sum of 775 nanoindentation tests is performed on their surface. The results indicated that during the AHP, the initial increase of Young's modulus of the samples to more than 34 GPa was followed by a relatively large decline and it starts fluctuating between 20 and 25 GPa from 350 to 450 °C. The hardness value during the AHP, on the other hand, increased to almost 0.77 GPa at 300 °C and then started a steady decrease to approximately 0.25 GPa at 365 °C. It then experienced an uprise to 0.39 GPa at 400 °C and finally, fell to 0.32 GPa in the last temperature step. During the HP, the trends were quite different, which reflects the impact of the presence of water on kerogen maturation. The hardness values reduced constantly ...