Deep and ultra-deep basin brittle deformation with focus on China

This volume describes progress in understanding brittle structures in deep and ultra-deep (>4 km to > 7 km) sedimentary basins. Under deep conditions in sandstone, carbonate rocks, shale, and other rocks, fluid charge and resource recovery are sensitive to faults and opening-mode fractures. In China, work is in progress on deep, deformed, and tectonically active basins including drilling of wells expected to exceed 10 km in depth. Papers describing fractures in horizontal wells indicate locally highly clustered spatial arrangements. Orientation patterns record protracted superposed deformation. Despite deep settings, open fractures are abundant, and wide (>1 mm) fractures with varying amounts of sealing calcite are common. Differences in cement abundances are due to the diagenetic history of fractures, not their origins (e.g., tectonic loading or elevated pore fluid pressure). In carbonate rocks, solution enhanced strike-slip faults and fractures with cavernous porosity are present, and in sandstone enigmatic enhanced host-rock porosity halos a few mm wide locally surround sealed fractures. Owing to differences in thermal exposure due to recent (>6 Ma to present) rapid deep burial (in some cases >2000 m) and locally low geothermal gradients, some fractures at great depths are less diagenetically altered than those at shallower depths in the North American Cordillera. Contrasts in diagenesis may affect fracture size, spatial arrangement, and connectivity.

Automated summary

This volume discusses the progress made in studying brittle structures in deep and ultra-deep sedimentary basins. The research focuses on the effects of faults and fractures on fluid charge and resource recovery in sandstone, carbonate rocks, shale, and other types of rock. The study includes drilling wells that are expected to exceed 10 km in depth in deep, deformed, and tectonically active basins in China. The results indicate that open fractures, fractures with sealing calcite, and enhanced host-rock porosity are present in these deep settings, and their abundances are related to the diagenetic history rather than their origins. Additionally, the study compares the diagenesis differences between deep and shallower depths, which may influence fracture size, spatial arrangement, and connectivity.