Self-induced differential stress and cascading reactions, fracturing, and permeability enhancement triggered by volatile-consuming reactions

Abstract

Reaction-induced fracturing is thought to be a key process controlling pervasive volatile-consuming reactions, including the serpentinization and carbonation of peridotites; however, the interactions between reactions, fluid flow, and fracturing remain poorly understood. We performed flow-through hydration experiments on sintered periclase aggregate [MgO + H₂O → Mg(OH)₂] samples with high and low porosities at temperatures of 180–200 °C, confining pressure of 20 MPa, and fluid pressures of 3–5 MPa. We monitored the solid volume, permeability, and axial stress simultaneously. For comparison, we also conducted batch experiments with the same samples. In the batch experiments, the high-porosity sample reacted uniformly with no macroscopic fracturing, whereas a sharp reaction front developed in the low-porosity sample. In the flow-through experiments with high-porosity samples, the reaction proceeded uniformly, with an initial decrease in permeability but no increase in volume. Axial stress then increased, and the sample subsequently yielded gradually. The reaction continued, causing circumferential expansion of the sample with no discrete failure while the permeability remained constant or increased. In the flow-through experiments with low-porosity samples, the reaction began slowly through surface layer spallation. After a prolonged initiation period, mechanical instability led to a sudden large failure. This failure triggered cascading reactions, with a build-up of reaction-induced stress followed by yielding and the formation of new fractures, resulting in the permeability increasing by two orders of magnitude and leading to reaction rates increasing by a factor of 18 compared with the batch experiments. The results suggest that (1) reaction-induced fracturing is strongly enhanced by self-induced differential stress related to the anisotropic elastic properties of the lithosphere, and (2) catastrophic failure can occur during the hydration and carbonation of impermeable mantle peridotite. These findings provide new links between microscopic failure at reaction interfaces and macroscopic fractures in a rock, and have implications for the pervasive serpentinization of the oceanic lithosphere, the formation of serpentine diapirs, and natural and anthropogenic CO₂ sequestration.