Lab-Scale Experimental Nano-to-Micro Scale Study of Ultramafic Rocks for Geologic Hydrogen Generation

ABSTRACT: At high temperatures, subsurface stimulation of ultramafic rocks via a thermo-hydro-chemical process can generate natural hydrogen due to its reaction with injected water through a process known as serpentinization. However, due to this subsurface hydrogen generation, there is no knowledge of the nano-to-micro scale changes in the host ultramafic reservoir rock. In this work, we experimentally characterized the microstructural (micro-scale) and nanomechanical (nanoscale) properties of ultramafic rock samples pre- and post-serpentinization, and further assessed its implication for geologic hydrogen. We used scanning electron microscopy (SEM) to assess changes in the microstructures of the rock samples. Nanoindenter was used to obtain hardness and mechanical parameters used to estimate the elastic modulus of the rock samples. Further, we assessed the implication of these nano-to-micro-scale alterations on the mechanical stability of the host reservoir for in-situ hydrogen generation. Results indicate significant increases in hardness (+19% H) and elastic modulus (+31% E) with microstructural alterations after serpentinization, which may impact stimulated geologic hydrogen.