Material Behavior in Deep Underground Energy and Resource Development

Deep underground engineering — spanning geothermal energy extraction, oil and gas recovery, deep mining, underground gas storage, and radioactive waste disposal — is progressively extending into environments characterized by high in-situ stress, elevated temperature, and complex fluid-rock interactions. Under these extreme conditions, earth and planetary materials such as rocks, soils, and rock masses exhibit mechanical, hydraulic, thermal, and chemical behaviors that differ substantially from those observed at shallow depths. Understanding and predicting these coupled thermo-hydro-mechanical-chemical (THMC) processes is not only a scientific challenge but also a practical imperative for ensuring the safety, efficiency, and sustainability of deep underground energy and resource development.

Recent advances in experimental rock mechanics, in-situ monitoring, and numerical modeling have improved our ability to characterize deformation, failure, and permeability evolution in deep geological formations. However, significant challenges remain in capturing the multi-scale, multi-physics processes that govern material response under deep underground conditions, including strain localization, fracture propagation, creep and long-term stability, and the effects of cyclic thermal-mechanical loading associated with energy storage operations.

This Research Topic aims to bring together original research and reviews addressing the fundamental and applied aspects of material behavior relevant to deep underground energy and resource development. We welcome contributions covering, but not limited to, the following themes:

• Mechanical, hydraulic, and thermal properties of deep rocks and rock masses under high stress and temperature

• Coupled THMC processes in geothermal reservoirs, hydrocarbon reservoirs, and underground storage systems

• Fracture initiation, propagation, and permeability evolution in fractured and porous media

• Creep, fatigue, and long-term stability of surrounding rock in deep excavations, boreholes, and caverns

• Constitutive modeling and numerical simulation of deep rock/soil behavior

• Novel laboratory and field-scale experimental techniques for characterising deep earth materials under extreme conditions

• Multi-scale characterisation and upscaling methods for linking laboratory-scale observations to field-scale behaviour

• Risk assessment and hazard mitigation (e.g., induced seismicity, borehole instability, rockburst) in deep underground operations

• Applications to emerging fields such as enhanced geothermal systems, compressed air/hydrogen energy storage, and deep geological carbon storage

By integrating perspectives from rock mechanics, geophysics, materials science, and reservoir engineering, this Research Topic aims to advance the fundamental scientific understanding necessary to underpin the safe, sustainable, and economically viable development of deep underground energy and resource systems.