Long-term stability in subsurface energy storage reservoirs

Wider research context / theoretical framework Abandoned mine compressed air energy storage (AM CAES) offers large scale, flexible storage to balance variable renewables and demand. Yet the long term stability of caverns under cyclic gas injection and extraction in complex in situ stress fields is not well understood. This project adopts a multi field continuum damage mechanics framework combining rock mechanics, gas thermodynamics and nonlocal damage modelling to assess AM CAES cavern durability and safety. Hypotheses / research questions / objectives We hypothesise that cavern stability is controlled by the interaction between gas thermodynamics and the thermo mechanical response of the surrounding rock, and by coupled creep fatigue processes that govern damage initiation and localisation. We ask how pressure differentials, cycling frequency and injection extraction rates affect time dependent deformation and damage, and how these effects can be captured in predictive models for design and operation. Objectives are to obtain targeted experimental data, develop a multi field constitutive model with creep fatigue and nonlocal damage, and build a 3D platform to evaluate and optimise long term cavern stability. Approach / methods A dedicated rock mechanics test programme will use a self developed apparatus to impose AM CAES relevant gas pressure cycles and injection extraction rates, quantifying thermo mechanical response, creep and damage. These results will support a multi field constitutive model linking gas behaviour and rock properties, extended by a creep fatigue law and nonlocal 3D damage. An independent 3D numerical platform will simulate time dependent deformation and progressive damage for realistic cavern geometries and operating schemes, and will underpin parametric studies and design recommendations. Level of originality / innovation The project will provide the first systematic experimental characterisation of surrounding rock under realistic AM CAES loading paths. It will introduce a new multi field theoretical model that explicitly couples gas thermodynamics, rock thermo mechanical response, creep fatigue and nonlocal damage in one framework. It will also deliver the first numerical platform dedicated to AM CAES for simulating long term deformation and cumulative damage and for supporting performance, risk and design assessment. Primary researchers involved Dr. Guanglei Zhou will work with Priv.-Doz. Dr. Yunteng Wang and collaborate with Univ. Prof. Dr.-Ing. Wei Wu to complete the research tasks in this ambitious research project.