Design of an experimental system and numerical simulation method for underground gas and energy storage

Underground gas and energy storage are emerging interdisciplinary fields that utilize subsurface geological space to store gaseous substances and, in some cases, surplus energy that is converted into gaseous carriers. The large-scale deployment of carbon, seasonal natural gas, geological hydrogen, and compressed air energy storage depends critically on a thorough understanding of multiphase flow mechanisms in porous media. However, accurately quantifying trace amounts of fluids under high-temperature and high-pressure conditions remains a major bottleneck in core-scale gas–liquid two-phase flow experiments. Conventional experimental approaches are largely limited to bulk statistical observations and fail to monitor the temporal and spatial evolution of fluid migration and distribution in real time. Furthermore, numerical simulation methods for accurate modeling through scale-up remain insufficiently developed. To address these challenges, this study conducts integrated experimental and numerical simulation investigations focused on underground gas and energy storage.

A comprehensive experimental platform was designed and constructed, consisting of three tightly coupled subsystems for displacement, nuclear magnetic resonance (NMR) measurement, and metering. Gas injection experiments into brine-saturated cores were conducted following standardized core-flooding procedures, employing stepwise injection and intermittent NMR scans. NMR measurements were performed using three complementary modalities: T2 relaxation spectra to quantify pore-scale fluid occupancy and movable pore space; SE-SPI maps to capture one-dimensional spatial distributions along the core axis via virtual slicing; and NMR imaging to obtain a two-dimensional visualization of dynamic displacement patterns and gravity segregation. To translate the laboratory findings to field scales, a hierarchical numerical simulation workflow was established. A core-scale model was constructed, enabling mechanistic interpretation of observed NMR patterns. Further, a two-dimensional plane radial flow model was developed to examine cyclic injection–production behavior and gas–water transition-zone evolution. Finally, a three-dimensional field-scale model was constructed to replicate the complex structures and heterogeneity of real formations and provide fully visualized multiphase–multicomponent dynamics for production forecasting and optimization.

The NMR-based experimental system enabled multidimensional, real-time quantification of gas–water processes, which are difficult to resolve using conventional methods. T2 spectra enabled accurate quantification of hydrogen-bearing fluids in porous media and revealed that evaporation is an additional transport pathway that can reduce residual water saturation, indicating a coupled “displacement–evaporation” mechanism. The SE-SPI maps revealed pronounced spatial non-uniformity in fluid distributions, indicating that injected gas preferentially concentrated in the upper part of the formation. NMR imaging indicated that the evaporation of residual water into the gas phase could mobilize water mass transport without requiring bulk liquid flow. Numerical simulations provided consistent mechanistic explanations and enabled reliable scale-up insights, and core-scale simulations successfully replicated key features observed in the experiments, including upward gas accumulation driven by gravity. The two-dimensional single-well model demonstrated a clear zonal storage pattern, comprising gas, gas–water transition, and outer water zones, and clarified the aquifer’s role in stabilizing reservoir pressure while driving water invasion during production. The three-dimensional field-scale model enabled visualization of convective behavior and heterogeneity-induced fingering and identified leakage-prone areas that require operational constraints and continuous monitoring.

This study proposes and validates an integrated experimental–numerical framework for underground gas and energy storage research. It combines an NMR-based laboratory system with multiscale, multiphase, multicomponent simulations spanning from core to field scale. This platform addresses longstanding limitations in trace fluid measurement and spatiotemporal visualization, enabling a systematic interpretation of storage mechanisms, migration behaviors, and distribution patterns under realistic formation conditions. By bridging laboratory measurements with well- and field-scale modeling, the framework establishes a practical basis for evaluating storage sites, designing injection and production processes, and optimizing underground gas storage in a risk-informed manner. Leveraging the China–Saudi “Belt and Road” joint laboratory, this methodology provides a scalable pathway for international collaboration and technology transfer in underground gas and energy storage, particularly in Middle Eastern regions with a number of depleted reservoirs and in China, which possesses extensive aquifer resources. This approach thus supports the development of cleaner and more diversified energy systems.