Field-Scale Storage of LOHCs in Depleted Reservoirs: Energy Storage and Enhanced Oil Recovery

Liquid Organic Hydrogen Carriers (LOHC), such as Toluene/Methylcyclohexane (MCH), offer a reversible, safe, and efficient method for storing and transporting hydrogen. This study investigates the dual potential of LOHC injection in depleted hydrocarbon reservoirs—enabling cyclic hydrogen storage while unlocking incremental oil recovery. By integrating energy storage with enhanced oil recovery (EOR), this approach aims to improve the feasibility of subsurface hydrogen initiatives, particularly in regions with existing petroleum infrastructure. High-resolution compositional reservoir simulations were performed using the commercial compositional simulator to evaluate the field-scale performance of LOHC storage in a representative depleted reservoir. Toluene was injected and later extracted as part of a reversible hydrogen cycle, accounting for its conversion to/from MCH. Multiple cyclic injection–withdrawal scenarios were modeled to mimic real-world operational conditions and evaluate key metrics, including LOHC recovery, pressure response, mass transfer, and oil mobilization. Thermodynamic behavior, fluid interactions, and flow properties were calibrated using available PVT data. A base model was constructed with realistic petrophysical properties (porosity, permeability, and initial saturation), and injection-production strategies were optimized to enhance recovery efficiency while maintaining reservoir stability. The reservoir response to each operational cycle was assessed in terms of fluid displacement efficiency, water cut, and compositional tracking of the LOHC components. Simulation results indicate that optimized cyclic injection strategies led to a LOHC recovery factor of approximately 75%, demonstrating the technical feasibility of reversible hydrogen storage in depleted formations. Moreover, injecting Toluene led to favorable thermodynamic and displacement conditions that enabled up to 40% incremental oil recovery from the depleted zones. The cyclic operation maintained effective pressure support across simulation periods, while water cut was consistently less than 0.0001%, confirming highly selective displacement behavior. These results suggest that LOHC injection not only supports the hydrogen economy through secure subsurface storage but also rejuvenates mature fields with additional oil production.