A simulation study of natural gas injection and storage in a partially depleted oil reservoir for seasonal underground energy storage

The supply of energy is a severe challenge for every country, particularly those that are industrially developed and highly populated. Natural gas is among the most essential energy sources due to its reasonably low cost and high heating value. One of the elements of a sustainable energy supply is underground gas storage (UGS). UGS systems consist of a cushion gas (base gas) and a working gas. The cushion gas is injected into a reservoir to sustain the pressure and remain there until the period of storage ends, while the working gas is the main gas to be stored and produced. Unlike prior studies on fully depleted fields, our research emphasizes the potential of UGS in the presence of remaining oil and integrates key concepts, such as enhanced oil recovery and CO₂ sequestration. A simulation study was conducted using Qatari Advanced Simulator for Reservoirs software to determine the feasibility of a UGS system in a partially depleted oil reservoir. N₂ and CO₂ gases were considered and analyzed over short, medium, and long injection/withdrawal cycles to investigate their potential as cushion gases for natural gas storage in a partially depleted oil reservoir. It was found that using CO₂ as a cushion gas produces 32 %, 57 %, and 90 % of CH₄ according to short-, medium-, and long-term energy storage scenarios, respectively, with the CH₄ production higher than when using N₂. This study sheds light on the feasibility of implementing underground gas storage systems in partially depleted oil reservoirs.