This PhD project at Heriot-Watt University investigates the synergistic and competitive effects between multiple gas storage operations in subsurface porous media, with a particular focus on the North Sea region. As CO₂ storage projects proliferate and interest in subsurface hydrogen storage grows, understanding the interactions between different injection sites and gas types becomes critical for safe, efficient, and sustainable geological resource management. The research aims to explore fluid migration behaviour and pressure dynamics when CO₂, H₂, and natural gas storage processes coexist in close proximity, examining both competitive and synergistic interactions. The project will employ advanced flow simulations using industry-standard software such as CMG, ECLIPSE, PFLOTRAN-OGS, and research codes like MATLAB to model these complex subsurface processes. The outcomes will inform strategic resource use, capacity planning, and pressure management, contributing to responsible stewardship of geological formations increasingly used for energy storage. The position is based in the School of Energy, Geoscience, Infrastructure and Society and is supported by a full EPSRC scholarship for UK-home students, including tuition fees and a generous annual stipend (£20,780) for 42 months, with additional funding from Crown Estate Scotland for research and travel. Applicants should have a strong background in geoscience, geology, earth science, or engineering, and must provide a comprehensive application including a supporting statement, CV, academic transcripts, reference, and proof of English proficiency. The application deadline is November 28, 2025, with a start date in January 2026. For further information or informal discussion, candidates are encouraged to contact the supervisory team.