The optimization recovery from mature resources requires the integration of various modelling resources and geological knowledge. This thesis addresses the challenge of maximising recovery from a mature, compartmentalised offshore reservoir, focusing on the Norne Field (Norwegian Sea). The study’s objective is to quantify the incremental value of Improved/Enhanced Oil Recovery (IOR/EOR) options, with emphasis on optimised waterflooding using a reproducible 3D numerical-simulation workflow. The workflow integrates (i) black-oil dynamic simulation in ECLIPSE with history-consistent controls and field constraints (e.g., injector/producer limits, BHP caps, water-cut and GOR cut-offs), and (ii) scenario design and ranking based on pressure support and incremental recovery. Three forward-forecast scenarios (Nov-2006 to Jan-2020) are tested: a do-nothing base case; targeted new producers selected by remaining-oil and interference criteria; and producer additions combined with strategically placed injectors to improve areal sweep.