Offshore plants have many inherent constraints and risks compared to onshore plants, and it is crucial to optimize the operation of the offshore plant by adhering to constraints. Previous studies proposed a framework of utility systems that operate under various conditions. However, few studies have addressed the optimization of utility systems during the operating life cycle. To fill in this gap, we propose a new methodology for the design and optimization of the utility systems in the offshore plants. The utility systems are designed and optimized in Aspen Utilities Planner, considering the full life cycle of the oil and gas wells. For this, we first developed steady-state models of the topside processes based on every feasible operating scenario throughout the full life cycle. Then the utility consumption data was extracted from the simulation results and analyzed. The power system was designed using Aspen Utilities Planner (AUP), and it was optimized to maximize the thermal efficiency of the utility system, satisfying power demand for all the scenarios. The optimized results illustrate the significant saving of the operating cost and reduction of CO2 emission rate. Our studies suggest a generic framework to design utility systems in offshore plants.