Ambitious carbon neutrality targets have been set in Europe. To achieve this goal, decarbonisation of heat production is essential. In this context, the district heating network of Grenoble wants to achieve a renewable energy rate of 100% by 2033, while today, 20% of their heat come from fossils fuels. This study aims to investigate the best options to decarbonize their heat production. To do this, a methodology based on the internal CEA optimization software PERSEE has been developed. The first step is the modelling of the actual production plants of Grenoble district heating network as a reference for comparison. Then, bibliographic studies, integrating local authorities inputs, are carried out to pre-identify a range of technical solutions. These technologies are modelled in the PERSEE tool within a superstructure in order to select the most relevant ones. The pre-identified technologies include low-carbon fuels (biomass), renewable energy, fatal energy recovery, electric boilers, fuel cells, carbon capture & power-to-gas, biomass-to-X and thermal energy storages. Lastly, a multi-objective optimization is carried out (minimization of the CO2 emissions and maximisation of the Net Present Value) and a Pareto front of optimal solutions is obtained. For tractability reasons, a methodology is developed with different time step precision. First, computations are done with a 4-hour time step without considering thermal energy storages, but offering a good compromise between computation time and accuracy. A Pareto front is obtained, where each simulation, corresponds to a maximum carbon emission authorized and an optimal NPV. Three optimal architectures are then selected, corresponding to three different type of solutions: carbon capture, biogenic fuel and fossil fuels. Then thermal storage (sensible heat and building inertia) are included in the optimisation of these three architectures with a 1-hour time step. Results show that different paths for district heating decarbonisation exist. In any case, biomass plays a crucial role in the zero-carbon emission objectives. The integration of thermal storage and building inertia also enhances the load factor of cogenerations, shifting the solution from operating of electric boilers to that of biomass.