Abstract: A method is disclosed for determining well placements, or drainage areas, in a hydrocarbon reservoir to facilitate operation of the reservoir. Drainage area configurations are generated randomly, by generating, for each configuration, placements for each drainage area. The placements of each drainage area are determined to optimize a quality criterion, by an iterative optimization algorithm during which for first iterations, the quality criterion is evaluated by a flow simulator, and for subsequent iterations, an approximate evaluation model of the quality criterion is constructed. The quality of the approximate model is evaluated and the quality criterion is determined by the approximate model or by the flow simulator according to the quality of this approximate model.