According to the invention, in order to initialize the use of a multipoint geostatistical technique (MPS), the method takes information, which was collected in wells drilled in the area of the subsoil to be modeled, into account. Particularly, the method takes inter-well connectivity data into account, which indicate one or more groups of cells of a reservoir grid that are located along a plurality of wells and between which hydrodynamic communications have been observed. For each of said groups, compatible thumbnail images are searched for in a training image used in the MPS technique. Said thumbnail images have, in the training image, facies that enable the flows between the cells of the group. The thumbnail images are applied onto the reservoir grid in order to initialize MPS simulation while ensuring that the inter-well connectivity constraints will be respected.