A method of developing a geological reservoir according to a development scheme defined from a reservoir model, said reservoir model comprising a grid pattern associated with at least one parameter of said reservoir, wherein static data is measured within the reservoir and dynamic data is acquired during development, and wherein the following steps are carried out: a) constructing, using computer software, said reservoir model by means of the following steps: i) generating in a stochastic manner, as a function of said static data, a first initial reservoir model MR1 0 consisting of a first grid comprising N 1 cells and at least a second initial reservoir model MR2 0 consisting of a second grid comprising N 2 cells, with N 2 greater than N 1, the stochastic generation of said second model MR2 0 being constrained by the generation of said first model MR1 0, ii) scaling up the second model MR2 to a simulation reservoir model suited to be used by a flow simulator, iii) determining an objective function measuring a difference between said acquired dynamic data and dynamic data simulated using said simulation reservoir model and a flow simulator, iv) repeating steps ii) and iii) in order to minimize the objective function after modifying at least one of said reservoir models MR1, MR2 and by applying the modification to said non-modified model, b) determining, using computer software, an optimum development scheme by simulating the development of the reservoir using said second reservoir model MR2 and said flow simulator, and c) developing said reservoir by implementing said optimum development scheme. a) constructing, using computer software, said reservoir model by means of the following steps: i) generating in a stochastic manner, as a function of said static data, a first initial reservoir model MR1 0 consisting of a first grid comprising N 1 cells and at least a second initial reservoir model MR2 0 consisting of a second grid comprising N 2 cells, with N 2 greater than N 1, the stochastic generation of said second model MR2 0 being constrained by the generation of said first model MR1 0, ii) scaling up the second model MR2 to a simulation reservoir model suited to be used by a flow simulator, iii) determining an objective function measuring a difference between said acquired dynamic data and dynamic data simulated using said simulation reservoir model and a flow simulator, iv) repeating steps ii) and iii) in order to minimize the objective function after modifying at least one of said reservoir models MR1, MR2 and by applying the modification to said non-modified model, i) generating in a stochastic manner, as a function of said static data, a first initial reservoir model MR1 0 consisting of a first grid comprising N 1 cells and at least a second initial reservoir model MR2 0 consisting of a second grid comprising N 2 cells, with N 2 greater than N 1, the stochastic generation of said second model MR2 0 being constrained by the generation of said first model MR1 0, ii) scaling up the second model MR2 to a simulation reservoir model suited to be used by a flow simulator, iii) determining an objective function measuring a difference between said acquired dynamic data and dynamic data simulated using said simulation reservoir model and a flow simulator, iv) repeating steps ii) and iii) in order to minimize the objective function after modifying at least one of said reservoir models MR1, MR2 and by applying the modification to said non-modified model, b) determining, using computer software, an optimum development scheme by simulating the development of the reservoir using said second reservoir model MR2 and said flow simulator, and c) developing said reservoir by implementing said optimum development scheme.