It is proposed a method which comprises providing a geomechanical model of the geological environment, measurements of a first geological attribute each performed at a respective first position of the geological environment, constraints on a second geological attribute related to a yield criterion and each assigned to a respective second position of the geological environment, and a geomechanical simulator. The method also comprises determining the stress field derivable from the data outputted by the geomechanical simulator taking as input the geomechanical model and an optimal set of one or more boundary conditions. This provides an improved solution for estimating in situ stress field of a geological environment.