Reservoir characterization is carried out by means of different techniques like well logging, core analysis, seismicity, well test interpretation, among others. Well test interpretation constitutes a key tool to obtain specific parameters in hydrocarbon reservoirs and it is the subject of this work. In the last decades it has been carried out studies that consider the change in rock properties due to the changes of pressure for the different activities. Having this in mind a software is developed that allows well tests interpretation and it can be used for different scenarios. The problem presents the diffusivity equation of monophasic flow of gas or petroleum in naturally fractured reservoir and it considers the pressure sensitivity with the permeability module. The solution is carried out with Stehfest algorithm, used thoroughly in the oil industry.