Hydraulic fracturing is one of the primary engineering tools to increase the productivity of a well. Stimulating a well by a hydraulic fracturing treatment usually leads to a high negative skin factor. This work aims to define the problem and to modify an existing reservoir simulation model, such that negative skin factors do not cause constant difficulties. Changing the negative skin factor in the simulation model below a threshold value leads to an abnormal end of the simulation run. The skin factor is defined by the geometry and the permeability of the grid block containing the now stimulated well. As the explicit discretization of hydraulic fractures in the reservoir model is time- and cost intensive, this thesis focuses on a method to handle a high negative skin factor in a commercial reservoir simulator. With the concepts of the effective wellbore radius and the pressure equivalent radius two approaches to calculate the threshold skin factor are given. Some considerations are demonstrated to avoid the use of a negative skin factor. The most accurate result is delivered by the connection transmissibility multiplier, which is included in the simulation file instead of a negative skin factor. Besides the application in a vertical gas injection well the precision of this multiplier is represented in multiple application examples, including changed geometry and permeability properties. Finally, the utilization of the multiplier in horizontal wells is also discussed.