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The main objective of the fourth phase of the project 680 was to optimize a complete fracturing operation in horizontal wellbores for maximum productivity. Thus, a workflow and numerical tool chain Frac- and Frac-Produ simulators were developed with consideration of the thermo-hydro-mechanical coupling for the history matching and optimization of stimulation and production, respectively. After the verification of the developed simulators, a full 3D reservoir model was generated based on a real tight gas field in North German Basin. The simulated fracturing results are comparable with the treating pressure measurement, while the simulated gas production rate has the similar tendency to that of in-situ measured data. The numerical sensitivity analysis results show that the influences of proppant type on fracture geometry and fracture conductivity is much larger than that of the fluid viscosity, while the influences of the injection time are the smallest. The optimization simulation results show that the injection rate is not the higher the better. The fracture spacing should also not be too small. Thus, there is no universal criterion to determine the optimal number and spacing of the fractures, should be analyzed and decided from case to case.