The process of retrieving rock samples from a subsurface formation is a complex and expensive operation. Still, coring is the only way of formation evaluation to determine the full potential of the reservoir. Therefore, this thesis investigates and analyses the processes during a coring operation of a fractured dolomite formation. The key objective is to analyse the coring process on site, to evaluate its efficiency and derive coring specific KPIs. This allows a comparison of similar coring jobs in the future. Furthermore, possible process improvements for each stage of the coring job are highlighted. To evaluate the performance of the observed coring operation, case studies with similar boundary conditions were reviewed and KPIs extracted. The field study took place in the south German Molasse basin in the course of a geothermal drilling campaign. The process description is governed by personal observations, interviews, evaluation of daily reports, and analysis of rig sensor data from seven core runs. During post-processing the information, efficiency-critical areas such as tripping speeds, coring parameters, and operational time schedules were further investigated resulting in deviation- and core jam analyses. The coring results of this study show a clear underperformance compared to the case studies with a total recovery factor and a total coring efficiency below 50%. Additionally, the operational time estimation deviates significant from the actual case. The key takeaway is that coring a fractured dolomite reservoir using conventional coring is highly challenging and will most likely not deliver results usually expected in the coring business.