Drilling Inside Fiberglass Casing, Wear Prediction and Management in Geothermal Wells

Abstract

Due to corrosive fluids being expected in the geothermal wells planned for the Champigny (Paris) district heating, fiberglass casing was used. It was deemed beneficial, if drilling operations could be performed with an exposed fiberglass casing, despite high expected wear. This paper will lay out how a feasible strategy was planned, utilizing advanced wear prediction techniques for drilling inside fiberglass casing. The study was conducted by CFG (compagnie Française de Géothermie) and funded by ADEME (Agence de la transition écologique) To achieve an accurate wear prediction three parameters are required: (1) Trajectory and actual tortuosity (2) Wear factors (3) Operations (number of rotations and distance slided). Tortuosity was calibrated on offset wells (Aichinger, 2021) and expected operations were covered in scenario analyses. Wear factors were determined using field calibration and laboratory testing. The field calibration was performed on three offset wells using an internal diameter interpretation method in which the wear is measured against the most probable elliptical casing shape and herby allowing wear measurement avoiding bias error. (Aichinger, 2016) The laboratory tests were conducted in Mines ParisTech / Armines including different fiberglass types, protectors, sideforce amplitude, rotation speed and lubricant. Based on the derived parameters various drilling scenarios and the associated wear levels were simulated to decide on a drilling strategy. The main results are: The main conclusions are: This paper should provide help to Engineers who plan to perform drilling operations inside fiberglass casing, mainly by providing Wear Factors, but also general guidelines on wear prediction and mitigation techniques.