Objectives/Scope

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)

Methods

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.

Results, Observations, Conclusions

The main results are:

  1. Steel to fiberglass wear factor is generally extremely high.

  2. Rubber protector to fiberglass wear factor is very low, even down to zero for specific fiberglass types (at least at testing temperature and without cuttings being present).

The main conclusions are:

  1. Wear completely prohibits standard drilling operations with steel pipes inside fiberglass casing, even just tripping in and out once will cause significant wear levels.

  2. Hence rubber protectors must be used so that steel to fiberglass contacts are avoided completely (Limitation: Clamp on protectors should not be placed in the open hole, hence a section of BHA and string equal to the open hole length remains unprotected).

  3. In the specific well the open hole section was approximately 200 m long, however the predicted wear was so high, that it only allowed for a sliding drilling operation with very limited amount of rotations.

  4. Tool joint contact can be easily avoided, but pipe body contact is dependent on the trajectory, the OD of the protectors, and string stiffness. Hence spacing out of protectors should be simulated using advanced string models.

Novel/Additive Information

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.

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