Drilling wells from offshore platforms is always a challenge because of the need to eliminate potential collision issues caused by the relatively close spacing of wellheads. On a platform offshore Abu Dhabi, the spacing of the wells is 7.4 ft center-to-center and less than 5 ft wall-to-wall. There are nine slots on the tower, with five slots already used. Based on the required kickoff azimuth, the most logical slot for a high- profile deep and high temperature well was slot 9 (on the corner of the template) to reduce the risk of a well-to-well collision. However, using slot 9 would make it very challenging and risky to use slot 3 in the future.
A detailed risk assessment was conducted, and the following risks were identified: 1. the motor producing an unknown amount of reactive torque while kicking off, could lead to a departure of the well from the plan and a collision with other wells or to block the empty slots. 2. Excessive dogleg at a shallow depth would incur high torque and drag in deeper sections, thus increasing the risk of string washout or twistoff and excessive casing wear. Also putting a higher loading on the top drive to drill the deeper sections. 3. Rig time would be taken for running the single-shot gyro. 4. As the circulation would have to be stopped to take the gyro single shot, there would be risk of hole packoff and stuck pipe. 5. There would be a long distance from the bit to the survey point if the single-shot gyro were run above Measurement-While-Drilling (MWD) tools, causing a "late reaction" to any deviation changes.
After discussion, and a detailed cost / benefit analysis and risk assessment, it was decided to use a Gyro-While-Drilling (GWD) service as this would remove or significantly reduce the identified risks. This was the first usage of this service in the UAE for ADNOC companies (ADMA, ZADCO, ADCO), and the results were excellent. The well was kicked off in the correct direction from the start. There were no violations of the anti-collision rules to offset wells or empty slots. The well was steered away from slot 9, leaving it to be used for future wells. There was no reduction in the drilling parameters used to drill this 26″ hole section. There were no hole packoffs or stuck-pipe incidents, and the service saved at least 8 hours of rig time. Tight communication ensured all personnel involved had timely access to required information, which increased the confidence in decisions to drill ahead.