Cook Inlet
Alaska 1988

 Problem: While cementing the 13 3/8" casing, well control was lost on the annulus. Although diverted, the situation turned into a blowout with a devastating fire which resulted in severe platform damage. Ultimately the well bridged at the surface and the gas breached the 20" casing, threatening the integrity of the platform and supercharging shallow sands in the vicinity. A subsequent snubbing operation was unsuccessful due to the presence of losses, shallow gas and rubble.
Remedial Strategy: A relief well was evaluated as the least risk intervention option and would be implemented to stop the crossflow. A semi-submersible would be used due to the high tidal currents and shallow gas hazards. Weak formation strength would not allow cement to be circulated from the bottom of the blowout casing to the surface and therefore two targets would have to be intersected. It was desired to use the same wellhead to avoid the double risk of spudding with high tidal currents and shallow gas charging. A small team of specialists worked with the operator to achieve these objectives.
Special Services: John Wright acted as Intersection Unit Leader. Jim Woodruff was Directional Drilling Unit Leader On-site project engineering supervision of the directional drilling, surveying, casing detection and milling operations were fundamental responsibilities for project success.
Challenges: The project was complicated by the following:
  • Tidal currents of 7-8 knots created mooring problems and spudding difficulties.
  • Tidal height variations of 30' complicated initial depth correlation.
  • Shallow gas charging and a complete loss of circulation zone below the 20" was expected and relief well planning included appropriate options.
  • Shallow targets and tides required anchoring less than 400' from the platform.
  • High dogleg severity rates would be required in unconsolidated formations.
  • Kill equipment and connection to wellhead would be from a semi-submersible.
  • Inability to monitor kill fluid and cement placement on the crossflow.
  • Approach angle required surface current injection for electromagnetic ranging.
  • Environmentally sensitive area mandated that all operations must prevent spills
Results:
  • Team concept involving industry specialists and extensive pre-spud planning was instrumental to success.
  • Semi was successfully moored adjacent to platform despite high tidal currents.
  • Semi was operated safely over a gas bubble plume of over 200 ft in diameter.
  • Extensive rig modifications were made for diverting, pumping and safety.
  • A 9 7/8" hole "shallow gas exploration hole" drilled riserless 100' from spud location was suspended after it blewout to the seabed.
  • Sonar methods were successfully used to monitor gas plume and tidal depth.
  • Gas was diverted and controlled drilling below the 20" due to loss of returns.
  • Loss zone was ultimately controlled with loss circulation materials and cement.
  • Relief well trajectory was significantly changed, as necessary, due to loss zones, directional responses and operational requirements.
  • Dogleg rates in excess of 12°/100' were utilized to make intersections.
  • Surface and downhole electromagnetic and magnetostatic ranging was used to confirm intersection after first "lower" cement job was completed.
  • Second intersection was made using a 13 3/8" cased hole whipstock.
  • Cement was successfully circulated into both intersections after positive communication was established.
  • After extensive repairs to the platform structure, field development was continued.