Southeast Asia 2002

 Problem:   While development drilling from a platform an unplanned event required a shallow casing sidetrack resulting in low kick tolerance. The reservoirs to be drilled were believed to be depleted. During drilling an unexpected pressurized thin sand was penetrated resulting in a kick. While circulating the kick out gas broached to the seabed below the platform for several hours and then bridged. Diagnostic logs inside the drillstring revealed various cross flows between the sand packages. The upper portions of the casing strings were found to have been cut by the broach to surface, resulting in a limited crater under the platform and damage to an adjacent well. No major damage occurred to the drilling unit or the platform. 
Remedial Strategy:  An intensive diagnostics investigation commenced utilizing wireline logs inside the drillpipe and hydraulic simulation software to model the probable crossflow scenarios and assess the risk of re-initiating the broach. After evaluating options, the decision was made to plug the existing well above the crossflow and drill a relief well to lower the pressure in the reservoirs to lower the broach risk. Additionally, the pressure relief well would be drilled to make a close proximity cross-by to reduce the intervention time to intersect the blowing well, if required at a later date. After the blowout well was plugged, the tender rig moved to an adjacent platform to drill the relief well. The well would additionally be drilled to deeper reservoirs (to produce the original objective) and maintain a ~70m proximity from the blowout when entering the reservoirs.
Special Services:  John Wright Company was contracted to provide both strategic and tactical special services. Technical assistance and onsite supervision during the initial diagnostic period and the P&A operations were provided. JWCO supervised the special services required for the relief well intervention project. This included pre-planning and on-site supervision of directional drilling, surveying, kill operations and casing detection. Vector Magnetics, responsible for electromagnetic ranging, was coordinated through JWCO on this project and worked together as one team. Well Flow Dynamics was instrumental in the diagnostic investigation and in simulating various kill scenarios for possible kill operations, both surface and relief well kills.
Challenges: The project was complicated by the following:
  • The platform was considered a worldwide critical asset by the owner and all operations were designed with significant safety factors to protect the asset.
  • A well slot on an adjacent platform was chosen for the relief well surface location requiring a slot recovery operation and several anti-collision concerns.
  • The target well has a ~28° inclination trajectory with a moderate displacement
  • Shallow gas was expected and the plan must include several contingencies.
  • The relief well would be converted to a production well, so dogleg rates, casing design and intervention time were critical design factors.
Results:
  • The ‘team concept’ for special services was successfully and efficiently utilized.
  • A conductor slot recovery whipstock window was utilized to initiate deflection.
  • No shallow gas was present during any pilot holes or final path.
  • The relief well crossed the blowout well at ~5m and then diverged to place the well at ~70m proximity at TD.
  • No abnormal pressure was present as the relief well drilled into and beyond the virgin pressured formation
  • The relief well was successfully drilled and converted into production well.