Pakistan 1996

Problem: The surface location of an exploration well drilled in 1990 on the flood plain of an Indus River tributary became flooded. The raging waters toppled the wellhead and buried it under 8m of mud and debris. The well had been temporarily plugged with two bridge plugs above the perforated intervals with no cement having been pumped. The exact location and condition of the wellhead was not known, and a permanent P&A was required. See Figure 2.
Remedial Strategy: Surface and subsurface intervention operations were evaluated based upon risk and it was concluded that concurrent operations were required. During mid-May the flood waters of the Indus River would rise, halting all surface operations. The relief well was planned as a replacement well and would be utilized if well control was lost during surface operations or if the rising flood waters prevented further surface operations. While the surface operation was continuing, the relief well would be drilled to locate the target well and an intersection kill readied for immediate intervention. After controlling the blowout, the relief well would then become a replacement well. See Figure 1.
Special Services: John Wright Company (JWCO) was contracted by Alert Disaster Control of Singapore to supervise the special services required for the relief well intervention project. This would include pre-planning and on-site supervision of: directional drilling, surveying 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 simulated various kill scenarios for the two proposed kill operations.
Challenges: The project was complicated by the following:
  • The surface location was chosen by the Operator prior to JWCO involvement.
  • An "S" shaped well design, with a 5/30m BUR in 17-1/2" hole to 56 was necessary to locate the target well.
  • Only low accuracy inclination surveys existed for the target well.
  • Electromagnetic ranging operations would be hindered by the high incidence angle (>50) between the two wells.
  • Kill operation was influenced by poor pressure integrity of wellhead equipment.
  • The 'team concept' for special services was successfully and efficiently utilized.
  • A large surface displacement, which was found to be 48m more than reported by the operator, complicated the relief well design.
  • Data showed the relief well path passed the target at approx. 2-3m proximity.
  • The surface operation required locating the wellhead and cutting of the casing strings prior to setting up the snubbing unit and plugging the well. See Figure 2.
  • The successful surface operation prevented the use of the relief well kill option.