Oman 1997

Problem: Deep gas well drilled to top of reservoir at 4700m, became stuck on trip 1000m off bottom. Abandoned BHA and sidetracked 350m BHA fish. Took kick at first permeable zone below fish with intensity of gas zone 1000m deeper. Set 9-5/8” casing and continued to drill to objective for testing. After testing completed, concern about gas crossflow and possibility of broach to shallow zones and the surface dictated management find a solution. See figure 1.
Remedial Strategy: Four options were evaluated for control. The option chosen would be to cut a window in the existing sidetrack through 9-5/8” casing. Then directional drill along side the fish BHA using electromagnetic ranging for proximity control. Set a 7” liner +/- 100m above the bit on the fish then intersect the open hole at an approach angle that would allow the original 12-1/4” wellbore to be re-entered after the well was killed. If re-entry was achieved the 12-1/4” hole would be cleaned out back to 4700m and plugged and abandoned.
Special Services: John Wright Company (JWCO) was contracted to supervise the special services for the relief well. This would include pre-planning and on-site supervision of directional drilling, surveying, casing detection, re-entry into the open hole and kill hydraulics. Vector Magnetics provided electromagnetic ranging services and Well Flow Dynamics provided hydraulic simulations support. Both companies worked together with JWCO to create a single team.
Challenges: The project was complicated by the following:
  • Casing from original sidetrack created error signal for electromagnetic ranging
  • Section of claystone formations would cause hole stability and loss problems.
  • Drilling parallel and alongside existing BHA and aligning for re-entry would require precise directional control and accurate casing detection techniques.
  • The re-entry intersection would be implemented with 4-3/4" directional tools.
  • Unknown gas flow situation in 12-1/4” hole created the necessity to be prepared for several different scenarios upon intersection (e.g. total losses, kick, H2S).
  • Team concept for special services was successfully and efficiently utilized.
  • Existing wellhead was successfully utilized for the remedial well.
  • Electromagnetic ranging techniques were critical for project success.
  • Directional drilling control required high dog-legs for final alignment.
  • Open hole was intersected below bit at 1 deg inclination and alignment was such that the relief well bit and BHA slipped into the 12-1/4” hole with only slight increase in torque.
  • No gas was encountered. The BHA was washed to total depth and the 12-1/4” wellbore plugged and abandoned.