Louisiana 1992

 Problem: A producing well, having a dual completion, blewout in 1964 after a burst in the 10-3/4” casing. A crater subsequently formed at surface when the blowout fluids cut out around the 16” surface casing. The wellhead fell over in the crater which had been measured with soundings to ~220’ deep. After a surface kill and relief well operation, the well was plugged and attempts to straighten the wellhead occurred. The wellhead was severely bent during the attempted straightening, preventing any After ~30 years, attempts were made to survey the upper portion of the well which had toppled over. Initial surveying instruments could not pass below ~55’ and the operator requested assistance from JWCO. See Figure 1.
Remedial Strategy: A strategy was developed to map the subsurface location of the well utilizing electromagnetic ranging techniques. Several small diameter boreholes would be required within the vicinity of the wellhead and adjacent to the predicted path to provide suitable information for future well re-entry. Through relief well experience it had been proven that electromagnetic ranging services could precisely locate and measure the well tortuosity. See Figure 2.
Special Services: John Wright Company (JWCO) was contracted to develop a strategy to accurately map the upper portion of the wellbore and to provide a strategy to plug the well. This would include pre-planning and on-site supervision of: electromagnetic ranging operations and surveying. Vector Magnetics, provided electromagnetic ranging services, and were coordinated through JWCO.
Challenges: The project was complicated by the following:
  • The original surface location was only known from old “as surveyed” data.
  • A previously run gyroscopic survey showed the upper portion has doglegs of up to 205 5°/100.
  • The subsurface presence of blowout debris was not known and could mask the actual location of the target well.
  • Electromagnetic ranging operations accuracy would be reduced in the near vertical boreholes unless combined with a gyroscopic system.
  • The accuracy of the ranging operations were critical for the future strategy.
Results:
  • The Team Concept for special services was successfully and efficiently utilized.
  • A very large surface displacement with high inclination and doglegs accurately measured to a depth of 200’.
  • A combined SDC gyro/Vector Magnetics ranging tool were utilized with success.
  • Two sets of two ranging boreholes were required for accurate mapping.
  • The successful operation showed that a top entry would be near impossible.