||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
|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
|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
- The Team Concept for special services was successfully and
- 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
- The successful operation showed that a top entry would be