Geyser Basin
California 1991

Problem: During the completion phase of this geothermal well, an unintentional sidetrack occurred, preventing the re-entry into Leg 1 of a two leg well. Leg 1 had been drilled and cased through the steam reservoir. A packer had been set at a shallow depth to seal off the steam and allow the drilling of a second leg. A 40' casing section was milled and Leg 2 was drilled and cased. The plan was to produce from both legs and the same wellhead. While attempting to re-enter and remove the packer from inside Leg 1, the stub was missed, a sidetrack occurred and attempts to re-enter were unsuccessful.
Remedial Strategy: A remedial operation was planned to parallel the Leg 1 casing and intersect the well below the packer but above the reservoir. Very close proximity and a low incidence angle would be required to allow the cutting of a slot into the well. A specially designed junk mill would be used to cut the slot into the casing and allow steam to be produced from the openhole of the sidetrack.
Special Services: John Wright Company (JWCO) was contracted to supervise the special services. This would include pre-planning and on-site supervision of: directional drilling, surveying, casing detection, milling and re-entry into the casing. Vector Magnetics provided electromagnetic ranging services and worked together with JWCO to create a single team.
Challenges: The project was complicated by the following:
  • High temperatures resulting in steam flashing, required pumping with no returns.
  • All borehole surveying and ranging operations must be inside DP or DCs.
  • Extreme vibrations would require testing of surveying systems for application.
  • Drilling, ranging, surveying and wireline operations, with an open leg of live steam, was considered risky.
  • Drilling parallel and alongside existing casing would require precise directional control and accurate casing detection techniques.
  • 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 and included ranging inside nonmagnetic drill collars
  • Casing was milled below the packer with custom mill.
  • Rate gyro system was the only tool which could cope with the high temperatures and large vibration amplitudes.
  • Steam communication was achieved and the well was put on production with two legs producing.