California 1991

 Problem: In 1938 the control of a well was lost resulting in a blowout with only the surface casing set. A 100 ft diameter crater formed and swallowed the rig. A relief well was drilled the following year, but was only partially successful. The crater had remained with a fence around it since that time. The well continued to bubble gas at various rates. The new field operator desired to permanently plug and abandon the well and backfill the crater.
Remedial Strategy: The flowing well would require unconventional plugging techniques in order to fulfill proper plug and abandon mandates. The original relief well had been spudded 165 ft from the center of the crater and would be utilized for the operation. Drilling would continue from the existing relief well casing into the area under the center of the crater. The electromagnetic ranging tools would be instrumental in locating the original drillstring that was left in the hole in 1938. After locating the old drillstring and establishing communication, a light weight cement slurry would be circulated to stop the gas migration and ultimately the crater would be backfilled with gravel.
Special Services: John Wright Company (JWCO) was contracted to supervise the special services required for this project. Special services included pre-planning engineering and on-site supervision of: directional drilling, surveying, and casing detection. The field operator and drilling contractor supervised the normal drilling activities. Vector Magnetics was contracted and was responsible for electromagnetic ranging services and worked together with the JWCO on this project as one team.
Challenges: The project was complicated by the following:
  • There were no borehole surveys of any kind on the flowing well.
  • It was not known if the existing relief well would pass pressure tests.
  • It was not known if the drillpipe was still intact after 50 years in saltwater flow.
  • Formation strength was low requiring light weight cement.
  • The fresh water zone was not sealed requiring precautions with chemicals.
  • The competency of the formations surrounding the blowout after 54 years was questionable and hole stability was a major concern.
Results:
  • Team concept for special services was successfully and efficiently utilized.
  • Existing relief well was successfully utiliized for the remedial well.
  • The existing drillpipe was not located immediately by electromagnetic ranging techniques. This indicated either severe corrosion or missing drillpipe altogether
  • The drillpipe was located deeper with a strong signal at distance of 7 ft.
  • Cement was squeezed into the reservoir and the crater was backfilled.