Southern California
Gas Well 1991

 Problem: A workover resulted in an unintentional sidetrack through the existing casing of this gas storage well. A packer had been set just above the storage reservoir and after pressure integrity was established, a retrieval would be made to resume gas injection. Perforations in the storage reservoir were open and storage gas was migrating to shallower sands through a casing leak. After two months of unsuccessful attempts, reentry into the well at the sidetrack point utilizing conventional methods became futile. The well perforations must be squeezed to prevent further flow to shallower zones for the field to yield optimum injection/withdrawal profile.
Remedial Strategy: The leaking well would have to be plugged by unconventional techniques. A remedial operation was planned to parallel the existing casing, below the sidetrack, to a depth just above an isolation packer set at 10,100 ft, a depth adequate to abandon the lower section of the well. Very close proximity and 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 a section of the casing away after intersection a cement squeeze would commence. After plugging the well, a second sidetrack would be drilled to the reservoir and ultimately completed for gas storage use.
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:
  • Borehole surveys from 1961 were considered to have high position uncertainty
  • Section of swelling claystone formations would cause hole stability problems.
  • The reentry intersection would be implemented with 4-3/4" equipment.
  • Condition of the casing string was suspect and flow was expected when close.
  • Drilling parallel and alongside existing casing with poor surveys would require precise directional control and accurate casing detection techniques.
Results:
  • 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.
  • Casing slot was milled from 9912 ft to 9934 ft with custom mill.
  • Remedial well intersection at 9912' with 1û incidence angle achieved.
  • Lower section was squeezed with cement and properly plugged and abandoned.
  • Second sidetrack was drilled to reservoir and completed for gas storage use.