Pau France 1997

 Problem: A workover resulted in a collapsed casing situation with the BHA becoming stuck in a claystone formation. Flow from a highly productive water zone at ~1100m TVD flowed into the two underpressured production zones separated by the collapsed claystone formation. The reservoirs were being "dump flooded" and the recoverable reservoir production was dropping dramatically. Flow was suspected into both the DP and the DP x 7" casing annulus. Fishing and other conventional methods and techniques resulted in several unsuccessful and very costly attempts to plug and re-enter the well. The predicted 10,000m3/day rate of downward flow presented an unusual kill problem, requiring careful analysis of all currently available mechanical plugging materials which would allow easy and complete removal if the plugging attempt was unsuccessful.
Remedial Strategy: The flowing well was to be plugged by unconventional techniques. The remedial operation, which utilized the existing wellhead, was planned to intersect the well in several intervals for initially plugging and then for confirmation that the flow was halted. The remedial path would begin at a sidetrack plug set atop the casing stub. After the setting of a 7" casing string, a milling operation would establish hydraulic communication. Communication must include milling of both the 3-1/2" DP and 7" casing to open all flowpaths. The flow would be halted by plugging all flowpaths with CaCO3. CaCO3 could be acidized and the flowpath re-opened if required. After evaluating the well conditions, a cement plug would plug the well above the intersection point. The final P & A would not occur until all evidence concluded that the well was permanently plugged.
Special Services: Applied Incident Management Inc (AIMI) was contracted to analyze intervention options, prepare project engineering plans and to supervise and coordinate the special services. On-site project engineering supervision of the directional drilling, surveying, casing detection and milling operations were fundamental responsibilities for project success.
Challenges: The project was complicated by the following:
  • Only low accuracy Dipmeter type surveys existed.
  • Lost circulation would be present for the majority of the drilling operations.
  • Magnetic interference would require extensive use of gyroscopic equipment.
  • Additional zones of casing collapse were suspected and required the intersection point below the 9-5/8" casing shoe.
  • The kill & plugging program must not prevent other control options if any operation failed.
  • Drilling parallel and alongside existing casing without surveys would require precise directional control and accurate casing detection techniques
Results:
  • The existing wellhead was successfully utilized for the remedial well.
  • Several zones of collapsed casing were found with thermal and magnetic data.
  • A rate gyro was successfully used to orient drill with less than 1º inclination.
  • A ~30m 9-5/8" casing contact at ~80m above intersection point was achieved.
  • Communication established after milling 4m of 7" casing and ~1m of 3-1/2" DP.
  • Approximately 35 tonnes of CaCO3 were pumped to plug the flow and a cement plug was placed in the casing and drillpipe above the intersection point
  • A downhole video camera recorded the milling, killing and pumping results and provided inconclusive intersection and plugging progress.