A case history of an attempted CT intervention in 43' of water through a wellhead leaning at a 45 degree angle is presented. A major concern for this intervention was the integrity of the intervention stack between the leaning wellhead and the CT injector located on a lift boat. The stack design, testing and stack performance during the job execution are presented.
Hurricane Katrina damaged many wells in the Gulf of Mexico. One well in 43 ft of water in the West Cameron field was left with the wellhead leaning at 57 degrees. The operator wants to P&A this well. An unsuccessful attempt was made to pull the wellhead upright. A CT intervention was attempted to P&A the well, with the CT unit located on a lift boat. Support structures were built to hold the CT injector at a 45 degree angle and to support the intervention stack between the wellhead and the lift boat.
There was significant concern that the intervention stack between the wellhead and the lift boat would be safe. Extensive stack modeling was performed during the job planning and equipment selection process. A dynamic finite element stack modeling package (Smalley 2005) was used to perform this analysis. The API 6AF bending limits were added to this analysis software because these flange bending limits became the most limiting aspect of the job. Based upon this analysis, the planned stack support structure was greatly simplified, reducing the installation time and cost.
A force and moment gauge (Newman 2004) was placed in the stack to measure the forces and bending moments. This gauge was useful in obtaining proper stack alignment, reducing bending in the stack. The gauge was then used to monitor the stack during the attempted P&A intervention.
Figure 1 shows a survey of the well from the mud line up and Figure 2 shows a picture of the wellhead above the water. The first concern was whether the outer 36", inner casings and the 2 3/8" tubing were kinked below the mud line. If they were, it would be impossible to plug and abandon (P&A) the well with a CT intervention.
An engineering analysis had been performed to calculate the deformed shape of the well below the mud line and the ovality of the well tubular based on this deformed shape. Figure 3 shows the deformed shape from this study. The smallest radius of curvature was calculated to be 14' at between 25' and 30' below the mud line. The amount of ovality in the 2 3/8" tubing was determined to be negligible. Thus, a CT P&A intervention was deemed feasible.
Previously an unsuccessful attempt had been made to pull the wellhead upright. It was decided that the CT intervention had to be performed at the current angle of the well. A support pylon was driven beside the wellhead to prevent further wellhead movement. The wellhead was lifted somewhat and attached to this pylon at an angle of about 45 degrees.