• Background

    In 2005, Hurricane Katrina damaged several wells located in the Gulf of Mexico. One well, in particular, in 43 feet of water was left with the wellhead leaning at a 57° angle, and the operator needed to be able to perform a plug and abandon (P&A) operation. An unsuccessful attempt was made to try and pull the wellhead upright in order to perform the P&A operation. 

    When exploring possible alternative solutions, the first concern with this angled wellhead was whether the outer 36" inner casings and the 2 ⅜" production tubing were kinked below the mud line. If they were, it would be impossible to P&A the well with a coiled tubing intervention. Fortunately, after an engineering analysis had been performed, it was concluded that the smallest radius of curvature was calculated to be 14 feet at a location ranging from 25 feet to 30 feet below the mud line. The amount of ovality in the 2 ⅜" production tubing was determined to be negligible and a P&A intervention was deemed feasible at the current angle of the wellhead. However, there remained significant concern regarding potential loading that would be applied to the intervention stack as it spanned the distance between the lift boat and the leaning wellhead.

    Solution

    CTES, a part of the Intervention and Stimulation Equipment Business Unit, was selected to perform an extensive stack modeling analysis, using the Zeta System, to ensure the intervention stack between the wellhead and the lift boat would remain within safe working limits while performing the P&A operation. Support structures were built to hold the coiled tubing injector at a 45° angle and to support the intervention stack between the wellhead and the lift boat. During rig-up, the Zeta Gauge was placed in the stack to measure the forces and bending moments in order to obtain proper stack alignment and reducing bending moments applied to the stack. The Gauge was subsequently used to monitor real-time stack loading during the attempted P&A intervention.

    Results

    • Modeling of the well intervention structure significantly reduced the complexity of the structure by eliminating multiple unnecessary components. The cost savings obtained by eliminating these components significantly exceeded the cost of modeling and measuring the behavior of the structure.
    • Including the Zeta Gauge (a real-time axial force and bending moment measuring device) in the intervention stack enabled proper alignment of the stack, avoiding a potential stack failure due to bending. 
     

    Contact Us For More Information

    Fore more information concerning the CTES Zeta Gauge, please contact us at ctessales@nov.com or visit the product page here.

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