• Zeta Model

    Advanced job-design model for use with the Zeta gauge in the Zeta Safety System 



    The Zeta Model software is one of the two primary components that comprise the Zeta Safety System for well intervention operations. The Zeta safety system utilizes data and modeling to eliminate the guesswork commonly associated with well intervention design and operations. Designed to avoid catastrophic buckling and bending failures of well intervention stacks, the Zeta Safety System consists of a real-time monitoring gauge and an advanced job design model for well intervention operations.
    These potential failures are costly and could involve human injury and unplanned release of wellbore pressure to the atmosphere.

    The Zeta model is based on a non-linear finite-element (FEA) approach, purpose-written for analyzing intervention structures. The FEA analysis is run repeatedly at very small time increments to perform a dynamic analysis. A finite difference, forward difference scheme is used to determine the acceleration of each component in the stack, and the associated dynamic forces. The model accurately calculates the buckling instability of the stack. It also calculates the Von Mises stress throughout the structure, and compares the guy-wire loads to user-defined limits. Thus, it examines the structure for both modes of failure: failure due to buckling instability and failure due to yielding of a component in the structure.

    The Zeta Model answers the following questions:

    • Stress levels for the entire well intervention stack
    • Accurate modeling of stacks with moving wellheads and or floating platforms (dynamic analysis)
    • Stress changes resulting from stack loading changes
    • Need for additional stack supports and their location
    • Weight required to buckle the stack
    • Maximum stress location
    • Stack vibration frequency


    • Tall well intervention stacks
    • Moving wellhead and/or floating structure (TLP, SPAR) intervention stacks



    • Cost-effective equipment selection (Gimble tables, load frames, lubricator size/material)
    • Adequate safety margin for the specific intervention operation
    • Optimized rig-up configuration
    • Avoid catastrophic buckling and bending failures of the intervention stack
    • Eliminate guesswork and unproductive rig-time



    Extensive work has been performed to validate the results of the Zeta model. The model predictions vs. analytical results were excellent.

    • Buckling load model comparison were within 1% of each other under the same conditions (zero gravity situations - as typically stipulated in the analytical solution).
    • Critical frequency model comparisons were within 2% of each other under the same conditions.  

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