Weak Wellhead Analysis
Understanding wellhead loads during operations is paramount to a well’s success. Using sophisticated software, combined with over 100-years of experience in wellhead analysis, AS Mosley helps maximise well operability and fatigue life by carrying out weak wellhead analysis. Data captured is then used to provide specialist advice and consultancy support to oil & gas companies.
The background of Subsea Wellhead Design
Over the years the design of subsea wellheads has improved with increased strength resistance and optimised fatigue characteristics. Early subsea wellheads were based on land wells with very little marinization. These older wells sometimes incorporated multiple casing heads with no heavy wall extensions. Modern wellheads have two housings locked together with preload and high strength heavy wall extensions for load transfer. The inner housing (HPH, most often 18 3/4” ID) provides pressure containment with provision to support casing, the outer housing (LPH – typically 36” OD) provides the structural support to transfer all the axial and bending loads into the soil foundation. Older wellheads may have low capacity HPHs (i.e. 13 5/8”) or weak LPH extensions (i.e. 30”).
The problem with weak wellheads can be greatly exacerbated by the marine riser equipment used during operations. Older wells may have been drilled originally with small stacks (i.e. 80Te) and lightweight risers. Conversely, modern 6th generation drilling rigs could have 400Te stacks with heavy wall riser joints – inducing far greater loads.
AS Mosley specialises in understanding wellhead loads during all operations and the effect this has on operability and fatigue. We assist our customers with rig selection and provide advice on methods of maximising operability and fatigue life during operations. Furthermore, we provide a wellhead screening study to estimate the fatigue life for the proposed operation based on a representative rig – including historical damage.
For more information on weak wellhead analysis, contact AS Mosley directly.
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