Mechanical stability analysis of subsea wellhead for deepwater drilling

As drilling operation moves into deeper water, the stability of subsea wellhead may be influenced by the complex forces. According to mechanical analysis of subsea wellhead for deepwater drilling, a comprehensive stability analysis method is established. The marine environmental loading, drilling vessel or platform drifting, riser mechanical behavior, nonlinear behavior between casing string and formations are considered. Case analysis shows, the lateral displacement and bending moment of wellhead increases along with riser top tension ratios and current velocities. The bigger top tension will cause the wellhead to be over-pulled and increase the probability of wellhead collapse. As the mean drifting of drilling vessel or platform increases, the wellhead displacement and bending moment nearly linear enlarges. The greater current velocity may result in wellhead instability because of its limited bearing moment capacity. Therefore the drifting control is very important to subsea wellhead stability. The wellhead stability may be improved by taking measures such as enhancing the conductor bending strength, controlling scour depth on seabed, getting geological data sampling of shallow formations.