Ultimate Capacity of a cemented Oil Well
Dynamic positioning (DP) drilling operations have been conducted for more than 40 years now, with significant advances in equipment and controls. Yet, some of the major concerns with DP vessels are associated with the consequences following the loss of vessel positioning and failure to disconnect. In this unfortunate event, the rig remains connected to the subsea Blow-Out-Preventer (BOP) and the Well, and as the vessel drifts away, the stressing on the system grows substantially. At the moment the tensioners break down, the loads increase rapidly until the weakest link, the riser or the well, fails first.
We were asked by our client, an oil company, to develop a modeling methodology through Finite Element Analysis (FEA) to assess the ultimate capacity of a cemented wellhead and casing system under the extreme loads transmitted from a deepwater drilling riser. The objective was to ensure that the drilling structure will by no means collapse below the (BOP) level (resulting in potential loss of hydrocarbon containment).
Our numerical methodology involved 3D non-linear FE analyses allowing the rigorous simulation of the soil-casing and the cement-casing interface. The importance of other low-probability phenomena such as voids within the cement or imperfect.