Drilling riser Download the model: Drilling_Riser.stask Figure 1. SIMA Drilling Riser 1. Description A drilling riser connects a floating drilling vessel at the surface to the subsea wellhead and blowout preventer (BOP) on the seabed, providing a conduit for the drill string and drilling fluids. Because it is a long, slender pipe hanging in deep water, it must be held in tension from the top to keep it stable and to limit bending; the key quantities to assess are the flex-joint angles at the top and bottom, the top tension, and the bending stresses along the riser. This example demonstrates such a top-tensioned drilling riser in a water depth of 330 m. 1.1. Riser stack The riser is built up as a realistic drilling-riser stack running from the wellhead on the seabed up to the drilling vessel, with a total riser length of about 341 m. From the bottom, a short well line runs from a seabed soil node to the wellhead, above which sits the BOP and the lower marine riser package (LMRP). A lower flex joint, a flex joint connector, connects the LMRP to the riser and allows the riser to angle relative to the wellhead. The main riser is then made up of a series of joints — slick (bare) joints, buoyancy joints that reduce the effective weight in water, and shorter pup joints for length adjustment. At the top, a telescopic slip joint (outer and inner barrel) accommodates the vessel’s heave, and an upper flex joint connects the riser to the vessel. The lower flex joint is modelled with non-linear rotational stiffness and rotational damping, while the upper flex joint uses linear rotational stiffness — both represent the angular compliance at the riser ends that keeps bending moments within limits. 1.2. Top tensioning The riser is top-tensioned through a tension ring (a nodal body of 11 400 kg) supported by six tensioner lines attached to the vessel. The applied top tension is set by the TopTension variable (≈ 1 733 kN). Tensioner behaviour includes friction, represented by separate static and dynamic friction coefficients (0.2 and 0.1). At the seabed, lateral soil interaction on the well line is modelled with a global spring, introduced through a dedicated spring step in the static analysis. Figure 2. Sketch of model, XZ-plane