In this study, a series of experiments were conducted in a wave/current flume to investigate the dynamic responses of a drilling riser for a jackup platform under the environmental loads, mainly for waves and combined waves and current conditions. The riser is made of a PVC pipe with outer diameter of 8 mm and length of 0.98 m. The riser is partially immersed in the water with a top part above the free surface. Three water depths were examined in the tests. The bottom end of the drilling riser was rigidly fixed at the bottom of the flume and the top end is pinned. The strain due to the vibration of the drilling riser in both in-line and cross-flow directions were measured with FBG strain sensors at four locations along the water depth. Meanwhile, the displacement of the riser are also videotaped with two cameras both in in-line and cross flow directions. The characteristics of vibrations of the riser are investigated based on the strain and displacement at the middle section of the riser.
A drilling riser is utilized during drilling and workover operations and isolates any wellbore fluids from the environment. The major functions of drilling riser systems are to provide fluid transportation to and from the well; support auxiliary lines, guide tools, and drilling strings. The drilling riser may undertake various loads during operations, including the ocean waves, current, vessel motions, and so and. These loads may produce more severe dynamic response in the riser. As a slender, single tubular structure, its fundamental period of vibration is typically in an order of seconds and is also close to the period of ocean waves, which may result in a resonance of the riser. Furthermore, for a jack-up platform in shallow seas, the drilling riser is partially immersed in the sea water and with a top part still above the water surface. Thus, the water depth also has an influence on the dynamics responses of a drilling riser.