Drilling riser damping can have a significant effect on the dynamic response of the drilling system, especially the fatigue response of the wellhead and conductor system. The presence of any drilling riser damping helps to diminish the transfer of riser motions into the wellhead system, which can improve any wellhead fatigue issues.

One of the little studied contributors to the system damping is the hydrodynamic damping effect of the interaction between the drill pipe and drilling fluid inside the riser. As part of the ongoing Structural Well Integrity Joint Industry Project (JIP), finite element analysis (FEA) with a wide range of drag and inertia coefficients is conducted to simulate the mud drag and inertia on the drill string and the riser. These sensitivity studies demonstrate that the mud drag and inertia on the drill string could be one of the key driving factors in riser system damping. To verify the FEA work, the Structural Well Integrity JIP conducted a laboratory test to determine the drag coefficient and added mass coefficient of drill pipe inside a marine drilling riser with and without flowing mud and water in the riser annulus.

In this paper, the test setup and the test matrix are introduced, and the methodology for determining drag coefficient and added mass coefficient are explained. The test results are also presented and compared with published test data for open water.

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