With drilling capability extends to water depths up to 3000m, significantly increased is the risk associated with a failed riser recoil control in the event of an emergency riser disconnect due to loss of vessel station keeping. In deeper waters the tensioner system undertakes higher top tension due to the accumulation of riser length and mud weight. During emergency disconnect, the riser is disconnected between the blow-out preventer (BOP) and the lower marine riser package (LMRP), releasing the base tension and mud pressure. Impact between the top riser system and the diverter housing system should be avoided, and the clearance between the LMRP and BOP should be secured. Efforts have been continuously made in the industry to achieve a more accurate predict of the riser recoil response. The relevance of mud discharge to recoil control has been widely discussed but little quantitative data has been revealed in the literature. In this paper, effect of mud shedding on riser recoil response is discussed. The Herschel-Bulkley rheology model is utilized for mud flow and is considered the latest advance in the drilling industry. Water hammer theories with column separation are modified to account for mud discharge in laminar, transitional and turbulent flow regimes. As a case study herein, recoil response of a drilling riser attached to a dynamically positioned semi-submersible drilling vessel is assessed to present the mud discharge effect on riser anti-recoil control. At emergency events, the riser is disconnected above the BOP, which is located at a water depth of about 2150m for this study. Mud is generally preferred to be freely discharged during an emergency disconnect for ease of anti-recoil control and riser integrity. The density difference between drilling mud in the riser annulus and sea water outside the riser outer casing before disconnect induces a high pressure difference, which drives mud shedding at riser disconnect. Mud flow rate plays an important role in the speed control of the riser uplift. 3D finite element analysis is performed in time domain to simulate riser response before and after disconnect. 2HRECOIL software is integrated into ANSYS user programmable features to better model the riser response and mud discharge.

One of the primary goals of riser monitoring is to build a database of measured riser behavior during different environmental conditions and compare against design predictions during each period. A comprehensive database of field measured riser response provides not only a dataset to benchmark riser performance but enables the calibration of design parameters for future risers. The calibrated set of design parameters would feedback to establish a more representative riser design process and provide greater confidence during future riser designs. The following paper establishes a methodology to benchmark riser behavior against software predictions with applications specific to a steel catenary riser (SCR) suspended from a spar platform. Aspects and challenges dealing with processing of inclined sensors to derive global motions and operational effects are discussed and addressed. A demonstration of the methodology is presented using field measurements from a Gulf of Mexico deepwater SCR under storm conditions. The riser behavior of interest for this study is specifically the touchdown motions and stress but additional comparisons are made along the entire riser length.

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.