Weather Window Determination of Top-Tensioned Riser Deployment With Guidewires

Abstract

To replace 20 of the 42 top-tensioned production risers for the Statoil Snorre A platform, the planned riser deployment will use a guidewire and guide frame system. A suitable weather window needed to be determined for the deployment to avoid clashing the deploying risers and adjacent connected risers. Such clashing could cause severe consequences such as connector leakage and equipment damage. Riser collision during operation and production was studied extensively [1, 2]. However, little investigation has been conducted on clashing during deployment. Due to the importance of the disturbed wave elevation and wave kinematic effects on the riser response by earlier study [3], RIFLEX was chosen for the simulation. RIFLEX simulates the disturbed wave kinematics. However, RIFLEX has limited capabilities to model the deployment guidance system and calculate the minimum riser clearance. This paper focuses on the simulation of the riser deployed with guidewires and guide frames and calculation of the clearance between the deploying riser and the connected risers. First, the guide frame and 4-guidewire system (see Fig. 2 and 3) was simplified as a rigid beam and a sliding linear spring (see Fig. 4 and 5). A derivation of the relationship between the guidewire tension and deployment depth was developed and implemented into a RIFLEX model. Second, due to different responses caused by the disturbed wave kinematics, different deploying and installed riser pairs in the well bay were selected to find the smallest clearance during a three-hour random sea state. The smallest clearance was determined from five different deployment depths and weather conditions in the initial plane of the riser pairs. Last, a clashing criterion is discussed and used for the deployment weather window determination. This paper also points out that a slightly wider weather window could be possible, depending on the deployment depth. Recent successful deployment of the new risers confirmed the riser installation analysis.