With drilling and exploration occurring in ever deeper waters and harsh environmental conditions, the ability to properly plan critical operations such as deployment and retrieval of the drilling riser becomes increasingly important. Particularly in deepwater high current environments, deployment and retrieval operations can be limited by the length of time it takes to deploy or retrieve the riser and the danger of the riser joints binding in the diverter housing. These limitations can have significant impact on both operations and riser integrity. Drilling contractors have devised a number of means of conducting operations in high current environments in order to increase operational up-time and mitigate the risks involved. One approach is drift-running, where the drilling rig is positioned upstream of the well at the start of the deployment operation and the rig is allowed to drift in a controlled manner to the well as the riser is deployed. This procedure effectively reduces the current loading on the riser, thereby allowing the riser to be deployed without risk of binding in the diverter housing. This paper describes an on-board simulation tool designed for use on dynamically-positioned (DP) drilling rigs that can be used to plan deployment/retrieval and drift-running operations. The tool is a development of an on-board drift-off simulator that has been in operation on-board the latest generation of DP drillships for some time. The simulator uses a fully-coupled 3D finite element (FE) model of the riser system, thereby allowing accurate determination of the riser response to current loading. The simulator computes the angle of the riser in the diverter housing throughout the deployment/retrieval process. Additionally, the simulator can compute the optimum drift speed of the vessel to minimise the riser angle. Based on the results of these simulations, the on-board tool can determine the feasibility of deploying or retrieving the riser and can compute the required vessel track for carrying out drift-running operations. The tool allows on-board personnel to plan these operations using either prevailing or forecast metocean conditions. The key features of the on-board simulator are discussed, with particular emphasis on the procedure used to compute the drift-running track for the drilling rig during riser deployment. The benefits of the system in planning deployment/retrieval operations are illustrated by means of a number of case-studies.

This content is only available via PDF.
You do not currently have access to this content.