Lessons Learned: The Free-Standing Production Riser
Authors: Franklin Robert , Herman Richard J. , Allen Timothy J. , Ambrose Michael 
Published: October 2008

The Free-Standing Production Riser (FPR) utilized on the EEX (nee Enserch) Garden Banks 388 Floating Production System (FPS) has been successfully retrieved for the second time. The FPR has performed successfully with two distinctly different Floating Production Vessels (FPV) and in two water depths. The FPR system has provided approximately six years of total service while surviving many winter storms, hurricanes and loop currents.

The basic FPR system was originally installed in the Gulf of Mexico with the Placid Green Canyon 29 project. The FPR system was retrieved and stored until Enserch purchased the FPR for utilization on the Cooper development. The FPR was refurbished, additional riser joints were manufactured and the system was reinstalled in 2,096 feet of water depth. During the field decommissioning the FPR was retrieved quickly, safely and in serviceable condition.

During both field applications of the FPR, the system demonstrated the serviceability and versatility of the concept and associated equipment. This paper addresses the issues and lessons learned from the application of the FPR in two different field locations and water depths.

INTRODUCTION

The philosophy behind the development of this type of FPS included dedicating a FPV to provide a platform for drilling and servicing subsea wells, controlling well production, processing the well production fluids and exporting the oil and gas into sales lines for delivery to the bank. All of the production and sales fluids will be conducted through the FPR. The well bore fluids will be brought from the seabed through the production lines of the template, the FPR rigid piping, the FPR flexible pipe catenaries and the process piping onto the FPV production deck. Water depth has no effect on the FPV due to loading from the FPR. The FPR supports all of the production and annulus tubing, sales lines and well control umbilical within the riser column.

The Enserch Garden Banks 388 FPR was installed in August of 1995. Production from previously drilled and completed wells began in early September of 1995 through the FPR.

The deployment procedures and installation tools were utilized to successfully and safely to install the FPR for a second time. However, the planned flexible pipe catenary deployment was incomplete. During the FPR installation process the 12" export line catenary was severely damaged. A temporary replacement 12" export line catenary was utilized from the Placid Green Canyon 29 project. The time required to incorporate this change adversely effected the project schedule. To meet the scheduled start of production, only 6 Production and Annulus (P&A) catenaries to access 3 well bays on the subsea template were installed.

New equipment and procedures were developed to allow the deployment of the flexible pipe catenaries for subsea diver installation. The procedures utilized diver friendly tools for transferring the flexible pipe from the rig to the Upper Riser Connector Package (URCP) for the catenary connection to subsea goosenecks. This procedure was performed with minimum FPV relocation and no interruption of production.