Development and Installation of the Drill Pipe Riser, An Innovative Deepwater Production and Completion/Workover Riser System
Authors: Moreira J.R.F. , Rovina P.S. , Couto P. , Neumann B. 
Published: October 2008

An original completion riser, the so-called Drill Pipe Riser (DPR) has been developed, which sharply decreases both subsea tree and tubing hanger running time. In addition, the cost of this system, including maintenance costs, is very low compared with conventional completion riser systems. The system is basically composed of drill pipes, control pod and control umbilical, which provides annulus access and pod Electro hydraulic multiplexed control. An existing type of drill pipe has been selected in order to minimize costs while improving reliability. This system has been modified to run a specially designed subsea tree from a dynamically positioned FPSO (SEILLEAN) to allow production of two piggy-back wells in water depths up to 2000 m (6500'). This paper describes the Drill Pipe Riser, the FPSO upgrade to operate in 2000 m water depth, the special subsea tree and its successful installation at 1853 m water depth, the current world record.

Introduction

The original scope of work of the Drill Pipe Riser (DPR) project was only the design and development of an ultra deepwater completion/workover riser aiming mainly at reducing running time while decreasing acquisition costs. This project has been developed through an EPC contract awarded, in July 1997, to KOS, responsible for the design and manufacture of two sets of DPRs.

In March 1998, when almost all DPR components were under manufacturing, a decision was made: to hire the SEILLEAN to reduce lead time to first oil in Roncador field to only 9 months. This would impact favorably on the project economics by enabling income to be generated at a much earlier stage of the development. In addition, valuable reservoir information could be attained in advance.

The SEILLEAN is a dynamically positioned floating production and storage vessel (FPS) which had been operating in the North Sea, at 150m (492') for BP since 1991. She is a completely self contained vessel, capable of handling up to 20,000 barrels per day and storing 310,000 barrels of oil. Oil production was through a heave compensated rigid riser deployed from the ship's moon pool. The riser was mated with the previously installed subsea tree by means of the Emergency Disconnection Package (EDP). During production, the ship vaned around the riser which was equipped with flexible joints to allow the vessel positional latitude.

The rigid riser consisted of 6 5/8"drill pipes with control umbilical attached, similarly to the Drill Pipe Riser.

When the oil tanks were full, the ship unlatched from the well and transported the oil to its destination, no shuttle tank being required.

This project was then known as SWOPS (Single Well Oil Production System) although producing from two subsea wells in piggy-back. The SWOPS was designed for operation in shallow water depths up to 200m.

Upgrading the SWOPS to work in Brazil at water depths up to 2000 m (6500'), ten times greater than before, in 9 months time, was a challenge whose critical path was soon identified as the riser design and fabrication.

In order to overcome this problem, one of the two Drill Pipe Riser sets has been adapted and made compatible with the SEILLEAN. The project was then renamed Early Production Riser (EPR) which was also developed through an EPC contract with the same company responsible for the DPR.

Unlike the SWOPS where the subsea tree had to be previously installed by a completion unit, the EPR should be designed to run the subsea tree from the ship's moon pool as well.