Deepwater Conductor Pre-Installation for First TLWP in Brazil
Authors: Pereira Milton F , Silvio Ariel de , Ruiz Joao Carlos 
Published: June 2014

This paper presents an EPCI project for pre-installation of 15 × 36?? conductors, 60 m long, to be integrated to a TLWP in Papa Terra Field at Campos Basin, Rio de Janeiro, in 3,940 feet water depth, located 65 miles from the coast. Such field development required 15 conductors to be installed under TLWP's footprint with accurate requirements for positioning, stick up and vertical inclination, all to avoid risers clashing during its 25 years production life. A patented installation method was chosen, which is comprised by a craned offshore construction vessel, an offshore installation barge and a deepwater subsea hydraulic hammer. To ensure installation within Client's specification, 5 subsea templates containing 3 slots were designed to orientate conductors' landing into the seabed. Template deployment was guided by an acoustic survey system measuring in real time the load's position and orientation.

All conductors were transported to the field and side launched by the installation barge using the project-specific handling tool named " shuttle system??. The conductor's weight was quickly transferred to the OCV's active heave compensated crane, which was connected to a multi-purpose tool named " STS Head", also project-specific. The penetration of each conductor occurred in three stages:self-weight,suction andhammering.

This EPCI project uniqueness is related to:the first TLWP to be installed in Brazil;patented method used to pre-install conductors;shuttle system specifically designed for conductors' side launching; andSTS Head.

Main objective of this method is to improve field development schedule saving rig drilling time. Successful project implementation definitively offers to Brazilian operators a field proven solution, since this technique is applicable for any type of conductor or subsea foundations, being used three times in Brazilian waters.

Introduction

Installation of the first Tension Leg Wellhead Platform (TLWP) in Brazil is one more challenge to develop the Papa Terra field in Campos Basin, 65 nautical miles offshore Arraial do Cabo, coast town of Rio de Janeiro state. The very first step towards the commissioning of TLWP P-61 in this field was correct positioning each wellhead. The cluster included 15 wells underneath the P-61's footprint.

To avoid risks of risers clashing, the cluster spread was carefully designed and the proper riser tensioning was defined. Such level of tensions induced high stresses over the well foundation, which includes the conductor casing. Another strong requirement from the cluster design was wellhead positioning tolerance, i.e., each wellhead needed to be installed within a 30 centimeters (11.8 inches) radius from the specified coordinates. A quick math shows this requirement means 0.025% of 1,200 meters water depth. Final measurement showed an average deviation of 14.1 centimeters (5.5 inches) and none outside the tolerance. Figure 1 shows scale between the conductor diameter, wall thickness, installation tolerance and installed position.

Install all conductor casings using the traditional method with a drill rig was clearly a challenge, especially if compared to the impact of a single incorrect positioned conductor casing. The field proven methodology described herein was the suitable solution to start the field development correctly.

The operation using an Offshore Construction Vessel (OCV) allows this project run off the critical path of the P-61 installation Client's project. Besides this first advantage, the OCV with a Dynamic Positioning (DP) system gives the chance to install the conductor casing within the biggest challenge of 30 centimeters tolerance.