Marlim Field: The Evolution of Subsea Techniques and Hardware

Abstract

As the development of Marlim field was planned back in the mid 80's the challenge was to develop subsea hardware and techniques that would allow completion of 148 wells in water depths ranging from 600 to 1100 meters. As the first Guidelineless Subsea Trees were designed and manufactured the key to success was, indisputably, the flowline connection method. Starting with the Lay Away method, a natural extension of the guideline concept, Petrobras is now purchasing subsea trees with a 4th generation flowline connection method. Subsea Trees interfaces were standardized among different manufacturers and a simplified Water Injection Tree was introduced in order to improve the economics of the project. Pigging capacity and ethanol injection (for hydrates prevention) became required features for all Subsea Trees. A total of six Subsea Diverless Guidelineless Manifolds are planned for Marlim field, two of which are already installed. These Manifolds were designed based on the experience from early ones that are now in operation in Albacora field. Marlim field has been a laboratory for the development of production techniques and hardware for ultra deep water. In keeping to its role, the Multiphase Pumping System, a boosting technology with far reaching application is scheduled for installation in Marlim field in 1999. Now, with the Marlim Project halfway to completion, the evolution of hardware and techniques will be presented, along with a discussion on the issues that drove this evolution and the resulting benefits. INTRODUCTION During the 80's the number of subsea completions increased worldwide due to several reasons. In Brazil this increase was due to Petrobras option to develop Campos Basin by way of subsea completions tied up to Floating Production Units. Early oil production, reduced financial commitment and flexibility for changes as more information about the field is gathered were the main advantages. Since the first subsea tree was installed at 189 m waterdepth in April 1979, the exploratory activity has been successfully moving to ever deeper waters. In 1984 it was installed a subsea tree at 307 m water depth, the first worldwide beyond diving limit, using a horizontal remote flowline connection system. In spite of being a great achievement, the remote flowline connection system showed to be troublesome, with leaks resulting from misalignment of connecting flowlines and requiring the use of complex pull-in tools. Shortly after, as more experience was acquired, the use of this system was discontinued and diver assisted flowline connection was made a standard for shallow water up to 300 m water depth. In 1984, Petrobras decided to use Dynamic Positioning(DP) Rigs on an exploratory drilling program in the 900 m water depth range which culminated with the discovery of the giant fields Albacora (250 to 950 m water depth) and soon after Marlim (600 to 1100 m water depth). The development of a new diverless flowline connection system was required. That is when the Lay Away Connection System appeared (1987), being first used with Guideline Subsea Tree in a conventionally moored rig, in water depth of 411 m in Marimba Field. In the Lay Away Connection Method the flowline bundle is run with the subsea Tree, thus eliminating many of the existing problems of subsea flowline connections.