The Albacora Field Subsea Development: A Case History

Abstract

ABSTRACT Subsea technology has proved itself as an alternative for marginal or deep water field developments. This paper will describe six years of operational experience on the Albacora field, an important subsea development project being carried out offshore Brazil. Main results and major difficulties encountered during this period will be discussed in the text. INTRODUCTION Albacora is one of the last decade discovered deep water giant fields, located at Campos Basin, offshore Brazil. Being explorated since 1968, Campos Basin became the main petroleum province in Brazil. Ranging from shore to 3,400 m WD, with a total area of 110,000 Km2 its total proved reserves, in WD u; to 1,000 m, reaches 2.78 X 109 barrels of oil and 58.2 × 109 std m3 of gas, 16 % of this being located in the Albacora field (Fig. 1). In 1984, with the wiIdcat well 1RJS297, drilled at 293 m WD, the Albacora field was discovered. Further efforts led to the knowledge of the field's full extension, which is presently accepted as covering an area of nearly 235 Km2. Since this first discovery and the following successes in Marlin field, the basin development strategies had been reviewed to attain those new chal Ienges in deep waters. GEOLOGY OF THE ALBACORA FIELD The Albacora field is located nearly 110 Km from the coast, in water depths varying from 230 to 1600 m. Its main oil occurrences are found in the Tertiary / oligocene, Eocene and Miocene sandstones (Campos/Carapebus) and in the Cretaceous/Albian sandstones (Macae/Namorado), all of turbiditic origin (Fig.2). A total of eight different oil reservoirs ranges from 2350 to 3260 m TVD, with a significant variation in porosity, water saturation, oil gravity, etc2. Its proved reserves are of 0.455 × 109 barrels of 26/29 °API oil and 8.48 × 109 std m3 of gas. FIELD DEVELOPMENT MILESTONES To cope with geological and reservoir uncertainties, as well as technological limitations and budget requirements related to the deep water / giant field combination, it has been planned to develop the Albacora field by stages. Each stage provides reservoir data, technology field testing and early cash flow to support the following stages3,4,5. The project's milestones are listed bellow:1984 - Drilling of the well 1RJS297, discoverer of the field;1987 - Drilling and successful testing of the well 1RJS367 at 1565 m WD, a world record;1987 - Phase 1 (Pilot System) start-up: The Pilot System comprised 6 wells connected to a diver assisted subsea manifold, producing to a FPSO consisted of a tanker (P.P. Moraes) and a monobuoy in SBS configuration, at 230 m WD. This conception combines a CALM type monobuoy rigidly connected through a yoke to the tanker. OiI sales were conducted through the SBS monobuoy to a shuttle tanker tied to a second monobuoy.