Barracuda and Caratinga Integrated Deepwater Site Investigation, Offshore Brazil

Abstract

Abstract The management of geotechnical risk is becoming more important as the offshore industry embarks into new frontiers such as deepwater environments. This paper presents the approach adopted by KBR in the planning, execution and management of such risks. It discusses the problems encountered and the technique used in the risk appraisal of the development area. Introduction KBR's (part of the Halliburton Group) largest ever EPC contract required the design, build, and installation of two 18- leg taut mooring FPSOs in the Campos Basin, offshore Brazil. The two FPSO sites, Barracuda and Caratinga (B&C), are in water depths ranging between 825m and 1030m. The subsea scope required the drilling and completion of 55 subsea wells and the connection of the flexible flow lines, risers, and umbilicals to the FPSO. The cost of the development was approximately ﹩2.5 billion. Figure 1 and 2 indicate the general location of the fields and a schematic of the subsea layout. Part of KBR's remit included a detailed site investigation (SI) to appraise the soil conditions and risks associated with design, construction and installation of flowlines, subsea manifolds, moorings and riser anchors. The investigation was executed over an eight-week period, between February and April 2001, using the single Multi Purpose Support Vessel (MPSV) Rockwater 1. The scope included both geotechnical (Refs. 5, 6 nd 7) and geophysical (Ref. 8) surveys together with existing wellhead inspections. Essentially, all aspects of seabed mapping and soil data acquisition were obtained in one offshore programme. This integrated approach is unusual for an investigation of such magnitude, yet worked well for the B&C project. Vessel Selection It was clear that an SI of this scale would be expensive, partly due to the mobilisation of suitable vessels, but also because of the 1000m water depth. The project schedule had a significant bearing in the final decisions made in selecting an appropriate vessel and SI contractor (Fugro). One important factor was that final soil parameters, anchor types and sizes were required by August 2001, making the SI fast track. Due to this constraint and other time consuming activities, such as obtaining permits and approvals for foreign vessels in Brazilian waters, KBR decided to use one Subsea7 (formerly Halliburton Subsea) vessel to transport all the SI equipment and obtain the necessary survey data. Geological Setting The regional history of the Campos Basin is related to and controlled by the break-up of Gondwanaland, the super continent on the southern hemisphere, and the consequent separation process between Africa and South America (Ref. 1), which began approximately 150 million years ago. The two continents broke apart allowing normal marine sediments to be deposited in the basin. The sedimentary rocks are divided up into a pre-salt non marine section, an evaporate section and a post-marine section. The development area belongs to the postmarine section. The development area is situated on the slope of the southeastern Brazilian continental margin.