Piling of Garoupa Platform

Abstract For the development of the first of the oil field in the Campos Basin,l namely Garoupa Field, PETROBRAS ordered a steel jacket type platform. The jacket was installed in May 1980 in a 120m water depth location and foundations consisted of 36 steel pipe piles all skirt type, with an average penetration of 87m. The offshore work was planned based on the previous experience of the installation Contractor and on the available information about environmental and geotechnical conditions at the site. Four piles were pre-installed in the structure in full length inserted in the pile guides and pile sleeve. Remaining piles were built in two sections to ease the offshore handling operations. In some cases, the installation procedures turned out to be meaningless due to unexpected conditions at the site. Environmental conditions happened to be the major limiting factor for the workability of the planned pile driving sequence, because of unexpected high swells and critical clearances for the handling of piles and followers. Unpredicted behavior of superficial calcareous sand resulted in hazards and delays and contingency remedials were necessary. Piles penetrated to 50m depth much easier than foreseen, raising doubts about soil resistance and pile capacity predictions. Pile driving instrumentation provided a better assessment of pile capacities. Much experience was gained from this installation which can be extended to the forthcoming installations in similar areas. Introduction After the transportation from Sao Roque Yard, Ba., to the site, the jacket was launched on May 1st. from M44 barge owned by MICOPERI S.p.A., Milan. This company in joint venture with MONTREAL Engenharia S.A., Rio de Janeiro, had the responsibility to build and install the platform. Figs. I and 2 show the site location and a view of the structure. The jacket was up-ended and positioned by the D/S Pearl Marine over a preinstalled steel template, through which 9 wells had already been drilled. When the jacket touched down it was noticed that the jacket was far off the vertical tolerance. Several tentatives were tried before the jacket was brought into the limits. The behavior of the superficial soils together with the environmental conditions were the main causes of delay for the pile installation. The original schedule was to pile the structure in 32 working days, but it only ended up after 77 working days. This paper describes the main aspects related to the piling of the jacket, outlining the problems faced and solutions undertaken in the field. It also points out potential problems possible to occur when a sandy calcareous formation is present at shallow depths underlaid by a soft soil. Background The Garoupa platform was designed to stand in 120m water depth and the structure is a steel jacket type platform with eight legs slightly inclined to the vertical (Fig. 2). Jacket dimensions are 56 × 26m at top level and 73 × 54m at base level.