This paper describes the installation and related analyses of a subsea production manifold in 620 meters water depth at Campos basin, offshore Brazil. A pre-installed mooring system was used to moor the crane barge which lowered the structure. Time domain and frequency domain computer programs were used to evaluate the response of the system A sensitivity study was conducted in order to assess the added mass, damping, stiffness and excitation forces influences on the system response and the importance of such parameters in the computer model calibration is discussed. Model tests were performed in order to determine the manifold hydrodynamic coefficients to be input to a computer program to evaluate the displacements and forces during the descent of the structure. Offshore measurements were performed on the hoist forces, vessel motions, crane boom tip vertical motions and manifold vertical motions. The anticipated responses are compared with some of these measurements. The method used for lowering the manifold, the mooring system and the manifold orientation and positioning system are described. The design and installation strategy considered to adapt a conventional crane barge for installation beyond its nominal specifications, but considering safety and cost-effectiveness, are also described. Introduction In December 1995 the DL-2 production manifold was installed in 620 meters water depth at the Albacora field on the continental slope at Campos basin, offshore Brazil. The contract for fabrication was granted to a Brazilian company and the operator of the field, Petrobras, undertook the installation of the manifold through its owned 122 by 30.5 by t3.5meters pipe lay and crane barge BGL-1, The structure was first loaded out on 18* of November onto the deck of Petrobras transportation barge BS-5, transported to BGL-1 inshore and then lifted by BGL-1 crane and sea-fastened to the crane barge deck. The manifold was landed on the sea bed on 19th of December. The manifold dimensions are 19 m by 14.5 m by 7.5 m high and it weighs 4120 kN in air, which includes a foundation substructure, the manifold itself and a installation lifting tool. Shallow foundations were adopted and four 40 m2 footings were utilized to provide the required bearing capacity. For details about the functional features of the manifold please see OTC paper 8236. The seabed has a 5 degrees slope and the substructure was built so as to have the mudmats at the same inclination. The manifold had to be landed within +/- 10 degrees in heading, in a target area with 10 meters radius and within +/- 2 degrees in leveling. Should the later not be achieved, the manifold leveling system would be used. In this case anothervessel with drill pipe handling capability would be required. Installation planning The installation alternatives considered for lowering the manifold involved a drilling rig, a dynamically positioned crane vessel and a conventionally moored crane barge.
This paper describes the OCTOS 1000 template manifold transport and installation method for its first location in Alhacora field, offshore Brazil. The original idea consisted in using a barge and a dynamically positioned rig But as it has imposed some operational restrictions, another method had to be developed. The selected one foresees the use of a PETROBRAS owned semi-submersible to transport the template sea fastened to the rig lower deck, allowing a dry tow of the structure towards its final location. The method described may be used to transport and install other kinds of templates and manifolds, using a rig'of opportunity as it requires minimum modifications on the rig. Its selection mainly depends on the foundation project and on the levelling devices of the subsea equipment, OCTOS 1000 concept features that simplify the installation task, and also on the relation between the overall dimensions of the equipment to be installed and the clearance area below the rig lower deck. INTRODUTION The exploitation of deep water oil fields is the principal goal of several studies and projects carried on by PETROBRAS. Considering the existing alternatives for Campos Basin Albacora and Marlim fields development, subsea completion and floating production system was the chosen one, basically due to the evaluated costs and to our know how on those systems for shallow water fields. However, some components of this scenario had to he upgraded in order to overcome the challenge of going deeper. The OCTOS 1000 template manifold project represents an evolution on the basic concepts for adeepwater template design, based on simplicity, reliability, safety and field experience. Orthogonally shaped with a central manifold and seven wells spaced in a radial way, it is linked to the production platform by the 8th arm's sales lines base. The foundations design consists on a central foundation and eight radial ones located at its eight arms extremities. Installation planning and designing followed thesame principles of the main project but aiming to maximize the use of our own human and material resources, in order to do it "in house". FORMER STUDIES The OCTOS 1000 transport and installation couldbe easily performed by a heavy lift vessel with dynamic positioning, for example, being this idea putaside at first to avoid high daily rates and mobilization fees. As one of the premises of the whole project was 1,000 m (3,281 ft) water depth rating, contracting an anchored lift barge or semi-submersible to perform the joh would result in a difficult anchoring and positioning over the location and in high costs also, due to the small availability of those units. The research was directed to dynamic positioned (OP) rigs, preferably with a long term contract under way. The structure design and installation initial studies considered the drillship Pacnorse II or the semi-submersible Sedco 709 as the rigs which could launch the OCTOS 1000 into the water.
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