Deepwater FPSO for Aquila Field Development in the Adriatic
Authors: Chimisso C. , Tagher H. , Biss N.C. , Stani G. 
Published: October 2008

The FPSO recently installed in 850 m water depth for the challenging Aquila Field incorporates a number of intresting features. Although the field was discovered some tune ago, development has only now been made possible due to the technical advances in both subsea and turret mooring/riser systems combined with cost savings obtained in the conversion of an existing FPSO. The original turret mooring system, designed for 97 m water depth has now been transformed to operate in 850 m and includes the use of suction anchors, which we believe are the deepest yet employed. The process has been designed to cater for 9000 ppm H2S, and incorporates a crude oil stabilization column to maximise recovery. Due to the strict environmental regulations in the Mediterranean, the produced water treatment is designed to achieve less than 10 ppm Oil m water, or to offload produced water via shuttle tanker. This paper describes the Aquila FPSO and highlights how the latest technology and reuse of existing systems have provided an innovative and cost effective approach to develop the deep water Aquila field.

Introduction

The Aquila field development called for the production of two subsea completed wells in 850 m of water in the Adriatic sea, 50 km NE of Brindisi, Offshore Italy, plus provision for a third well. As there is no production or export infrastructure nearby, a stand alone FPSO system was envisaged. At the start of the project, the technical challenges to achieve this were considerable, especially in the following areas:–subsea tree design and installation,–riser armour wire material selection to withstand the high partial pressure of H2S (0.4 barg) in a potentially wet environment,–mooring and anchor system design,–mooring and riser installation requirements.

Furthermore, the field has only moderate reserves and a maximum production of 18,800 BOPD for a 5-7 years field life. This entailed strict budget restrictions for the project. By 1995, technical progress had been made and the projectcould be considered more seriously:–A deepwater subsea tree installation system called "Sistemi Alti Fondati" (SAF) had been sucessfully proven in shallow water.–Monohull FPSO's with flexible risers were being installed in 350m of water using technology which could be extrapolated to 850 m.–The existing FPSO "AGIP FIRENZE" was made available to the project.–Material tests were being carried out to qualify a suitable wire armour material for the flexible risers in sour service

By December 1995, the project was given the go-ahead. A Project management team was established and engineering started immediately on the various elements of the project. These covered subsea, turret/mooring, risers, topsides, their integration into the existing vessel and the vessel refurbishment and conversion itself. The approach taken with the specific project challenges for each of these elements are described below and general project and environmental data are given in Appendices A and B. The FPSO has now been sucessfully installed on site and at the time of writing is being prepared for first oil.

Subsea

The basic guideline for the subsea production system is to utilise the SAF concept. In addition to this, the safety of the system is the mandatory philosophy used and stressed in all selections.