Aquila Field - Advanced contracting strategies for the offshore development, in 850 meter water depth
Authors: Cerrito E. , Ciprigno M. 
Published: December 2007

Aquila oil field is located in 850 meters of water in the middle of the Otranto Channel, in the Mediterranean Sea, at about 45 km from the shore and is subject to both difficult sea and weather conditions. The many difficulties, mainly due to the very high water depth, imposed the use of advanced technology, that could be obtained only through the direct association of contractor companies, leaders in their own field. Such a solution safeguards the technological reliability and allows the maximum control of time and cost.

The selection of an FPSO (Floating, Production, Storage and Offloading) comes from a feasibility study indicating this solution as the only one, allowing the economical exploitation of the Aquila field. This paper deals with a series of technical solutions and contractual agreements with a Joint-Venture embracing two leading world contractors for developing, manufacturing and installing the FPSO "Agip Firenze", permanently anchored at a world record 850 m water depth. The system includes flowlines and control lines. The ship, has been especially redesigned and purchased by contractors. They will use the vessel to manage the field development. Agip will provide the subsea production system: christmas tree and control system with artificial lift.

The Aquila field development project aims to identify an economically viable, low risk method of producing hydrocarbons from a deep water location where previously the reserves were technologically and economically out of range.

Introduction

Targeted innovative contractual strategies nowadays allow field development that would have been doubtful a few years ago. The use of an alliance, merging together different interests, will permit the development of the Aquila offshore field, with its limited reserves, in extreme water depth (850 m), at a fixed price, and without the need of the bidding phase. The field will come on stream 8 months earlier than planned.

Agip and two selected main contractors, making use of their own core competences, while sharing different economic, technical or reservoir risks, have reached an agreement based on reciprocal trust and will proceed together towards the common goal - the successful development of the Aquila field.

Field Development concept

The Aquila field is located at a water depth of 850 m in the Otranto Channel some 45 km off the coast of Southern Italy (Fig. 1).

The reservoir is situated in the carbonatic Mesozoic formation in the Umbro-Marchigiano sedimentary basin.

Reservoir depth is about 3900 m below sea level. Reservoir pressure is close to hydrostatic pressure and the gas/oil ratio is 115 std m3/stdm3. The recoverable reserves have been estimated at approximately 20 mill. std barrels of 36 API oil and peak production flowrate has been assumed to be 17000 BOPD (Tab. 1).

The field will be exploited by means of two horizontal wells: Aquila 2, which, in 1993, was under lengthy production testing (two months), and Aquila 3, drilled in 1995. The horizontal sections are respectively of 200 and 700 m and are expected to improve reservoir drainage and increase well production rate.

The combination of deepwater, remote field location, difficult weather conditions and limited recoverable reserves have excluded the use of conventional field development technology for Aquila.

Main selections, in this respect, are the "horizontal trees" and an optimized gas lift system with remote control operations. Three independent lines will connect each well to the surface: production line, service line and umbilical. Production and service lines will be flexible in pliant wave configuration.

P. 465