Aquila-field project overview

M. Ciprigno, C. Chimisso and S. Bracchi, Eni-Agip Division

The Aquila project, developed by Eni-Agip Division, was completed in April 1998 after the first well came onstream in March 1998. The field, with its 850-m (2,790-ft) water depth – among the 10 deepest fields in the world and the deepest in Europe – is located about 45 km offshore Brindisi, Italy, in the south Adriatic Sea. Recoverable reserves are estimated at 22 MMbbl of 36° API oil, with peak production estimated to be 17,000 bopd. Field exploitation has been by means of two wells directly connected to a permanently moored FPSO.

Development scheme. Agip started exploring the deepwater Adriatic Sea in the late 1970s. Of two oil discoveries, Aquila and Rovesti, Aquila 1 (drilled in 1982) was the most significant, and a comprehensive R&D program was started to exploit deepwater fields. Aquila is exploited by two previously drilled subsea wells connected directly to the FPSO. Once processed, the oil is stored in central tanks to wait for the export shuttle tanker. Each satellite well is completed with horizontal subsea trees and multiplex control systems connected to the riser system which comprises, for each well, a 6-in. production line, a 2-1/2-in. service line and the control umbilical. All lines are flexible.

The mooring system comprises a turret structurally connected to the bow of the ship, and four twins, equally spaced, of catenary chain / wire mooring lines, each terminating to a foundation pile on the seabed. The process plant essentially comprises gravity separators, a stabilizer column to maximize oil recovery, and auxiliaries needed for ship operation and safety. Stored oil is transferred via side-by-side offloading. Produced water is processed through hydrocyclones and flotation tanks, then disposed to sea. Associated gas is utilized for power generation and gas lift. Remaining gas is flared.

Each well has single-point, gas-lift injection. Control parameters inside the tubing are controlled by the SCRAMS (Surface Controlled Reservoir Analysis & Management System). Continuous chemical injection prevents asphaltene deposition. In addition, facilities for periodic well clean-up or acidizing are provided.

FPSO Firenze permanently moored in Aquila field.

Project background / management. Aquila 2 was drilled in 1993, and after a long test, an integrated engineering team was formed to analyze test results and carry out a feasibility study which assessed all technical possibilities. Aquila 3, drilled in mid-1995, confirmed previous reservoir analysis, giving the green light to the project. During the feasibility study, AGIP Firenze was selected for the FPSO. Basic engineering was performed in cooperation with Saipem and SBM in joint venture. The JV acquired and renamed the vessel, carried out her refurbishment for Aquila and made her available for production on a daily-rate basis.

Meanwhile, the subsea production systems were manufactured and the SAF (Sistemi Alti Fondali) installation was updated. Offshore operations started in August 1997, and the FPSO, including flowlines and umbilicals, was installed in November. Well completions followed. The first, Aquila 3, started production in March 1998; the field was fully producing in April, after completion of Aquila 2.

A "project oriented approach" was adopted for all aspects of the project. Internally, a taskforce was established; some of the technical challenges facing the team included: 1) an FPSO permanently moored at the greatest depth in European waters and among the deepest worldwide; 2) new configurations of flexipipes in dynamic conditions; 3) first utilization of the SAF in its design conditions; and 4) deepest installation of horizontal, subsea production systems.

To maximize production and recovery required these innovations: 1) wells with horizontal drains; 2) installation of SCRAMS; 3) enhanced recovery by gas lift (unique on an FPSO); 4) acidizing from the FPSO; and 5) the processing plant, including an oil stabilizer column (unique on an FPSO).

Efforts to reduce costs can be summarized in the approach that allowed improvements in both capital and operating expenditure. CapEx reduction was achieved mainly by: horizontal tree use; installation performed by means of SAF; use of an existing, already-converted tanker; and FPSO rental on a long-term basis. On the OpEx side, cost reduction areas were: well completion design, whole field-life cost approach for the FPSO and maintenance intervention, if any, by SAF.

This summary article was prepared from the paper "Aquila project – An overview," presented by the authors at OMC 99 in Ravenna, March 24—26, 1999, as part of a nine-paper Aquila-project session.