Deepwater Oil Export Systems: Past, Present, and Future

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractTo date, nine deepwater export systems have been installed by Oil Companies, or are under construction. The first deepwater export system, on the GIRASSOL field (Angola), was installed in 2001. Since then, a further three systems are now in place, one on the BONGA field (Nigeria) and two on the KIZOMBA field (Angola). A further five are under design or construction (ERHA, DALIA, GREATER PLUTONIO, AGBAMI and AKPO).All these export systems are based on the concept of a large surface buoy, shaped, in most cases, like a flat cylinder. These buoys are anchored to the sea bed by an array of semi-taut composite anchor lines and support several -generally twomid-water export lines.Although these systems show clear differences in anchor line arrangement and composition, and also in export line diameter and configuration, they indicate that the design of deep water export systems has reached maturity.In its first part, the paper gives a general outline description of the nine export systems mentioned above. It explains what the key design drivers are and describes the design process, addressing successively the following issues:a. derivation of mooring force and definition of the anchoring system; b. buoyancy requirements and hydrostatic stability; c. coupled motion response in waves; d. fatigue in anchor lines and export lines.In the second part, the paper highlights the major limitations of the present systems. It describes the various concepts recently developed in the Industry and discusses their relative merits and drawbacks.In conclusion the paper will propose a way forward, facing the challenge of deeper water and harsher environments.