Qualification and Verification of Spoolable High Pressure Cornposite Service Lines for the Åsgard Field Development Project
Authors: Hansen A.B. , Asdal B. , Meland T. , Grytdal I. 
Published: October 2008

The exploration and production of offshore hydrocarbon reserves drives the oil industry to look for cost-effective technology. New fields are often marginal in character, e.g. smaller reservoirs and located in deeper waters and existing technology is not always cost-effective or reliable, and often exhibits high maintenance costs.

Modem offshore developments in harsh environments and in steadily deeper waters often consist of floating production and offload systems (FPSO) tied to a vast number of subsea templates. These tie-backs require extensive use of service injection lines to transport hydraulic control fluids and hydrate prevention chemicals, i.e. methanol or glycol. Part of the Ågard field development consist of an FPSO and subsea wells. Long continuous high pressure pipes made from composite materials were considered to be an attractive alternative for methanol and glycol service lines.

This paper will review and discuss the requirements for the methanol and glycol static service at the Ågard field and present results from a qualification and verification project that is completed. A project was initiated by the Ågard operator to complete necessary steps in making spoolable composite high pressure pipes an acceptable alternative. Furthermore, aspects related to test methodology, writing of specifications and simulating operating conditions are discussed and results presented.

Introduction

The development of the Åsgad field situated in a harsh environment off Mid-Norway is the largest ongoing subsea development project in the world. Ågard consists of three fields that will be connected: SmØrbukk, SmØrbukk South and Midgard. The fields were discovered in 1981. 1984 and 1985. Planned production of oil is 1998 and production of gas and condensate is scheduled for 2000. Recoverable reserves are 123 million m3 of oil/condensate and 232 billion sm3 of sales gas. Planned peak production of oil: 200,000 bbl/d, of rich gas: 30 million sm3/d and of condensate: 14,000 m3/d, giving an anticipated field lifetime of 20-30 years. Figure 1 shows the field lay-out and position of the 17 subsea templates comprising 59 production and injection wells. All subsea wells are tied back to surface facilities by a complex of flowlines, umbilicals and service lines. The Ågard water depth is 245-320 m.

Oil production commences in 1998 from a floating production, storage and offload vessel (FPSO) in position A in Figure 1. The FPSO is the world's largest with a length of 276 m, a width of 45.6 m and a draught of 26.6 m. Storage capacity is 950,000 barrels of oil and the produced oil will be transferred to shuttle tankers. The gas/condensate will be processed on a semi-submersible floating production unit (B) and the gas will be exported trough a 42" pipeline to KårstØ on the Norwegian coast. Condensate is transferred to a storage tanker (C) for further export by shuttle tankers. Total capital investment is estimated to approximately 4.2 billion USD.

The design data for the Ågard field is shown in Table 1. 17 electro-hydraulic umbilicals with lengths varying from 1 km to 34km (0.62 to 21 miles) control the subsea templates. Continuous or intennittent methanol and glycol injection prevents hydrate formation.