The Malampaya field development comprises subsea wells in 820 metres water-depth producing via a subsea manifold and two 16 inch diameter inconel clad flowlines to a shallow water platform 30 km distant in 43 metres water-depth. Condensate is removed on the platform and the dry gas is then transported via a 504 km long 24 inch export pipeline to an onshore gas plant for at Tabangao (Batangas, Luzon Island) for extraction of H2S. The condensate is stored in the platform CGS caisson prior to export via a short 3 km long 24 inch diameter pipeline and CALM buoy (Fig. 1).
The Malampaya development is unusual insofar as it is in a remote deepwater location offshore the Philippines and utilises subsea wells as the sole supply of gas to electricity power generation stations located on the mainland. Many challenges had to be overcome to realise this latest advance in the development of deep water subsea production capability:
High reliability and system availability requirements;
Difficult flow assurance aspects including hydrate prevention and high liquid hold-up in the flowlines;
High production rate wells, high H2S and CO2 content of produced fluids requiring CRA materials;
Installation and operation in a remote location devoid of the customary support infrastructure.
The Subsea System design focussed on achieving the highest levels of overall system availability. This was achieved by a combination of simplifying the design where possible and providing suitable levels of redundancy. Thisapproach was supplemented by applying the highest levels of quality assurance and control during the manufacturing phase. Finally, a full system integration test was undertaken prior to installation offshore to simulate the in-service conditions and verify the system performance.
This paper describes how these unique challenges were addressed during the realisation of the Malampaya Subsea System.
The Malampaya Subsea System consists of a 10-slot subsea manifold with the wells positioned on both sides of the manifold (Fig. 2). The wells are tied-in to the manifold using rigid tie-in spools and separate flexible "flying leads" for providing electric and hydraulic control to each well. The two 16 inch dia flowlines are connected to the subsea manifold using rigid tie-in spools approximately 50 - 65m in length. The flowline tie-in spools are designed to accommodate the thermal expansion at the ends of the flowlines of approximately 2m. Electric and hydraulic control, methanol injection and annulus venting capability for the Subsea System is provided by two subsea umbilicals tied-in to the subsea manifold. The capability to tie-in the third 16 inch dia flowlineis provided by using a "tap it later" tee located on the subsea manifold. The capability to tie-in a third subsea umbilical to the manifold is also provided.