Malampaya Deep Water Gas Pipeline and Flowlines: Technical and Engineering Challenges faced in the Execution of the Malampaya Pipeline Scope

Abstract

Abstract The Malampaya field development comprises subsea wells in 850 metres water-depth producing via a subsea manifold and two 16 inch diameter inconel clad flowlines to a shallow water platform 30 km distant. 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 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. The field flowlines and export pipeline route selection, design and installation are at the forefront of deep-water technology. The pipelines traverse structurally complex terrain with varied seabed characteristics and sections of high bottom relief. The Philippines archipelago is recognised as being one of the most seismically active areas in the world. The gas export pipeline crosses active faults, an extensive system of submarine channels and areas susceptible to mass gravity flowand other soil instabilities. This paper addresses the pipeline route selection, design process and some of the specialist techniques employed in the seismic design of the Malampaya pipeline. The paper also addresses some of the novel installation techniques employed and challenges encountered in the execution phase of the project. In particular the deepwater PLES installation, deepwater span rectification and the removal of ordnance in 460 metres water depth will be addressed. Introduction Following detailed reviews of competing concepts for the Malampaya field, the gas only development, comprising a deep water subsea tieback to a shallow water platform was selected in June 1996 as the preferred option for the development of the field (Fig. 1). Common to all of the concepts under consideration however was the provision of a subsea trunk export pipeline from the Malampaya field to the gas markets situated on the island of Luzon. Of the technical challenges to be faced in the engineering of the Project, it was recognised the feasibility of the export a pipeline in the structurally complex and seismically active terrain was critical. Early survey and datagathering work was essential to resolve the feasibility question. Offshore survey field work was therefore kicked off in December 1996 and continued throughout 1997 in one of the most comprehensive offshore data gathering campaigns performed in the industry. In addition to the pipeline routing and design challenge the deep waters of Malampaya were to throw-up a number of additional technical and engineering challenges in the installation of the pipelines. These included:Installation of 16 inch PLES units in 820 metres depth;Rock dump optimisation (for span correction) in water depths down to 600 metres depth; These and other challenges were successfully overcome and in doing so the boundaries of existing pipeline design and installation experience extended. The Malampaya export pipeline and flowlines as part of the overall Malampaya Development Project were put into service and supplying gas to the customer on time on 1st October 2001.