Alcorn International Inc., Houston, is producing about 16,500 b/d of oil from West Linapacan A field in the South China Sea off the Philippines.
The field's current production alone is more than fivefold the Philippines' total average oil flow of 3,000 b/d in 1991. It's part of a string of oil and gas strikes off Palawan Island that has made the region one of the hottest exploration/development plays in the Asia-Pacific theater (OGJ Apr. 13, p. 27). West Linapacan oil is flowing in about equal volumes from three subsea wells to a floating production, storage, and offloading unit (FPSO) in about 1,200 of water.
Alcorn, a unit of Vaalco Energy Inc., Houston, placed the field on stream May 30 following a 6 month, $44 million development project (OGJ, June 8, p. 33).
Clough Stena (Asia) joint Venture, Perth, installed the 125,000 dwt converted tanker FPSO 11 and associated mooring and flow line systems in 350 m (1,148 ft) of water. Clough Stena believes the water depth is a world record for a catenary anchor leg mooring with rigid yoke single buoy installation.
LINAPACN PRODUCTION
Each West Linapacan A well produces to FPSO 11 through a 5,000 ft, 5 in. flexible subsea flow line outfitted with a 1,500 ft flexible riser and an umbilical to control and monitor the subsea trees.
Sometime in spring 1993, Alcorn expects to drill a test well on the lookalike West Linapacan B structure, about 5 miles from West Linapacan A.
The company will complete further development plans based on the outcome of that wildcat and on production performance of the three existing West Linapacan wells.
"We believe we need three to five more wells on the existing structure, and the B structure-if we decide it could be economic-would be a three to five well development," Alcorn said. "But we want to see what we have before we decide whether to go with another FPSO or some kind of more permanent structure."
West Linapacan A subsea wellheads are about 30 ft apart on the seabed with bottomhole locations about 1 km apart. Alcorn had to anchor FPSO II about 1 mile from the wellheads to keep its moorings outside the anchor pattern of the drilling rig.
FPSO 11 is owned by Terminal Installations Inc. (TII), a subsidiary of Single Buoy Mooring, Monaco, in turn a unit of Dutch company I. H. Calland.
After a decade of service in Cadlao field off the Philippines, FPSO 11 in November 1991 was taken to Singapore for refurbishing. Clough Stena installed FPSO II on its present site last May 25. Alcorn laid flow lines May 25-30 to place West Linapacan A on production.
CLOUGH STENA'S RECORD CLAIM
TII let separate contracts to Clough Stena for mooring and installation of FPSO II and installation of flow line systems required to connect FPSO II to the three subsea completions.
The first contract called for installation of six composite mooring legs consisting of 25 ton anchors, chain of as much as 6 in. diameter, and 5 in. wire rope, with each mooring leg weighing about 330 tons.
The project's extremely tight schedule required development, within weeks of award, of an installation system capable of resisting 200 ton plus anchor leg deployment loads.
The system Clough Stena developed consisted of a flattop construction barge converted to enable deployment of mooring leg components over a stern mounted gypsy wheel using multiblock rigging.
MOORING INSTALLATION
The construction barge was moored alongside the dynamically positioned Essar Stena 1 diving support vessel.
The support vessel's thruster configuration and other characteristics enabled Clough Stena to refine mooring arrangements for the cargo barge to the extent that, during mooring installation, the vessel and barge remained connected as one spread-at all times under dynamic positioning and changing vessel headings affected by various installation activities and even in poor weather and rough seas.
The installation required no diver support. All subsea tasks were performed by a Scorpion remote operated vehicle (ROV) system.
The mooring installation equipment was received at Clough Stena's Singapore facility and loaded on the construction barge, which was mobilized to West Linapacan early last April.
FLOW LINE HOOKUP
With installation of the anchors and mooring leg components and successful anchor leg tensioning complete, Clough Stena took delivery in the field of FPSO 11 and completed hookup to the mooring system.
On completion of the moorings contract, the construction barge was demobilized from the field, and Essar Stena 1 commenced flow line installation.
The second contract required installation of three 2 km, 5 in. flow lines and control umbilicals to hook up FPSO II to three wells.
Because of the water depth, Clough Stena chose the layaway method of installing the flexible flow lines to the wellheads.
The high flow line catenary tensions required Clough Stena to upgrade its purpose built reels and laying equipment mounted onboard Essar Stena I.
Each flow line system was positioned on the seabed with assistance of a long baseline acoustic transponder array.
Essar Stena 1 dynamic positioning was guided by deepwater transponders and an Artemis station on a nearby drilling rig.
For both contracts, all temporary work was conducted and installation aids fabricated at Clough Petrosea's Singapore facility.
Flow lines and umbilicals were transported from Singapore to West Linapacan aboard a chartered heavy lift vessel, where they were transferred onto Essar Stena 1 upon completion of FPSO II installation.
Copyright 1992 Oil & Gas Journal. All Rights Reserved.
