The Langsa Offshore Technical Assistance Contract (TAC) is located in the offshore part of the North Sumatra Basin in the Straits of Malacca.
It covers an area of 77km², 90km east-north-east of Mobil / Exxon’s giant Arun gas / condensate field.
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Two commercial oil pools have so far been discovered in the contract area, known as the H and L fields.
Oil drilling
A total of four successful oil wells were drilled into the two fields by Mobil in the 1980s.
The wells flowed at a combined rate of 18,833 barrels of oil per day (bopd), plus 9.6 million standard cubic feet a day (MMscfd) gas.
Mobil, as the former operator, spent about $33 million before relinquishing the area when oil prices collapsed in 1986.
Three wells have been brought on-stream during the new developments, producing 10,000bopd.
Seismic survey
A range of 2D seismic data was recorded during the 1970s on a grid of approximately 1km in size.
The control on the velocities required for seismic interpretation was constrained to just two wells.
However, in the 1990s, Matrix Oil ran 3D seismic data of higher quality, on a 25m grid that allowed for a much more accurate picture of the structural framework of the two oilfields.
In addition, a total of five wells were available to the new operator, enabling a more accurate calibration of the seismic data.
The new interpretation suggests that oil accumulation in the L field extends over a greater area than previously indicated.
Recoverable proven reserves were consequently increased from six million barrels to 13 million barrels, while proven and probable reserves of the area were upgraded from 18 to 33.5 million barrels of oil.
Field development
Production commenced at the Langsa oilfields in November 2001.
The Langsa field has been developed using the 32,000t MV Alpine as the central point of its floating production, storage and offloading (FPSO) system.
This is located between the two commercial fields and secured by eight anchors.
The tanker holds approximately 230,000 barrels of oil and was taken to Singapore to be converted.
The first off-take of Langsa oil from the FPSO vessel was 100,000 barrels of oil.
MODEC and ITOCHU will operate the field under a $47 million three-year lease contract for the FPSO and the subsea flowlines to tie-in the three wells.
Langsa has announced plans for a fourth well to lift oil from the Langsa L field.
Flowlines
MODEC awarded Wellstream a contract in June 2001 to supply flowlines and risers. The award included 4in risers, as well as 4in and 6in flowlines.
Delivery of the flowlines and risers was carried out in August 2001.
As the conveyed fluid is sour and flows at high temperatures, Wellstream used unplasticised PVDF for constructing the internal fluid.
