Output from Vietnam's Su Tu Den oilfield has slid by 40 percent to about 50,000 barrels per day (bpd) and could stay around that level for a decade or more, Korea National Oil Corp (KNOC), one of the operators, said on Thursday.
The remark by Joeng Chang Seok, managing director of KNOC Vietnam, confirmed those of oil traders who had said production was down sharply from last year when the field produced 80,000-85,000 bpd.
PV Oil, Petrovietnam's trading arm, has not offered any spot Su Tu Den cargoes for December after production hit a sharp natural decline this year.
Joeng also said KNOC had made no decision yet about whether or not to consider buying ConocoPhillips' 23.25 percent stake in a complex of five oil fields in Cuu Long basin block 15-1.
In July state oil and gas group Petrovietnam said it may buy the stake in the field, which lies in the East Sea.
Petrovietnam's chief executive Phung Dinh Thuc said ConocoPhillips may sell the oil assets because it was scaling back its presence, possibly as part of a restructuring.
In Block 15-1 its partners include Petrovietnam with a 50 percent interest, KNOC with 14.2 percent, South Korea's SK Corp , with 9 percent and Monaco's Geopetrol with 3.5 percent.