This second sidetrack was drilled by UK-based operator Premier Oil to evaluate potential reservoirs in the southern fault block of the Dua Structure, after the original vertical well, Dua-4X, and an initial sidetrack, discovered oil and gas within the northern flank.

Dua-4X ST2 intersected a gas column in limestones above the primary target. But technical difficulties occurred when the well was operating close to the base of the limestone column.

Santos said the decision was made to plug Dua-4X ST2 and re-drill it as Dua-5X so that the safety of the operation was not compromised.

Once this well is completed, the rig will be moved within the permit to drill well 12E-CS-1X on the Blackbird prospect. This well will explore a large tilted fault block updip of a pre-existing well (12E-LK-1X), which encountered very good oil shows.

Santos said it moved into Vietnam to help diversify its international operations by focusing on material positions in proven hydrocarbon basins. It is also currently assessing other opportunities to increase its exposure in the South-East Asian nation.

Partners in Blocks 12E and 12W are Premier Oil, which holds a 37.5% stake, Santos (37.5%) and Delek Energy (25%).