Tap also said it had to run a 178mm liner to ensure the well objectives could be reached, leading to slower drilling penetration rates that added to the delay.

Marley-2 was spudded on April 22 and drilling was expected to take about 48 days to reach total depth.

According to Tap, the total depth of 4100m is expected to be reached in about five days.

The Ensco 106 jack-up rig is drilling at a depth of 3851m and has drilled about 100m into the main objective with indications of gas and reservoir sands.

Tap said the target section would be assessed with wireline tools to ascertain if a gas reservoir has been encountered once the well reaches total depth.

Marley-2 is in the Harriet JV's TL/5 permit in Western Australia's Barrow sub-basin. It is 143km north of Marley-1, where drilling was halted in January 2006 due to mechanical problems.

The vertical well was designed to test Jurassic sandstones that Marley-1 failed to reach.

The Harriet Joint Venture comprises Apache Northwest (operator and 68.5%), Kufpec Australia (19.2771%) and Tap (12.2229%).