Instead, the company has decided to bring forward the production testing of the Epenarra-Darwin formation to later this week and later plans drill another, separate well to test the Plover's potential.

MEO started sidetracking the Heron-2 well on Friday, but by Sunday the drill bit became stuck about 3m away from the previous borehole when the now unconsolidated Elang shale unit collapsed around the drill string.

"It is apparent that the rapid reduction in pressure - drawdown and other operations - during the open-hole production testing of the Elang/Plover formation caused a collapse of the Elang shale unit into the well," it said.

"This prevented the deeper Plover sands contributing to the flow and appears to have disturbed the shale formation in the vicinity of the original wellbore."

But MEO remained optimistic of the Plover's potential, which it planned to appraise further with a new well.

"Contrary to the joint venture's pre-drill expectation that the Plover sands of Heron North would most likely contain low quality, high CO2 gas, Heron-2 has provided sufficient log data to indicate that in fact a higher quality and more valuable hydrocarbon resource may be present warranting further production testing," it said.

"However, the joint venture believes it would be neither prudent nor economic to attempt to continue re-drilling and testing of the Plover formation in Heron-2 in such close proximity to the original wellbore."

For now, the company is turning its attention back to the Darwin formation, which was the pre-drill primary objective.

Results from drilling, electric logs and core sample interpretation in the Darwin formation confirm "strong indications of a significant gas accumulation," which will be production tested later in the week, MEO said.

The well is currently being plugged back to just below the Darwin formation at a depth of 3200m, where a production packer will be set in the 9-inch casing at 3080m.