Coro Energy reports speed bump in development at West Natuna

South east Asia-focussed upstream oil and gas company Coro Energy updated the market on the drilling campaign in the Duyung Production Sharing Contract in the West Natuna basin, offshore Indonesia, in which it holds a 15% interest, on Friday.

The AIM-traded firm said that following the drilling of the Tambak-2 well, as announced on 15 October, operations had been focussed on conducting a drill stem test (DST) across the intra-Muda reservoir.

It said the operator had reported that those DST efforts had not been successful, due to formation damage in the “highly permeable and porous” reservoir.

Two separate DST attempts had been conducted across the intra-Muda reservoir without success, due to extreme formation damage, the board explained.

It said operational issues encountered while setting the bridge plug - needed to isolate the gas-bearing reservoir - resulted in a “swabbing” of the well, which led to a substantial gas kick, with gas flowing to surface.

Heavy mud was used to control the well, resulting in large volumes of barite mud being lost to the permeable reservoir, with the reservoir formation becoming plugged and damaged by the barite mud.

Prior to the DST attempts, a full logging suite was acquired, including formation pressure measurements, in the Tambak-2 well.

Coro said that confirmed a 10 metre gross gas zone, with formation permeabilities calculated to be in the 200 millidarcy to three darcy range across the best quality zone - a “highly permeable reservoir”, as predicted.

The pressures indicated the well encountered the same gas accumulation as at Mako South-1, more than 13 kilometres away, with mud gas readings indicating a dry methane gas almost wholly C1 with minor C2, again consistent with Mako South-1.

Petrophysical analysis of the log data suggested any DST testing would have yielded similar high flow rates to the discovery well.

The firm said the next step in the drilling campaign would be to mobilise the rig to the Tambak-1 location, where the well spud was anticipated in the coming days.

“While the lack of a successful DST at Tambak-2 is disappointing, the main objectives of the well have been met, namely demonstrating a continuous gas-bearing reservoir over a large distance; confirming the same pressure system and gas-water contact as seen at Mako South-1 and in addition, the same quality of reservoir but with better sand development than expected,” said Coro Energy chief executive officer James Menzies.

“In light of these results, we remain confident of a material uplift in contingent resources and asset value.

“The Asian Endeavour 1 rig is now being prepared to mobilise to the Tambak-1 location where we will further appraise the Mako field and also test the underlying Tambak structure, an exciting amplitude supported prospect with mid-case prospective resource potential of 250 Bcf.”