Tullow Oil’s first wildcat on its Orinduik block off Guyana, which is set to spud in the first half of next year, has been given a change of success of more than 40% by one of the partners.

The Anglo-Irish operator is also closing in on the award of a rig charter for the two-well campaign in 2019, with the list of drillship candidates narrowed down to two.

Minority block partner Eco Atlantic Oil & Gas revealed on Wednesday that the partners, also including French supermajor Total, will drill the first of two planned wells on Orinduik on a prospect called Jethro-Lobe in late May or early June.

Eco chief executive Gil Holzman told Upstream that the well is most likely to spud in the third or fourth week of May and will actually zone in on an Upper Tertiary target called Lobe within what is described as the Jethro complex, which is assessed as having a series of targets.

An initial statement from Eco on Wednesday morning said the prospect is in the Upper Cretaceous horizon. However, a later statement corrected this to Upper Tertiary, with Holzman also clarifying that total depth is in the Cretaceous.

Eco has also said the gross prospective resource estimate at Lobe is 250 million barrels of oil, with a chance of success estimated at 44%.

Although Holzman clarified that the figure of 44% should be read as Eco’s number, he added: “The number is not materially different from what our partners think.”

However, Tullow exploration director Angus McCoss said last week ahead of the company's capital markets day in London that the 2019 drilling candidates were each being given a chance of success "in the twenties" of percent.

Holzman added: “One could think that the 250 million is a small number, but we don’t consider it as one target, it is complex – very much like TEN in Ghana,” referring to the under-development Tweneboa-Enyenra-Ntomme field complex, operated by Tullow.

"Tullow and the project Ghana team on this, they see it as very similar to what they have in TEN and this is why we are targeting it first, because the first target might open a big field," he continued.

“Jethro is a complex, Lobe is the immediate drilling target. It is a big canyon, a big channel with a lot of sand… (If) we prove Lobe contains oil, it will open up a very big complex.”

Tullow said last week that it had identified four 2019 drill candidates on the block: Jethro, Kumaka, Amaila and Aurituk. The last is seen as possibly on trend with ExxonMobil’s Hammerhead discovery on the Stabroek block, a find that is assessed as extending over into Orinduik.

“We consider Hammerhead in many ways to extend into our block, meaning that Hammerhead is a discovery also on our block,” Holzman said.

“We believe that it will be some time in the near to mid-term future subject to unitisation talks and we (will) try to start those talks based on the geophysics, which are very clear to all parties, instead of spending some $40 million on a well that basically nobody needs to drill.”

Holzman said the partners may be in a position in January or February to nominate the second well on Orinduik, although he agreed it is most likely they would drill on Aurituk next, with both wells possibly drilled back-to-back.

“I think eventually this block can easily be a target for 10 or more wells,” he said.

Eco, which is a 15% stakeholder in Orinduik, has put the estimated net cost to it of the first well at $7.6 million, although Holzman cautioned that the company was being conservative on the high side with that estimate.

With Tullow on 60% and Total on 25%, this would assume a gross well cost of $50 million, which would be very high considering current drillship dayrates.

However, Holzman explained: “Because it is the first well, we are probably going to put some extra casing, etc, just to be on the safe side.”

He also said the cost assumes a duration of 43 days to drill the well, whereas ExxonMobil in reality is drilling its wells on Stabroek in 20 days or less, he added.

“There are two candidates at the moment, both with the same daily rates, both confirmed that they can drill in our timeframe,” Holzman said of an impending rig charter, without identifying the finalists.

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Tullow's Guyana wildcat 'to target TEN-like complex'