Santos CEO Kevin Gallagher conceded during Santos' first-half analyst call that one Roma area, Raslie, was underperforming, although two others - Pleasant Hill and Hermitage - were in line with expectations.

When this caused a predictable storm of questions about risk to meeting LNG contracts and potential reserves downgrades, Gallagher reminded analysts that Santos was in the early stages of reviewing the data and was yet to understand why the Roma field was underperforming.

While Gallagher said it was also unclear whether this would impact the estimated ultimate recovery, which is a key driver of economics, he said it was definitely too early to be thinking about reserves downgrades.

Koenders, a petroleum engineer and CSG specialist, agrees, but went further when probed by Energy News, saying the fields have plenty more potential that will benefit GLNG.

Bernstein analyst Neil Beveridge said the news of GLNG's Raslie issues "sent shivers down our spine" and consequently downgraded the firm's expectations of production from the project's second train.

The analyst now assumes GLNG will not reach full production capacity until 2020, two years later than previously assumed.

GLNG has 5.5 trillion cubic feet of 2P reserves with contracts to buy 2.2Tcf from third parties, and Beveridge believes GLNG will only have 85% of the gas it needs to support its two production trains in the long-term, raising questions about their viability.

"With six trains collectively that have a lot of buyers who don't want gas, and a collective upstream that can't deliver it for 20 years anyway, we still hope common sense prevails on Curtis Island through some form of consolidation," Credit Suisse's Mark Samter said.

Koenders said that while analysts fretted about reserves, it was important to remember that there were also areas within GLNG that are booked in 2C resource that Santos haven't done sufficient work to book as 2P proven reserves.

The issue also appears to be riling investors as Santos shares were up 0.5% intraday before Gallagher made the concession to analysts but subsequently finished down 2% that day.

Koenders said there were many explanations for why parts of the Roma field could underperform against assumptions.

"Under the SPE guidelines for booking reserves, which the ASX transitioned to in the past two years, you needed to have proven commercial flowrates from fields before you can book them as reserves; hence why there were reserve downgrades from many companies as they hadn't done sufficient drilling under the new classification standards," Koenders said.

"This included Arcadia for GLNG, which has lower permeability than Fairview but for all intents and purposes is the same coal measures. But given they hadn't found a proven well design that produced gas flow rates commercially they couldn't book it as reserves, which is fair.

"Then in the equity market people think, ‘that's it, we'll never see reserves from Arcadia'. They forget that QGC started off in the Surat Basin producing at flow rates of 100,000-200,000 cubic feet per day, and it took them six years of trial and error on well design to see those flow rates increase by tenfold to get to the world-class resource it is today."

Koenders believes GLNG merely hasn't done the work to get to that point with trial and error on well designs; while Santos did state on its results it fracture stimulated some wells in Arcadia and got some "very encouraging" results.

Santos is looking to move compression equipment into the Surat Basin for an extended well test later this year, which Koenders believes may be an indication that the company is getting to the point of "cracking the code" in terms of what could be commercial flow rates.

Citi's own estimates of what gas could be recovered from Arcadia on a longer-term basis if proven to be commercial is around 2-3Tcf.

"So there is still a lot of gas in the ground that's not included in reserves, but there's still a lot of work to be done to make it commercial," Koenders said.

However, he dismissed fears that Santos was behind the eight-ball even though QGC had done all its work well before the $US20.4 billion Queensland Curtis LNG project started exports from the first train in January.

"It's a question of risk tolerance and balance between de-risking the asset versus project return and capital allocation," Koenders said.

"Do you want to spend hundreds of millions of dollars proving the correct well design for Arcadia if production in the field is not needed for 10 years?

"The original budget included capex for appraisal of Arcadia to be done at the same time as project execution, but when they saw significant rain in the early stages of project execution and experienced delays in the drilling program they delayed all appraisal drilling and focused on production.

"These things take time. It's not like conventional [wells] where you start off with reserves."

He added that, while it was "important and prudent" to focus on what's going on with Roma, "it's not the be-all and end-all".