Soco International’s TGD prospect off the coast of Vietnam could hold 1bn barrels of oil and gas, the company’s chief executive has said, even as it reported inconclusive results from its first well on the field.

In spite of the bullish view, shares in Soco fell 7 per cent on Monday, closing 141p lower at £18.60, after it said that while the well had flowed gas and liquids to the surface, damage in the hole “precluded recording meaningful sustained flow rates”.