Chevron is currently producing 70 mmcfd gas from the field.

The official said the most modern technology was being used in the six-month long survey encompassing nearly 152 sq km (59 sq mile) including about 20 percent within the national forest, and that would leave no significant impact on the environment.

The official said this would consist of small charges, which would be buried about 22 metres (72 ft) underground.

"The survey work is being conducted in an environmentally sensitive and careful manner and will protect the conservation values of the area," Wilson told a news conference.

The Moulavi Bazar natural gas field with an estimated reserve of 400 billion cubic feet, was discovered in 1999 and started production in 2005 by Unocal, which was later acquired by Chevron.

Chevron is also producing nearly 450 mmcfd from Bibiyana and 150 mmcfd from Jalalabad natural gas fields, also located in northeast of Bangladesh, officials said.

It has invested $820 million in Bangladesh, making it the biggest investor in the country's energy sector.

Bangladesh's proven and recoverable gas reserves are 13.54 tcf and the gap between demand and supply will widen further over the next five years if no new gas is found, officials said.