China's state-run Zhenhua Oil has signed a preliminary deal with Chevron to buy the US oil major's natural gas fields in Bangladesh that are worth about $2 billion, two Beijing-based Chinese oil executives said.

Zhenhua is a subsidiary of China's defence industry conglomerate NORINCO. A completed deal would mark China's first major energy investment in the South Asian country, where Beijing is competing with New Delhi and Tokyo for influence.

Bangladesh, though, holds the right of first refusal on the assets and could block the transaction. The country, via its national oil company Petrobangla, is keen to buy the gas fields and is talking to international banks to raise financing, according to a banking source familiar with the process.

Bangladesh is in the process of hiring global energy consultant Wood Mackenzie to assess the fields' reserves before placing a formal bid to buy the assets, two Bangladesh sources familiar with the matter told Reuters. The Bangladesh sources said they were not aware of Zhenhua Oil's competing interest in the Chevron fields.

Chevron, which is the largest foreign investor in Bangladesh's energy sector, operates the Bibiyana, Jalalabad and Moulvibazar gas fields and sells all the production to state oil company Petrobangla.

In 2015, its net daily production averaged 720 million cubic feet of natural gas, which is about one-third of the total production of Bangladesh. It also produced 3,000 barrels of natural gasoline.