Nigeria took a major step in its quest to earn revenue from its vast gas reserves, signing a deal with joint venture partners to supply gas to a proposed $3.5 billion Brass fertilizer and petrochemical plant, an official said on Friday.

Under the agreement, joint venture partners including Shell TotalEnergies and Eni will deliver an estimated 270 million standard cubic feet of gas per day to the plant in Brass, in Nigeria's coastal Bayelsa state.

Petroleum Ministry Permanent Secretary Nicholas Agbo Ella said the Gas Sale and Purchase Agreement is a part of the Brass Fertilizer and Petrochemical Project, which is expected to generate at least $1.5 billion annually from exports of petrochemicals and other gas-based products.

"This agreement represents a significant milestone in our ongoing efforts to monetize Nigeria's vast gas reserves," Ella said.

Nigeria, Africa's top energy producer, holds the continent's largest gas reserves of more than 200 trillion cubic feet and seeks to develop the commodity to boost supplies to industries, power plants and for exports, and to end routine flaring by 2030.

"In addition to boosting exports, the project will reduce fertilizer imports by 30%, saving Nigeria approximately $200 million in foreign exchange annually," Ella said.