State oil giant Saudi Aramco has opened bidding to develop a plant to process gas from the Midyan field to supply a power plant, industry sources said, as the world's largest oil exporter moves to stop burning crude oil and diesel to generate power industry.

Seven companies will submit their offers by the end of November to build the plant, to have a processing capacity of 75 million standard cubic feet per day (scfd) of gas and a pipeline to a power plant in the western port city of Dheba, one of the sources said.

In January, Aramco's CEO Khalid al-Falih identified Midyan as one of the new gas fields in the northwest area to produce gas for power plants and potentially to supply other industries in a region rich in iron ore deposits.

Saudi Arabian Mining Co (Maaden) plans to invest 21 billion riyals ($5.6 billion) in a phosphate project as part of a new industrial city in the north. However, the phosphate ore is located near a gas field in Jalamid where extensive exploration is taking place.

Aramco also invited companies to bid for the upgrade of Riyadh's 124,000 barrels per day oil refinery. Companies are due to bid by Oct. 20 for the project, estimated to cost around $300 million, to produce cleaner fuels.

The state-owned firm has embarked on a programme to upgrade its refineries to produce cleaner fuels. It spent $2 billion for a clean fuels project at its joint venture refinery with U.S.-based Exxon Mobil due to be operation in 2013. The project is expected to cut sulfur content for gasoline by 2013 and for diesel by 2016.

The second phase of the upgrade involves plans to start cleaner fuels and aromatics production at its largest crude oil refinery in Ras Tanura by 2016.