Iran started drilling operations on Phase 11 of the South Pars gas field in southern Iran after years of delay, semi official SHANA news agency reported.

The aim is "to achieve a daily production capacity of 1 billion cubic feet of sour gas from the phase," said Mohsen Rezaei, caretaker of the project, adding 12 wells will be developed in two stages.

During the first stage, five appraisal/development wells will be drilled and completed, with an output of 500 million cubic feet per day.

In the second stage, seven development wells will be added until the goal of extracting 1 billion cubic feet gas per day is attained.

Iran's Petropars Company, the main contractor of the project, is implementing the development plan in both surface and subsurface sections, after foreign companies were forced to leave because of the U.S. unilateral sanctions against Iran.

The purpose of the drilling operations is to feed Iran's South Pars onshore refineries with 2 billion cubic feet of rich gas per day.

Iran's South Pars field is divided into 24 phases, most of which are in operation, while Phase 11 is near the Iran-Qatar joint water frontier in the Gulf.

As the world's largest gas field shared between Iran and Qatar, the South Pars field, also known as North Dome field, holds an estimated 1,800 trillion cubic feet of in-situ natural gas and some 50 billion barrels of natural gas condensate, according to the International Energy Agency, a Paris-based intergovernmental organization.