Explanation:

Under it, CO2 gas is injected with residual oil in the ageing field in which total oil production has been declining.
It reduces its viscosity and makes it easier to displace oil from the rock pores. CO2 gas also swells oil, thereby pushing it towards the producing well for extraction.
CO2-EOR works most commonly by injecting CO2 into already developed oil fields where it mixes with and “releases” the oil from the formation, thereby freeing it to move to production wells. CO2 that emerges with the oil is separated in above-ground facilities and re-injected into the formation.
CO2-EOR projects resemble a closed-loop system where the CO2 is injected, produces oil, is stored in the formation, or is recycled back into the injection well.
Learning: While the technology is a proven concept in the West specially the US and Canada, ONGC’s project would be the first large scale CO2-injected project in Asia. ONGC is planning to introduce CO2 injection technology in its Gandhar oil field in Gujarat.
Its purpose is to recover extra 20 million barrels of crude oil under enhanced oil recovery (EOR) programme. EOR programme aims at recovering up to 20% of residual oil from ageing oil fields to improve India’s energy security.