Definition - What does Abandonment mean?
Abandonment is the act of giving up on a well when its economic limit is reached. In the Abandonment process, the tubing gets removed from the well and the sections of the wellbore are brimmed with concrete to isolate the flow path between the gas and water zones from each other and from the surface as well. The well is not completely filled with concrete as it is costly, instead the wellhead is evacuated. After that the chasing and wellhead are cut off and a cap is welded in place and then it is buried.
Petropedia explains Abandonment
When the economic limit of a well rises, the life of the well is shortened and all the reserves of proven oil are lost. If the economic limit is lowered, the life of the well is prolonged. When the well gets abandoned, it is important to fill it with concrete to make the flow path secluded between the zones of water and gas. Even when the economic limit is reached, some amount of oil which is unrecoverable is left in the reservoir. In cases where the organization holds on the physical Abandonment, temporary plugs are placed downhole and locks are attached to the wellhead that prevent tampering.