The objective of abandonment is to prevent the migration of all formation fluids, but especially hydrocarbons, between formations and to the surface. There are two types of conduit which must be closed off - the open hole plus casing and the annuli.
In the open hole all intervals which contain hydrocarbons should be covered by a cement plug extending some 50 m above and 50 m below the limits of the hydrocarbons. Water-bearing porous and permeable formations from different geological units or under different pressure gradients should be separated by a plug, across . . .