The invention relates to the use of a casing or liner (3) with pre-formed, selectively openable apertures (5), in plug and abandon operations at the end of life of a hydrocarbon well. The casing or liner (3) is installed at the start of the well's life and the apertures (5) are provided over a length of the casing/liner above the reservoir where a permanent plug would normally be formed when the well is abandoned at the end of its life. Associated with the apertures are sliding sleeve closure members (6) which are designed to remain operational over the 20-30 year lifetime of the well.