wall 26 of the structure 16 it will be readily appreciated that one or more of the wellbores could be drilled outwardly through a sidewall of the structure to line the wellbores 24 a liner string 34 may be connected to the structure 16 preferably the liner string 34 is sealed to the structure 16 so that the interior of the structure remains isolated from the formation 18 surrounding the intersection of the wellbores 14 24 as depicted in fig3 the liner string 34 is provided with an outwardly extending flange 36 which sealingly engages the interior of the bottom wall 26 the seal between the flange 36 and the bottom wall 26 may be a metal to metal seal or it may be provided by an elastomer or nonelastomer seal an adhesive sealant or any other type of seal the flange 36 is depicted in fig3 as one method of attaching the liner string 34 to the structure 16 other methods are described below however it will be readily appreciated that many alternative methods may be used in keeping with the principles of the invention for example the liner string 34 could be provided with outwardly extending keys or dogs which engage an internal profile of the.