and the innermost riser conduit 80 of course any reasonable number of inner casing strings can be used the lowermost end of intermediate riser conduit 78 is connected through j slot 72 to the cemented casing 62 in the borehole and likewise the lower end of innermost riser conduit 80 is connected to the cemented innermost casing 66 which is shown as the smaller one in the drawing thus we have a casing 62 and intermediate riser conduit 78 forming a fluid tight conduit extending from the bottom of the casing to the top of the intermediate riser conduit 78 likewise a smaller fluid tight conduit is formed from the lower end of the innermost casing 66 through riser conduit 80 to the top of the platform if desired intermediate riser conduit 78 can be run before the hole for the inner casing 66 is drilled the connecting arrangement between the riser pipe and the casing set in the wellbore is shown in fig4 shown thereon also is the j slot 70 on the upper end of the enlarged end portion of conduit casing 54 and a j lug 76 which is on the lower end of riser 24 seal means 82 are provided between the lower end of riser 24 and the enlarged portion of the upper end of conduit casing 54 connection 72 for intermediate riser conduit 78 and cemented casing 62 and connection 74 for innermost riser conduit 80 and cemented casing 66 can be like that shown in fig4 attention is now directed to means for supporting the upper end of intermediate riser conduit 78 and innermost riser conduit 80 to the upper end of the riser pipe such that the inner riser conduits 78 and 80.