by the weight of the tubing string provide production fluid seals between the tubing hanger 54 and the spool tree 34 provision is made in the top of the tubing hanger 54 for a wireline set plug 66 the keyed shoulder 56 of the tubing hanger lands in a complementary machined step in the spool tree 34 to ensure ultimate machined accuracy of orientation between the tubing hanger 54 and the spool tree 34 fig7 shows the final step in the completion of the spool tree this involves the running down on drill pipe 67 through the bop an internal isolation stopper 68 which seals within the top of the spool tree 34 and has an opening closed by an in situ wireline activated plug 69 the bop can then be removed leaving the wellhead in production mode with double barrier isolation at the upper end of the spool tree provided by the plugs 66 and 69 and the stopper 68 the production fluid outlet is controlled by a master control valve 70 and pressure through the tubing annulus outlet ports 62 and 64 is controlled by an annulus master valve 71 the other side of this valve is connected through a workover valve 72 to a lateral workover port 73 which extends through the wall of the spool tree to the void between the plugs 69 and 66 with this arrangement wireline access.