Downhole lubricator for installation of extended assemblies

The wellbore is adapted for use as a lubricator for assembly of lengthy installations. The subsurface safety valve is used in conjunction with a nipple inserted into the wellbore and held in position by a packer. A plug is part of the nipple assembly. Upon setting of the packer, two barriers downhole are created to facilitate assembly of tools such as a perforating gun in the wellbore behind two barriers. The tool, such as a perforating gun, has a running tool below it which engages the plug. When the assembly is made up in the wellbore, the plug is engaged by the running tool and released from the nipple. The plug can then be advanced through the open subsurface safety valve to the proper location for deployment of a perforating gun, for example. Upon completion of the downhole procedures, such as perforating, the tools are brought uphole and the plug is sealingly relatched in the nipple, thus recreating the necessary two barriers to permit opening the wellbore at the surface to remove the assembly of the downhole tools and the running tool. The plug can be reengaged as many times as necessary for installation of a variety of equipment. The nipple can then also be removed after the packer is released.