A system for facilitating the insertion of a tool into a wellbore, especially a non-vertical wellbore. In one embodiment a tool is fixable in a wellbore and includes centralizing, friction-reducing members that serve to keep the body of the tool off the walls of the wellbore. In another embodiment the tool includes a wiper ring that partially fills an annular area formed between the centered tool and the wellbore walls. The surface of the ring facing the upper end of the wellbore provides fluid resisting piston surface and permits the centered tool to be pumped down the wellbore more effectively.