Abstract: A hydraulic oil and gas well downhole packer apparatus for use in a well casing below a wellhead and in combination with a coil tubing unit provides a tool body having a longitudinally extending tool bore and an upper end portion that connects to the lower free end of the coiled tubing unit during use. The tool body includes an inner elongated hollow mandrel with a hydraulic piston movably disposed upon the external surface of the mandrel. The piston is movable between an initial “running” position and a final “setting” position. An external sleeve is engaged by the piston when it moves between the running and setting positions, the external sleeve engaging slips that expand to anchor the tool body to the well casing. An annular packer member is expandable responsive to sliding movement of the external sleeve and is positioned below the slips for forming a seal between the tool body and the casing at a position near the lower end portion of the tool body.