A method is provided for multistage isolation and fluid treatment of a borehole, in which a first frac valve tool and a second frac valve tool are provided, a first packer is mounted downstream from the first frac valve tool, a second packer is mounted between the first frac valve tool and the second frac valve tool, a third packer is mounted upstream from the second frac valve tool, at least one of the first, second and third packers being a hydraulic set packer having a single packing element, the first frac valve tool being moveable between a closed and an open position, the second frac valve tool moveable between a closed and an open position; running the liner into a wellbore; hydraulically setting the single element packers; conveying means for moving the first frac valve tool to the open position; and forcing stimulation fluid out through the first frac sleeve tool.