Patent ID: 8657007

Claim:
A hydraulic jarring tool for use with a well conduit in an oil or gas well, the tool comprising: a housing; a mandrel; wherein one of the mandrel and the housing is attachable to the well conduit and the other of the mandrel and the housing is attachable to a fixed object in the well; wherein the housing and the mandrel have telescopically engaged portions that are axially movable relative to each other to fire and reset the tool; wherein the telescopically engaged portions of the housing and the mandrel are configured to form a hydraulic chamber therebetween, the hydraulic chamber including a low pressure chamber, a high pressure chamber, and a narrow diameter seal bore therebetween; wherein the seal bore has a smaller diameter section and a larger diameter section between the smaller diameter section and the high pressure chamber; wherein the low pressure chamber includes an inwardly tapering bevel that contacts the seal bore, and the high pressure chamber includes an inwardly tapering bevel that contacts the seal bore; an impact surface formed on each of the housing and the mandrel; a piston supported in the hydraulic chamber for relative movement between the high and low pressure chambers through the seal bore, wherein the piston comprises a cup with an open end terminating in a lip, the open end of the cup facing the high pressure chamber, the cup being deformable in response to fluid pressure, so that as the piston moves through the seal bore towards the high pressure chamber, the lip of the cup expands permanently to a diameter larger than the smaller diameter section of the seal bore; an unrestricted flow path configured to allow hydraulic fluid to pass through the seal bore as the piston moves through the seal bore towards the low pressure chamber to reset the tool; and a restricted flow path configured to restrict the flow of hydraulic fluid as the piston moves through the seal bore towards the high pressure chamber to fire the tool and create a jarring impact between the impact surfaces.