Patent ID: 8316944
Filing Date: 2012-11-27
Classification: E21B

Abstract:
1. A down-hole tool which is operable to create cyclic pulses in liquid from a reservoir being injected out from a hole in the ground into the surrounding ground formation, wherein: the tool includes a pulse-valve, having a valve-member and a valve-housing; the valve-member is movable relative to the valve-housing between an open position of the pulse-valve, in which pressurized liquid can pass through the pulse-valve out of the tool and into the formation, and a closed position; the tool includes an accumulator, which is arranged for storing pressurized liquid from the reservoir at a magnitude of pressure termed the accumulator-pressure, ready for presentation to the pulse-valve; the tool and the reservoir are so arranged that, during operation, when the pulse-valve is closed the PDAF increases, and when the pulse-valve is open the PDAF decreases; the tool includes a valve-cylinder and relatively movable valve-piston; the valve-piston is so connected to the valve-member as to be movable therewith; an accumulator-surface of the valve-piston is defined as that surface of the valve-piston, the whole of which, throughout operation of the tool to create cyclic pulses, is exposed to accumulator-pressure; a formation-surface of the valve-piston is defined as that surface of the valve-piston, the whole of which, throughout operation of the tool, is exposed to formation-pressure; the tool is so arranged that, throughout operation of the tool, accumulator-pressure acting on the accumulator-surface urges the valve-piston in a direction to open the pulse-valve, and the formation-pressure acting on the formation-surface urges the piston in a direction to close the pulse-valve, whereby the valve-piston is subjected to a net force, termed the PDAF-force; the tool includes a valve-piston-seal, which seals the valve-piston to the valve-cylinder, between the accumulator-surface and the formation-surface, throughout operation of the tool; the tool is so arranged that, in operation, the accumulator-pressure being higher than the formation-pressure, the PDAF-force acting on the valve-piston is so directed as to urge the valve-piston to move in the direction to open the pulse-valve; the tool includes a piston-biassing means, which is so arranged in the tool as to provide, throughout operation of the tool, a biassing-force that acts upon the valve-piston in such direction as to urge the pulse-valve to its closed position.