Abstract: During a surge-pulsing operation in a borehole (e.g an oil-well undergoing remediation) liquid is stored under pressure upstream of a valve, and then released through the valve suddenly enough to create a seismic wave, which propagates into the formation around the borehole, and assists the surge-pulsing to improve the conductivity and liquid-injectability of the formation. The downhole valve achieves the rapid-opening requirement by virtue of its geometrical layout, as dictated by the strictures of the downhole environment.

Abstract: A well tool is operable to receive a flow of fluid. The well tool includes a first hydraulic area on which the fluid acts tending to move a first body to substantially seal against passage of fluid through an aperture. A second, larger hydraulic area is provided on which the fluid acts tending to move a second body. The second body is movable by the fluid acting on the second hydraulic to displace the first body from substantially sealing against passage of fluid through the aperture. An energy storing device is provided that is configured to store energy from movement of the second body until at least a specified amount of energy is stored and release the energy when the second body is moved to displace the first body from substantially sealing against passage of fluid through the aperture.