Various subterranean formations contain hydrocarbon based fluids that can be produced to a surface location for collection. Generally, a wellbore is drilled, and a completion is moved downhole to facilitate production of desired fluids from the surrounding formation. In many applications, the wellbore completion includes a hydraulic tool that is actuated by hydraulic pressure applied, for example, in the annulus surrounding the tool.
Actuation of the hydraulic tool often is controlled by using a rupture disk placed in the flow path of the hydraulic fluid that would otherwise actuate the hydraulic tool. In other words, the rupture disk is used to avoid premature actuation before a predetermined level of pressure is applied in the annulus. Once sufficient pressure is applied, the disk ruptures to create a flow path for hydraulic fluid to flow into and activate the hydraulic tool. In applications with multiple hydraulic tools, rupture disks which rupture at different pressure levels can be used to provide some individuality as to actuation of the hydraulic tools. Pressure levels within the annulus or completion tubing can be controlled by pumps disposed at a surface location.
When rupture disks are used, however, the hydraulic tool having the disk with the lowest pressure setting is always the tool that must be actuated first. Additionally, each rupture disk requires approximately a 500-1000 psi window for rupture. Thus, if multiple hydraulic tools are to be actuated at different times, multiple pressure ranges are required across a potentially large pressure spectrum. For example, if seven different rupture disks are used in a completion, a 7000 psi window above the normal hydrostatic pressure is required for dependable actuation of the corresponding hydraulic tools at the desired times.