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An actuator assembly for effective interventionless activation of a valve in wells of multilateral architecture. The assembly may be pressure actuated from an oilfield surface even in certain circumstances where another valve in another leg of the well has been opened in a manner compromising pressu

An actuator assembly for effective interventionless activation of a valve in wells of multilateral architecture. The assembly may be pressure actuated from an oilfield surface even in certain circumstances where another valve in another leg of the well has been opened in a manner compromising pressure control of the well. Due to the multi-stage nature of the actuator, pressure based activation remains viable as a result of supplemental and/or fail-safe modes of actuation, for example, where such pressure control becomes compromised.

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1. A completions assembly for a multilateral well, the assembly comprising: an isolation device disposed in a branch of the well;a tubular device disposed through said isolation device within the branch;a valve for regulating fluid communication between said tubular device and the branch; andan actu

1. A completions assembly for a multilateral well, the assembly comprising: an isolation device disposed in a branch of the well;a tubular device disposed through said isolation device within the branch;a valve for regulating fluid communication between said tubular device and the branch; andan actuator coupled to said valve and having a primary actuation mechanism for driving open said valve and a fail-safe actuation mechanism having capacity for opening said valve upon failure of the driving wherein the primary actuation mechanism comprises a primary mandrel axially translatable along an axis and wherein the fail-safe actuation mechanism comprises a fail-safe mandrel, concentric to the primary mandrel, that transitions from being secured to released responsive to an increase in fluid pressure and that, in being released, drives open said valve responsive to a decrease in the fluid pressure. 2. The assembly of claim 1 wherein said isolation device is a downhole packer, said tubular device is production tubing, and said valve is a formation isolation valve. 3. The assembly of claim 1 further comprising a toolstring for running through said tubular device to a location within the branch from an oilfield surface adjacent the well. 4. The assembly of claim 3 wherein said toolstring comprises an interventional element for running an application at the location. 5. The assembly of claim 4 wherein the application is selected from a group consisting of a gravel packing application and a cleanout application. 6. The assembly of claim 3 wherein said toolstring comprises a shifting device for closure of said valve upon withdrawal thereof from the location. 7. The assembly of claim 1 wherein said isolation device is a first isolation device, said tubular device is a first tubular device, said valve is a first valve and said actuator is a first actuator, the assembly further comprising: a second isolation device disposed in another branch of the well;a second tubular device disposed through said second isolation device to within the other branch, said second tubular device coupled to said first tubular device and sharing a common fluid pathway therewith;a second valve for regulating fluid communication between said second tubular device and the other branch; anda second actuator coupled to said second valve and having an active mandrel for driving open an operator of said second valve and a release mandrel for opening the operator upon failure of the driving. 8. The assembly of claim 7 wherein said actuators are responsive to fluid pressure through the common fluid pathway for the driving and the opening. 9. A method comprising: providing a completions assembly for a multilateral well where the assembly comprises an isolation device disposed in a branch of the well; a tubular device disposed through the isolation device within the branch; a valve for regulating fluid communication between the tubular device and the branch; and an actuator coupled to the valve and having a primary actuation mechanism for driving open the valve and a fail-safe actuation mechanism having capacity for opening the valve upon failure of the driving wherein the primary actuation mechanism comprises a primary mandrel axially translatable along an axis and wherein the fail-safe actuation mechanism comprises a fail-safe mandrel, concentric to the primary mandrel, that transitions from being secured to released responsive to an increase in fluid pressure and that, in being released, drives open the valve responsive to a decrease in the fluid pressure;responsive to an increase in fluid pressure, transitioning the fail-safe mandrel from being secured to released; andresponsive to a decrease in the fluid pressure, driving the valve open via the released fail-safe mandrel.