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A system and method for use in a wellbore that includes a string comprising a housing. The housing comprises a valve including a valve seat having an inner channel and a flapper configured to pivot relative to the valve seat between a first position and a second position in which the inner channel i

A system and method for use in a wellbore that includes a string comprising a housing. The housing comprises a valve including a valve seat having an inner channel and a flapper configured to pivot relative to the valve seat between a first position and a second position in which the inner channel is obstructed. A valve actuating device may be provided for selectively opening the valve and comprising a first hydraulic device. In addition, a retention device including a second hydraulic device may be provided and configured to selectively retain the flapper in the first position. In some cases, the first hydraulic device and the second hydraulic device may be driven by the same fluid source.

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What is claimed is: 1. A system for use in a wellbore, comprising: a string having a housing comprising a valve in which the valve comprises a valve seat having an inner channel and at least one flapper configured to pivot relative to the valve seat; wherein the at least one flapper is configured t

What is claimed is: 1. A system for use in a wellbore, comprising: a string having a housing comprising a valve in which the valve comprises a valve seat having an inner channel and at least one flapper configured to pivot relative to the valve seat; wherein the at least one flapper is configured to move between a first open position and a second position in which the inner channel is obstructed; a valve actuating device for selectively opening the valve, comprising a first hydraulic device and a first contact member to urge the flapper towards the first open position; and a retention device having a second contact member to retain the at least one flapper in the first open position after the first contact member has urged the flapper towards the first open position, the retention device comprising a second hydraulic device to move the second contact member into contact with the flapper. 2. The system of claim 1, wherein the first hydraulic device and the second hydraulic device are concurrently driven by the same fluid source. 3. The system of aim wherein the valve is a fluid loss control valve. 4. The system of claim 1, wherein the second hydraulic device comprises a cylinder and a piston. 5. The system of claim 1, wherein the inner channel of the valve seat is substantially unobstructed by the retention device. 6. The system of claim 1, wherein the second hydraulic device has an increased release time relative to the first hydraulic device, such that the second contact member does not release the flapper until after the first contact member allows the flapper to move towards the second position. 7. The system of claim 6, wherein the second hydraulic device has a distance of travel longer than that of the first hydraulic device. 8. The system of claim 6, wherein the second hydraulic device overcomes greater friction forces than the first hydraulic device. 9. The system of claim 6, wherein the second hydraulic device overcomes greater hydraulic resistance than the first hydraulic device. 10. A method for controlling wellbore fluids in which a well comprises a string having a housing containing a valve in which the valve comprises a valve seat having an inner channel and at least one flapper configured to pivot between a first position and a second position relative to the valve seat, the method comprising; providing a valve actuating device for selectively opening the valve, comprising a first hydraulic device driven by a hydraulic pressure applied via a hydraulic control line; providing a retention device configured to selectively retain the at least one flapper in the first position, the retention device comprising a second hydraulic device driven concurrently with the first hydraulic device by the hydraulic pressure applied via the hydraulic control line; configuring the second hydraulic device to have an increased actuation time relative to the first hydraulic device upon application of the hydraulic pressure to the first and second hydraulic devices via the hydraulic control line. 11. The method of claim 10, wherein the second hydraulic device has a distance of travel longer than that of the first hydraulic device. 12. The method of claim 10, wherein the second hydraulic device overcomes greater friction forces than the first hydraulic device. 13. The method of claim 10, wherein the valve is a subsurface safety valve. 14. The method of claim 10, wherein the second hydraulic device overcomes greater hydraulic resistance than the first hydraulic device. 15. The method of claim 10, wherein the inner channel of the valve seat is substantially unobstructed by the retention device. 16. A valve for use in a wellbore comprising: a valve seat, the valve seat having an inner channel; a flapper configured to pivot relative to the valve seat between a first position and a second position in which the inner channel is obstructed; and a valve actuating device for selectively opening the valve, comprising a first hydraulic device to extend a first contact member into contact with the flapper to urge the flapper towards the first position; and a retention device configured to selectively retain the flapper in the first position, the retention device comprising a second hydraulic device, wherein the first hydraulic device and the second hydraulic device are driven by the same fluid source, and wherein, in response to a loss of hydraulic pressure, the valve actuating device retracts the first contact member to allow the valve to close prior to the retention device releasing the flapper. 17. The system of claim 16, wherein, upon the loss of the hydraulic pressure, the second hydraulic device has an increased release time relative to the first hydraulic device. 18. The system of claim 16, wherein the second hydraulic device has a distance of travel longer than that of the first hydraulic device. 19. The system of claim 16, wherein the second hydraulic device overcomes greater hydraulic resistance than the first hydraulic device.