Wells – Valves – closures or changeable restrictors – Fluid operated
Reexamination Certificate
2000-09-05
2002-05-21
Bagnell, David (Department: 3672)
Wells
Valves, closures or changeable restrictors
Fluid operated
C166S373000, C137S460000, C137S498000, C137S509000
Reexamination Certificate
active
06390199
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a safety valve for use in a wellbore formed in an earth formation, comprising a valve body having a fluid passage for passage of a stream of hydrocarbon fluid flowing from the earth formation via the wellbore to the earth surface, a closure member movable relative to the valve body between an open position in which the fluid passage is open and a closed position in which the closure member closes the fluid passage. The safety valve serves to shut down production from the wellbore either by control from surface or automatically in case of undesirable flow conditions. The latter situation occurs for example in case of increased hydrocarbon fluid flow rate as a result of an accident at a surface production facility. Therefore it is generally aimed to design a safety valve for a wellbore such that the valve closes upon the flow rate in the wellbore reaching a selected threshold flow rate.
However, experience has shown that conventional safety valves generally have a low accuracy with regard to the flow rate at which the valve closes.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved downhole safety valve which overcomes the drawbacks of the conventional downhole safety valves.
In accordance with the invention there is provided a safety valve for use in a wellbore formed in an earth formation, comprising
a valve body having a fluid passage for passage of a stream of hydrocarbon fluid flowing from the earth formation via the wellbore to the earth surface;
a closure member movable relative to the valve body between an open position in which the fluid passage is open and a closed position in which the closure member closes the fluid passage;
an activating device for selectively subjecting the closure member to a drag force of selected magnitude, the drag force being exerted by the stream of fluid and inducing the closure member to move from the open position to the closed position thereof; and
control means for controlling the activating device to subject the closure member to said drag force.
By selectively subjecting the closure member to the drag force it is achieved that a step-change in the resulting force acting on the closure member is created rather than a gradual change as in conventional safety valves. As a result the closure member closes the fluid passage in response to the step-change of force. It is to be understood that the drag force can act directly onto the closure member or onto a drag surface connected to the closure member.
Suitably the activating device is operable between a first mode in which flow of the stream of fluid against the closure member is substantially prevented, and a second mode in which flow of the stream of fluid against the closure member is allowed.
In a preferred embodiment the closure member is arranged in a conduit and wherein in said first mode the activating device substantially prevents flow of the stream of fluid into the conduit, and in said second mode the activating device allows flow of the stream of fluid into the conduit.
Preferably the activating device includes a flapper valve having a flapper element arranged upstream the closure member, which flapper element in said first mode substantially closes the conduit and in said second mode substantially leaves the conduit open.
The invention will be described hereinafter in more detail and by way of example with reference to the accompanying drawings in which:
REFERENCES:
patent: 2370584 (1945-02-01), Schneider
patent: 4708163 (1987-11-01), Deaton
patent: 4911199 (1990-03-01), Bontenbal et al.
patent: 5979870 (1999-11-01), Junier
patent: 6233919 (2001-05-01), Abel et al.
Shell Oil Company
Stephenson Daniel P
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