Wells – With electrical means – Valve
Reexamination Certificate
1997-12-09
2001-07-03
Bagnell, David (Department: 3673)
Wells
With electrical means
Valve
C166S332800
Reexamination Certificate
active
06253843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a surface controlled subsurface safety valve (SCSSV) for a sub-terranean well and, more particularly, to a safety valve utilizing an electrical actuation mechanism controlled from the surface or by a downhole intelligent controller.
2. Prior Art
Employment of a downhole safety valve is well known for subterranean oil and gas wells. Such valves, which can comprise a plug or pocket type, a sleeve valve, a flapper valve or ball valve, are normally positioned downhole to close the bore of the tubing string leading from one or more production zones to the well surface. Safety valves of this type are normally biased to a fail safe condition whereby any significant reduction in the opening force acting upon a valve will allow a pre-energized arrangement such as a spring to close the valve.
Commonly, downhole safety valves are actuated by hydraulics. A hydraulic system is connected to a piston arrangement; pressure from the surface via a small diameter control line is directed upon the piston which, in turn, moves a flow tube past a flapper valve thereby opening the flapper valve. In this position the flapper is essentially locked in the open position by the presence of the flow tube. A spring is generally placed in contact with the flow tube and with a non-moveable housing so that when the flow tube is urged downhole it is against the bias of the spring, thus energizing the spring for closing of the valve should the opening impetus caused by the hydraulic pressure from above be lost or reduced. While these valves are highly effective in the field, they do have drawbacks. One such drawback is that since these valves are installed many thousands of feet below the earth's surface, thus necessitating many thousands of feet of hydraulic control line, the hydrostatic pressure of the control line is sufficient to render the closing of the safety valve a slow process. In order to close the valve, the spring must lift the hydraulic column all of the fluid contained in the piston cylinder back into the control line by forcing, for instance, six thousand feet of fluid in that control line uphole. This requires a strong closure spring to lift the hydraulic fluid column. Necessarily, the control line is susceptible to damage during the running process and the joints in the control line may develop leaks over time. Such a leak would indicate a reduction in the opening impetus and the fail safe feature of the valve would close the same. Loss of integrity of the control line, in general, requires that the entire tubing string be pulled from the well and necessary repairs made.
More recently electric actuation of downhole safety valves has become of interest. Electrically operated safety valves are becoming increasingly popular with the introduction of intelligent downhole systems such as those disclosed in U.S. patent application Ser. No. 08/386,504 now U.S. Pat. No. 5,706,896 assigned to the assignee hereof and incorporated herein by reference. Downhole intelligence allows an electrically actuated downhole safety valve to receive commands from the surface or downhole and thereby operate either completely automatically or with input if desired.
One of the drawbacks associated with the use of solenoid actuated downhole safety valves arises from the use of the solenoid itself to directly open the valve. Opening valves of larger sizes requires a reasonably long throw. Solenoids, however, generally operate on throws shorter than that necessary. In many cases the throw of the solenoid is not sufficient to completely open the safety valve. This impedes flow of production fluid and risks damage to the safety valve due to the bending moment on the pivot point of the valve caused by production flow. To remedy the drawback, either a larger solenoid or various levering arrangements have been employed with some success. There is still a need, however, for improved methods of electrically actuating the downhole safety valve.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the electrically actuated downhole safety valve of the invention.
The invention employs a rotational motor and lead screw to interact with an engageable yoke which moves the flow tube. Extending around the I.D. of the housing is an engageable and disengageable yoke similar to a half nut which when engaged is moveable along the lead screw. The yoke is also attached to a flow tube which is disposed within the I.D. of the yoke such that upon engagement of the yoke with the lead screw and the movement imparted to the yoke is also imparted to the flow tube. As the flow tube is urged toward and through the flapper valve, it is aligned with and connects with the downhole production tube.
In order to actuate the yoke of the invention, a solenoid is connected to a camming rod which urges the yoke apart at one point thereof and together at a point diametrically opposed to the first point. This allows engagement of the yoke with the lead screw at the second point. As will be understood by one of skill in the art in order to provide such movement the yoke is divided in two parts (half yokes) and mounted on guide rods. Therefore, separation of the half yokes at one end will produce the movement of the other ends of the half yokes closer together and thus into communication with the lead screw.
In another aspect of the invention the friction commonly associated with a half nut for a lead screw is avoided by providing follower screws mounted on bearings and connected to the engagement side of the yoke. Since frictional characteristics are dramatically reduced the effective power requirement of the rotational motor need not be as high as it otherwise might have to be. Several embodiments of actuation mechanisms and particular assemblies are discussed in detail in the pages following.
The yoke and lead screw design of the present invention replace the hydraulic actuation of the prior art shown in
FIG. 1
while other aspects of the safety valve remain the same as the prior art.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
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Rawson Michael S.
Trott Doug
Bagnell David
Baker Hughes Incorporated
Cantor & Colburn LLP
Singh Sunil
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