Wells – Processes – Operating valve – closure – or changeable restrictor in a well
Patent
1997-02-24
1999-01-12
Dang, Hoang C.
Wells
Processes
Operating valve, closure, or changeable restrictor in a well
166 70, 166 971, 166321, 166379, E21B 33068, E21B 3410
Patent
active
058575235
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a downhole safety valve for use in a wellbore and particularly but not exclusively for use in through tubing intervention work horizontal production completions.
The use of horizontal drilling techniques has seen a considerable increase in the use of stiff wireline to log and to intervene in horizontal wells. A major disadvantage of such horizontal drilling techniques is the long length of the intervention equipment required in the well. String lengths of over 100 ft. are commonplace and, consequently, the rigging up of pressure retaining equipment on surface is both hazardous and time consuming.
A conventional safety valve used in wells is a downhole lubricator valve and such valves are commonly used in floating vessel operations. Such a conventional safety valve is a "failsafe close" valve which, if it fails, closes the valve to isolate the well. Conventional lubricator valves cannot be utilised in connection with horizontal drilling techniques because with the very large string lengths this would involve constructing a substantial structure above the surface test tree and this is, as mentioned above, hazardous and time consuming. A further problem with existing horizontal well completions is that all-through tubing intervention work has to be performed by coil tubing and the surface rig up for this type of operation is also hazardous and time consuming. In addition, the downhole safety valve should enable the surface test tree to be leak-off tested on a regular basis and enable the SSTT valves to be pressure tested before opening and after relatch. This is not possible with existing valves.
An object of the present invention is to provide an improved apparatus and a method of isolating the well to allow intervention equipment to be installed in the upper section of tubing and surface equipment to be tested prior to running in the well which obviates or mitigates at least one of the aforementioned disadvantages of the prior art systems.
This is achieved by installing a fail open valve above a conventional downhole safety valve, the fail open valve being closable by the application of hydraulic closure pressure to allow a pressure differential to be supported from above. This allows the intervention equipment to be installed in the upper section of the tubing and the surface equipment to be tested prior to running in the well and enables the injection head to be installed immediately upon the production tree.
In a preferred arrangement the completion lubricator valve is provided by two flapper valves; the upper flapper valve known as a fail open test valve, (FOTV) is normally biased closed and if the valve fails, it fails in to the open position. The lower valve is a standard sub-sea safety valve which is a failsafe close valve and, in the event of valve failure, closes to isolate the well. The completion lubricator valve is the combination of the FOTV and SSSV.
The FOTV and SSSV have hydraulic control lines for actuating the valves with and also springs for biasing the valves into an open or a closed position.
According to a first aspect of the present invention there is provided a completion lubricator valve for use with horizontal well completions, said completion lubricator valve comprising: failure, said upper test valve means having first means for moving said valve between an open position and a closed position, said first valve being urged into an open position in the absence of external force applied to said upper test valve means, arranged to close the bore of the completion lubricator valve in the event of failure of said lower test valve means, said lower test valve means having second means for moving said valve between an open and a closed position, said second valve means being urged into a closed position in the absence of an external force applied to said lower test valve means, upper test valve means said valve is moved to a closed position and a pressure test can be performed against said closed valve from above, and in the absence of an external force b
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Dang Hoang C.
Expro North Sea Limited
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