Patent Application
20080149344
The field of the invention is a pressure sensing and transmitting device that can be used for downhole tools that have pressure charged chambers to confirm an adequate charge before placing them in service or while in service.
There are downhole tools that have integrated pressurized gas chambers that are generally used to offset hydrostatic pressure from a fluid column in a control line that extends from the surface to thousands of meters into the wellbore. Such chambers are illustrated in a subsurface safety valve (SSSV) in U.S. Pat. No. 6,109,351. These downhole tools, when assembled for service are charged with pressure and can sometimes sit in storage for extended periods of time before being deployed downhole. Due to the passage of time from initial charging to actual use, there is uncertainty as to whether the charge is actually still in the chamber or concern that it might not have been charged at all upon assembly. Due to the nature of the service of such tools, they do not feature external gauges to indicate internal pressure because of the risk that such devices may break off during run in. As a result, the tools need to be picked up and mounted in a test fixture and function tested to determine that the gas chamber or chambers are properly charged with the required pressure.
Once the tool is in the hole, there again has been no way to determine if the pressure in the chambers is being retained or if it is slowly dissipating or gone. There are times when a SSSV closes and refuses to open downhole, leaving doubt as to what among several causes could be the reason for such an event.
Accordingly, it is advantageous to know whether there is a charge in a gas chamber of a downhole tool before it goes into service and after it is in service as a diagnostic tool for a malfunction or an early warning tool of an eventual failure. The present invention addresses this need and one application of the invention in a SSSV is described in the description of the preferred embodiment and associated drawing. Those skilled in the art will appreciate that the full scope of the invention is determined by the claims attached to the application.
A sensor and transmitter is employed with a pressurized chamber of a downhole tool to be able to tell at a glance when the tool is delivered for service that it is properly charged. The sensor and transmitter can be integrated within the tool so as to be protected from damage during run in. While in service the sensor and transmitter can monitor pressure in real time and include a capability to send surface signals for real time monitoring of chamber pressures corrected for the service depth, temperature and density of the hydraulic fluid, for example. The signal can be acoustic through the control line or the annulus or delivered through a fiber optic cable or signal wire run in the hydraulic control line, an auxiliary line or through the annulus.
This illustrated control system for a SSSV has a control line 12 that extends from the surface to the tool body. In normal operation, raising the pressure in line 12 shifts a piston 14 against a spring 16 so that a tab 18 drives a flow tube (not shown) that in turn rotates a flapper (also not shown) to hold the SSSV open. Chamber 20 is preferably charged with nitrogen and the pressure in it offsets the hydrostatic pressure from fluid in the control line 12 from the surface down to piston 14. Chamber 22 acts on an equalizer piston 24 which can selectively put piston 14 in pressure balance by communicating control line 12 to the underside of piston 14 through passage 26 when certain seals in the system fail or if the charge pressure in chamber 20 is reduced or disappears due to leakage.
As also shown in
With this system in place, a slow leak in chambers 20 or 22 can be detected to allow a planned shutdown to take place to remove the SSSV for repair.
In the case of receiver 32 the original charging pressure and temperature can be stored in it as well as a processor that corrects any subsequent reading back to the baseline temperature of the original pressurization.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
