GB2163789A

GB2163789A - Leak detection tool for oilwell casing tools

Info

Publication number: GB2163789A
Application number: GB08417397A
Authority: GB
Inventors: Rolf Ruesse
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-07
Filing date: 1984-07-07
Publication date: 1986-03-05
Also published as: GB8417397D0

Abstract

A leak detection device 5 is installed between the drill pipe 6 and test plug 4 of a casing seal arrangement. There is provided an outer seal 7 that separates test fluid B in contact with the casing seal 3 from the test fluid pressure source A. A slideable piston 10 is in contact with both fluid volumes A and B and will be forced downward if the lower volume B decreases for instance due to a leak. After a predetermined amount of piston travel the piston 10 opens a relief valve 8, releasing test fluid pressure into the drill pipe unpressured area C. <IMAGE>

Description

SPECIFICATION Leak detection tool for subsea casing seals This invention relates to a tool that positively detects leaks when pressure testing casing seals in subsea wellheads, as used when drilling from floating drilling rigs.

When drilling offshore wells from floating rigs, the wellhead is located at the seafloor. The wellhead provides a means of sealing offwellpressures and supportsthe concentric strings of pipe, called casing, that linetheweilbore and may have to contain very high pressures. The casing is sealed to the wellhead housing by means of a seal assembly. The failure of a seal assembly may cause a catastrophic blowout undercertain adverse conditions. In orderto assure the pressure integrity of the wellhead including the seal assembly and pressure control armatures (called blowout preventors) connected to the top of the wellhead, frequent tests at high pressures are conducted.To facilitate such tests, typically a plugging device is run from the surface on pipe and seals offthe inside ofthe casing nearthe seal assembly. A blowout preventorram is closed aroundthe pipe, sealing off a small area from the seal assembly and plug to below the blowout preventor ram. This area is then pressurised through a separate line from the surface. If high test pressure leaks pastthe seal assembly, it will enter the annulus between two concentric strings of casing.

Ifthis leakage is maintained long enough, pressure equal to the tes pressure may build up in the annular space. This pressure may be high enough to burstthe outer string or collapse the inner string of concentric casings. At presentthe only way of detecting such a leak is by monitoring both, volume offluid pumped in to build up the pressure and observing closed in pressure to detect any pressure drop indicating a leak.

Both methods do not indicate the location of a leak, and require a high degree of skill and experience by the operator. As a result, many operators restrict test pressure belowthe rate where casing could be damaged in case of a leak, ratherthan use the higher test pressureforwhich the equipment is designed.

According to the present invention there is provided a tool that will positively detect a leak at the seal assembly and provide a positive indication by releasing thetest pressure. The tool is placed between the test plug and the pipe on which it is run. A large lip seal on the outer circumference seals against the inside of the wellhead housing wall, thus effectively isolating the testfluid between the tool and the seal assembly fromthetestfluid above the tool. Internal parting in the tool provides a reliefflow path for test fluid from below the tool into the running pipe orwellbore which are not pressurised during the test.

This reliefflow path is normally blocked by a valve.

A piston in the tool is in contact with the test fluid above the tool on one side and the test fluid belowthe tool on the other side. In case of loss oftestfluid below thetool,the piston will be pressed down, epentually causing the valve blocking the reliefflow path to open, thus releasing test pressure.

A specific embodiment ofthe invention will now be described by way of example with reference to the accompanying drawing in which Figure 1 shows a part section of the wellhead housing with a test plug and the leak detection tool in place.

Referring to the drawing there is shown the wellhead housing 1, the top of a casing string, called casing hanger 2, a seal assembly 3 sealing offthe casing hanger 2 against housing 1. test plug 4 to seal offthe wellbore, the leak detection tool 5, and the drill pipe 6 on which the plug and tool are run and around which the blowout preventor rams close (not shown).

Plug 4, tool 5 and pipe 6 are threadedly and leaktight connected to each other. This arrangement divides the tested space into following test fluid areas: uppertest fluid area A, which is connected to the pressure source, lowertestfluid between seal assembly 3 and tool 5, and non-pressurised area C.

During a pressure test lip seal 7 seals against housing 1, isolating test fluid in space Afrom space B.

Poppet valve 8 is blocking relief part 9, isolating test fluid in Bfrom pressurefreearea C. Ring piston 10 is held up by springs 11. When test fluid is space A is pressurised piston 10 moves down slightly until pressure in spaces A and B is equal. Iffluid is lost in space B due to a leak, piston 10 will continue moving down and eventually unseat poppet valve 8, releasing pressure from space Bthrough relief part9 into the unpressurised space C. When piston 10 is all the way down, fluid from A can pass the piston 10 to rough opening 12 into space B and thus be released into C.

As a modification (not shown) seal 7 may be constructed in such a way, that it is contracted while it is run and expanded into contact with the housing wall by mechanical means once landed over the seal assembly or by hydraulic means when test pressure is building up.

1. A leak detection tool for oilwell casing seals providing a means of positively detecting a leak during testing of a casing hanger seal assembly as typically used when drilling oil or gas wells from floating drilling rigs.

2. A leak detection tool for oilwell casing seals as claimed in Claim 1 wherin a seal on its outer circumference seals against the wellhead innerwall to separate the pressurized test fluid volumne in a lower volumne in direct contact with the seals to be tested and an uppervolumne connected to the test pressure source.

3. A leak detection tool for oilwell casing seals as claimed in Claims 1 and 2 in which is provided a moveable piston sealed slideably in the tool and exposed to the uppertestfluid volumne on it's upper side and the lower test fluid volumne on the lower side so that a reduction in the lowerfluid volumne will cause a downward movement of such piston.

4. A leak detection tool for oilwell casing seals as claimed in Claim 3 in which is provided a relief valve thatwill be actuated open buy a predetermined amount

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Leak detection tool for subsea casing seals This invention relates to a tool that positively detects leaks when pressure testing casing seals in subsea wellheads, as used when drilling from floating drilling rigs. When drilling offshore wells from floating rigs, the wellhead is located at the seafloor. The wellhead provides a means of sealing offwellpressures and supportsthe concentric strings of pipe, called casing, that linetheweilbore and may have to contain very high pressures. The casing is sealed to the wellhead housing by means of a seal assembly. The failure of a seal assembly may cause a catastrophic blowout undercertain adverse conditions. In orderto assure the pressure integrity of the wellhead including the seal assembly and pressure control armatures (called blowout preventors) connected to the top of the wellhead, frequent tests at high pressures are conducted.To facilitate such tests, typically a plugging device is run from the surface on pipe and seals offthe inside ofthe casing nearthe seal assembly. A blowout preventorram is closed aroundthe pipe, sealing off a small area from the seal assembly and plug to below the blowout preventor ram. This area is then pressurised through a separate line from the surface. If high test pressure leaks pastthe seal assembly, it will enter the annulus between two concentric strings of casing. Ifthis leakage is maintained long enough, pressure equal to the tes pressure may build up in the annular space. This pressure may be high enough to burstthe outer string or collapse the inner string of concentric casings. At presentthe only way of detecting such a leak is by monitoring both, volume offluid pumped in to build up the pressure and observing closed in pressure to detect any pressure drop indicating a leak. Both methods do not indicate the location of a leak, and require a high degree of skill and experience by the operator. As a result, many operators restrict test pressure belowthe rate where casing could be damaged in case of a leak, ratherthan use the higher test pressureforwhich the equipment is designed. According to the present invention there is provided a tool that will positively detect a leak at the seal assembly and provide a positive indication by releasing thetest pressure. The tool is placed between the test plug and the pipe on which it is run. A large lip seal on the outer circumference seals against the inside of the wellhead housing wall, thus effectively isolating the testfluid between the tool and the seal assembly fromthetestfluid above the tool. Internal parting in the tool provides a reliefflow path for test fluid from below the tool into the running pipe orwellbore which are not pressurised during the test. This reliefflow path is normally blocked by a valve. A piston in the tool is in contact with the test fluid above the tool on one side and the test fluid belowthe tool on the other side. In case of loss oftestfluid below thetool,the piston will be pressed down, epentually causing the valve blocking the reliefflow path to open, thus releasing test pressure. A specific embodiment ofthe invention will now be described by way of example with reference to the accompanying drawing in which Figure 1 shows a part section of the wellhead housing with a test plug and the leak detection tool in place. Referring to the drawing there is shown the wellhead housing 1, the top of a casing string, called casing hanger 2, a seal assembly 3 sealing offthe casing hanger 2 against housing 1. test plug 4 to seal offthe wellbore, the leak detection tool 5, and the drill pipe 6 on which the plug and tool are run and around which the blowout preventor rams close (not shown). Plug 4, tool 5 and pipe 6 are threadedly and leaktight connected to each other. This arrangement divides the tested space into following test fluid areas: uppertest fluid area A, which is connected to the pressure source, lowertestfluid between seal assembly 3 and tool 5, and non-pressurised area C. During a pressure test lip seal 7 seals against housing 1, isolating test fluid in space Afrom space B. Poppet valve 8 is blocking relief part 9, isolating test fluid in Bfrom pressurefreearea C. Ring piston 10 is held up by springs 11. When test fluid is space A is pressurised piston 10 moves down slightly until pressure in spaces A and B is equal. Iffluid is lost in space B due to a leak, piston 10 will continue moving down and eventually unseat poppet valve 8, releasing pressure from space Bthrough relief part9 into the unpressurised space C. When piston 10 is all the way down, fluid from A can pass the piston 10 to rough opening 12 into space B and thus be released into C. As a modification (not shown) seal 7 may be constructed in such a way, that it is contracted while it is run and expanded into contact with the housing wall by mechanical means once landed over the seal assembly or by hydraulic means when test pressure is building up. CLAIMS

4. A leak detection tool for oilwell casing seals as claimed in Claim 3 in which is provided a relief valve thatwill be actuated open buy a predetermined amount of downward movement of the moveable piston and thus expose porting to the unpressurized inside of the tool to which the lowertestfluid volumne can escape.

5. A leak detection tool for oilwell casing seals as claimed in Claims 3 and 4 in which there is provided a groove that will deactivate the sealing ofthe moveable piston once it has completed its downward movement and allowfreecommunication betweentheupperand lowertestfluid volumne and through the relief valve into the unpressurized area ofthetool.

6. A leak detection tool for oilwell casing seals as claimed in Claims 2 in which the outer circumferential seal is expanded into sealing contact with the well- head wall buy a mechanism activated buy a presettest pressure.

7. A leak detection tool foroilwell casing seals as claimed in any preceding claim which isthreadedly connected between a test plugging device and a string of pipe.

8. A leak detection tool for oilwell casing seals substantially as described herein with reference to figure 1 ofthe accompanying drawing.