Wells – Submerged well
Patent
1997-03-20
1999-03-23
Dang, Hoang C.
Wells
Submerged well
166 7511, 166368, E21B 33035
Patent
active
058847065
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pressure compensated plug for use with subsea trees and particularly, but not exclusively, for use with horizontal subsea trees.
The use of horizontal subsea trees is rapidly becoming the norm for subsea completions because of the cost reduction offered over conventional technology. As subsea completions enter deep water, the cost saving increases dramatically, up to 25% in some cases, as reported in an article entitled "Horizontal Trees Provide Quick Wellbore Access", Offshore International Magazine November 1993. A further advantage of horizontal wellheads is that they allow for larger completions to be utilised than conventional technology, thereby allowing an oilfield to be exploited by fewer wells. The conventional method of isolating a horizontal wellhead, after intervention but before production, is carried out by situating a wireline plug in the upper section of the tubing hanger and an additional plug or valve in the upper cap.
A horizontal tree safety valve is described in copending United Kingdom Patent Application No. 9326062.8. This safety valve replaces the upper cap and reduces problems associated with the retrieving of wireline plugs and allowing well access. Although this safety valve offers substantial advantages in comparison with existing technology, it will be understood that it is critical that both systems provide a seal with a high degree of pressure integrity to prevent the communication from the well to the exterior environment which would cause not only significant pollution but would compromise both well integrity and well safety.
Because well intervention is an infrequent requirement, it is normal to achieve seal integrity by using metal-to-metal seals or sealing systems which are not adversely affected by exposure to temperature cycles or to chemical attack. Because the integrity of these seals is critical it is normal practice to perform a pressure test between the seal after either or both plugs are set or the lower plug is set and the safety valve closed. This is done by filling the void space between the plugs or the valve and a plug with an incompressible liquid, such as water, which is then pressurised and monitored for any subsequent reduction in pressure indicating a leak.
Pressurisation is normally performed using an annulus flow line which is connected to the production platform. If the pressure test is satisfactory, the pressure in the cavity between the plugs (or valve and plug) is reduced and an external test port is isolated to provide a secondary barrier between the well bore and the external environment. It will be understood that because the horizontal tree is located in the seabed the process of bleeding the cavity only reduces the pressure to hydrostatic; therefore, this leaves the fluid within the space between the plugs in a partially pressurised condition.
After testing the tree plugs or valve and plug, the well is returned to production by opening a side valve and oil or gas or a mixture of oil and gas flows from the well through the tree and out through the valve. Because the oil and gas producing zones are located in subterranean reservoirs several thousand feet below the seabed, they are, as such, at a substantially higher temperature than the ambient temperature of the horizontal tree. As the well is being used in production, the temperature of the surface equipment increases by heat transfer from the produced effluent. It is well known that if a liquid is heated and its volume is restrained, the pressure of the liquid increases rapidly. This is also true for liquid when it is trapped between the tree plugs or a plug and valve. It will be understood that the increase of pressure of the liquid is a function of the temperature and is not controllable. This increase in pressure could possibly exceed the maximum design pressure of the caps or the tree itself which is an undesirable situation. It will also be understood that the effect of the problem could manifest itself in several undesirable events, such as the inabil
REFERENCES:
patent: 3166124 (1965-01-01), Johnson
patent: 3414056 (1968-12-01), Brown et al.
patent: 4121660 (1978-10-01), Koleilat
patent: 5372199 (1994-12-01), Cegielski et al.
patent: 5544707 (1996-08-01), Hopper et al.
Dang Hoang C.
Expro North Sea Limited
LandOfFree
Horizontal subsea tree pressure compensated plug does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Horizontal subsea tree pressure compensated plug, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Horizontal subsea tree pressure compensated plug will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2117436