1994-02-28
1995-11-21
Dang, Hoang C.
Wells
Packers or plugs
277188A, E21B 33126
Patent
active
054678226
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a pack-off tool, and in particular to the pack-off element of such a tool, for use in conjunction with downhole tools such as bridge plugs.
Pack-off elements are used to provide a seal between the inner and outer diameter of co-axial tubes, for example the mandrel of a downhole tool which carries the pack-off element and the well tube against which the element expands when subjected to an axial force.
Examples of downhole tools including such pack-off elements are described in GB-A-1 283 295, GB-A-2 106 957, GB-A-2 222 845 and GB-A-2 236 129.
A disadvantage of such known pack-off elements is that a high axial force is required to provide the necessary expansion and pre-stressing of the element to resist the high pressures which the pack-off elements must contain.
It is among the objects of various aspects of the present invention to obviate or mitigate this disadvantage.
According to one aspect of the present invention there is provided a pack-off tool comprising a main tubular body and a mandrel, the body including an expandable sealing element connected to a non-expandable ring member at one end of the body for reinforcing the end of the element against distortion, and a communicating bore towards the other end of the body and extending through the body, the body being mounted on the mandrel and in sealing engagement therewith at least at said one end, the tubular body being axially compressible to expand the sealing element into a radially extended configuration for sealing engagement with a bore wall and the communicating bore allowing higher pressure fluid from said other end of the tool to enter between the sealing element and the mandrel to exert radial pressure forces on a portion of the sealing element between the bore and the ring member to press the sealing element into tighter sealing engagement with the bore wall.
According to another aspect of the present invention there is provided a method of sealing a bore against a pressure differential comprising the steps:
(a) providing a pack-off tool comprising a main tubular body and a mandrel, the body including an expandable sealing element connected to a non-expandable ring member at one end of the body for reinforcing the end of the element against distortion and defining a communicating bore located towards the other end of the body and extending through the body, the body being mounted on the mandrel and in sealing engagement therewith at least at said one end;
(b) locating the tool in a bore with said other end of the tool oriented towards the higher pressure end of the bore;
(c) applying an initial setting force to the body sufficient to axially compress the sealing element into a radially extended configuration to provide an initial sealing contact with the bore wall; and
(d) permitting increasingly higher pressure fluid to flow through the communicating bore from the exterior of the tool to between the sealing element and the mandrel to exert correspondingly increasingly higher radial pressure forces on a portion of the sealing element between the bore and the ring to press the sealing element into tighter sealing engagement with the bore wall such that the resulting sealing contact is capable of withstanding a pressure differential greater than that which could be withstood by said initial sealing contact and which resulting sealing contact corresponds to a sealing contact which, in the absence of said radial pressure forces, would require application of a greater setting force than said initial setting force.
In the preferred embodiment, in which the communicating bore is centrally located in the sealing element, a higher pressure fluid on the other side of the tool pushes between the high pressure side of the tubular body and the bore wall, through the communicating bore and into a space between the tubular body and the mandrel, and tends to push the lower pressure side of the body outwardly into tighter sealing engagement with the bore wall, while the non-expandable ring member controls expansion of the sealing
REFERENCES:
patent: 2138156 (1938-11-01), Halliburton
patent: 2565130 (1951-08-01), Humason
patent: 2830540 (1958-04-01), Vincent
patent: 3227462 (1966-01-01), Tamplen
patent: 3433303 (1969-03-01), Clark et al.
patent: 4032159 (1977-06-01), Zitting
patent: 4428590 (1984-01-01), Pippert et al.
patent: 4630833 (1986-12-01), Boyle et al.
patent: 4809989 (1989-03-01), Kernal
patent: 5096209 (1992-03-01), Ross
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