Centralizer

Details Centralizer Centralizer

2000-03-30

2001-10-09

Hook, James (Department: 3752)

Pipes and tubular conduits

Combined

With means to support disparate element therein

C138S112000, C138S155000

Reexamination Certificate

active

06298883

ABSTRACT:

This invention relates to centralizers for use in the construction of oil and gas wells.
During the construction of oil and gas wells a borehole is drilled in the ground. A string of tubulars is then lowered down the borehole and the annular space between the tubulars and the borehole filled with cement.
It is important to ensure that the tubulars are held centrally in the borehole during cementation and it is usual to provide the tubulars with a plurality of centralizers which act between the tubulars and the borehole.
One type of centralizer which is commonly used comprises a pair of annular bands which are spaced apart by a plurality of hollow members which extend therebetween. Such hollow members may extend parallel to the longitudinal axis of the centralizer or may, as disclosed in our co-pending application 96 17789.4, be inclined thereto. The hollow member may be designed to withstand great radial load or to collapse irreversibly when the radial load exceeds a predetermined value. The centralizer may, in use, be secured fast on a tubular, or may be rotatably mounted thereon and retained against significant axial movement by stop collars disposed on the tubular to either side of the centralizer.
This later arrangement is generally used when it is desired to rotate the tubulars during cementation. Rotation is intended to improve the distribution of the cement in the annular space between the tubulars and the borehole and reduce the occurrence of voids when the cement sets. It is desirable that the tubulars should be free to rotate relative to the centralizers and conventionally this has been achieved by the simple expedient of making the inner diameter of the centralizers slightly larger than the outer diameter of the tubular. Although this works to some extent there is still significant friction between the centralizers and the tubulars. If the string of tubulars is sufficiently long the torque which must be applied to the uppermost tubular to ensure rotation of the entire string of tubulars can exceed the maximum torque permitted to be applied to the threaded joints between the tubular which can damage the joints. This is undesirable.
In order to help reduce this problem the present invention provides a centralizer which comprises a pair of annular bands which are spaced apart by a plurality of hollow members, characterised in that each annular band is provided with an opening which underlies a hollow member so that, in use, liquid can flow through the said opening in one of said annular bands, along said hollow member, and out of the opening in the other of said annular bands.
The hollow member may extend substantially parallel to the longitudinal axis of the centralizer or may be inclined thereto, for example at an angle of from 30° to 60°, preferably from 30° to 45° to the longitudinal axis of the centraliser.
The hollow member is preferably of rounded cross-section, although it could be of any convenient shape, for example rectangular or square.
Preferably, the hollow member has a radial inner surface which is substantially flush with the radial inner surface of the annular bands.
Advantageously, the hollow member is tapered towards each end.
Preferably, the hollow member will, in use, substantially permanently collapse against casing when subjected to a lateral load of from 5 to 15 tonnes.
Advantageously, the annular bands are formed in one piece although they could also be made in two separate pieces which can be mounted circumjacent casing.
Preferably, each annular band is provided with a plurality of holes each of which underlies a respective hollow member.


REFERENCES:
patent: 3318335 (1967-05-01), Heller
patent: 3417785 (1968-12-01), Andrews
patent: 3565118 (1971-02-01), Stearns
patent: 4036617 (1977-07-01), Leonard et al.
patent: 4942905 (1990-07-01), Takemae et al.
patent: 5908288 (1999-06-01), Moran

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