GB2487896A

GB2487896A - A non-uniform flow-by centraliser

Info

Publication number: GB2487896A
Application number: GB201020210A
Authority: GB
Inventors: Stuart James Ellison
Original assignee: Aker Subsea Ltd
Current assignee: Aker Solutions Ltd
Priority date: 2010-11-30
Filing date: 2010-11-30
Publication date: 2012-08-15
Anticipated expiration: 2030-11-30
Also published as: GB2487896B; GB201020210D0

Abstract

A flow-by centraliser for maintaining a inner member centrally within an outer member having a substantially cylindrical interior, and is rotatable within the outer member, comprises a sleeve defining a central axial aperture for accommodating the inner member and has exterior planar facets, whereof there are 2n facets where n is an integer greater than unity, there being n larger facets of equal breadth disposed alternately with n smaller facets each of equal breadth.

Description

NON-UNIFORM FLOW-BY CENTRALISER

This invention relates to flow-by centralisers.

Background to the invention

This invention is specifically intended for use where an inner body, such as a running pipe or a running tool, must pass through a outer hollow body, such as a well. During such applications it is often a requirement that the internal body maintain a central position within the larger hollow cylinder so as to prevent damage to the system or hindrance of its operation. It is also necessary to allow fluid, which usually includes particulate matter, to flow in a space or spaces between the centraliser and the outer body.

Centralisers for this purpose are known. However, there is a basic conflict between a requirement of maximising the outside diameter of the inner body and a requirement for maximising the size of particles which may be allowed to pass by the centraliser in the space or spaces between the centraliser and the outer body.

Moreover, the centraliser may be required to rotate within the outer body and it is desirable to avoid features which may cause damage or may inhibit such rotation.

The present invention provides a new design which achieves a balance between the conflicting requirements.

Summary of the invention

The invention provides a flow-by centraliser for maintaining a inner member centrally within an outer member having a substantially cylindrical interior, the centraliser comprising a sleeve defining a central axial aperture for accommodating the inner member and having exterior planar facets, wherein there are 2n facets where ii is an integer greater than unity, there being n larger facets of equal breadth disposed alternately with n smaller facets each of equal breadth.

The invention also provides an assembly comprising an inner member moveable though an outer hollow pipe having a substantially cylindrical interior and a centraliser which engages the interior of the pipe and is rotatable therein, the centraliser maintaining the inner member centrally within the pipe, the centraliser comprising a sleeve defining a central axial aperture for accommodating the inner member and having exterior planar facets, wherein there are 2n facets where n is an integer greater than unity, there being n larger facets of equal breadth disposed alternately with n smaller facets each of equal breadth.

Brief description of the drawings

Figures 1 and 2 illustrate known centralisers. Figure 3 illustrates one embodiment of the invention.

Detailed description

It is known to provide a centraliser as shown in Figure 1. It comprises a hollow hub 1 which accommodates the inner body 2 and has a multiplicity of vanes 3 which extend to the inside surface of the outer body (not shown). When the internal body is relatively large typically a centraliser ring is added if there is room; otherwise as shown in Figure 2, slots 4 are machined into the outer diameter of the internal body as shown in Fig 2.

Both types have limitations. For the centraliser in Figure 1 there is a large flow by area through the pipe in spite of the presence of an internal body and there is good clearance for large particles (assumed to be spherical) to pass the centraliser. However the centraliser is prone to damage especially if the internal body has a requirement to be rotated within the pipe, as will often be the case in a well.

The centraliser shown in Fig 2. is typically used when there is a requirement to accommodate a relatively large internal body 2 and the centraliser feature can become integral to the body in the form of milled slots 4 running axially up the outer diameter of the body and delimiting lands 5 which engage the outer body.

This centraliser is more robust however it can still become difficult to rotate because the slots may catch on internal features or damaged surfaces within the pipe. This centraliser also has a limited flow by area and limited clearance for allowing large particles to pass the centraliser.

Figure 3 illustrates one embodiment of the invention. It comprises a multi faceted sleeve 7 which fits over the internal body 2 to be run in a pipe 6. The exterior facets of the sleeve alternate between two sizes each of substantial breadth, the two sizes being substantially different. In particular there are four facets such as facet 8 which (viewed in section) have the same breadth and four facets such as facet 9 which alternate with the facets 8 around the periphery of the sleeve. Each facet 8 has in this example approximately half the breadth of a facet 9. These dimensions are selected to maximise the size of the inner body and to maximise the size of a spherical item 10 that is able to pass the centraliser. The centraliser is also capable of rotating within the pipe with a reduced likelihood of an edge fouling the pipe waIl and preventing further rotation, something that can prevent the operation of critical functions in a down hole location. This is due to the open nature of the exterior of the sleeve; the series of planar faces it has no sharp abutments that are liable to prevent rotation.

A general design method for the centraliser comprises selecting for a given size of inner body a chord which gives the minimum tolerable thickness of the sleeve. Suppose the length of this chord (between the points where it intersects the inside circumference of the outer member) is A. A partial polygon composed of n end-to-end chords of length A leaves a final gap. If the chords are now redistributed around their circumscribing circle (the inside circumference of S the outer member) so that their centres are 360°/n apart, there will be n gaps which may be occupied by n smaller chords of length B. The lengths A and B are the breadths of the facets of the centraliser.

Claims

Claims 1. A flow-by centraliser for maintaining a inner member centrally within an outer member having a substantially cylindrical interior, the centraliser comprising a sleeve defining a central axial aperture for accommodating the inner member and having exterior planar facets, wherein there are 2n facets where n is an integer greater than unity, there being n larger facets of equal breadth disposed alternately with n smaller facets each of equal breadth.
2. A flow-by centraliser according to claim 1 in which n is equal to 4.
3. A flow-by centraliser according to claim 1 or 2 in which the breadth of each smaller facet is substantially half the breadth of a larger facet.
4. An assembly comprising an inner member moveable though an outer hollow pipe having a substantially cylindrical interior and a centraliser which engages the interior of the pipe and is rotatable therein, the centraliser maintaining the inner member centrally within the pipe, the centraliser comprising a sleeve defining a central axial aperture for accommodating the inner member and having exterior planar facets, wherein there are 2n facets where n is an integer greater than unity, there being n larger facets of equal breadth disposed alternately with n smaller facets each of equal breadth.
5. An assembly according to claim 4 in which n is equal to 4.