A CENTRALISER APPARATUS [0001 ] The present invention relates to a centraliser apparatus.

[0002] More particularly the present invention relates to a centraliser apparatus for centralising a downhole tubing within an aperture, for example a drill borehole or casing.

BACKGROUND OF THE INVENTION

[0003] It is known to use a centraliser apparatus to assist with the deployment of downhole tubing and/or casing, into an aperture, for example a wellbore. Centraliser apparatuses are used to provide stand-off for centralisation of the downhole tubular string within the aperture allowing for the effective removal of drilling and wellbore fluids and particulates, as well as enabling even distribution of cement during casing cement operations.

[0004] It is known in the art to provide a centraliser apparatus comprising a plurality of stand-off features, or blades, running along the length of the centraliser.

[0005] One example of prior art used for these purposes is described in Australian Patent Application 2011239247 in the name of the present applicant, the disclosure of which is incorporated herein by reference.

[0006] It is further known that centraliser apparatuses comprising wider blade sections allow the stand-off to be maintained for longer distances and under heavier loads, as the wear of the blade is generally inversely proportional to the blade width.

[0007] Cavities between the blades of centraliser apparatuses are known as flow-by areas, and serve as fluid passages, permitting the flow of drilling fluid, containing particulate matter from the prior drilling operation. This fluid also has the beneficial effect of acting as a lubricant between the centraliser blade outer surface and the inner surface of the aperture, thereby reducing the friction.

[0008] Following the tubing/casing installation operation the aperture may be encased in cement to secure the wellbore, which is typically carried out by pumping cement from the surface to a distal point. The cement may travel along the annulus of the bore, passing through the flow-by areas. Therefore the flow-by areas must be of adequate size to firstly permit passage of drilling fluid containing particulate matter, and subsequently permit passage of cement.

[0009] A further constraint when designing centraliser apparatus with wide blades is the supply of lubricant to a centre of the contact surface. The wider contact surface means the drilling fluid is less able to lubricate the centre of a wide blade.

[0010] Modern centraliser apparatuses are often constructed from polymers, which have a lower coefficient of friction than metallic constructions. A common method of manufacture of polymer centraliser apparatuses is by injection moulding. This method of manufacture has a limitation regarding the wall thickness of material which can be moulded, as the rate of cooling when the part is removed from a mould may vary with the depth of the wall thickness, with a surface cooling more rapidly than a centre of the mass. Where the temperature differential is too great, undesirable cracks and voids may form in the structure.

[0011] The balance of the aforementioned criteria of large surface area, low friction, large flow-by area and manufacturability, which are typically at odds with each other, is a challenge in the design of centraliser apparatuses.

[0012] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previously known centraliser apparatuses.

SUMMARY OF THE INVENTION

[0013] In accordance with one aspect of the present invention, there is provided a centraliser apparatus for use in centralising a downhole tubular within an aperture, the centralising apparatus comprising a body portion having an inner body surface and an outer body surface, the inner body surface being arranged for abutting the tubular; and the outer body surface comprising at least two spaced apart protruding blades, shaped to provide a standoff between an inner wall of the aperture, and the outer body surface, each blade comprising an outer blade surface having at least one longitudinally extending groove to provide a fluid flow path to facilitate lubrication of the outer blade surface [0014] The number, dimensions, and pitch spacing, of the grooves within the blade may be selected to permit successful manufacture by injection moulding.

[0015] The number, dimensions, and pitch spacing, of the grooves within the blade may further be selected to permit adequate passage of drilling fluid to maintain lubrication of the outer blade surfaces.

[0016] The blades may be radially spaced to provide a flow-by area between adjacent blades, to allow passage of drilling fluid and particulate matter, wherein the size of the cavity provided is determined by the height and spacing of the blades, and is selected to prevent blockage by build-up of particulate matter and / or cement.

BRIEF DESCRIPTION OF THE DRAWINGS

[00 7] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0018] Figure 1 is a perspective view of a centraliser apparatus according to a first embodiment of the present invention;

[0019] Figure 2 is a schematic section view of the apparatus of Figure 1 ;

[0020] Figure 3 is a perspective view of a centraliser apparatus according to a second embodiment of the present invention;

[0021] Figure 4 is a schematic section view of the apparatus of Figure 3; and [0022] Figure 5 is a partial section view of a blade of the apparatus of Figure 3.

DETAILED DESCRIPTION [0023] Figure 1 shows an upper perspective view of a first embodiment of a centraliser apparatus 10 in accordance of the present invention which comprises four equally spaced external blades 20 extending axially, a chamfered blade end 15, an upper end 11 and a lower end 12.

[0024] Figure 2 shows a cross section of the embodiment of Figure 1, and further shows a groove 30 in each blade 20, and flow-by areas 40, determined by the height and spacing of the blades 20. Figure 2 further shows an inner body surface 14 and an outer body surface 13 of the centraliser apparatus.

[0025] Figure 3 shows an upper perspective view of a second embodiment of the centraliser apparatus 10, in which comprises four equally spaced blades 20 extending axially, of wider section than those shown in the embodiment shown in Figure 1.

[0026] Figure 4 shows a cross section of the second embodiment of the centraliser apparatus 10 shown in Figure 3, and further shows three grooves 30 in each blade 20, and a flow-by area 40, determined by the height and spacing of the blades 20.

[0027] Figure 5 shows a cross section of one of the blades 20 described in the embodiment of the centraliser apparatus 10 shown in Figure 3, and further shows the blade edge 21 , the outer blade surface 23, the outer body surface edge 22, the groove edge 31, the groove bottom 32 and the groove flanks 33.

[0028] The centraliser apparatus 10 comprises a body portion having an inner body surface 14 and an outer body surface 13, the inner body surface 14 being arranged for abutting a tubular, and the outer body surface 13 comprising at least two protruding blades 20, configured to provide a standoff between an inner wall of the aperture and the outer body surface 13, each blade 20 comprising an outer blade surface 23 having at least one longitudinally extending groove 30 to provide a fluid flow path to facilitate lubrication of the outer blade surface.

[0029] The centraliser apparatus 10 may comprise a circular section inner body surface 14 and outer body surface 13, being substantially cylindrical, for use in a wellbore. [0030] The centraliser apparatus 10 may comprise at least two blades 20, spaced equally and circumferentially.

[0031] The blades 20 may traverse the outer body surface 13 from the upper end 1 1 to the lower end 12.

[0032] The traverse of the blades 20 may be axial or helical.

[0033] The centraliser apparatus 10 may comprise blades 20 which are not spaced equally.

[0034] An outer body surface edge 22 shown in Figure 5 may comprise a radius, wherein the size of the radius is selected to suit manufacture.

[0035] The blades 20 may comprise chamfered ends 15, to maintain a circular cross section, being flush with the outer body 13, at the upper end 1 1 and lower end 12.

[0036] The radial spacing and / or height of the blades 20 may be selected to provide an adequate flow-by area 40 to permit passage of drilling fluid containing particulate matter, and / or cement.

[0037] The size of the or each groove 30 may be selected to provide adequate passage of drilling fluid to enable lubrication of the outer blade surface 23.

[0038] The depth of the or each groove 30, being measured from the outer blade surface 23, (see Figure 5) to the bottom of the groove 32, may be less than, or equal to, the overall height of the blades 20.

[0039] The cross-sectional profile of the or each groove 30 may be vee shaped, with the angle between the flank faces 33 being less than, or equal to, 90 degrees.

[0040] A blade edge 21 (see Figure 5) may be rounded, and may have a radius less than, or equal to, 20mm

[0041] A groove edge 31 (see Figure 5) may be rounded, and may have a radius less than the radius of the blade edge 21. [0042] A bottom of a groove 32 may be rounded or flat, and may comprise minimum radii suitable for manufacture.

[0043] The width of the or each groove 30, being measured between the groove edges 31 (see Figure 5) at the outer blade surface 23, may be constant along the length of the or each groove 30 and may be less than, or equal to, 20mm.

[0044] The width of the or each groove 30, being measured between the groove edges 31 at the outer blade surface 23, may vary along the length of the or each groove 30.

[0045] The depth of the or each groove 30, being measured from the outer blade surface 23, to the bottom of the groove 32, may be constant or may vary along the length of the groove 30, and may be greater than 10% of the width of the or each groove 30 at the outer blade surface 23.

[0046] Where more than a single groove 30 is present in a blade 20, each groove 30 may or may not be identical in cross section.

[0047] The surface area of the blade 20 occupied by the or each groove 30 may not exceed 40% of the total outer blade surface 23.

[0048] In use, the centraliser apparatus encases the downhole tubular, and the arrangement comprising the tubular and the centraliser apparatus is inserted into a drilled borehole or external casing.

[0049] A number of centraliser apparatus may commonly be used, being space apart along a length of tubular.

[0050] The centraliser apparatus serve to maintain the tubular centrally within the borehole or casing, maintaining a reasonably constant gap between the tubular and the wall of the borehole.

[0051] Wide blades of the centraliser apparatus allow the apparatus to withstand greater loads imparted by the walls of the borehole or casing. [0052] The grooves along the outer blade surface allow drilling fluid to be supplied to the outer blade surface to act as a lubricant, allowing an arrangement comprising the tubular and multiple centraliser apparatus to be inserted and passed into the borehole more easily. Without the supply of lubricant, the wider blades required can become stuck against the wall of the borehole.

[0053] The easier insertion of the arrangement, due to the use of the centraliser apparatus according to the present invention, allows longer arrangements to be inserted into deeper boreholes, or alternatively allows the arrangement to pass through more tortuous paths.

[0054] Once the arrangement is inserted to the desired depth, the borehole can be reinforced, by pumping cement into the casing or borehole, along the annulus between the tubular and the borehole or casing.

[0055] The use of centralisers is important, firstly to ensure that the tubular does not contact the casing or borehole, which would result in a hole in the cement wall, and secondly to ensure an even thickness of resultant cement wall, thus providing structural integrity.

[0056] The use of wider blades allows the cement to be pumped more readily into the flow by areas, which are maintained as relatively large spaces, less subject to blockage than a greater number of smaller spaces. This further contributes to the successful creation of the cement wall.

[0057] The centraliser may be manufactured by injection moulding, where a suitable thermoplastic material is injected into a mould. In such operations, large volumes may be difficult to produce due to the differential rates of cooling at the surface and the centre of the mass, which may lead to cracking.

[0058] The use of grooves along the blades of centraliser apparatus according to the present invention has the further beneficial effect of reducing the actual volume of a wider blade, thus enabling blades of larger cross sectional area to be manufactured.

[0059] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.