Downhole tools

Details Downhole tools Downhole tools

2000-07-13

2003-12-23

Tsay, Frank (Department: 3672)

Wells

Guide for device or conduit

Surrounding existing device or tubing

C166S241100, C175S325300

Reexamination Certificate

active

06666267

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to downhole tools; particularly, though not exclusively, to an improved casing centraliser; and more particularly, though not exclusively, to a casing centraliser for facilitating cementing of casing in a well.
2. Description of Related Art
After a well section has been drilled, it is necessary to secure a borehole of the well section by lining it with a pipe known as oilfield “casing” or “liner”—or generically “tubular”.
Having installed the casing or liner within the borehole, it is necessary to make a seal in an annular space formed between the borehole and an outer surface of the pipe. This seal provides both a strengthening role forming a composite structure of the steel pipe and the seal itself, as well as a barrier to the possible flow of fluid contained in one geological strata to another to the surface at a well head. Such a seal is usually achieved by displacing the drilling fluid in which the pipe was run, and which is thus contained in the annular space, with a cement slurry which subsequently hardens forming an impermeable barrier or sheath.
The success of cementation operations is largely determined by the displacement efficiency of the cement slurry as it displaces drilling fluid from the annulus.
This displacement efficiency is maximised by a number of factors, these include “centralisation” of the pipe (i.e. aligning the axis of rotation—longitudinal axis—of the pipe with a centre of the borehole). This keeps the pipe off the borehole wall as much as possible. In addition reciprocation of the pipe where practicable; and the creation of a degree of turbulent flow in the annulus while pumping the slurry.
From the foregoing it is clear that pipe movement forms a critical role in securing a borehole after drilling operations, both in terms of getting the pipe to the bottom of the well, where drag forces are critical factors and in maximising the displacement efficiency of the cement slurry, in which rotational forces and centralisation are critical factors.
Boreholes are generally becoming deeper and more tortuous than ever before as Operators strive to access near field potential hydrocarbon reserves (i.e. marginal reserves close to existing infrastructure) in an effort to extend the life of their facilities. There is, therefore, a need in the industry to reduce the dynamic forces, drag and torque, required to secure the casing and liner in these boreholes thereby creating a competitive advantage over conventional equipment.
Known casing/liner centralisation and cementing accessories are made of metals such as steel, zinc and aluminium.
U.S. Pat. No. 5,095,981 (MIKOLAJCZYK) discloses a casing centralizer comprising a circumferentially continuous tubular metal body adapted to fit closely about a joint of casing, and a plurality of solid metal blades fixed to the body and extending parallel to the axis of the body along the outer diameter of the body in generally equally spaced apart relation, each blade having opposite ends which are tapered outwardly toward one another and a relatively wide outer surface for one another and a relatively wide outer surface for bearing against the well bore or an outer casing in which the casing is disposed, including screws extending threadedly through holes in at least certain of the blades and the body for gripping the casing so as to hold the centralizer in place.
WO 91/05093 (WEATHERFORD) discloses apparatus for use with a tubular member, which apparatus comprises: a generally cylindrical hollow body having an inner surface of substantially uniform diameter, an outer surface, a first end and a second end, and disposed on a tubular member a plurality of ribs extending from and spaced apart on said body, characterised in that the distance between at least one adjacent pair of ribs and/or the thickness of the generally cylindrical hollow body is not uniform throughout the length of the apparatus.
EP 0 671 546 A1 (DOWNHOLE PRODUCTS) discloses a casing centraliser comprising an annular body, a substantially cylindrical bore extending longitudinally through said body, and a peripheral array of a plurality of longitudinally extending blades circumferentially distributed around said body to define a flow path between each circumferentially adjacent pair of said blades, each said flow path providing a fluid flow path between longitudinally opposite ends of said centraliser, each said blade having a radial outer edge providing a well bore-contacting surface, and said cylindrical bore through said body being a clearance fit around tubular casing intended to be centralised by said casing centraliser, the centraliser being manufactured from a material which comprises zinc and preferably a zinc alloy.
The content of the abovementioned prior art citations is incorporated herein by reference.
BRIEF SUMMARY OF THE INVENTION
It is an object of one or more aspects of the present invention to obviate or mitigate problems in the prior art.
It is a further object of one or more aspects of the present invention to seek to meet the aforementioned industry need.
According to a first aspect of the present invention there is provided a casing centraliser at least a portion of at least one surface of which is selected from a material comprising a plastics material or a ceramic material, cermet or submicron grained cemented carbide.
Each material has a number of advantages over the other.
Advantageously the plastics material may be a polymer of carbon monoxide and alpha-olefins, such as ethylene.
Advantageously the material may be an aliphatic polyketone made prom co-polymerisation of ethylene and carbon monoxide—optionally with propylene.
Advantageously the material may be CARILON (Trade Mark) available from Shell Chemicals. CARILON (Trade Mark) is a class of semi-crystalline thermoplastic materials with an alternating olefin—carbon monoxide structure.
Alternatively the plastics material may be a nylon resin.
Advantageously the plastics material may be an ionomer modified nylon 66 resin.
Advantageously the plastics material may be ZYTEL (Trade Mark) available from Du Pont. ZYTEL (Trade Mark) is a class of nylon resins which, includes unmodified nylon homopolymers (e.g. PA 66 and PA612) and copolymers (e.g. PA 66/6 and PA 6T/MPMDT, etc.) plus modified grades produced by the addition o heat stabilizers, lubricants, ultraviolet screens, nucleating agents, tougheners, reinforcements, etc. The majority of resins have molecular weights suited for injection moulding and some are used in extrusion.
Alternatively the plastics material is VESCONITE (Trade Mark) available from Vesco Plastics Australia Pty Ltd.
Alternatively the material may be polytetrafluoroeth(yl)ene (PTFE).
In such case the material may be TEFLON.
The ceramic material may be, for example, zirconia, titania and/or alumina. The ceramic material may be toughened by addition of a further material, for example zircoria with the addition of alumina.
The casing cencraliser may comprise a tubular body.
The tubular body may have a bore extending longitudinally therethrough.
The body may provide an outermost surface and an innermost surface.
The outermost surface may provide a plurality of raised portions.
The raised portions may be in the form of longitudinally extending blades or ribs or may alternatively be in the form of an array of nipples.
Adjacent raised portions may define a flow path therebetween such that fluid flow paths are defined between first and second ends of the tubular body.
Where the raised portions comprise longitudinal blades, such blades may be formed substantially parallel to an axis of the tubular body.
Alternatively, the blades may be formed in a longitudinal spiral/helical path on the tubular body.
Advantageously adjacent blades may at least partly longitudinally overlap on the tubular body.
Preferably adjacent blades may be located such that one end of a blade at one end of the tubular body is at substantially the same longitudinal position as an end of an adjacent blade at another end of the tubular

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