WO2017145042A1

WO2017145042A1 - Spiral centralizer for wellbore casings

Info

Publication number: WO2017145042A1
Application number: PCT/IB2017/050968
Authority: WO
Inventors: Abhishek AVASTHI
Original assignee: Avasthi Abhishek
Priority date: 2016-02-23
Filing date: 2017-02-21
Publication date: 2017-08-31

Abstract

A single piece spiral spring type centralizer is disclosed that has no joints leading to a robust construction. The centralizer includes a first end ring and a second end ring that is spaced apart from the first end ring along a longitudinal axis of the centralizer. The two end rings are made of metal strip formed in a complete or near complete circular shape. A spiral shaped part extends concentrically between the two end rings along the longitudinal axis, wherein the first end ring, the second end ring and the spiral shaped part are made of a single metal strip, the strip shaped to form the first end ring integrally continues to form the spiral shaped part, and thereafter integrally continues to form the second end ring. The disclosed centralizer can be manufactured from a metal strip by forming process followed by heat treatment.

Description

SPIRAL CENTRALIZER FOR WELLBORE CASINGS

TECHNICAL FIELD

[0001] The present disclosure relates to field of equipment for oil well drilling. In particular, it relates to centralizers used during oil well drilling.

BACKGROUND

[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] An oil well is a boring in Earth designed to bring hydrocarbons to surface. The hydrocarbons may include natural gas and petroleum oil. A well that is designed to produce mainly or only gas may be termed a gas well. Production of oil or gas is a complex, time- consuming and cost-intensive undertaking; and in principle, every oil well goes through three phases.

[0004] In first phase, drilling is done using drill pipes to create a wellbore. Drill pipes are steel pipes that conduct the force to a drill bit. The drill bit cuts into the rock until it reaches oil / gas deposits. During drilling, drilling mud cools the drill bit and carries rock cuttings to the surface.

[0005] In the second phase, the wellbore is lined with tubes called casing to protect the layers of soil and to prevent groundwater from being contaminated by drilling mud and/or fracturing fluids used during the drilling. Drilling and casing processes alternate - the drill string is taken out at specific intervals and the wellbore is lined with casing. Casings are fitted with centralizers on their outer diameters to place the casing in concentric alignment with axis of the wellbore. At this stage centralizers minimize sticking of the casing to the wellbore walls when they are being lowered within the bore.

[0006] In the third phase, oil well is prepared for production, and the process may include cementing of the casing. Cementing of the casing involves channeling cement in annulus area between outside of the casing and the wellbore. In all vertical, inclined, and horizontal wells, main goal to achieve a good cementation is effective displacement of the mud by the cement. One of the many factors that affect mud removal efficiency is pipe centralization, where centralizers play a crucial role. They also allow cement to circulate freely around the casing by preventing contact between the casing and formation and thereby ensure that casing is cemented all along its circumference to provide a robust cement seal.

[0007] Centralizers may be rigid or flexible. However, since wellbores have irregularities and obstructions, a flexible centralizer incorporating springs that compress or expand as a casing carrying the centralizer is lowered into it, is a preferred choice in many applications.

[0008] Most flexible centralizers comprise a pair of spaced and axially aligned collars adapted to fit exterior surface of casing and a plurality of outwardly bowed spring staves that extend between the collars and are welded at each end to respective collars. The staves are circumferentially spaced around the collars and are of spring steel so that the staves (also termed as bows) press against the wellbore walls and resiliently urge the casing toward the center of the wellbore. The pair of collars is structured to form a cylindrical shape of inside diameter slightly greater than outside diameter of the casing pipe on which the centralizer will be used.

[0009] Collars of centralizers may be made of two half collars hinged together or from a single length of sheet metal rolled into a split ring and welded together to form a solid collar. The collars are then placed on a welding jig mandrel and spaced apart. The spring bows can be manufactured in any one of a number of ways of making leaf springs such as heating a length of flat spring stock to the required temperature, bending the spring stock to the desired bow shape, and quenching the bow to obtain the desired hardness and spring characteristics. The bows are then placed on the collars positioned on the mandrel and each end of the bow is welded to the respective collar. This welding step is duplicated for each of the bows, there being generally six or eight bows provided on the more common sizes of centralizers. It is readily apparent that in these sizes, twelve or sixteen individual welds of bow-to-collar must be made.

[00010] Sometimes a wellbore may be slanted when a proportion of weight of casing is supported by the staves. Such and other forces on the centralizer can cause failure of one or more of the welds between the staves and the collars if the weld is not structurally or metallurgically adequate. A failure such as breaking of bows/staves on a centralizer can be extremely expensive in drilling and can delay completion of wells as it may be necessary to take various remedial steps to correct the defect caused by the malfunction. Approximately 400 wells worldwide a year are affected by centralizer problems, causing a well downtime loss of about US Dollars 0.6 billion that can be avoided by installation of better and innovative centralizers. Therefore, centralizers must be rugged and strong to handle stresses they encounter.

[00011] Under certain conditions, it is advantageous to scrape the wellbore as the casing is lowered into it and devices such as spiral centralizers, as against those having longitudinally positioned bows/staves (in case of flexible centralizers) or blades (in case of rigid centralizers), have been found useful for this purpose. In spiral centralizers the blades or spring staves extend spirally between the spaced collars. .

[00012] As can be appreciated from above, an ideal centralizer should have minimum or zero weak points such as hinges, welds or mechanical interlock; with substantial flexibility and; restoring force applicable to absorb both axial and radial loads. It should give the lowest coefficient of friction and should provide maximum torque reduction in open and cased hole. Advancements have been made to improve centralizers in terms of their safeguarding, abrasion and wear resistance properties. Shape or appearance of centralizers has been varied to improve their functionality and performance in casing operations.

[00013] United States Patent number U.S. 4,483,395 discloses a centralizer as one-piece wire guard device composed of non-metallic material engageable with a well casing for preventing abrasion of casing, electric wires, ropes and the like with the well casing. More specifically, object of this invention is to provide a split-ring type guard device which may be readily opened at the split to permit the guard device to be slipped over the casing and fastened thereon. Although this approach provides a centralizer that can be conveniently fixed over a casing, it does not provide any means for making a strong centralizer eliminating weak points such as hinges and weld joints.

[00014] Chinese Patent number CN103306614 discloses an open type spiral wing mud drum-preventing centralizer for well drilling. It comprises a tubular centralizer body with at least one spiral centralizing wing arranged on outer wall of middle section of the centralizer body; a mud block cutting belt extending along the spiral centralizing wing arranged on one side of the spiral centralizing wing, wherein the mud block cutting belt and the centralizer body maintain preset distance. The mud block cutting belt is arranged on one side of the spiral centralizing wing, so that mud blocks scraped from the wall of the well by the spiral centralizing wing, and gathered to a certain degree, are changed under the action of the mud block cutting belt into long and thin strips and are pushed to the lower part of the mud block cutting belt to be washed away by high speed liquid. Although this approach provides for a multifunctional centralizer, it does not provide any means for making a strong centralizer eliminating weak points such as hinges and weld joints.

[00015] United States Patent number US3312285 discloses a centralizer and its method of manufacturing from a single blank of material, and where the spring bows for producing the centering forces are not welded to the collars. Thus theone piece construction hasmaterial extending seamlessly from each collar portion through the bow portions without any circumferential joints. However, the disclosed structure does include at least one longitudinal joint which may be a welded or hinged or riveted joint.

[00016] Therefore, there is a requirement in the art for optimized centralizers with reduced frictional properties, minimum weak points such as hinges, welds or mechanical interlock, and have substantial flexibility and restoring force with capability to absorb both axial and radial loads.

[00017] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[00018] In some embodiments, the numbers expressing quantities or dimensions of items, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term "about." Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. [00019] As used in the description herein and throughout the claims that follow, the meaning of "a," "an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.

[00020] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[00021] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION

[00022] A general object of the present disclosure is to provide an optimized centralizer for wellbore casings.

[00023] An object of the present disclosure is to optimize centralizer for wellbore casings by eliminating potential weak points.

[00024] Another object of the present disclosure is to provide a single piece centralizer to eliminate potential weak points. [00025] Yet another object of the present disclosure is to provide a single piece spiral centralizer that enables 360 degree casing centering in a wellbore with extremely easy casing rotation.

SUMMARY

[00026] Aspects of the present disclosure relate to centralizers used in oil well drilling. In particularly, the disclosure pertains to a single piece spiral spring type centralizer that does not have any joints - longitudinal or circumferential and provides 360 degree of casing centering in a wellbore with extremely easy casing rotation and reciprocation and eliminates any potential weak points such as weld joints.

[00027] In an aspect, the single piece spiral centralizer can include two end rings (also known as collars in the related art) such as a first end ring and a second end. The two end rings are concentric and spaced apart from each other along longitudinal axis of the centralizer. It further includes a spiral shaped part extending from one end ring to the other end ring say from the first end ring to the second end ring, wherein the first end ring integrally continues to form the spiral section which in turn integrally continues to form the second end ring. Thus, the complete centralizer is made of a single piece without any joints - longitudinal joints or circumferential joints, - such as weld joint or riveted joint or hinged joint. Further the disclosed spiral spring centralizer does not have any connectors and other accessories to join two or more constituent parts together.

[00028] In an aspect, the disclosed centralizer incorporates a single spiral spring extending from first end ring to second end ring. The single spiral spring provides a diameter that presses against wellbore wall when a casing mounted with the disclosed centralizer is lowered in the wellbore. The outer diameter of the spiral spring can be under gauge in order to minimize running forces during lowering of the casing in the oil well. Further, the first end ring and second end ring can be configured to fit over casing.

[00029] In an embodiment, the end rings of the disclosed centralizer can incorporate at least one hole for accommodating/receiving a hardware wherein the hardware can enable fixing position of the centralizer on a casing on which the centralizer is mounted. In an aspect, fixing position of the on the casing can prevent centralizer' s movement when the casing is lowered in a bore well. [00030] In an aspect, the disclosed centralizer can be manufactured by forming during which straight sheet of metal strips can be wound/wrapped around a rotating mandrel having a suitable shape/profile to replicate desired shape.

[00031] In an alternate embodiment, the present disclosure provides a method of manufacturing the disclosed spiral centralizer out of a blank. The method can include steps of:

(a) blanking, out of a sheet metal, a developed profile of the spiral centralizer, wherein the developed profile of the spiral centralizer includes a first part and a second part wherein the first part and the second part are mutually parallel and space apart, and a third part that extends from the first part to the second part such that the blank of the developed profile is generally Z shaped;

(b) forming the blanked profile to get a desired shape/profile, wherein during the forming operation the first part and the second part are shaped to form generally complete circles so as to function as first end ring and a second end ring of the centralizer, and the third part in between the first part and the second part is formed to a spiral shape that is concentric to the first end ring and the second end ring; (c) heat treating the formed centralizer to realize optimum physical properties of the sheet metal.

[00032] In an embodiment, forming operation can be either cold forming or hot forming depending on material and other parameters, and the forming can be done in a single stage using a multi-piece forming mandrel or in more than one stages using more than one mandrel there being one for each stage during which a different portion of the centralizer can be formed to get final shape

[00033] In an aspect, the disclosed centralize rowing to its single piece joint less construction, can have high reliability with high load stress bearing capacity. Accordingly the proposed centralizer can lead to low or no downtime attributable to wear and tear or breakage.

[00034] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.

BRIEF DESCRIPTION OF DRAWINGS

[00035] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:

[00036] FIG.1 illustrates an exemplary side view of the proposed centralizer in accordance with embodiments of the present disclosure.

[00037] FIG. 2 illustrates an exemplary top view of the proposed centralizer in accordance with an exemplary embodiment of the present disclosure.

[00038] FIG. 3A and 3Billustrate an exemplary profile for metal sheet strip and blank respectively for manufacturing of the proposed centralizer in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

[00039] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[00040] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[00041] Various terms as used herein. To the extent a term used in a claim is not defined, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[00042] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details. [00043] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[00044] Embodiments explained herein relate to a centralizer for use in oil well drilling. More particularly, the invention relates to a single piece spiral spring type centralizer so as to give 360 degree casing centering in a wellbore with extremely easy casing rotation and reciprocation with no weak points.

[00045] In an embodiment, the disclosed single piece spiral centralizer includes a first end ring, a second end ring that is spaced apart from the first end ring along longitudinal axis of the centralizer, and a spiral shaped part extending from the first end ring to the second end ring, wherein the first end ring is of sheet metal strip formed in a complete or near complete circular shape that integrally continues to form the spiral section. The sheet metal strip that forms the first collar and the spiral shaped part in turn integrally continues to form the second end ring that, in same way as the first end ring, is of a complete or near complete circular shape of the sheet metal strip. Thus, the complete centralizer is made of a single piece without any joints such as longitudinal joints or circumferential joints. Further the disclosed spiral spring centralizer does not have any connectors and other accessories to join two or more constituent parts together.

[00046] As is clear from above, the disclosed centralizer incorporates a single spiral shaped part extending from first end ring to second end ring, and the single spiral shaped part provides a diameter that presses against wellbore wall when a casing mounted with the disclosed centralizer is lowered in the wellbore. The outer diameter of the spiral shaped part can be under gauge in order to provide zero running forces during lowering of the casing in the oil well. Further, the first end ring and second end ring can be configured to fit over casing.

[00047] In an embodiment, the spiral shaped part extending from first end ring to second end ring can have a constant helix angle. In an alternate embodiment, the helix angle can vary from one end to other, for example starting from one of the end rings it can be a large helix angle reducing to a smaller helix angle in the middle and again increasing towards the other end ring. [00048] In an embodiment, the spiral shaped part extending from first end ring to second end ring can have a profile envelop that is combination of a cylindrical profile in middle and two conical profiles at two ends where it joins the two end rings, wherein outer diameter of the cylindrical profile can be selected to meet requirement of wellbore. In an alternate embodiment, the spiral shaped part can have a barrel shaped profile envelop having a larger diameter at middle that reduces towards two ends to join with the two end rings, wherein the diameter at middle can be selected to meet requirement of wellbore.

[00049] In an embodiment, the sheet metal used for the disclosed centralizer can be any one but not limited to medium carbon steel, high carbon steel, alloy steel, Silico-manganese spring steel, Boron steel or any other spring material possessing high tensile strength and elasticity to be suitable for the proposed application.

[00050] In an aspect, the present disclosure provides a method of manufacturing the disclosed spiral centralizer. The method can include steps of: (a) blanking, out of a sheet metal, a developed profile of the spiral centralizer, wherein the developed profile of the spiral centralizer includes a first part and a second part wherein the first part and the second part are mutually parallel and space apart, and a third part that integrally extends from the first part to the second part such that the blank of the developed profile is generally Z shaped; (b) forming the blanked profile to get a desired shape/profile, wherein during the forming operation the first part and the second part are shaped to form generally complete circles so as to function as first end ring and a second end ring respectively of the centralizer, and the third part in between the first part and the second part is formed to a spiral shape that is concentric to the first end ring and the second end ring; (c) heat treating the formed centralizer to realize optimum physical properties of the sheet metal.

[00051] In an embodiment, forming operation can be either cold forming or hot forming depending on material and other parameters, and the forming can be done in a single stage using a multi-piece forming mandrel or in more than one stages using more than one mandrel there being one for each stage during which a different portion of the centralizer can be formed to get final shape

[00052] In an aspect, the disclosed centralizer owing to its single piece joint less construction can have high reliability with high load stress bearing capacity. Accordingly the proposed centralizer can lead to low or no downtime attributable to wear and tear or breakage. [00053] Referring now to FIG. l and 2 wherein exemplary side and top views of the disclosed centralizer 100 are disclosed. As shown, the disclosed centralizer 100 can have a first end ring 102, a second end ringl04 that is spaced apart from the first end ringl02 along longitudinal axis of the centralizer 100. The first end ring 102 and the second end ringl04can be adapted to fit around a casing on which the centralizer 100 is to be used. In particular they both are made of strip of sheet metal that is formed to a complete or near complete circular shape as shown in FIG. 2. As is evident, flat inner surface of the strip provides contact surface with the casing when the centralizer 100 is fitted on a casing. In an aspect, springing action of the flat strip forming the two end rings 102/104 can provide gripping force for the centralizer to be retained in position on the casing.

[00054] In an embodiment, the end rings 102/104 of the centralizer 100 can incorporate at least one hole (not shown) for accommodating/receiving a hardware wherein the hardware can enable fixing position of the centralizer 100 on a casing on which the centralizer is mounted. In an exemplary embodiment, the hardware can be a grub screw which on being tightened through the hole in the end ring(s), can dig into the casing thereby firmly holding the centralizer on the casing. In an aspect, firmly holding the centralizer on the casing can prevent centralizer' s shifting /movement when the casing is lowered in a bore well.

[00055] In an embodiment, the centralizer 100 can further incorporate a spiral shaped part 106 (also referred to as spiral spring 106 and the two terms used interchangeably hereinafter) extending between two end rings i.e. from the first end ringl02 to the second end ring 104, wherein the sheet metal strip that forms the first end ring 102, integrally continues to form the spiral section; and in turn integrally continues to form the second end ringl04. Thus, the complete centralizer 100 is made of a single piece of strip without any joints such as longitudinal joints or circumferential joints. Further the disclosed spiral spring centralizer 100 does not have any connectors and other accessories to join two or more constituent parts together.

[00056] As is clear from above, the disclosed centralizer incorporates a single spiral shaped part/ spiral spring 106 extending between the two end rings 102/104, and the single spiral shaped part/ spiral springl06provides a diameter that presses against wellbore wall when a casing mounted with the centralizer 100 is lowered in the wellbore. In particular, flat outer surface of the strip forming the spiral shaped part/ spiral springl06 can provide contact surface with wellbore. The outer diameter of the spiral shaped part/spiral spring 106 can be under gauge i.e. have diameter that is less than wellbore diameter, in order to minimize running forces during lowering of the casing in the oil well.

[00057] In an aspect, number of coils in the spiral shaped part 106 can vary depending on length of the centralizer 100 and helix angle. Number of coils can vary depending on requirement. In an aspect, there can be at least one coil in center that has diameter meeting requirement of wellbore where it is going to be used so as to provide a complete 360 degree centering.

[00058] In an embodiment, the spiral shaped part 106 can have a constant helix angle. In an alternate embodiment, the helix angle can vary from one end to other, for example starting from one of the end rings 102/104, the helix angle can be a larger angle which reduces to a smaller angle in the middle and again increasing towards the other end ring 102/104.

[00059] In an embodiment, profile envelop formed by spiral shaped part 106 can be combination of a cylindrical profile in middle and two conical profiles at two ends where it joins the two end rings 102/104, with outer diameter of the cylindrical profile selected to meet requirement of wellbore. In an alternate embodiment, the spiral shaped part can have a barrel shaped profile envelop having a larger diameter at middle that reduces towards two ends to join with the two end rings 102/104, wherein the diameter at middle can be selected to meet requirement of wellbore.

[00060] In an embodiment, the sheet metal used for the disclosed centralizer can be any one but not limited to medium carbon steel, high carbon steel, alloy steel such as chromium steel, Silico-manganese spring steel, Boron steel or any other spring material possessing high tensile strength and elasticity to be suitable for the proposed application.

[00061] In an embodiment, proposed centralizer 100 can be manufactured by forming during which straight sheet of metal strips 300 as shown in FIG. 3A, can be wound/wrapped around a rotating mandrel having a suitable shape/profile to replicate desired shape. Forming or metal forming is a metal working process of fashioning metal parts and objects through mechanical deformation; wherein the work piece is shaped without adding or removing material, and its mass remains unchanged.

[00062] In an alternate embodiment, metal forming operation can be done on a blank prepared out of a sheet metal and having a developed profile of the centralizer 100. FIG. 3B illustrates an exemplary view of blank 350 having a profile that matches developed profile of the centralizer 100. The developed profile of the centralizer 100 includes a first part 302 and a second part 304 wherein the first part and the second part are mutually parallel and spaced apart. A third part 306 extends from the first part 302 to the second part 304 such that the blank 300 is generally Z shaped. It is to be appreciated that the third part 306 has been shown to be straight the exemplary representation of FIG. 3 as applicable for a centralizer having fixed helix angle (from one end to other), and shape of the third part 306 can change depending on variation in the helix angle from one end to the other.

[00063] In an aspect, method of manufacturing the disclosed centralizer 100 using the blanking route can include steps of: (a) blanking, out of a sheet metal, a developed profile of the spiral centralizer, wherein the developed profile of the spiral centralizer includes a first part and a second part wherein the first part and the second part are mutually parallel and space apart, and a third part that extends from the first part to the second part such that the blank of the developed profile is generally Z shaped; (b) forming the blanked profile to get a desired shape/profile, wherein during the forming operation the first part and the second part are shaped to form generally complete circles so as to function as first end ring and a second end ring of the centralizer, and the third part in between the first part and the second part is formed a spiral that is concentric to the first end ring and the second end ring; (c) heat treating the formed centralizer to realize optimum physical properties of the sheet metal.

[00064] In an embodiment, forming operation whether using a straight strip route or bank route can be either cold forming or hot forming depending on material and other parameters, and can be done on a mandrel. As would be apparent to those skilled in the art, the centralizer 100 having profile as disclosed cannot be formed in a single stage using a single piece mandrel as it would not be possible to take the mandrel out of the formed centralizer being narrow at both ends. Therefore, it requires a special mandrel made of a number of pieces that can be assembled to form complete mandrel for forming the centralizer, and thereafter can be dismantled to remove individual pieces out of the formed centralizer. Thus the forming can be done in a single stage using a multi-piece forming mandrel or in more than one stages using more than one mandrel there being one for each stage during which a different portion of the centralizer can be formed to get final shape. [00065] In an aspect, the disclosed centralizer owing to its single piece joint less construction, can have high reliability with high load stress bearing capacity. Accordingly the proposed centralizer can lead to low or no downtime attributable to wear and tear or breakage.

[00066] In yet another aspect, proposed centralizer can easily bypass ledges encountered during boring by a little rotation or reciprocation of the casing.

[00067] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION

[00068] The present disclosure provides an optimized centralizer for wellbore casings.

[00069] The present disclosure optimizes centralizer for wellbore casings by eliminating potential weak points.

[00070] The present disclosure provides a single piece centralizer to eliminate potential weak points.

[00071] The present disclosure provides a single piece centralizer that does not have any longitudinal or circumferential joints such as weld joint or riveted joint or hinged joint.

[00072] The present disclosure provides a single piece spiral centralizer that enables 360 degree casing centering in a wellbore with extremely easy casing rotation.

Claims

I Claim:

1. A centralizer for centering a casing tube in a bore, the centralizer comprising:

a first end ring;

a second end ring that is spaced apart from the first end ring along a longitudinal axis of the centralizer; wherein the first end ring and the second end ring are made of metal strip formed in a complete or near complete circular shape; and

a spiral shaped part extending concentrically from the first end ring to the second end ring along the longitudinal axis,

wherein the first end ring, the second end ring and the spiral shaped partare made of a single metal strip, the strip shaped to form the first end ring integrally continues to form the spiral shaped part, and thereafter integrally continues to form the second end ring.

2. The centralizer as claimed in claim 1 , wherein flat inner surface of the strip forming the first end ring and the second end ring provides contact surface with the casing, and wherein springing action of the strip forming the first end ring and the second end ring provides gripping force for the centralizer to be retained in position on the casing tube.

3. The centralizer as claimed in claim 1, wherein flat outer surface of the strip forming the spiral shaped part provides contact surface with the bore.

4. The centralizer as claimed in claim 1, wherein material of metal strip used for the centralizer is selected out of group of materials comprising medium carbon steel, high carbon steel, alloy steel, Chromium steel, Silico-manganese spring steel, Boron steel.

5. The centralizer as claimed in claim 1, wherein the spiral shaped part has a constant helix angle.

6. The centralizer as claimed in claim 1, wherein the spiral shaped part has a varying helix angle starting with a higher helix angle from the first end ring or the second end ring and reducing to a smaller helix angle in middle, and again increasing towards the other end ring.

7. The centralizer as claimed in claim 1, wherein the spiral shaped part has a profile envelop that is combination of a cylindrical profile in middle and two conical profiles at two ends where it joins the first end ring and the second end ring.

8. The centralizer as claimed in claim 1, wherein the spiral shaped part has a barrel shaped profile envelop having a larger diameter at middle that reduces towards two ends to join the two end rings.

9. The centralizer as claimed in claim 1, wherein the centralizer is manufactured out of straight metal strip by metal forming operation.

10. The centralizer as claimed in claim 1, wherein the centralizer is manufactured by metal forming of a blank of sheet metal.