# Patent

## Title
Method and apparatus for reaming well bore surfaces nearer the center of drift

## Abstract

The present invention provides a method and apparatus for increasing the drift diameter and improving the well path of the well bore, accomplished in one embodiment by cutting away material primarily forming surfaces nearer the center of the drift, thereby reducing applied power, applied torque and resulting drag compared to conventional reamers that cut into all surfaces of the well bore.

## Background
CROSS-REFERENCED APPLICATIONS
This application is a continuation of, and claims the benefit of the filing date of, U.S. patent application Ser. No. 13/517,870 entitled METHOD AND APPARATUS FOR REAMING WELL BORE SURFACES NEARER THE CENTER OF DRIFT, filed Jun. 14, 2012, which is a continuation of, and claims the benefit of the filing date of, U.S. patent application Ser. No. 13/441,230 entitled METHOD AND APPARATUS FOR REAMING WELL BORE SURFACES NEARER THE CENTER OF DRIFT, filed Apr. 6, 2012, which relates to, and claims the benefit of the filing date of, U.S. provisional patent application Ser. No. 61/473,587 entitled METHOD AND APPARATUS FOR REAMING WELL BORE SURFACES NEARER THE CENTER OF DRIFT, filed Apr. 8, 2011, the entire contents of which are incorporated herein by reference for all purposes.


BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to methods and apparatus for drilling wells and, more particularly, to a reamer and corresponding method for enlarging the drift diameter and improving the well path of a well bore.
Description of the Related Art
Extended reach wells are drilled with a bit driven by a down hole motor that can be steered up, down, left, and right. Steering is facilitated by a bend placed in the motor housing above the drill bit. Holding the drill string in the same rotational position, such as by locking the drill string against rotation, causes the bend to consistently face the same direction. This is called “sliding”. Sliding causes the drill bit to bore along a curved path, in the direction of the bend, with the drill string following that path as well.
Repeated correcting of the direction of the drill bit during sliding causes friction between the well bore and the drill string greater than when the drill string is rotated. Such corrections form curves in the well path known as “doglegs”. Referring to FIG. 1a, the drill string 10 presses against the inside of each dogleg turn 12, causing added friction. These conditions can limit the distance the well bore 14 can be extended within the production zone, and can also cause problems getting the production string through the well bore.
Similar difficulties can also occur during conventional drilling, with a conventional drill bit that is rotated by rotating the drill string from the surface. Instability of the drill bit can cause a spiral or other tortuous path to be cut by the drill bit. This causes the drill string to press against the inner surface of resulting curves in the well bore and can interfere with extending the well bore within the production zone and getting the production string through the well bore.
When a dogleg, spiral path or tortuous path is cut by a drill bit, the relatively unobstructed passageway following the center of the well bore has a substantially smaller diameter than the well bore itself. This relatively unobstructed passageway is sometimes referred to as the “drift” and the nominal diameter of the passageway is sometimes referred to as the “drift diameter”. The “drift” of a passageway is generally formed by well bore surfaces forming the inside radii of curves along the path of the well bore. Passage of pipe or tools through the relatively unobstructed drift of the well bore is sometimes referred to as “drift” or “drifting”.
In general, to address these difficulties the drift diameter has been enlarged with conventional reaming techniques by enlarging the diameter 16 of the entire well bore. See FIG. 1a. Such reaming has been completed as an additional step, after drilling is completed. Doing so has been necessary to avoid unacceptable increases in torque and drag during drilling. Such additional reaming runs add considerable expense and time to completion of the well. Moreover, conventional reaming techniques frequently do not straighten the well path, but instead simply enlarge the diameter of the well bore.
Accordingly, a need exists for a reamer that reduces the torque required and drag associated with reaming the well bore.
A need also exists for a reamer capable of enlarging the diameter of the well bore drift passageway and improving the well path, without needing to enlarge the diameter of the entire well bore.
SUMMARY OF THE INVENTION
To address these needs, the invention provides a method and apparatus for increasing the drift diameter and improving the well path of the well bore. This is accomplished, in one embodiment, by cutting away material primarily forming surfaces nearer the center of the drift. Doing so reduces applied power, applied torque and resulting drag compared to conventional reamers that cut into all surfaces of the well bore.



BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:
FIGS. 1a and 1b are a cross-section elevations of a horizontal well bore;
FIG. 2 is a representation of a well bore illustrating drift diameter relative to drill diameter;
FIG. 3 is a representation an eccentric reamer in relation to the well bore shown in FIG. 2;
FIG. 4 is a magnification of the downhole portion of the top reamer;
FIG. 5 is illustrates the layout of teeth along a downhole portion of the bottom reamer illustrated in FIG. 1;
FIG. 6 is an end view of an eccentric reamer illustrating the eccentricity of the reamer in relation to a well bore diameter;
FIG. 7 is an end view of two eccentric reamers in series, illustrating the eccentricity of the two reamers in relation to a well bore diameter;
FIG. 8 illustrates the location and arrangement of Sets 1, 2, 3 and 4 of teeth on another reamer embodiment;
FIG. 9 illustrates the location and arrangement of Sets 1, 2, 3 and 4 of teeth on another reamer embodiment;
FIG. 10 is a perspective view illustrating an embodiment of a reamer having four sets of teeth;
FIG. 11 is a geometric diagram illustrating the arrangement of cutting teeth on an embodiment of a reamer;
FIG. 12A-12D illustrate the location and arrangement of Blades 1, 2, 3, and 4 of cutting teeth;
FIG. 13 is a side view of a reamer tool showing the cutting teeth and illustrating a side cut area; and
FIGS. 14A-14D are side views of a reamer tool showing the cutting teeth and illustrating a sequence of Blades 1, 2, 3, and 4 coming into the side cut area and the reamer tool rotates.



DETAILED DESCRIPTION
In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail. Additionally, for the most part, specific details, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the understanding of persons of ordinary skill in the relevant art.
FIG. 1 is a cross-section elevation of a horizontal well bore 100, illustrating an embodiment of the invention employing a top eccentric reamer 102 and a bottom eccentric reamer 104. The top reamer 102 and bottom reamer 104 are preferably of a similar construction and may be angularly displaced by approximately 180° on a drill string 106. This causes cutting teeth 108 of the top reamer 102 and cutting teeth 110 of the bottom reamer 104 to face approximately opposite directions. The reamers 102 and 104 may be spaced apart and positioned to run behind a bottom hole assembly (BHA). In one embodiment, for example, the eccentric reamers 102 and 104 may be positioned within a range of approximately 100 to 150 feet from the BHA. Although two reamers are shown, a single reamer or a larger number of reamers could be used in the alternative.
As shown in FIG. 1, the drill string 106 advances to the left as the well is drilled. As shown in FIG. 2, the well bore 100 may have a drill diameter D1 of 6 inches and a drill center 116. The well bore 100 may have a drift diameter D2 of 55⁄8 inches and a drift center 114. The drift center 114 may be offset from the drill center 116 by a fraction of an inch. Any point P on the inner surface 112 of the well bore 100 may be located at a certain radius R1 from the drill center 116 and may also be located at a certain radius R2 from the drift center 114. As shown in FIG. 3, in which reamer 102 is shown having a threaded center C superimposed over drift center 114, each of the reamers 102 (shown) and 104 (not shown) preferably has an outermost radius R3, generally in the area of its teeth 108, less than the outermost radius RD1 of the well bore. However, the outermost radius R3 of each reamer is preferably greater than the distance RD2 of the nearer surfaces from the center of drift 114. The cutting surfaces of each of the top and bottom reamers preferably comprise a number of carbide or diamond teeth 108, with each tooth preferably having a circular cutting surface generally facing the path of movement PM of the tooth relative to the well bore as the reamer rotates and the drill string advances down hole.
In FIG. 1, the bottom reamer 104 begins to engage and cut a surface nearer the center of drift off the well bore 100 shown. As will be appreciated, the bottom reamer 104, when rotated, cuts away portions of the nearer surface 112A of the well bore 100, while cutting substantially less or none of the surface 112B farther from the center of drift, generally on the opposite side of the well. The top reamer 102 performs a similar function, cutting surfaces nearer the center of drift as the drill string advances. Each reamer 102 and 104 is preferably spaced from the BHA and any other reamer to allow the centerline of the pipe string adjacent the reamer to be offset from the center of the well bore toward the center of drift or aligned with the center of drift.
FIG. 4 is a magnification of the downhole portion of the top reamer 102 as the reamer advances to begin contact with a surface 112 of the well bore 100 nearer the center of drift 114. As the reamer 102 advances and rotates, the existing hole is widened along the surface 112 nearer the center of drift 114, thereby widening the drift diameter of the hole. In an embodiment, a body portion 107 of the drill string 106 may have a diameter DB of 51⁄4 inches, and may be coupled to a cylindrical portion 103 of reamer 102, the cylindrical portion 103 having a diameter DC of approx. 43⁄4 inches. In an embodiment, the reamer 102 may have a “DRIFT” diameter DD of 53⁄8 inches, and produce a reamed hole having a diameter DR of 61⁄8 inches between reamed surfaces 101. It will be appreciated that the drill string 106 and reamer 102 advance through the well bore 100 along a path generally following the center of drift 114 and displaced from the center 116 of the existing hole.
FIG. 5 illustrates the layout of teeth 110 along a downhole portion of the bottom reamer 104 illustrated in FIG. 1. Four sets of teeth 110, Sets 110A, 110B, 110C and 110D, are angularly separated about the exterior of the bottom reamer 104. FIG. 5 shows the position of the teeth 110 of each Set as they pass the bottom-most position shown in FIG. 1 when the bottom reamer 104 rotates. As the reamer 104 rotates, Sets 110A, 110B, 110C and 110D 110A, 110B, 110C and 110D pass the bottom-most position in succession. The Sets 110A, 110B, 110C and 110D of teeth 110 are arranged on a substantially circular surface 118 having a center 120 eccentrically displaced from the center of rotation of the drill string 106.
Each of the Sets 110A, 110B, 110C and 110D of teeth 110 is preferably arranged along a spiral path along the surface of the bottom reamer 104, with the downhole tooth leading as the reamer 104 rotates (e.g., see FIG. 6). Sets 110A and 110B of the reamer teeth 110 are positioned to have outermost cutting surfaces forming a 61⁄8 inch diameter path when the pipe string 106 is rotated. The teeth 110 of Set 110B are preferably positioned to be rotated through the bottom-most point of the bottom reamer 104 between the rotational path of the teeth 110 of Set 110A. The teeth 110 of Set 110C are positioned to have outermost cutting surfaces forming a six inch diameter when rotated, and are preferably positioned to be rotated through the bottom-most point of the bottom reamer between the rotational path of the teeth 110 of Set 110B. The teeth 110 of Set 110D are positioned to have outermost cutting surfaces forming a 57⁄8 inch diameter when rotated, and are preferably positioned to be rotated through the bottom-most point of the bottom reamer 104 between the rotational path of the teeth 110 of Set 110C.
FIG. 6 illustrates one eccentric reamer 104 having a drift diameter D3 of 55⁄8 inches and a drill diameter D4 of 6 1/16 inches. When rotated about the threaded axis C, but without a concentric guide or pilot, the eccentric reamer 104 may be free to rotate about its drift axis C2 and may act to side-ream the near-center portion of the dogleg in the borehole. The side-reaming action may improve the path of the wellbore instead of just opening it up to a larger diameter.
FIG. 7 illustrates a reaming tool 150 having two eccentric reamers 104 and 102, each eccentric reamer having a drift diameter D3 of 55⁄8 inches and a drill diameter D4 of 6 1/16 inches. The two eccentric reamers may be spaced apart by ten hole diameters or more, on a single body, and synchronized to be 180 degrees apart relative to the threaded axis of the body. The reaming tool 150 having two eccentric reamers configured in this way, may be able to drift through a 55⁄8 inch hole when sliding and, when rotating, one eccentric reamer may force the other eccentric reamer into the hole wall. An eccentric reaming tool 150 in this configuration has three centers: the threaded center C coincident with the threaded axis of the reaming toll 150, and two eccentric centers C2, coincident with the drift axis of the bottom eccentric reamer 104, and C3, coincident with a drift axis of the top eccentric reamer 102.
FIGS. 8 and 9 illustrate the location and arrangement of Sets 1, 2, 3 and 4 of teeth on another reamer embodiment 200. FIG. 8 illustrates the relative angles and cutting diameters of Sets 1, 2, 3, and 4 of teeth. As shown in FIG. 8, Sets 1, 2, 3 and 4 of teeth are each arranged to form a path of rotation having respective diameters of 55⁄8 inches, 6 inches, 61⁄8 inches and 61⁄8 inches. FIG. 9 illustrates the relative position of the individual teeth of each of Sets 1, 2, 3 and 4 of teeth. As shown in FIG. 9, the teeth of Set 2 are preferably positioned to be rotated through the bottom-most point of the reamer between the rotational path of the teeth of Set 1. The teeth of Set 3 are preferably positioned to be rotated through the bottom-most point of the reamer between the rotational path of the teeth of Set 2. The teeth of Set 4 are preferably positioned to be rotated through the bottom-most point of the reamer between the rotational path of the teeth of Set 3.
FIG. 10 illustrates an embodiment of a reamer 300 having four sets of teeth 310, with each set 310A, 310B, 310C, and 310D arranged in a spiral orientation along a curved surface 302 having a center C2 eccentric with respect to the center C of the drill pipe on which the reamer is mounted. Adjacent and in front of each set of teeth 310 is a groove 306 formed in the surface 302 of the reamer. The grooves 306 allow fluids, such as drilling mud for example, and cuttings to flow past the reamer and away from the reamer teeth during operation. The teeth 310 of each set 310A, 310B, 310C, and 310D may form one of four “blades” for cutting away material from a near surface of a well bore. The set 310A may form a first blade, or Blade 1. The set 310B may form a second blade, Blade 2. The set 310C may form a third blade, Blade 3. The set 310D may form a fourth blade, Blade 4. The configuration of the blades and the cutting teeth thereof may be rearranged as desired to suit particular applications, but may be arranged as follows in an exemplary embodiment.
Turning now to FIG. 11, the tops of the teeth 310 in each of the two eccentric reamers 300, or the reamers 102 and 104, rotate about the threaded center of the reamer tool and may be placed at increasing radii starting with the #1 tooth at 2.750′′ R. The radii of the teeth may increase by 0.018′′ every five degrees through tooth #17 where the radii become constant at the maximum of 3.062′′, which corresponds to the 61⁄8′′ maximum diameter of the reamer tool.
Turning now to FIGS. 12A-12D, the reamer tool may be designed to side-ream the near side of a directionally near horizontal well bore that is crooked in order to straighten out the crooks. As shown in FIG. 12A-12D, 30 cutting teeth numbered 1 through 30 may be distributed among Sets 310A, 310B, 310C, and 310D of cutting teeth forming four blades. As plotted in FIG. 11, the cutting teeth numbered 1 through 8 may form Blade 1, the cutting teeth numbered 9 through 15 may form Blade 2, the cutting teeth numbered 16 through 23 may form Blade 3, and the cutting teeth numbered 24 through 30 may form Blade 4. As the 51⁄4′′ body 302 of the reamer is pulled into the near side of the crook, the cut of the rotating reamer 300 may be forced to rotate about the threaded center of the body and cut an increasingly larger radius into just the near side of the crook without cutting the opposite side. This cutting action may act to straighten the crooked hole without following the original bore path.
Turning now to FIG. 13, the reamer 300 is shown with the teeth 310A of Blade 1 on the left-hand side of the reamer 300 as shown, with the teeth 310B of Blade 2 following behind to the right of Blade 1, the teeth 310C of Blade 3 following behind and to the right of Blade 2, and the teeth 310D of Blade 4 following behind and to the right of Blade 3. The teeth 310A of Blade 1 are also shown in phantom, representing the position of teeth 310A of Blade 1 compared to the position of teeth 310D of Blade 4 on the right-hand side of the reamer 300, and at a position representing the “Side Cut” made by the eccentric reamer 300.
Turning now to FIGS. 14A-14D, the extent of each of Blade 1, Blade 2, Blade 3, and Blade 4 is shown in a separate figure. In each of the FIG. 14A-14D, the reamer 300 is shown rotated to a different position, bringing a different blade into the “Side Cut” position SC, such that the sequence of views 14A-14D illustrate the sequence of blades coming into cutting contact with a near surface of a well bore. In FIG. 14A, Blade 1 is shown to cut from a 51⁄4′′ diameter to a 51⁄2′′ diameter, but less than a full-gage cut. In FIG. 14B, Blade 2 is shown to cut from a 53⁄8′′ diameter to a 6′′ diameter, which is still less than a full-gage cut. In FIG. 14C, Blade 3 is shown to cut a “Full Gage” diameter, which may be equal to 61⁄8′′ in an embodiment. In FIG. 14D, Blade 4 is shown to cut a “Full gage” diameter, which may be equal to 61⁄8′′ in an embodiment.
The location and arrangement of Sets of teeth on an embodiment of an eccentric reamer as described above, and teeth within each set, may be rearranged to suit particular applications. For example, the alignment of the Sets of teeth relative to the centerline of the drill pipe, the distance between teeth and Sets of teeth, the diameter of rotational path of the teeth, number of teeth and Sets of teeth, shape and eccentricity of the reamer surface holding the teeth and the like may be varied.
Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

## Claims

1. An apparatus for increasing the diameter of a well bore, comprising:
at least two reamers, each having a plurality of cutting blades extending a distance radially outwardly from the outer surface of each reamer, wherein, in an order counter to the direction of rotation, a first cutting blade extends a first distance and each additional cutting blade extends an equal or greater distance than the preceding cutting blade, the plurality of blades defining a curved cutting area extending approximately 50% of the circumference of each reamer;
wherein the plurality of cutting blades of each reamer are angularly displaced from the plurality of cutting blades of each other reamer about an axis of rotation.

2. The apparatus of claim 1, wherein each reamer is disposed to urge at least one of the one or more blades of each other reamer into engagement with the surface of the well bore nearest a center of drift of the well bore.

3. The apparatus of claim 1, further comprising a drill bit to which the reamers are coupled.

4. The apparatus of claim 1, further comprising a drill string to which the reamers are coupled.

5. The apparatus of claim 4, wherein the teeth of each of the plurality of cutting blades are longitudinally overlapping from the teeth of the adjacent cutting blades.

6. The apparatus of claim 1, wherein each cutting blade comprises a plurality of cutting teeth.

7. The apparatus of claim 6, wherein the plurality of cutting teeth extend tangentially to each reamer.

8. The apparatus of claim 6, wherein the teeth of each of the plurality of cutting blades of each reamer are offset from the teeth of an adjacent cutting blade.

9. The apparatus of claim 6, wherein each tooth is comprised of carbide or diamond.

10. The apparatus of claim 6, wherein the teeth face the direction of rotation.

11. The apparatus of claim 6, wherein the teeth of each of the plurality of cutting blades are longitudinally overlapping from the teeth of the adjacent cutting blades.

12. The apparatus of claim 11, wherein the apparatus is positioned at least 100 feet behind the drill bit.

13. The apparatus of claim 1, wherein each cutting blade extends along a spiral path on a portion of the outer surface of the reamer, wherein the spiral path traverses an acute angle relative to the longitudinal axis of the reamer.

14. The apparatus of claim 1, further comprising grooves disposed between the cutting blades.

15. The apparatus of claim 1, further comprising a coupling adapted to receive a bottom hole assembly.

16. An drill string, comprising:
a bottom hole assembly;
at least two reamers coupled to the bottom hole assembly, each having a plurality of cutting blades extending a distance radially outwardly from the outer surface of each reamer, wherein, in an order counter to the direction of rotation, a first cutting blade extends a first distance and each additional cutting blade extends an equal or greater distance than the preceding cutting blade, the plurality of blades defining a curved cutting area extending approximately 50% of the circumference of each reamer;
wherein the plurality of cutting blades of each reamer are angularly displaced from the plurality of cutting blades of each other reamer about the axis of rotation of the drill string.

17. The apparatus of claim 16, wherein the apparatus is positioned at least 100 feet behind the bottom hole assembly.

18. The apparatus of claim 16, wherein the bottom hole assembly comprises a drill bit.

19. The apparatus of claim 16, wherein each reamer is disposed to urge at least one of the one or more blades of each other reamer into engagement with the surface of a well bore nearest the center of drift of the well bore.