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BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to downhole tools useful for drilling oil, gas and water wells. More specifically, the present invention relates to a downhole drilling tool used to pass through a smaller hole and drill a larger hole.  
         [0003]     2. Description of the Prior Art  
         [0004]     Various methods have been devised for passing a drilling assembly through an existing cased borehole and permitting the drilling assembly to drill a new borehole that is of a larger diameter than the inside diameter of the existing upper cased borehole. One such method uses an under-reamer, which is collapsed to pass through the smaller diameter existing, cased borehole and then expanded to ream the new, larger diameter borehole for the installation of larger diameter casing. Another method is the use of a winged reamer disposed above a conventional bit.  
         [0005]     Under-reamers usually have hinged arms with attached cutters. The tool typically has pocket recesses formed in the body where the arms are retracted when the tool is in a closed state. Most of the prior art under-reamers utilize swing out cutter arms that are pivoted at an end opposite the cutting end of the reamer and are actuated by mechanical or hydraulic forces acting on the arms to extend or retract them. Some examples of these types of under-reamers are shown in U.S. Pat. Nos. 3,224,507; 3,425,500; and 4,055,226.  
         [0006]     An example of a hydraulically expandable, concentric reaming tool is the RHINO reamer of Smith International, Inc. The tool includes three cutter blocks that are equally spaced around the tool circumference and carrying PDC cutting elements. The cutter blocks are extended from a collapsed position by hydraulic actuation. The cutter blocks include a stabilizer gauge pad and a formation cutting structure. A lock-up system restricts fluid from actuating the cutter blocks during shoe track drill out.  
         [0007]     Another example of a hydraulically expandable, concentric reaming tool is the REAMASTER reamer of Smith International, Inc. This tool is illustrated in U.S. Pat. No. 4,431,065, which describes it as having a tubular body for connection to a drill string and a cutting arm received within a recess in the tubular body. The cutting arm is moved between a retracted position approximately aligned with the axis of the tubular body and a deployed position extending laterally outwardly of the body by a hydraulic plunger that actuates the cutting arms from a fully retracted to a fully deployed position.  
         [0008]     An example of a mechanically actuated expandable drill bit that does not use pivoting cutter arms to ream a borehole is shown in U.S. Pat. No. 3,365,010. Blades with cutters ride in opposed, axially oriented channels angled with respect to the axis of the tool. When the blades impact the bottom of the borehole, shear pins retaining the blades are broken allowing the blades to move up the channels thereby expanding out against the borehole wall for subsequent borehole enlargement. A large pin for each blade retains the expanded blades in a desired position to control the gage of the borehole. When the expandable drill bit is tripped out of the borehole, the blades fall down the angled tracks through frictional and gravitational forces.  
         [0009]     The under-reamer shown in U.S. Pat. No. 3,433,313 has a tubular body with a sleeve movably positioned therein and adapted to move responsive to the pressure of drilling fluid. Movement of the sleeve deploys the cutters to their cutting position. The sleeve is moved in the opposite direction with a wireline tool to retract the cutters from their cutting position and also stop the flow of drilling fluid to allow retraction of the cutters.  
         [0010]     An expandable under-reamer is disclosed in U.S. Pat. No. 6,378,632 having an under-reamer body forming at least a pair of opposed downwardly and inwardly angled slots. Fluid is circulated through the under-reamer body. At least a pair of cutter assemblies housed within the under-reamer body is adapted to engage in the opposed angled slots formed by the under-reamer body. Each cutter assembly consists of a cutter support body having a track at a first end, a piston at a second end, and cutters formed in between the ends. The piston is slides within a sleeve formed in the under-reamer body and extending parallel with the angled slots formed in the under-reamer body. The sleeve is in fluid communication with a control port formed in the under-reamer body. Fluid under pressure, when admitted to the piston sleeve below the piston, drives the cutter assembly upwardly and outwardly along the angled slots to commence an under-reaming operation. A spring means in the under-reamer body retracts the cutter assemblies when fluid is shut off at the control port. The hydraulically operated under-reamer opens a borehole below a restriction that is larger than the restriction itself. The under-reamer has a cutter system with a pair of cutters that engage the formation by traversing upward and outward along a track that is angled with respect to an axis of the under-reamer body. The cutters are forced to the extended position by a piston built into each cutter support. Pressure acting on the piston comes from the pressure differential between the annulus and the drill string during circulation of the drilling fluid.  
         [0011]     A related type of tool available from Halliburton Security DBS is the Near Bit Reamer. The tool is designed to open the borehole to a larger diameter than the pilot bit. Once the tool is below the casing shoe, the reamer blades are hydraulically actuated. The Near Bit Reamer is adapted for use just above the drill bit or above a rotary steerable system. Also available from Halliburton Security DBS is the XL2 Series under-reamer. This tool can be provided as an expandable stabilizer and is run in conjunction with an under-reamer for better stability. The arms are opened hydraulically and closed mechanically by a return spring.  
         [0012]     Another tool described as an eccentric adjustable diameter blade stabilizer is shown in U.S. Pat. No. 6,227,312. The eccentric stabilizer is adapted for mounting on a bi-center bit having an eccentric reamer section and a pilot bit. A pair of adjustable stabilizer blades is recessed within openings in a housing. The blades are radially extended by a camming action produced upon axial movement. An extender piston causes the blades to radially extend and a return spring causes the blades to retract.  
         [0013]     Bi-center bits have been used as an alternative to under-reamers as a downhole drilling tool. The bi-center bit is a combination reamer and pilot bit. The reamer section is disposed up-hole of the pilot bit. The pilot bit drills a pilot borehole and the eccentric reamer section follows the pilot bit reaming the pilot borehole to the desired diameter for the new borehole. A desirable aspect to the bi-center bit is its ability to pass through a small hole and then drill a hole of a larger diameter. The drill out diameter of a bi-center bit is limited by the pass-through diameter and the maximum tool diameter. The maximum drill out diameter is related to these parameters by the equation D drill out =2*D pass-through −D max tool . It would be desirable to have a downhole tool capable of drilling to a diameter significantly larger than the pass-through diameter.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a downhole tool to be disposed in a drill string up-hole of a conventional drill bit. In one embodiment, the downhole tool provides a drilling tool for drill out diameter for the borehole that is significantly larger than a pass-through diameter. In another embodiment, the downhole tool provides a stabilizer tool.  
         [0015]     An elongated body defining a longitudinal axis has first and second ends for attachment to a drill string. An internal space of the body is supplied with a drilling fluid under pressure. A reamer blade having a plurality of cutter elements is housed within the elongated body and actuated by the pressure of the drilling fluid to radially extend for deployment to a drill out diameter larger than a pass-through diameter. The reamer blade has a curved outer edge configuration that positions the cutters thereon to prevent them from engaging a casing of a well borehole upon deployment. The body has an eccentrically shaped outer surface configuration to house the reamer blade. The downhole tool can be characterized as an “expandable eccentric reamer” and is distinguishable from “concentric” reamers, which have a body with a tubular shaped outer surface configuration.  
         [0016]     In a method of drilling a well borehole, a drill bit is affixed to a drill string and an expandable eccentric reamer is provided in the drill string up-hole from the drill bit. The drill bit can be a bi-center bit having reamer blades. If so, an area of eccentricity on the eccentric reamer is aligned with the reamer blades of the bi-center bit. A second expanded eccentric reamer can be provided in the drill string up-hole from the first eccentric reamer. The first eccentric reamer deploys its cutters to a first drill out diameter and the second eccentric reamer deploys its cutters to a second drill out diameter. The first and second drill out diameters may be the same or different wherein the second drill out diameter is larger than the first drill out diameter. An area of eccentricity on the first expandable eccentric reamer is evenly spaced radially from an area of eccentricity on the second expandable eccentric reamer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a cutaway illustration of the expandable eccentric reamer with the blade in the retracted position;  
         [0018]      FIG. 2  is a cutaway illustration of the expandable eccentric reamer with the blade in the extended position;  
         [0019]      FIGS. 3A and 3B  illustrate the manner in which damage to a casing is avoided in the event of premature deployment of the blade in the extended position;  
         [0020]      FIG. 4  shows a cross-section view of an alternate embodiment wherein the blade is angled with respect to the longitudinal axis of the tool body;  
         [0021]      FIG. 5  shows an eccentric stabilizer coupled to a bi-center bit;  
         [0022]      FIG. 6  shows a cross-section view of the eccentric stabilizer in  FIG. 5 ;  
         [0023]      FIG. 7  shows a side view of a stacked arrangement of downhole tools;  
         [0024]      FIG. 8  shows a top view of the stacked arrangement of downhole tools shown in  FIG. 7 ; and  
         [0025]      FIG. 9  shows a cross-section view of the upper downhole tool of the stacked arrangement shown in  FIG. 7 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     In  FIGS. 1 and 2 , a down-hole tool  10  in accordance with the present invention is shown. Tool  10  is generally of a type known as a “reamer.” Tool  10  has a body  12  adapted for coupling along the length of a drill string (not shown) by attachment at the proximal end  14  and the distal end  16 . Ends  14  and  16  preferably have threaded couplings to mate with the threaded ends of drill pipe. Tool  10  would be placed in the drill string up-hole of conventional drill bit. The elongated body  12  defines a longitudinal axis and in relation thereto has an eccentric outer surface configuration due to a hump area  18  between ends  14  and  16 . Preferably, the eccentric shape of body  12  closely matches the shape of conventional bi-center bits and allows the tool  10  to be aligned with and run behind a conventional bi-center bit. An example of such a bi-center bit is that shown in U.S. Pat. No. 5,678,644, which is hereby incorporated by reference in its entirety. In use with a bi-center bit, the hump area  18  is aligned with the reamer blades of the bi-center bit. Tool  10  can also be used with a standard drill bit and without necessity of alignment of the eccentric shape with the drill bit. Also, the spacing between the tool  10  and the drill bit may vary. The tool  10  may, for example, be “stacked” directly above the drill bit by providing suitable mating threaded connections on the drill bit body and the tool  10  body.  
         [0027]     Housed within a cavity  20  of body  12  is a piston, which forms a reamer blade  22 . The cavity  20  is in the form of an elongated, radial slot. The length of the slot extends parallel to the longitudinal axis of tool  10  and the depth of the slot extends radially of the longitudinal axis of the tool  10 . As seen in  FIG. 1 , blade  22  carries a plurality of cutter elements  24  of conventional design, for example, polycrystalline diamond compact (“PDC”) cutters. The blade  22  is radially extended to the position shown in  FIG. 2  under the influence of the fluid pressure of drilling fluid or mud that is pumped into the interior space  26  within body  12 . It is in this manner that the backside surface of blade  22  acts as a piston. As seen in  FIG. 1 , blade  22  travels axially along retention shaft  28 . An end  30  of shaft  28  is anchored in the hump area  18  of body  12 . Blade  22  is coupled to shaft  28  by a collar that slides along shaft  28  until the stop limit member  32  at the opposite end  34  of shaft  28  is reached as shown in  FIG. 2 . The length of travel permitted by shaft  28  and limit stop member  32  determine the drill out diameter of tool  10 .  
         [0028]     The blade  22  is extended by exposure to the drilling fluid pressure in the internal space  26 . In order to assure that blade  22  is maintained in the retracted position until time of deployment, a retaining shear pin  36  is provided. Until drilling fluid pressure builds to a sufficient level to break pin  36 , blade  22  remains within body  12 . The force necessary to break pin  36  can, of course, be varied as desired. To insure proper deployment and use of blade  22 , the internal space  26  must be sealed from the external fluid pressure of the well bore. Two O-rings  38  and  40  are provided to isolate the internal space  26  from the external fluid pressure of the well bore.  
         [0029]     To maintain proper deployment of blade  22 , a reservoir  42  of grease is provided within the body of blade  22 . The reservoir is closed-off by cap  44 . The cap is in direct contact with the drilling fluid pressure, which pushes down on cap  44  and forces grease from the reservoir  42  into the region between the O-rings  38  and  40 . The grease provides lubrication of the steel surfaces to permit easier movement of the piston arm. Further, the region between the O-rings is pressurized to assist in maintaining the seal between the internal space  26  and the external space of the well bore.  
         [0030]     Retraction of blade  22  can be accomplished by reducing fluid pressure within internal space  26  and pulling the tool  10  into the casing. To this end, the edge  46  of blade  22  has a tapered portion  50 . The angle of the tapered edge provides a cam action that causes the blade to be retracted into slot  20 .  
         [0031]     Referring to  FIGS. 3A and 3B , there is illustrated the manner in which damage to a casing is avoided in the event of premature deployment of the blade  22  in the extended position. Shown in these views is the blade  22  in the non-retracted position. Each view is from above and looking down upon a cross section of the tool  10 . In  FIG. 3A , blade  22  is shown prematurely deployed while still in the casing. The cutting element  24  and non-cutting elements  48  are shown mounted on blade  22 . As seen, while the tool is in the casing, there is a gap distance “d” between the radius of curvature of the pass through diameter and the cutting element  24 . Thus, while the non-cutting elements  48  can contact the casing, the cutting element  24  cannot. When the blade  22  is fully deployed outside the casing, the radius of curvature of the larger drill out diameter provides for the cutting element  24  and the non-cutting elements  48  to be in contact with the formation. As seen the thickness “t” of the blade  22  and the radius of curvature “r” of the outer end surface of the blade  22  are selected to match the intended drill out diameter. Because the casing diameter is smaller than the intended drill out diameter, the blade has contact points at its edges where non-cutting elements  48  are located. The non-cutting elements  48  contact the casing and prevent cutting element  24  from contacting the casing.  
         [0032]     In  FIG. 4 , an alternative embodiment to tool  10  is shown. In this embodiment, tool  100  has a blade  102  that is angled or canted with respect to longitudinal axis  104  at an angle “a”. The angle “a” is preferably about 10°. Tool  100  has a body  106  that is adapted for coupling along the length of a drill string by attachment at the proximal end  108  and the distal end  110 . Ends  108  and  110  preferably have threaded couplings to mate with the threaded ends of drill pipe. Tool  100  would be placed in the drill string up-hole of conventional drill bit. The elongated body  106  defines the longitudinal axis  104  and in relation thereto has an eccentric outer surface configuration due to a hump area  112  between ends  108  and  110 . Preferably, the eccentric shape of body  106  closely matches the shape of conventional bi-center bits and allows the tool  100  to be aligned with and run behind a conventional bi-center bit.  
         [0033]     Blade  102  is housed within a cavity  114  formed in body  106 . The cavity  114  is in the form of an elongated, radial slot. The length of the slot extends parallel to the longitudinal axis of tool  100  and the depth of the slot extends radially of the longitudinal axis of the tool  100 . As seen in  FIG. 4 , blade  102  carries a plurality of cutter elements  116  of conventional design, for example, polycrystalline diamond compact (“PDC”) cutters. The blade  102  is radially extended from cavity  114  as shown in  FIG. 4  under the influence of the fluid pressure of drilling fluid or mud that is pumped into the interior space behind blade  102 . It is in this manner that the backside surface of blade  102  acts as a piston. As seen in  FIG. 4 , blade  102  travels axially along a pair of retention shafts  118  and  120 . An end  122  of shaft  118  is anchored in the hump area  112  of body  106 ; and an end  124  of shaft  120  is anchored in the hump area  112 . Blade  102  is coupled to shafts  118  and  120  by collars  126  and  128  that slide along shafts  118  and  120 , respectively, until the stop limit members  130  and  132  at the opposite ends of shafts  118  and  120  are reached. The length of travel permitted by shafts  118  and  120  together with limit stop members  130  and  132  determine the drill out diameter of tool  100 . Retraction of blade  102  can be accomplished by reducing fluid pressure within the internal space of body  106  and pulling the tool  100  into the casing. To this end, the edge  134  of blade  102  is tapered. The angle of the tapered edge provides a cam action that causes the blade to be retracted into the slot.  
         [0034]     In a method of drilling a well borehole, tool  10  or tool  100  can be provided up-hole of a drill bit. In the case of a bi-center bit, its reamer blades can produce a large cutting force. The blade of the tool extends from the opposite side and serves to offset the bi-center reamer blades cutting force. The opposing forces assist in stabilizing the bi-center reamer and makes for a more accurate well borehole size. In order to further increase hole size and stability, in a method of drilling, a pair of tools  10  or  100  can be coupled into the drill string up-hole from a drill bit. When used behind a bi-center bit, a first of the tools  10  or  100  is aligned with the bi-center bit as described. The second tool  10  or  100  will have the eccentricity of the body extending in the opposite direction. The tools  10  or  100  would drill to the same drill out diameter and serve to act as a two-bladed stabilizer. As an alternative drilling configuration, the stacked tools  10  or  100  could be sized to drill to a different diameter. In that situation, the distal tool nearer the drill bit would have a smaller drill out diameter than the proximal tool, which would extend to the final drill out diameter. If multiple tools are used, preferably a standard drill bit rather than a bi-center bit would be employed. Also, if multiple tools are used, the hump area on each would be evenly spaced radially from one another. That is, if two tools were used, the hump areas on them would be spaced apart  180 °. If three tools were used, the hump areas on them would be spaced apart  60 °.  
         [0035]     In  FIG. 5 , there is illustrated an eccentric stabilizer  200  coupled to a bi-center bit  202 . As shown, a stabilizer pad  204 , which is a non-cutting surface, is shown in the extended position. Pad  204  may be a smooth surface comprising carbide blocks with hard-facing to permit it to slide along the formation wall. The body  206  of stabilizer  200  has an eccentric outer configuration provided by a hump area  208 . The proximal end  210  is adapted to be connected to a drill string. The bi-center bit is coupled to the distal end  212 .  FIG. 6  shows a cross-section of stabilizer  200 . As seen, the stabilizer  200  is similar to tool  100  of  FIG. 4 . However, rather than having cutting elements, blade  206  has pad  204 .  
         [0036]      FIG. 7  shows a stacked arrangement of downhole tools  300  and  400 . Tool  300  is in accordance with either tool  10  ( FIGS. 1 and 2 ) or tool  100  ( FIG. 4 ). Tool  400 , however, is of a different configuration. The body of tool  400  has an eccentric-shaped outer surface configuration. But, the blade  402  with cutting elements  404  extends from the hump area  406  of body  408 . When two “eccentric” tools are stacked, the humps must be aligned in order for the assembly to be able to trip into the hole.  FIG. 8  is a top view of the stacked arrangement of tools  300  and  400  with the blades of the tools in the extended position for drilling.  
         [0037]      FIG. 9  shows tool  400  in cross-section. Tool  400  has a similar internal mechanical construction to tool  100 . Tool  400  has blade  402  angled or canted with respect to the longitudinal axis of the tool body. The body  408  is adapted for coupling along the length of a drill string by attachment at the proximal end  410 . The distal end  412  is configured for coupling to tool  300  either directly or indirectly through a short section of drill pipe. Blade  402  is moved by hydraulic pressure to extend from hump area  406  of body  408 . The beveled surface  414  engages the casing to urge blade  402  into the retracted position when the tool is being retrieved. Shafts  416  and  418  are anchored at one end within body  408 . Blade  402  slides along shafts  416  and  418  as it is being extended and retracted.  
         [0038]     A stacked arrangement of tools can comprise a combination of a stabilizer in accordance with tool  200  and a reamer tool in accordance with tool  10 . Thus, a method of drilling a wellbore may be implemented using a combination of a stabilizer, a reamer tool, and a drill bit. It is to be understood that, as in the stacked combination shown in  FIG. 7 , when two “eccentric” tools are stacked, the humps must be aligned in order for the assembly to be able to trip into the hole. Thus, the stabilizer and the reamer tool will necessarily have opposing eccentric shaped bodies.  
         [0039]     The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and it will appreciated by those skilled in the art, that various modifications and may be made in the illustrated embodiments. While the present invention has been described in connection with presently preferred embodiments, it is to be understood that the illustrated embodiments are not intended to be limiting of the invention to those embodiments. Rather, the scope of the invention contemplates all alternatives, modifications, and equivalents that are included within the scope of the appended claims.

Summary:
An expandable eccentric reamer for placement in a drill string up-hole of a conventional drill bit. The reamer blade is actuated by drilling fluid pressure to radially extend to a drill out diameter greater than a pass-through diameter. The reamer body is shaped to have an eccentric outer surface configuration to accommodate the reamer blade therein. The reamer blade acts as a piston arm in response to drilling fluid pressure and moves along a shaft anchored in a hump region that forms an eccentricity in the outer surface configuration of the body. The reamer blade has an outer edge configuration that positions the cutters thereon to prevent them from engaging a casing of a well borehole upon deployment.