US20090272524A1

US20090272524A1 - Method and apparatus for cleaning internal surfaces of downhole casing strings and other tubular goods

Info

Publication number: US20090272524A1
Application number: US12/387,520
Authority: US
Inventors: Rickey C. Voth
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-05-02
Filing date: 2009-05-04
Publication date: 2009-11-05

Abstract

A downhole cleaning assembly and method of cleaning a tubular. Generally, the downhole assembly is connected to a work string concentrically located within a casing string. In one embodiment, the downhole assembly comprises a tool body operatively connected to a work string. At least one pad member is connected to the tool body, with the pad member having cutting technology, such as, for example, hardened elements or “inserts,” (commonly used in connection with drill bits) along certain outer peripheral surfaces of the pad member. Such cutting technology includes, but is not necessarily limited to, Polycrystalline Diamond Compact (PDC) inserts, tungsten carbide inserts or diamond bit elements commonly used in connection with drill bit technology.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

THIS APPLICATION CLAIMS THE BENEFIT OF, AND PRIORITY FROM, U.S. PROVISIONAL PATENT APPLICATION SER. NO. 61/126,333 FILED MAY 2, 2008, SER. NO. 61/128,724 FILED MAY 23, 2008, AND SER. NO. 61/134,853 FILED JUL. 14, 2008, WHICH ARE INCORPORATED BY REFERENCE HEREIN.

STATEMENTS AS TO THE RIGHTS TO THE INVENTION MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

NONE

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention pertains to a method and apparatus for removing debris from the inner surfaces of well bores. More particularly, the present invention pertains to a method and apparatus for mechanically removing dried cement and other hardened debris from internal surfaces of casing and/or other tubular goods. More particularly still, the present invention pertains to a method and apparatus for cleaning the inner surfaces of casing strings and/or other tubular goods using cutting technology, such as, for example, hardened elements or inserts.
2. Brief Description of the Prior Art
It is frequently desirable to remove cement and/or other debris from internal surfaces of oil or gas wells. In many instances, it is especially beneficial to remove dried cement and/or other debris from internal surfaces of casing strings and other tubular goods installed in well bores.
After a well has been drilled to a desired depth, large diameter pipe called casing is typically installed in the well and cemented in place. Such casing provides structural integrity to the well bore, and isolates downhole formations from one another. After a sufficient length of casing is installed into a bore hole, cement is typically pumped down the internal bore of said casing, out the bottom of the casing, and up the annular space existing between the outer surface of the casing and the inner surface of the bore hole. When the cement hardens, a cement sheath is formed around the outer surface of the casing.
During cementing operations, a portion of the cement that is pumped down the inner bore of the casing often adheres or sticks to the inner surfaces of the casing. Additionally, drilling mud (typically containing suspended solids and/or additives) can likewise adhere or stick to the inner surfaces of the casing or other tubular goods. Such cement and other debris can negatively impact the ultimate productivity of a well. Therefore, it is frequently beneficial to clean the inner surfaces of the casing string to remove debris (including, without limitation, excess or residual cement), especially in advance of well completion operations.
By way of illustration, but not limitation, it is typically very important to remove cement and/or other debris (such as hardened drilling mud or additives) from internal surfaces of casing prior to engaging in well completion activities. In such cases, drilling mud is totally removed from a well bore, and replaced with brine or other “clear” completion fluid that is less damaging to downhole formations. It is generally very desirable to remove cement and/or other debris from the inner surfaces of the casing before such drilling mud is totally replaced with completion fluid(s).
Although different methods have been employed for this purpose, mechanical cleaning devices have historically been used to remove such cement and other debris from internal surfaces of well bores. For this reason, after casing is cemented in a well, mechanical scraping devices (commonly referred to as “scrapers”) are often conveyed into such well (typically on drill pipe or other tubular workstring) and used to mechanically scrape or abrade the inner surfaces of the casing in order to remove such cement and/or other debris. However, existing scrapers and related devices are inefficient, susceptible to wear, and have provided less than optimal results.
In many cases, existing scrapers fail to fully remove cement and other debris from internal surfaces of casing and other tubular goods. Frequently, existing scrapers can “ride over” cement and other hardened debris adhering to the inner surfaces of the casing and/or other tubular goods, and will fail to break up such cement or other debris for ultimate removal from the well bore. Further, when the amount of cement or other hardened debris on the internal surfaces of casing is excessive, existing scrapers have been known to fail and/or break apart downhole. Such failure can result in portions of the scraper tool being lost in the well, which can negatively impact subsequent operations in the well and/or productivity of such well. In many cases, the amount of cement or other debris present on the internal surfaces of casing is not known when the scrapers are initially being run into a well. While conventional scrapers may be sufficient to remove relatively small amounts of debris from casing, there is great risk that such conventional scrapers can fail or break apart when confronted with greater amounts of cement or other debris.
Thus it is an object of the present invention to efficiently and effectively clean the inner surfaces of casing strings and/or other tubular goods using mechanical scrapers or other devices employing cutting technology, such as, for example, hardened elements or inserts.

SUMMARY OF THE PRESENT INVENTION

The present invention comprises a method and apparatus for cleaning the internal surfaces of well bores, casing strings and/or other tubular goods using mechanical cleaning assemblies or other devices employing cutting technology, such as, for example, hardened elements or “inserts,” (commonly used in connection with drill bits) disposed along certain outer peripheral surfaces of said cleaning assemblies or other devices. Such cutting technology includes, but is not necessarily limited to, Polycrystalline Diamond Compact (PDC) inserts, tungsten carbide inserts or diamond bit elements commonly used in connection with drill bit technology.
The apparatus of the present invention generally comprises a downhole cleaning assembly. Although said downhole scraper assembly can have many different shapes, sizes and configurations, the present invention as described herein has a general configuration following a conventional “M&M”-type scraper design that is well known to those having skill in the art. However, it is to be observed that the present invention can also be used in connection with other cleaning assemblies, mechanical scrapers and/or downhole tools embodying many different configurations.
In a preferred embodiment, said downhole cleaning assembly is adapted to be connected to a tubular work string and can be concentrically received—and manipulated—within a well bore (especially any casing or other tubular goods installed within such well bore). Such downhole cleaning assembly generally comprises a central mandrel operatively connected to such tubular work string. A central flow bore extends longitudinally through said mandrel, and permits fluid communication with the central bore of said tubular work string.
At least one recess is disposed along the outer peripheral surface of said mandrel, with at least one pad member received within each such at least one recess. In said preferred embodiment, at least one biasing member is operatively positioned between the mandrel and each of said at least one pad members. Said biasing member urges said at least one pad member radially outward relative to said mandrel. When said downhole cleaning apparatus is concentrically received within a well bore, said biasing member beneficially urges said at least one pad member against the inner surfaces of such well bore.
In said preferred embodiment, said pad members have a substantially arcuate shape and are disposed at different points along the length of said mandrel. Further, said pad members are disposed about the periphery of said mandrel, and are phased or staggered circumferentially relative to one another. As such, said pad members have an effective coverage area of 360 degrees around the outer periphery of said mandrel, while forming at least one flow path passing between said pad members. Said flow path permits fluid to flow along the length of the cleaning apparatus, even when said scraper pad members are mechanically contacting the inner surface of a casing string.
In the preferred embodiment, drill bit cutting elements are disposed on or in connection with said pad members. Such bit technology improves the performance of the cleaning assembly in removing dried cement, drilling mud and/or other debris from the internal surfaces of well casing and/or other tubular goods.
Also disclosed herein is a method of cleaning the internal surfaces of tubular goods. The method comprises lowering a work string concentrically within the casing string or other tubular goods to be cleaned. The work string will have provided therewith a downhole cleaning assembly operatively associated with the work string. Pad members of the cleaning assembly are biased against the inner surface of the casing string, thereby resulting in constant pressure of said pad members against the internal casing wall. The method provides for cleaning the inner diameter of the casing string as the downhole cleaning assembly is lowered, rotated and/or reciprocated on such work string. The method further comprises circulating a drilling fluid through the inner bore of the work string, out the bottom of the work string or other bottom hole assembly, and around the outer surface of such bottom hole assembly and work string. The work string may be stationary or rotating during circulation.
An advantage of the present invention includes the ability to thoroughly clean the internal surfaces of casing and other tubular goods of a course material such as cement and other materials. Another advantage is a design that permits easy removal, replacement and/or interchangeability of pad members (and related cutting technology) including, without limitation, at remote locations such as on drilling rigs and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, the drawings show certain preferred embodiments. It is understood, however, that the invention is not limited to the specific methods and devices disclosed.

FIG. 1 depicts a side perspective view of a prior art cleaning assembly.

FIG. 2 depicts a side sectional view of the prior art cleaning assembly depicted in FIG. 1.

FIG. 3 depicts a side perspective view of a prior art pad member of the prior art cleaning assembly depicted in FIGS. 1 and 2.

FIG. 4 depicts a side perspective view of a pad member embodiment of the present invention.

FIG. 5 depicts an overhead sectional view of the cleaning assembly of the present invention along line 5-5 of FIG. 6.

FIG. 6 depicts a side sectional view of the cleaning assembly of the present invention concentrically installed within a casing string.

FIG. 7 depicts a frontal view of a pad member of the present invention.

FIG. 8 depicts a side perspective view of an alternative embodiment of a pad member of the present invention.

FIG. 9 depicts a side perspective view of the alternative embodiment of the pad member of the present invention depicted in FIG. 8.

FIG. 10 depicts a side perspective view of an alternative embodiment of a pad member of the present invention.

FIG. 11 depicts a frontal view of the alternative embodiment of the pad member of the present invention depicted in FIG. 10.

FIG. 12 depicts an overhead view of the alternative embodiment of the pad member of the present invention depicted in FIGS. 10 and 11.

FIG. 13 depicts an exploded view of the pad member of the present invention depicted in FIG. 4.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 depicts a perspective view of conventional prior art cleaning assembly 10. Said prior art cleaning assembly 10 has the general configuration of an “M&M-type” scraper that is well known in the art. Cleaning assembly 10 is adapted to be connected to a tubular work string and can be concentrically received—and manipulated—within a well bore (especially any casing or other tubular goods installed within such well bore). Cleaning assembly 10 generally comprises a central mandrel 11. Upper mandrel 30 connects to the upper portion of central mandrel 11, while lower mandrel 20 connects to the lower portion of central mandrel 11. Cleaning assembly 10 can be operatively connected to a tubular work string via thread profiles (not shown in FIG. 1) on upper mandrel 30 and lower mandrel 20. A plurality of pad members 40 is disposed on the outer peripheral surface of central mandrel 11.
FIG. 2 depicts a side sectional view of prior art cleaning assembly 10 depicted in FIG. 1. Prior art cleaning assembly 10 includes central mandrel 11 having an inner longitudinal bore 14 and outer surface including external thread profile 13 at the upper portion of central mandrel 11. Upper mandrel 30 has central longitudinal bore 33, as well as internal thread profile 31 defining extension lower lip 32. Said extension lower lip 32 generally defines a substantially cylindrical sleeve near the bottom of upper mandrel 30. External thread profile 13 of central mandrel 11 is adapted to be received within, and threadably connected to, internal thread profile 31 of upper mandrel 30. When upper mandrel 30 is connected to central mandrel 11, longitudinal bore 33 of upper mandrel 30 becomes aligned (and in fluid communication with) longitudinal bore 14 of central mandrel 11. Upper mandrel 30 also has an external thread profile (not shown) that may be attached to a work string (not shown) such as, for example, drill pipe, snubbing pipe, coiled tubing and/or production tubing; the longitudinal through bore of said work string is aligned, and in fluid communication with, bores 33 and 14. Although not depicted in FIG. 2, lower mandrel 20 may be attached to central mandrel 11 in similar fashion, and may, in turn, be connected to and in fluid communication with another downhole tool such as a bit.
Central mandrel 11 has a plurality of recesses formed along its outer peripheral surface, with FIG. 2 depicting recess 15 and recess 16. Central member 11 may also include other recesses that will be described later in the application. Recess 15 defines lower retaining lip 17, while recess 16 defines lower retaining lip 18. Pad members 40 are operatively positioned within recesses 15 and 16.
Prior art pad members 40 are operatively associated with biasing means 12 (typically helical springs) for biasing said pad members 40 radially outwardly relative to central mandrel 11. When cleaning apparatus 10 is concentrically inserted within casing, spring loaded pad members 40 will allow for substantially constant pressure of the external surfaces of pad member 40 against the casing wall at all times. Additional biasing means 12 may be employed, for instance, when additional force is required to adequately urge the pads radially outward relative to central mandrel 11.
In most cases, prior art pad members 40 are disposed at different points along the length of central mandrel 40 (as depicted in FIG. 1). Further, said prior art pad members 40 are typically phased or staggered circumferentially relative to one another. As such, said pad members 40 have an effective coverage area of 360 degrees around the outer periphery of cleaning apparatus 10, while forming at least one flow path passing between said pad members 40. Said flow path permits fluid to flow along the length of cleaning apparatus 10, even when pad members 40 are mechanically contacting or engaged against the inner surface of a casing string.
FIG. 3 depicts a side perspective view of a prior art pad member 40. Although the exact design and configuration of pad member 40 may vary between tools and applications, prior art pads such as pad member 40 typically have a substantially arcuate shape. Said pad member 40 has body section 41, as well as upper lip member 42 and lower lip member 43. Tapered section 44 extends between upper lip member 42 and body section 41, while tapered section 45 extends between lower lip member 43 and body section 41. In many cases, pad member 40 will have a plurality of recessed channels 47 extending into body section 41, thereby defining a plurality of cutting ridges 47 along the outer surface of body section 41.
Referring back to FIG. 2, it is to be observed that pad members 40 are operatively positioned within recesses 15 and 16. Lower lip member 43 of pad member 40 is inserted behind lower retaining lip 17 of recess 15 (or, in the case of recess 16, behind lower retaining lip 18). When upper mandrel 30 is installed, lower extension lip 32 of upper mandrel 30 fits over upper lip members 42 of pad members 40. In this manner, pad members 40 are secured to central mandrel 11. Pad members 40 can be easily removed, replaced and/or interchanged, even when cleaning apparatus 10 is at a remote location, such as on a drilling rig or the like.
Central mandrel 11 of cleaning assembly 10 typically has a plurality of recesses (such as recesses 15 and 16) about its outer peripheral surface for placement of additional pad members. With a staggered configuration of multiple pad members 40 about the body of central mandrel 11 (such as depicted in FIG. 1), a 360 degree circumference about the inner diameter of the casing may be cleaned, while still permitting fluid to flow along the length of cleaning assembly 10 via flow channels formed between pad members 40.
FIG. 4 depicts a side perspective view of a pad member embodiment 50 of the present invention having PDC inserts 60. Although the exact design and configuration of pad member embodiment 50 may vary between tools and applications, pad member embodiment 50 is depicted as having substantially similar dimensions as prior art pad member 40. As such, pad member embodiment 50 has a substantially arcuate shape. Said pad member embodiment 50 further has body section 51, as well as upper lip member 52 and lower lip member 53. Tapered section 54 extends between upper lip member 52 and body section 51, while tapered section 55 extends between lower lip member 53 and body section 51. Pad member embodiment 50 further has a plurality of recessed channels 57 extending into body section 51, thereby defining a plurality of cutting ridges 57 along the outer surface of body section 51. Pad member 50 can be installed on a cleaning apparatus (such as cleaning apparatus 10) in the manner described above for prior art pad member 40. In this manner, pad member embodiment 50 can be easily removed, replaced and/or interchanged, even at remote locations, such as on a drilling rig or the like.
FIG. 13 depicts an exploded view of the pad member embodiment 50 of the present invention depicted in FIG. 4. In the preferred embodiment, a plurality of cylindrical bores 58 is disposed within body section 51 of pad member 50. Substantially cylindrical PDC inserts 60, sized to match cylindrical bores 58, are received within bores 58 in pad member 50. Referring back to FIG. 4, in the preferred embodiment of the present invention said PDC inserts 60 do not extend beyond the outer edge of cutting ridges 57 of pad member 50 so as to avoid damage to a casing wall. However, it is to be observed that the depth and orientation of said PDC inserts 60 may be changed, as desired, to meet particular well conditions or applications.
FIG. 6 depicts a side sectional view of the cleaning assembly 110 of the present invention having pad member embodiment 50 concentrically disposed within a casing string 170. Cleaning assembly 110 includes central mandrel 111 having an inner longitudinal bore 114 and outer surface including external thread profile 113 at the upper portion of central mandrel 111. Upper mandrel 130 has central longitudinal bore 133, as well as internal thread profile 131 defining extension lower lip 132. Said lower lip extension 132 generally defines a substantially cylindrical sleeve near the bottom of upper mandrel 130. External thread profile 113 of central mandrel 111 is adapted to be received within, and threadably connected to, internal thread profile 131 of upper mandrel 130. When upper mandrel 130 is connected to central mandrel 111, longitudinal bore 133 of upper mandrel 130 becomes aligned (and in fluid communication with) longitudinal bore 114 of central mandrel 111. Upper mandrel 130 also has an external thread profile (not shown) that may be attached to a work string (not shown) such as, for example, drill pipe, snubbing pipe, coiled tubing and/or production tubing; the longitudinal through bore of said work string is aligned, and in fluid communication with, bores 133 and 114. Although not depicted in FIG. 6, lower mandrel 120 may be attached to central mandrel 111 in similar fashion, and may, in turn, be connected to and in fluid communication with another downhole tool such as a bit.
Central mandrel 111 has a plurality of recesses formed along its outer peripheral surface (including recesses 115 and 116) in much the same manner as central mandrel 11 of prior art cleaning assembly 10 (depicted in FIG. 2). It is to be observed that pad member embodiments 50 are affixed to cleaning apparatus 110 in much the same manner that pad members 40 are affixed to prior art cleaning apparatus 10, as more fully described above. Further, pad member embodiments 50 are operatively associated with biasing means 112 (typically helical springs) for biasing said pad member embodiments 50 radially outwardly relative to central mandrel 111. Said pad member embodiments 50 can be quickly and easily removed, replaced and/or interchanged.
FIG. 5 depicts an overhead sectional view of cleaning assembly 110 of the present invention along line 5-5 of FIG. 6. Pad member embodiments 50 are phased or staggered circumferentially relative to one another. As such, when combined with other pad member embodiments disposed at other positions along the length of central mandrel 111, said pad member embodiments 50 have an effective coverage area of 360 degrees around the outer periphery of central mandrel 111 of cleaning apparatus 110, while forming at least one flow path passing between said pad member embodiments 50. Said flow path permits fluid to flow along the length of cleaning apparatus 110, even when pad members 50 are mechanically contacting or engaged against the inner surface of a casing string 170.
When cleaning apparatus 110 is concentrically inserted within casing 170, spring loaded pad member embodiments 50 will allow for substantially constant pressure of the external surfaces of pad member embodiments 50 against the internal wall surfaces of casing 170. Additional biasing means 112 may be employed, for instance, when additional force is required to adequately urge the pads radially outward relative to central mandrel 111.
Still referring to FIG. 5, as cleaning apparatus 110 is rotated downhole (via a work string), PDC inserts 60 contact debris 160 present on the inner surface of casing 170. It is to be observed that while debris 160 can comprise any number of different contaminants, such debris will typically comprise cement, dried drilling mud and/or other materials adhered to the inner walls of casing 170. Said PDC inserts 60 remove debris 160 from the casing wall. Further, said PDC inserts act to break up or cut such debris 160 into smaller pieces, thereby resulting in removal of such debris from the casing wall. Once removed, such debris 160 can be circulated out of the well bore using drilling fluid.
FIG. 7 depicts a frontal view of a pad member embodiment 50 of the present invention. In the preferred embodiment of the present invention, from the perspective illustrated in FIG. 7, PDC inserts 60 are disposed at or near the left edge of pad member embodiment 50. It is the custom in the oil and gas industry to utilize threaded connections having “right hand” threads. As such, tubular work strings are generally rotated in a clockwise direction, as counter clockwise rotation can result in unintentional downhole separation of tubular members from one another. It is therefore beneficial to position PDC inserts 60 at or near the left edge of pad member embodiment 50, which will be the leading edge when cleaning assembly 110 is rotated in a clockwise direction, in order to be the first portion of pad member embodiment 50 to contact debris 160.
FIG. 8 depicts a side perspective view of an alternative embodiment of a pad member 80 of the present invention, while FIG. 9 depicts a side perspective view of alternative embodiment of the pad member 80 of the present invention depicted in FIG. 8. In such embodiment, PDC inserts 60 are disposed along the sides and upper surfaces of the body section of pad member embodiment 80. In this embodiment, PDC inserts 60 are positioned at the leading edges of pad member embodiment 80 when cleaning apparatus 110 is rotated or reciprocated within a well bore. Although such rotation will likely be primarily in the clockwise direction as is the custom during oil and gas operations, it is to observed that rotation may be in the counter-clockwise direction in certain instances.
FIG. 10 depicts a side perspective view of an alternative embodiment of a pad member 90 of the present invention, while FIG. 11 depicts a frontal view of pad member 90 of the present invention depicted in FIG. 10. FIG. 12 depicts an overhead view of pad member 90 of the present invention depicted in FIGS. 10 and 11. Pad member embodiment 90 includes tungsten carbide inserts 95. Although such tungsten carbide inserts can be disposed at multiple different locations on pad member embodiment 90, in the embodiment depicted in FIGS. 10 through 12, said inserts 95 are disposed along the “left” edge of pad member embodiment 90, so that such inserts 95 are on the “leading” edge when a cleaning apparatus (such as, for example, cleaning apparatus 110) is rotated in a clockwise direction. In the preferred embodiment, pad member 90 has machined opening(s) or recess(s) formed at desired location(s) on the body of said pad member 90. Tungsten carbide inserts 95 are received within said opening(s) or recess(es).
Although the apparatus set forth herein is described primarily in connection with scraper tools having removable pad members, it is to be observed that drill bit cutting technology (such as, for example, PDC or tungsten carbide inserts, or diamond bit elements) can be incorporated on any number of different tools in any number of configurations. By way of example, but not limitation, such drill bit cutting technology can be incorporated on the outer surfaces of conventional stabilizers, well bore cleanout tools, mills, stabilizer sleeves, mill sleeves, stabilizer blades and/or other devices, or particular elements thereof, that can be inserted into a well bore. Further, such tools incorporating drill bit cutting technology can be used to mechanically clean the inner surfaces of virtually any tubular goods; such uses are not limited solely to cleaning cement from the inner surfaces of casing.
It is to be further observed that the conventional scraper described herein is just one type of existing scraper embodiment that could be used in accordance with the present invention; other scraper embodiments can also be used.
The above-described invention has a number of particular features that should preferably be employed in combination, although each is useful separately without departure from the scope of the invention. While the preferred embodiment of the present invention is shown and described herein, it will be understood that the invention may be embodied otherwise than herein specifically illustrated or described, and that certain changes in form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention.

Claims

1. A pad member adapted to be received on a scraper tool comprising at least one cutting element disposed on said pad member.

2. The pad member of claim 1, wherein said at least one cutting element comprises at least one polycrystalline diamond compact insert.

3. The pad member of claim 1, wherein said at least one cutting element comprises at least one tungsten carbide insert.

4. The pad member of claim 2, wherein said pad member further comprises:

a. a body section having at least one bore disposed in said body section; and

b. a polycrystalline diamond compact insert received within each of said at least one bore.

5. The pad member of claim 3, wherein said pad member further comprises:

a. a body section having at least one recess in said body section; and

b. a tungsten carbide insert received within each of said at least one recess.

6. An apparatus for cleaning cement and hardened debris from the inner surface of casing and other tubular goods comprising:

a. a body having an outer peripheral surface;

b. at least one pad member disposed along the outer peripheral surface of said body; and

c. at least one cutting element disposed on said pad member.

7. The apparatus of claim 6, wherein said at least one cutting element comprises at least one polycrystalline diamond compact insert.

8. The apparatus of claim 6, wherein said at least one cutting element comprises at least one tungsten carbide insert.

9. The apparatus of claim 7, wherein said pad member further comprises:

a. a body section having at least one bore disposed in said body section; and

10. The apparatus of claim 8, wherein said pad member further comprises:

a. a body section having at least one recess in said body section; and

b. a tungsten carbide insert received within each of said at least one recess.

11. A downhole assembly for use in a well bore on a work string concentrically located within a casing string, said downhold assembly comprising:

a. a mandrel operatively connected to said work string, said mandrel having a longitudinal through-bore and a recess along its outer peripheral surface;

b. pad member received within said recess, said pad member having an opening formed therein;

c. a cutting element, operatively positioned within said opening of said pad member; and

d. a biasing member, operatively positioned between said mandrel and said pad member, adapted for biasing said cutting element against the inner diameter of said well bore.

12. The downhole assembly of claim 10, wherein said at least one cutting element comprises at least one polycrystalline diamond compact insert.

13. The downhole assembly of claim 10, wherein said at least one cutting element comprises at least one tungsten carbide insert.