Patent Application
20100276145
1. Field of the Invention
Embodiments disclosed herein relate generally to a downhole mill assembly.
More particularly, the embodiments disclosed herein relate to a downhole mill assembly and a method of milling using diamond enhanced elements.
2. Background Art
When an existing cased oil well becomes unproductive, the well may be sidetracked in order to develop multiple production zones or redirect exploration away from an unproductive zone. Generally, sidetracking involves the creation of a window in the well casing by milling the steel casing in an area either near the bottom or within a serviceable portion of the well. The milling operation is then followed by the directional drilling of rock formation through the newly formed casing window. Sidetracking enables the development of a new borehole directionally oriented toward productive hydrocarbon sites without moving the rig, platform superstructure, or other above ground hole boring equipment, and also takes advantage of a common portion of the existing casing and cementing in the original borehole.
Thus, sidetracking is often preferred because drilling, casing, and cementing the borehole are avoided. As mentioned above, this drilling procedure is generally accomplished by either milling out an entire section of casing followed by drilling through the side of the now exposed borehole, or by milling through the side of the casing with a mill that is guided by a wedge or “whipstock” component.
The casing window is generally created with a combination of mills mounted on a shaft or mandrel at the bottom end of a drill string and wedging between the casing and a whipstock, which is generally set in the hole in combination with the first milling run. The peripheral surface of mills is generally covered with abrasive or cutting inserts made of hard material such as sintered tungsten carbide compounds brazed on a steel shaft. The hardness of the whipstock is generally designed so that minimum wear will be generated by the rotation of mills peripheral surface onto the whipstock face while the assembly is pushed and rotated against the casing wall under deflecting action of the whipstock. The milling action generally results from unbalanced pressures between the mill(s) and the whipstock on one hand and the mill(s) and the casing wall on the other hand.
U.S. Pat. No. 4,266,621, which is herein incorporated by reference, describes a milling tool for elongating a laterally directed window in a well casing. The disclosed system requires three trips into the well, beginning with the creation of an initial window in the borehole casing, the extension of the initial window within a particular cutting tool, and the elongation and further extension of the window by employing an assembly with multiple mills. While the window mill is aggressive in opening a window in the casing, the number of trips, typically three, to accomplish the task is expensive and time consuming.
By integrating a whipstock into the milling operation and directionally orienting the milling operation to a more confined area of well casing, the number of trips required to effectively mill a window in a well casing has been decreased. A whipstock having an acutely angled ramp is first anchored inside a well and properly oriented to direct a drill string in the appropriate direction. A second trip is required to actually begin the milling operations. Newer methods integrate the whipstock with the milling assembly to provide a combination whipstock and staged sidetrack mill, allowing for casing windows to be milled in one trip. The milling assembly is connected at its leading tool to the top portion of the whipstock by a bolt, which upon application of sufficient pressure, may be sheared off to free the milling assembly. The cutting tool employed to mill through the metal casing of the borehole has conventionally incorporated cutters that include at least one material layer, such as preformed or crushed tungsten carbide, designed to mill pipe casing. Several such one-trip milling systems include those described in U.S. Pat. Nos. 5,771,972, 6,102,123, 6,648,068, which are herein incorporated by reference in their entirety.
Conventional milling systems are, however, unable to mill windows in chrome casings, casings which are steadily increasing in number of wells due to the number of wells in severe drilling environments, such as severely corrosive environments, deep wells, cold environments, and sea bottoms, that are more commonly drilled due to exhaustion of easily drillable wells. The presence of and exposure to corrosive fluid, necessitates the use of corrosion resistant alloys (CRA), frequently duplex chrome, in the downhole components including casings. Other typically corrosion and/or erosion resistant CRA-type materials include: (1) stainless steel including conventional austenitic, martensitic, precipitation hardened, duplex, and ferritic stainless steels; (2) precipitation hardened and solid solution nickel-based alloys and nickel copper alloys; and (3) cobalt-based, titanium, and zirconium alloys. Although desired corrosion resistance can be obtained, for example, using a 25% duplex chrome, the material proves to be difficult in handling, specifically, in cutting and machining. The material tends to be abrasive to cutting tools, as well as leading to work hardening, smearing, galling, and welding. The difficulties associated with milling through a chrome casing leaves many mature wells neighbored by significant quantities of oil otherwise unreachable without the cost of either pulling the chrome casings and recompleting the existing well or forming a new well. The ability to sidetrack a well would not only allow for a multilateral well, but would also allow for sidetracking of a stuck drill string.
Furthermore, as the mill cutting structure meets the casing wall, the cutting structure typically encounters severe vibrations that frequently lead to cracks in the cutters. Such cracks may lead to failure of the cutters, reducing the life of the mill and likely preventing the mill from being used to drill through the sidetracked, secondary borehole (through the earth formation) after the window is milled.
However, further improvements in milling systems would allow for increased longevity of mills in an operational environment that frequently leads to failure of mills by cracking of cutters.
In one aspect, embodiments disclosed herein relate to a mill for milling a window through metal casing in a well bore that includes a body having a plurality of blades; a plurality of cylindrically bodied cutting elements on said blades; and a plurality of diamond enhanced elements having a non-planar diamond working surface on said blades; wherein said cutting elements initiate cutting into said casing and mill said window into said well bore.
In another embodiment, embodiments disclosed herein relate to a mill for milling a window through metal casing in a well bore that includes a body having a plurality of blades; a plurality of diamond enhanced elements having a non-planar diamond working surface on said blades; wherein said diamond enhanced elements initiate cutting into said casing and mill said window into said well bore.
In yet another aspect, embodiments disclosed herein relate to a method of milling a window in a casing in a wellbore that includes rotating a mill having a body with a plurality of blades, and a plurality of diamond enhanced elements having a non-planar diamond working surface on said blades; cutting a window in the metal casing with the mill; and passing the mill through the window.
In yet another aspect, embodiments disclosed herein relate to a mill for milling a window through metal casing in a well bore that includes a body having a plurality of blades; and a plurality of elements have a non-planar, conical working surface; wherein said elements initiate cutting into said casing and mill said window into said well bore.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
Embodiments of the present disclosure relate to a milling assembly having at least one diamond enhanced or conical shaped element (located on a mill). Such mill may be used to mill a window in well casing and/or liner or open hole completion wells and, optionally, subsequently drill rock formation without the sequential removal of the milling assembly and replacement with a drilling assembly. As used herein, “casing” refers to steel pipe placed in a wellbore from approximately the ground surface, and “liner” refers to steel pipe placed in a wellbore and suspended from some level (referred to as a liner hanger point) below the ground surface. Typically, casing and/or liner is cemented in the wellbore with a cement grout. However, as both casing and liner are steel pipe, any reference to casing equally refers to casing or liner, and is only used for simplicity.
Referring briefly to
In accordance with embodiments of the present disclosure, at least one diamond enhanced element may be provided on at least one mill of a milling assembly. As used herein, the term diamond enhanced elements refers to an element having a non-planar diamond working surface. Referring to
The diamond enhanced elements 128 (variations of which are shown in
As used in the embodiments of the present disclose, it also within the scope that element 128 may be non-diamond based, and thus, may have a tungsten carbide conical working surface. It is also within the scope of the present disclosure that any of diamond enhanced elements 128 shown in
As used in mill 120, diamond enhanced elements 128 are placed rearward or behind cutting elements 126 (from the leading edge or face of blade 122), and are located in holes formed in blade 124. Such elements 128 may be secured in place through interference fit, brazing, or any other type of available retention mechanism.
Additionally, while diamond enhances elements 128 are shown as staggered with cutting elements 126 in the embodiment shown in
Further, while the embodiment shown in
Referring to
While the embodiments shown in
Further, in the various embodiments having both cutting elements 126 and diamond enhanced elements 128, it may be desirable to place diamond enhanced elements 128 in a proud or protruding manner with respect to cutting elements 126. For example, in the embodiment shown in
In addition to the presence or amount of protrusion, the placement of cutting elements 126 and diamond enhanced elements 128 may be described with respect to rake angle, including side rake and/or back rake. Side rake is defined as the angle between the plane of cutting face 150 and the radial plane of the bit (x-z plane), as shown in
Additionally, while the above embodiments show the use of the diamond enhanced element along the blades, it is also within the scope of the present disclosure that a diamond enhanced element may be located in the mill face center.
While each of the embodiments shown in the above figures shows a lead mill, embodiments disclosed herein may also relate to mill assemblies having a single mill attached to the end of a shank, and mill assemblies having a lead mill, one or more second mills, and a shank therebetween. As used herein, “second mill” refers to any type of mill, e.g., dress mill, watermelon mill, string mill, follow mill, etc., that may elongate and/or dress the window to full gage. One of ordinary skill in the art would recognize that in some embodiments, a mill assembly may include multiple second mills, i.e., a third mill, etc., or in other embodiments a mill assembly may instead include a lead mill followed by a motor or stabilizer attached to the shaft a distance above the lead mill, rather than a second mill.
The diamond enhanced elements having a non-planar diamond working surface may be included on any one of the various mill types without departing from the scope of the present disclosure. Further, any of such mills may be mounted on a shaft via connections (e.g. threaded connections) or the mill, including the body and blades, may be integral with the shaft. In one embodiment, a mill may be formed from a solid body having integral flow paths formed, for example, by machining, formed therein. In another embodiment, a mill may be formed from a mold via an infiltration or casting process.
As shown in the above figures, the blades are straight blades positioned about the perimeter of the mill body at substantially equal angular intervals. However, other blade arrangements may be used with embodiments of the present disclosed, and the embodiments shown in above figures are not intended to limit the scope of the embodiments disclosed herein. For example, the blades may be positioned at unequal angular intervals or be spiral instead of straight.
In a particular embodiment, a mill assembly such as the one disclosed herein may be included a one-trip milling/whipstock system, such as those described in U.S. Pat. Nos. 5,771,972, 6,102,123, 6,648,068, which are herein incorporated by reference in their entirety. Briefly, a one trip mill system, as shown in
The whipstock 44 has a diameter DW that approximates the inside diameter of the interior wall of casing 11 which allows whipstock 44 to be lowered through cased borehole 9. Whipstock 44 also includes a profiled ramp surface 28 having a curved or arcuate cross section and multiple surfaces, each of the multiple surfaces forming its own angle with the axis 26 of whipstock 44. Profiled ramp surface 28 includes a starter surface 45 having a steep angle preferably 15°, a vertical surface 46 preferably parallel to the axis 26, an initial ramp surface 47 having a standard angle ranging from about 0.5 to 3°, a “kick out” surface 48 having a steep angle preferably 15°, and a subsequent ramp surface 49 having a standard angle ranging from about 0.5 to 3°. It should be appreciated that these angles may vary. For example, the starter ramp surface 45 may have an angle A in the range of 1 to 45° in one embodiment, 2 to 30° in another embodiment, 3 to 15° in yet another embodiment, and about 15° in still another embodiment. The vertical surface 46 may have a length approximately equal to or greater than the distance between mills 32 and 33. In a particular embodiment, ramp surfaces 46, 49 may range from greater than zero to 15°. One of ordinary skill in the art would recognize that the surfaces angles may be selected depending on the desired window dimensions.
The backside 62 of the whipstock 44, especially adjacent the upper end of the whipstock 44, is contoured to conform to the inside diameter DI of the interior wall of the pipe casing 11 for stability of the top of the whipstock 44. The opposite lower end of the whipstock 44 is secured to, for example, a hydraulically actuated anchor (not shown). A typical anchor is shown in U.S. Pat. No. 5,657,820, incorporated herein by reference in its entirety.
The mill 32 and whipstock 44 disclosed herein are configured such that the mill 32 tends to cut the wall of the casing 11 and not the whipstock 44. To achieve this objective, various factors are taken into consideration including the contact area and contact stress between the mill 32, casing 11, and whipstock 44 and the cutability of the metal of the casing and of the metal used for the whipstock 44.
Use of the elements described herein may render the mill as suitable for the dual functions of milling steel casing and drilling rock formation. In a particular embodiment, the casing may be formed of a corrosion resistant alloy, and the elements described herein may render the mill as suitable for both milling a window in the CRA as well as drilling rock. Thus, one skilled in the art would appreciate that the mills of the present disclosure may be used in conjunction with a bottom hole assembly which stabilizes the cutting tool, provides the motive force for rotating the cutting tool, and after milling through casing, directionally controls the movement of the cutting tool in rock formation.
Further, reference to the term “diamond” (and its use in the elements of the present disclosure) is understood to include polycrystalline diamond (natural or synthetic), thermally stable diamond (formed such as by leaching), vapor deposited diamond, silicon bonded diamond, diamond impregnation, cubic boron nitride, etc. Thus, no limitation exists on the type of diamond or diamond-like materials that may be used.
Further, while many of the embodiments of the present disclosure described milling through a casing, it is also within the scope of the present disclosure that the mill may be used to sidetrack through an open hole completion.
Embodiments of the present disclosure may provide at least one of the following advantages. As described above, as the mill cutting structure meets the casing wall, the cutting structure typically encounters severe vibrations that frequently lead to cracks in the cutters. Such cracks may lead to failure of the cutters, reducing the life of the mill and likely preventing the mill from being used to drill through the sidetracked, secondary borehole (through the earth formation) after the window is milled. The use of the diamond enhanced elements having a non-planar diamond working surface may provide protection from vibration induced damage to the cylindrical cutting elements by being placed in a position that protrudes slightly more than cutting elements. Additionally, the strategic placement of both element types may provide maximum milling action, as well as drilling action once the mill reaches the formation. Further, when using conical shaped diamond enhanced elements, even as the cone point becomes blunt, the element may continue to provide milling and/or drilling action. Further, in the initial milling stages, protrusion of the diamond enhanced element also result in creation of initial gouges in the casing, thus providing better grip for the cylindrical cutting element as they engage with the casing. Use of a diamond enhanced element in the mill face center may provide an anti-coring effect.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
This applications claims priority to U.S. Patent Application No. 61/175,182, filed on May 4, 2010, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61175182 | May 2009 | US |
