This application relates to a centralized bi-center reamer and a method for drilling and enlarging a hole with such device; specifically, to a bottom hole assembly that provides a centralizing underreamer or roller assembly to centralize a bi-center reamer, which enlarges a drilled hole mounted above.
During the drilling of subterranean holes for the exploration and production of oil and gas, by way of example, it may be useful to both drill and enlarge a smaller diameter or pilot hole. At other times, a small diameter or pilot hole has been drilled which must be enlarged to properly install casing in the well. In a normal bi-center application, the pilot hole provides the centralizing element guide to keep a bi-center bit centered so it will ream a larger hole. Although inherently unstable, bi-centered bits having shear-type (PDC) cutter elements which enlarge the bore-hole have long been used in the industry. See, for example, U.S. Pat. No. 5,678,644 for a Bi-Center and Bit Method for Enhancing Stability issued Oct. 21, 1997 and U.S. Pat. No. 5,957,223 for a Bi-Center Bit with Enhanced Stabilizing Features issued Sep. 28, 1999. Bi-centered technology has a tendency to move off the true desired line of drilling because of the nature of the eccentric side forces acting on the tools. The present disclosure relates to an apparatus and method for using the bi-centered technology for underreaming while overcoming this inherent tendency for the bi-center assembly carried on the bottom hole assembly (BHA) to move off the desired direction of travel.
- SUMMARY OF INVENTION
To run a conventional bi-center bit, normally there is no pilot hole and the hole is drilled and reamed simultaneously. The drill bit and reamer diameter size is always smaller than the pass-through diameter. In many cases, however, drillers need to open a hole that has been previously drilled to the pass-through diameter or just slightly smaller. In this case, an underreamer is normally run to open the hole to the desired size that is larger than the pass-through diameter. The preferred embodiment of the present invention utilizes one or more fixed low-torque cutters that are cantilevered from the bottom hole assembly (BHA). This avoids using an expandable arm as found in a standard underreamer that is inherently weaker than a fixed cutter cantilevered from a body. Alternatively, the centralized bi-center underreamer could utilize a shear type polycrystalline diamond compacts (PDC) underreamer, which would be centralized and stabilized in the center of the well bore by the accompanying centralizer/underreamer.
An apparatus for enlarging a bore hole provides a selectively-engageable centralizer to engage a well bore on a proximal portion of a bottom hole assembly and a bi-centered reamer on a distal portion of the bottom hole assembly. This apparatus can be fabricated so the selectively-engageable centralizer provides hard-facing on a face of a plurality of well bore engaging arms, thereby preventing wear from movement over the well bore as well as starting the underreaming function of the tool assembly.
Alternatively, this apparatus could provide a selectively-engageable centralizer having a plurality of rolling cutter cones for engaging the well bore. This apparatus could alternatively be fabricated the bi-centered reamer is composed on one large roller or several smaller roller cutter cones mounted eccentrically on the reamer portion of the bottom hole assembly such that the outer diameter of the reamer portion is smaller than the inner diameter of a passage through which the apparatus passes on the distal portion of the bottom hole assembly.
The apparatus can also be fabricated wherein the bi-centered reamer is a scraping reamer have a plurality of PDC buttons on a portion of the extending reamer eccentric body. The apparatus can be fabricated to provide the centralizer and the reamer portion of the bottom hole assembly on two tubular bodies connected together or, alternatively, fabricated on an integral body.
The apparatus can additionally provide a bit connected to the reamer portion of the bottom hole assembly or may be inserted in a well bore utilizing a bull-nose plug connected to the reamer portion of the bottom hole assembly.
A method for enlarging a pilot bore hole is also disclosed herein comprising inserting a centralizer and an bi-center underreamer apparatus in a zone to be enlarged while keeping the centralizer arms from deployment; opening the centralizer arms by increasing hydraulic pressure to thereby centralize and stabilize the bi-center underreamer as it engages the bore hole; and, rotating the centralizer and reamer combination to enlarge the pilot bore hole. This method can further comprise comprising rotating the BHA while increasing pump pressure on the centralizer to fully extend the centralizer arms to engage the well bore before advancing the centralizer and bi-centered underreamer in the well bore.
FIG. 1 is a schematic cross-sectional view of an embodiment of the centralized bi-center reamer assembly.
FIG. 2 is a schematic end view of the relative spacing of the centralized bi-center reamer assembly.
FIG. 3 is a schematic cross-sectional view of an alternative embodiment of the centralized bi-center reamer assembly utilizing cones on the underreamer assembly.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
FIG. 4 is a partial schematic view of a PDC blade reamer portion of the embodiment of this present disclosure.
The present application relates to a centralized bi-center reamer having eccentrically spaced cutters run below a conventional underreamer operating as a centralizer used to stabilize and centralize the bi-center reamer in the pilot hole. This embodiment of the present invention is an apparatus for insertion through a smaller diameter casing or tubing (not shown) with the centralizer arms disengaged from the well bore wall 52. As shown in FIG. 1, upon reaching the desired portion of the well bore 70, the arms 30 having a wall-engaging pad 31 of the expandable centralizer or underreamer 10 located on a proximal portion of the BHA, are selectively expanded to engage the well bore wall 52 thereby stabilizing and centralizing the bi-center reamer or hole opener 20 located on the distal portion of the BHA below. These wall-engaging pads 31 are placed on the arms 30 of the underreamer to substitute for the roller cutters or PDC cutter elements normally found at this location. The manner of fabrication and deployment of the underreamer is well known to those skilled in the art and the substitution of the pads 31 on arms 30 for the cutters could be easily accomplished by a person having ordinary skills in the fabrication of this type of tool. The arms 30 are selectively engageable with the well bore 52 by increasing hydraulic pressure on a piston arrangement which moves the arms 30 into engagement in a fashion found in a number of prior art underreamer devices.
The underreamer or centralizer arms 30 are not primarily intended to cut the formation, but serve to centralize and stabilize the bi-center reamer portion in the center of the hole thereby allowing the hole or well bore to be opened to the desired diameter. However, the hard-facing on the pads 31 on the extendable arms 30 will function to minimally underream the formation in the well bore. It is also suggested that the underreamer be allowed to reach full extension through rotation while increasing pump pressure to move the arms into full contact before moving the reamer 20 forward in the well bore 70. Expandable rollers may be substituted to centralize and stabilize the reamer while it performs its primary function.
Alternatively, cutter cones 33, as shown in FIG. 3, could be deployed to roll against the adjacent well bore wall 52 to centralize and stabilize the bi-center reamer or hole opener 20 having the integral cantilevered cutter arms 42. In most uses of a bi-center arrangement for reaming after drilling, the drill bit provides some stabilizing force to counteract the lateral forces resulting from the action of the bi-center reamer. In the present disclosure, this stabilizing effect need not be present since the original drill bit is not necessarily deployed with the reamer in the existing pilot hole. A bull nose or smaller drill bit cone (not shown) can be deployed to permit the flow of fluid through the well bore and to remove cuttings from the reamer up through the annulus 70. The description found in U.S. Pat. No. 5,957,223 discusses these lateral forces in detail. As previously noted, the stabilizing and centralizing action of the centralizer or underreamer 10 counteracts the lateral forces, which prevent clean and straight hole enlargement by the bi-center reamer 20. Without this centralizing and stabilizing action of the underreamer, the eccentrically located cutters on the reamer would move off the wall of the pilot hole 50 deviating from the central axis of the pilot hole and spiraling out of directional control.
The reamer or hole opener portion 20 of this apparatus enlarges a pre-existing pilot hole 50 in a well bore to a larger hole size 52. The cantilevered fixed post 42, journal 43 and cutter body 40 are inherently stronger than typical underreamer extendable arm cutters. The present embodiment adds the strength of these fixed cantilevered arms to the bi-center technology permitting deployment through smaller diameter casing or tubing thereby permitting enlarging of particularly difficult bore holes.
As more fully shown in FIG. 2, by way of example only and without limitation to the exact dimensions shown therein, a 26 inch pilot hole 50 is opened to a 32 inch hole 52 by the reaming action of the eccentrically placed integral bodied cutters 40 which can be passed through a 28 inch inner diameter of a 30 inch casing or tubing 55. The underreamer body 10 has a 22-inch outer diameter and can therefore be easily transported by the drill string to the desired location through the casing. As shown in FIG. 2, the two eccentrically spaced cutter cones are only 60° apart allowing their end profile to fit within the 28 inch inner diameter of the 30 inch casing or tubing, i.e., the pass-through diameter. As shown in FIGS. 1 and 3, each cone is mounted on an integral journal 43 formed in the outer surface of the reamer portion of the body 20. Alternatively, a single larger cutter cone could be mounted eccentrically on the reamer portion 20 of the body without departing from the spirit or intent of this disclosure. The choice of materials for the cutters is well known to those skilled in the hole opener art and can include, without limitation, PDC elements or hardened teeth or cutter elements or hard-facing placed on the exterior surface of each cone.
The choice of the number and size of the cutter cones is also derived from knowledge of those experienced in this art and although the preferred embodiment shows two cones, and as noted the devices could conceivable be fabricated with a single larger cone or several smaller cones. The limitation on the number of cones used is the pass-through size, which must be accommodated. The benefits of a fixed post cantilevered reamer or hole opener are more fully described in U.S. Pat. No. 5,992,542, which is incorporated herein by reference as if copied herein verbatim.
Returning to FIG. 1, additional features may be added to the apparatus to accomplish the enlargement of the pilot hole. For example, a hydraulic jet 60 can be positioned on the reamer or hole opener portion 20 of the apparatus on a side opposite the eccentrically positioned cutters 40 to clear cuttings up the annulus 70. Additionally, while underreamer body 10 and reamer or hole opener body 20 are shown in FIG. 1 as being connected by threaded connection 80, this apparatus could alternatively be fabricated as an integral body without departing from the spirit or intent of this disclosure. This arrangement would allow the centralizer on the proximal portion of the BHA to be positioned in closer proximity to the bi-center reamer on the distal portion of the BHA, thereby assuring less lateral movement of the bi-center reamer as it rotates. The dotted reamer cutter body 41 of FIGS. 1 and 3 shows the cutting path of the eccentrically located cutters as they move around the lip 53 of the pilot hole 50 as it is cut. Finally, these same features may be applied to the embodiment shown in FIGS. 3 and 4 without diminishing the substance or intent of this disclosure. FIG. 4 shows a bi-center PDC reamer attachable on the distal portion of the BHA. This assembly would be connected to a bit or bull-nose plug below (not shown) connected at threaded surface 21 and would be connected to a centralizer which is selectively engageable to centralize and stabilize the PDC reamer as it opens the hole from the pass through diameter to the desired well bore diameter without unduly deviating from the center of the well bore desired path. Reamer body 22 would have a PDC supporting wing 25, which is populated by a number of PDC cutter elements 26, all in a manner well known in this art.
As one may readily appreciate from disclosure of FIGS. 1, 3 and 4, the present embodiment stabilizes the bi-center reamer both from above and below the lateral forces that tend to move the bi-center reamer from the well bore wall, thereby permitting a straighter, cleaner well bore.
The foregoing description has been directed to particular embodiments of the invention in accordance with the requirements of the statutes and for purposes of illustration and explanation of the manufacture and use. It will be apparent to those skilled in the art that many modifications and changes in the procedures set forth will be possible without departing from the scope and spirit of the invention. It is the applicant's intention to encompass all such modifications and variations.