GB2301386A - Drill bit - Google Patents

Abstract

A drill bit 300 comprises a body 312 having on its exterior surface a plurality of circumferentially spaced, downwardly and inwardly extending channels (336 figure 1), a plurality of blades or wings 340 carrying cutting means 66 thereon and having radially inner portions slidably receivable within said channels and means for securing said blades in fixed relationship with said body. The blades may be selectively removed from the body and may be securable in a plurality of positions in said channel to define a plurality of gage sizes for the bit 340', 340''. The cutting means may be diamond inserts carried in pockets on the blades. A replaceable gage pad 350 may be provided on each blade. The cutting means may comprise a rotatable roller cone cutter.

Description

DRILL BIT This invention relates generally to drill bits used in drilling subterranean wells or in core drilling of such wells. The invention relates specifically to drill bits whose effective diameter can be varied using standard components.

Equipment for drilling into the earth is well known and long established in the art. The basic equipment used in drilling generally includes a drill bit attached to the bottom-most of a string of drill pipe and may include a motor above the drill bit for effecting rotary drilling in lieu of or in addition to a rotary table or top drive on the surface. In conventional drilling procedures, a pilot hole for the setting of surface casing is drilled to initiate the well. A smaller drill bit is thereafter placed at the bottom of the pilot hole surface casing and is rotated to drill the remainder of the well bore downwardly into the earth.

Many types and sizes of drill bits have been developed especially to accommodate the various types of drilling which are done (e.g., well drilling and coring). A drill bit typically comprises a body having a threaded pin connector at one end for securement to a drill collar or other drill pipe, a shank located below the pin, and a crown. The crown generally comprises that part of the bit which is fitted with cutting means to cut and/or grind the earth. The crown typically has portions designated as the chamfer (the portion below the shank which flares outwardly from the shank), the gage (the annular portion of the cutting means below the chamfer which is usually concentric with the shank), the flank (a tapered portion of the cutting means below the gage), and the nose (the bottommost portion of the cutting means and that which acts upon the bottom of the hole).

Drill bits include cutting elements for cutting the earth. The two major categories of drill bits are diamond drag bits. which have small natural diamonds or planar or polyhedral synthetic diamonds secured to certain surfaces of the bit body, and roller cone bits, which typically comprise at least two rotatable cones having carbide or other cutting elements disposed on the surfaces thereof.

From time to time, the cutting elements of any drill bit become dull and must be replaced or the bit itself replaced. During drilling operations, drilling fluid or mud is pumped down into the hole to facilitate drilling and to carry away formation cuttings which have been cut away by the cutting elements.

The present application is divided from British Patent Application 9401325.7 (Serial No. 2275067) which relates to a drill bit with movable cutting means to adjust the effective diameter of the bit. The present invention is set out in claim 1.

The slidably insertable blades or wings which have been fixed to the bit body may subsequently be removed for repair or replacement. It is contemplated that this arrangement affords the ability to fabricate bits of various diameters within certain size or gage ranges by adjusting the position of the blades with respect to the bit body prior to affixation thereto.

Examples of the invention will now be described with reference to the accompanying drawings in which: FIG. 1 is a partial lateral, cross-sectional view (looking upwardly) of a drill bit having a fixed, replaceable cutting structure according to the present invention; FIG. 2 is a side-elevational view of the drill bit of FIG. 1; and FIG. 3 is an enlarged section of a cutting element as mounted in one of the cutting structures of the bit of FIGS. 1 and 2.

In FIG. 1, bit 300 includes channels 336 in body 312.

Blades or wings 340 are fabricated separately from body 312, and slide into channels 336 where they are secured by welding, brazing, adhesive bonding or mechanical securement means known in the art such as bolts, screws, pins or keys.

Alternatively, body 312 may be heated, blades 340 dropped into channels 336, and body 312 cooled, resulting in shrinkage of body 312 and retention of blades 340 therein.

With such an arrangement, damage or wear to a particular blade or cutting elements thereon may be addressed by removal of the damaged blade, repair thereof and reinsertion in body 312 or if the blade is irreparably damaged, by replacement with a new one. Gage pads 350 as well as cutting elements 66 constitute replaceable elements on blades 340.

As shown in FIGS. 1 and 2 by way of example, blades 340 may be secured in body 312 by weld beads 360. Downward movement of blades 340 in channels 336 is arrested by contact of the lower end 342 of each blade key 334 with shoulder 338 in a channel 336. It should be noted that the inner portion of blade key 334 and those of channel 336 are of larger cross section than the intermediate portions, as in the other embodiments of the present invention, to maintain blades 340 within channels 336.

Blades 340 would normally not be identical, in that one channel 336 and cooperating blade 340 are extended so that the cutting elements 66 of that blade 340 cut the very centre of the well bore, as shown in FIG. 2, the centreline or axis of bit 312 being designated as 380. Alternatively, a group of cutters may be mounted directly on the nose of the bit to cut the centre of the wellbore (see FIG. 6 of the parent application for such a grouping) . With such a design, all of the blades 340 may be made identical, it being understood that even with identical blade size and configuration, the number and location of the cutters 66 of the blades may or may not differ for optimum performance.

FIG. 3 depicts an exemplary cutting element 66 usable with drill bit 300. Cutting element 66 includes a layer 400 of diamond or other superhard material formed on a metallic substrate 402 (typically WC) and secured to cylindrical carrier element 404 of sufficient length to provide adequate surface area for brazing or otherwise bonding element 66 to blade 340. Further, as shown in FIG.

3, the length of carrier element 404 provides continued bond strength throughout the wear life of cutting element 66, until roughly 75% of diamond layer 402 is worn away, shown at line 406 for element 400, disposed at a 20O angle to the axis or centreline 380 of bit 300.

It may also be readily appreciated from perusal of FIGS. 1 and 2 that the present invention as applied in those figures permits an entire size or gage range of bits to be fabricated from a single body size 312, by utilizing different size blades 340. In such a manner, odd-gauge sizes may be easily accommodated without inventorying entire bits. Even more preferably, a single size of blades 340 may be employed within a given gage size range, and the blades 340 positioned selectively in channels 336 before affixation therein, the upward or downward change in position effecting a change in gage size (se 340' and 340") while using the same blade. In such a manner, a 15 cm range of bits might be fabricated to extend from a 14.7 cm gage size to a 17 cm gage size, or a 20 cm range of bits might be fabricated to extend from a 19.7 cm gage size to a 22 cm gage size.

Claims (8)

1. A drill bit for drilling subterranean formations, comprising a body having a plurality of circumferentially spaced channels extending downwardly and radially inwardly on the exterior thereof; a plurality of blades carrying cutting means thereon and having radially inner portions slidably receivable within said channels; and means for securing said blades in fixed relationship to said body.

2. A bit as claimed in claim 1 wherein said means for securing is adapted to permit selective removal of said blades from said body.

3. A bit as claimed in claim 1 or claim 2 wherein said blades are securable in a plurality of positions in said channels to selectively define a plurality of gage sizes for said drill bit.

4. A bit as claimed in any one of claims 1 to 3 wherein said cutting means include diamond cutters.

5. A bit as claimed in any one of claims 1 to 4 wherein < said blade carries a replaceable gage pad thereon.

6. A bit as claimed in any one of claims 1 to 5 wherein t said cutting means is carried in a pocket on said blade.

7. A bit as claimed in any one of claims 1 to 6 wherein s said cutting means comprises a rotatable roller cone cutter.

8. A drill bit as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.