Expandable gage bit for drilling and method of drilling

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BACKGROUND OF THE INVENTION

1. Field of the Invention

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 having a variable effective diameter which facilitates placement of the drill bit downhole and retrieval thereof. The drill bit of the present invention is particularly suitable for passing through narrow spots in the well bore, sluffing spots and through casing to drill an expanded well bore therebelow. The invention may also be employed in drill bits having replaceable blades.

2. State of the Art

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 bottom-most 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.

From time to time during drilling of a well, the drilling activity will stop for a number of reasons. For example, another length or joint of drill pipe must periodically be added to the drill string in order to continue drilling. At other times drilling will stop because the drill bit may become lodged or jammed downhole, or the drill bit will have become dulled and will need to be replaced. In response to any of these scenarios, the drill bit must be brought out of the hole to either diagnose the reason for the stoppage or to replace the old, worn cutting elements with new elements.

It frequently occurs that when a drill string is tripped or brought out of a hole, the bit will become jammed downhole because of an encounter with debris or with an irregularity in the wall of the hole. Jamming is particularly prevalent when the well bore includes a non-vertical segment, either inadvertently or by design, such as during highly deviated or horizontal drilling. In the former case, during drilling, the bit may wander or move temporarily from a strictly vertical orientation resulting in a hole which curves away from the vertical. A phenomenon of this type, particularly where the departure from the vertical is abrupt, may be known as a "dog leg." In the latter instance, the well bore is caused to depart from the vertical by use of a whipstock or by directional or navigational drilling bottom hole assemblies. In both cases, because of the curvature of the hole, tripping a state of the art drill bit in or out of the hole is often time-consuming or even impossible, in the latter instance necessitating the severance of the drill string at the stuck point, retrieval thereof, setting of a whipstock and drilling a new hole around the remaining portion of the drill string and the bit at the end thereof.

In some instances, due to drill bit cutter damage or unusual formation characteristics, bore holes may be drilled which are "under gage" (i.e., having an undersize diameter in comparison to the design diameter or gage diameter of the drill bit), or out of round as well as undergage. Subsequent removal of the drill string and, in particular, the bit in such situations is difficult to effect.

Thus, it would be an improvement in the art to provide a drill bit which includes cutting means which are variably positionable to expand to full or design gage while downhole and in an operative drilling mode, and to retract when raised in the hole to facilitate tripping the drill bit in and out of the hole.

It would also be an improvement to provide a drill bit which will pass through a smaller diameter well bore or casing and drill a larger, expanded diameter hole therebelow.

Expandable cutting means associated with drilling equipment have been known for many years, but such expandable cutting means have been directed to solving other problems encountered in drilling procedures. For example, expandable cutters attached to a drilling sub and located intermediate to the drill string have been used as apparatus to underream previously drilled holes. Underreaming is a procedure well-known in the drilling industry to enlarge a portion of a previously drilled hole below a point of restriction. Thus, underreaming apparatus are used to enlarge holes below a casing in order to place the next length of casing (See, e.g., U.S. Pat. No. 1,944,556 to Halliday, et al.; U.S. Pat. No. 2,809,016 to Kammerer; U.S. Pat. No. 4,589,504 to Simpson) or to enlarge a previously drilled pilot hole in preparation for insertion of explosives therein (See, e.g., U.S. Pat. No. 4,354,559 to Johnson; U.S. Pat. No. 3,817,339 to Furse).

Drill bit assemblies directed to drilling a well bore have been designed in which the cutting means grind out a diameter exceeding the diameter of the drill bit body or drill string. For example, in U.S. Pat. No. 1,468,509 to Overman, a wedge-shaped drill bit has corresponding slips which dovetail with the drill bit so that when the bit is lowered to the bottom, the slips slide upwardly to come into complementary registration with the body of the drill bit. Drill rollers designed to finely crush or comminute the material in the bottom of the hole are positioned at a slight angle to a central longitudinal bore so that as the rollers turn, they drill out a diameter of earth slightly larger than the diameter of the drill bit. The rollers of Overman, however, do not expand outwardly from a vertical axis to achieve a diameter significantly in excess of that of the drill bit. Further, the elongated design of the Overman device would be disadvantageous in curved well conditions.

In U.S. Pat. No. 1,838,467 to Stokes, a drill bit assembly includes two cutter blades positioned within a bit head, both cutter blades moving from a retracted position within the bit head to an expanded position relative to the bit head when a spring biased plunger is forced downwardly to engage the cutter blades. Upward motion on the bit carrier housed within the bit head urges the plunger upwardly to move the cutter blades into a retracted position for tripping out of the hole.

Expandable cutter means in the prior art have not been specifically developed to facilitate easy removal of the drill bit from a hole, particularly under special drilling conditions such as non-vertical or curved holes. Therefore, it would be an improvement in the art to provide cutting means associated with a drill bit which are appropriately expandable and retractable under all drilling conditions and which do not require complex subassemblies within the bit head.

SUMMARY OF THE INVENTION

A drill bit is provided which has a body and cutting means associated therewith which move between a first position effecting a smaller diameter relative to the diameter of the body and a second position effecting a larger diameter relative to the diameter of the body, the larger diameter comprising the effective gage of the drill bit. The movable cutting means advance from the first, retracted position to the second, expanded position as a result of pressure applied to the bottom or leading end of the cutting means. Such pressure is provided by the weight of the drill string or by a mechanism used to advance the drill string in the hole (common in horizontal drilling) when the drill bit is placed downhole and the movable cutting means come to rest on the bottom of the hole. When the drill bit is raised, the movable cutting means retract from the second position to the first position, thereby effecting a gage diameter equal to or smaller than the bit body to facilitate removal of the drill bit from the hole.

The body of the present invention is structured to retain the movable cutting means in slidable association therewith. Particularly suitable structure of the body includes the formation of channels in the face of the body sized to receive a portion of the movable cutting means therein to facilitate slidable movement of the cutting means relative to the body.

The outer configuration of the body is adapted to facilitate movement of the cutting means from a first position effecting a smaller diameter to a second, expanded position effecting a larger diameter. A particularly suitable configuration for the body is one generally having a conical shape with a top portion having a diameter approximately equal to or slightly larger than that of the drill pipe and a lower portion tapered toward the nose of the drill bit.

The cutting means may be of any suitable size, shape or dimension provided that the cutting means are movable, relative to the body, to effect a gage diameter greater than that of the drill pipe. One suitable configuration for the cutting means of the invention is a blade or wing. The cutting means may preferably include a portion thereof which is slidably disposable within a channel formed in the body of the drill bit. The cutting means further includes cutting elements which may be either conventional carbide teeth, natural or synthetic diamonds of any configuration, or other suitable cutting elements known in the art.

The drill bit of the present invention may be used in connection with both well drilling and core drilling. When used in connection with well drilling, the body further includes secondary cutting means which are secured to the bottom of the body centered with the longitudinal axis of the drill bit. The secondary cutting means is configured to allow unobstructed movement of the movable cutting means between the first and second position. The secondary cutting means include cutting elements which may be carbide teeth, diamonds or other suitable cutting elements known in the art. When the drill bit of the present invention is used in connection with core drilling, the movable cutting means are positioned about a central opening in the nose at the bottom of the body which allows the cut core to enter into the inner bore of a core barrel above the bit.

It is also contemplated that the drill bit design of the present invention may be employed in a drill bit having slidably insertable blades or wings which are then fixed to the bit body, and which may subsequently be removed for repair or replacement. It is also contemplated that this embodiment of the invention 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.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention,

FIG. 1 is an elevational view of a first preferred embodiment of the drill bit of the invention illustrating the cutting means in the first position;

FIG. 2 is a view in cross section of the drill bit taken at line X--X of FIG. 1;

FIG. 3 is an elevational view of the drill bit illustrating the cutting means in the second, expanded position;

FIG. 4 is a partial view of a core bit in cross section illustrating the cutting means in the first position;

FIG. 5 is a partial view of a core bit in cross section illustrating the cutting means in the second position;

FIG. 6 is a plan view of the bottom of a drill bit of the present invention used in well drilling depicting both cutters fixed directly to the bit body and cutters fixed to movable portions of the bit crown;

FIG. 7 is a plan view of the bottom of the core bit illustrated in FIGS. 4 and 5;

FIG. 8 is a lateral, cross-sectional view of a second preferred embodiment of the present invention;

FIG. 9 is a side elevational view of the embodiment shown in FIG. 8;

FIG. 10 is a longitudinal, cross-sectional view of the embodiment shown in FIG. 9;

FIG. 10A is a longitudinal, cross-sectional view of an alternative bearing structure employed in the present invention;

FIG. 11 is a lateral, cross-sectional view of a third preferred embodiment of the present invention;

FIG. 12 is a side-elevational view of the embodiment shown in FIG. 11;

FIG. 13 is a lateral, cross-sectional view of a fourth preferred embodiment of the present invention;

FIG. 14 is a side-elevational view of the embodiment shown in FIG. 13;

FIG. 15 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. 16 is a side-elevational view of the drill bit of FIG. 15;

FIG. 16A is an enlarged section of a cutting element as mounted in one of the cutting structures of the bit of FIGS. 15 and 16; and

FIG. 17 is an enlarged, partial, quarter-sectional view of a rotationally expandable gage drill bit according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment of the drill bit of the present invention, generally indicated by reference numeral 10 in FIG. 1, includes a body 12 and cutting means 14 associated therewith. The drill bit is attachable to the downhole end of conventional drilling apparatus (not shown) such as a string of drill pipe, drill collar or other drilling sub element, including without limitation the output shaft of a downhole motor. The drill bit 10 may be attached to the drilling apparatus by means of a threaded pin connector 16. Below the pin connector 16 is the shank 18 of the drill bit 10, and below the shank 18 is the chamfer 20.

The outer body diameter 22 of the drill bit 10 generally defines the outermost circumference 24 of bit body 12, which in conventional bits would also define the gage of the bit. However, in the drill bit 10 of the present invention, the bit body 12 is structured to permit variable positioning of movable cutting means 14 between a first, retracted and a second, expanded position, the former in most cases defining a diameter no larger than that of bit body 12, while the latter defines a substantially larger diameter. The second, expanded position of cutting means 14 defines the gage or working diameter of the bit 10 of the present invention. The bit body 12 may preferably be structured to taper inwardly (see FIG. 1) from the outer body diameter 22, the inward taper in combination with the cutting means 14 in the retracted position facilitates lowering the drill bit into the hole, a process commonly known as "tripping in," and facilitates removal of the drill bit from the hole, a process commonly known as "tripping out."

In one exemplary embodiment illustrated by FIG. 1, the bit body 12 is configured with three columns 26, 28, 30 each of which serves to support cutting means 14. The columns 26, 28, 30 extend from the bottom edge 31 of the outer body diameter 22 to the nose 32 of the bit body 12 and are tapered inwardly from the outer body diameter 22 to the nose 32. Each column 26, 28, 30 has formed therethrough a channel 36, shown in phantom, in which a portion of the cutting means 14, designated as blades or wings 40, 42, 44 is slidably positioned.

As suggested in phantom line by FIG. 1, the blade 44 may move upwardly and downwardly in the channel 36 in the directions shown at 46. Blades 40 and 42 are similarly movable in cooperating channels. As further suggested in phantom line by FIG. 1, each blade (44 serving as an example) has a slot 48 formed through the thickness thereof and a positioning pin 50, inserted laterally through each column 26, 28, 30 fits within the slot 48 of the blade. Each blade 40, 42, 44 is therefore maintained within its respective channel by the pin 50. The movement of each blade 40, 42, 44 in its respective channel 36 is dictated by the traverse of the pin 50 in the slot 48. It will of course be understood that bit body 12, and specifically columns 26, 28 and 30 may be slotted instead of blades 40, 42 and 44, the latter carrying pins to cooperate with the slotted columns.

The relationship of the blade 44, channel 36, slot 48 and pin 50 may be more completely understood by reference to FIG. 2 which illustrates a cross section of the bit body 12 of FIG. 1 taken at line X--X thereof. It can be seen that pin 50 extends laterally through the column 30 and through the slot 48 formed through the blade 44. It may also be seen that the portion 52 of the blade 44 which extends outwardly from the column 30 may be slightly broader than the portion of the blade 44 which is positioned within the channel 36. This configuration of the blade 44 helps prevent debris from entering channel 36.

Bearing means 54 may be associated with each channel 36 to facilitate movement of the blade 44 therewithin. As illustrated by FIG. 2, the bearing means 54 may be a cylindrical rod 56 formed or secured in the bottom 58 of the channel 36 which cooperates with a reciprocating race 60 formed along the inward face 62 of the blade 44. Thus, as the blade 44 slides within the channel 36, race 60 of the blade 44 slides over rod 56 to provide ease of movement. Alternatively, rod 56 may be replaced by a plurality of balls, either closely or loosely placed in a race or groove in body 12.

The cutting means 14 of the drill bit 10 may be sized and configured in any manner which provides an appropriate cutting profile. By way of illustration, the blades 40, 42,