Underreamer Having Variable Arm Extension

Abstract

An underreamer for enlarging a well bore wherein a plurality of cutter cones are rotatably supported on pivoted cutter arms which pivot outwardly from the body of the tool in response to fluid pressure. The amount of outward pivotal movement is adjustable without the removal and replacement of the cutter arms. This permits the same tool body and pivotable arms to be used for bore enlargements to different diameters relative to the contracted diameter of the tool.

Description

BACKGROUND OF THE INVENTION

Underreamers are employed extensively for enlarging portions of the well bore in oil and gas wells for various purposes, as for example, to provide clearance for running casing, to obtain adequate annular space in the hole for cementing, to enlarge zones for gravel pack completion or cementing and for other purposes.

One type of underreamer known to the prior art employs three cutter cones that are rotatably supported on respective pivoted arms which swing from an initial retracted position, wherein the arms and cutter cones are completely withdrawn into the body of the tool, outwardly to an extended or expanded position, wherein the cutter cones project radially outward from the body of the tool so as to enlarge the existing bore. In such conventional underreamers the cutter cones are all of the same length in the radial direction relative to the body of the tool. Similarly, in conventional underreamers the three pivoted arms upon which the cutter cones are rotatably supported swing outwardly to the same radial extent. The length of the cutters is limited in such conventional underreamers by the requirement that the cutters all fit completely within the diameter of the body of the tool when in the retracted position. The amount of hole enlargement that can be accomplished is in general limited to the cutter length since the cutters may generally operate upon the full annular formation area between the wall of the original bore and the wall of the enlarged bore. It can thus be seen that conventional underreamers having cutter cones of equal length and cone support arms which swing outwardly to equal extents are limited in the amount of bore enlargement which they can achieve. It is desirable with this type of tool to obtain the largest possible effective cutting diameter relative to the retracted tool diameter, i.e., it is desirable to obtain the maximum possible outward extension of the cutters consistent with efficient cutting and durability of the cutters in operation.

One prior art attempt to obtain a greater amount of cutter extension is described in U.S. Pat. No. 3,483,934 by Benjamin H. Fuchs which patent is assigned to the assignee of the present application. The underreamer of that patent utilizes pivoted arms which swing outwardly from the body of the tool by different radial amounts to thereby dispose the respective cutter cones in radially stepped relationship. By means of this arrangement the underreamer obtains a greater radial spread of cutter surface and provides greater bore enlargement relative to the contracted diameter of the tool than with conventional underreamers described above wherein the arms all swing out by the same amount.

The present invention is equally applicable to underreamers of both types, i.e., those in which the cutter cones all swing outwardly to the same radii and those described in the aforementioned patent in which the cutter cones swing out to different radii. The present invention is however, presently utilized with an underreamer of unequal arm extension and will accordingly be described in connection with such a utilization.

SUMMARY OF THE INVENTION

In the underreamers of both types described above it is desirable to utilize the same tool body for underreaming several sizes of hole. For example, the tool body for underreaming holes to diameters from seven to eleven inches all utilize a 53/8 inch outside diameter tool body. However, in order to underream to the desired diameter it is necessary to have a specific set of arms. In order to change the diameter to which the underreamer opens the hole a different set of arms must be inserted into the tool body. The present invention provides an underreamer apparatus which utilizes the same tool body and the same pivoted arms for underreaming holes to different predetermined diameters. The construction of the apparatus is such that easily replaceable portions of the expansion assembly are utilized to pivot the cutter arms outwardly to different desired radii.

An underreamer in accordance with the present invention comprises an elongate body with the series of circumferentially spaced arms pivotally mounted thereon. A longitudinally movable wash-barrel includes a replaceable camming member having camming surfaces which force the cutter arms outwardly to the desired respective radius. The camming surfaces are defined by the replaceable portion of the wash-barrel which mates with cam follower surfaces on the pivoted cutter arm assemblies. Additionally the camming member has an inverse surface which engages with a stop surface on the cutter arm to limit the radial extension of the cutter arm assembly. By means of the present invention the radius to which the underreamer operates can be varied without the replacement of cutter arms or tool bodies but merely by replacing the camming member on the wash-barrel. By providing a camming and stop surface member exterior of the cutter arm the cross-section of the cutter arm can be maximized for the required strength. Thus the present invention provides an underreamer which can be used for different hole size operations by interchanging the camming portion of the wash-barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view in elevation illustrating an underreamer embodying the present invention with the cutter arms disposed in the collapsed position;

FIG. 2 is a view in elevation taken along line 2--2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a detailed partial view in elevation showing the relationship of the expansion member and the cutter arms in the collapsed position;

FIG. 5 is a view comparable to FIG. 4 showing the relationship of the expansion member and the cutter arms in the extended operative position;

FIG. 6 is an enlarged view in exploded prospective of the wash-barrel and expansion member; and

FIG. 7 is a view of the expansion member illustrating the means for extending to different radii.

DETAIL DESCRIPTION

Referring now to the drawings an expandable underreamer embodying the present invention is shown. The underreamer is illustrative of the type known as a full coverage underreamer which has two arms which are extendable to gauge size while the third arm is only partly extended from its cone pocket. It has been found that the most common problem in maximum size hole opening has been cone failure which occurs not at the gauge area but at the cone ends nearest the tool body. This is due to the face that the amount of cone available at the end nearest the tool body is substantially less in proportion to the amount of material to be removed. By only partially extending the third arm a larger tooth area works upon the formerly weak zone of the underreamer.

The arm with a smaller radius engaged the formation at a lower plane creating a two-level saucer shaped pattern on the bottom of the shelf. By means of the present invention the same relationship of the cutter arms can be employed at different diameters in order to utilize the same apparatus to underream through a range of hole sizes without the necessity of replacing the cutter arms.

The apparatus of the present invention comprises a tubular elongated body 12 which is threadedly connected to a suitable tubular top sub 14. Three cutter arms 16, 18 and 20 described in detail hereinafter are circumferentially arranged at regularly spaced intervals about the tubular body 12 in the lower portion thereof. The arms 16, 18 and 20 are pivotally supported in respective elongated slots 22, 24 and 26 in the body 12. The cutter arms 16, 18 and 20 are pivotally supported proximate their upper ends to swing generally in respective vertical planes which are radially oriented relative to the axis of the body 12 on horizontal support pins 28 which are mounted in the body 12. The cutter arms 16, 18 and 20 are provided with arcuate upper ends which are seated in complimentary recesses in arm retainers 30 which are welded or otherwise secured to the body 12 and serve as thrust bearing means for applying drill string weight to the cutters. Conventional cutter cones 32 and 34 (only two of which are visible in the views) are rotatably mounted at the lower ends of the respective cutter arms 16, 18 amd 20.

A tubular wash barrel 38 is axially mounted within the tubular body 12 and is slidably supported near its lower end in a bushing 40. The wash barrel has a piston 42 secured to its upper end portion which piston is slidable within an enlarged cylindrical portion 44 of the tubular body 12. In the collapsed or retracted position of the underreamer the wash barrel 38 and piston 42 are in the uppermost position as shown in FIG. 1. In the expanded or fully operative position of the tool the wash barrel 38 and piston 42 are in the lowermost position as shown in FIG. 5. The lowermost position of the piston is determined by engagement of the piston with an upwardly facing shoulder 46 at the bottom of the cylinder 44. A helical spring 50 is mounted in an enlargement of the intermediate diameter surrounding the wash barrel beneath the piston 42 and normally urges the piston and wash barrel toward their uppermost positions as illustrated in FIG. 1. The piston and wash barrel are moved downwardly to the extended position of the tool by the pressure of drilling fluid introduced into the drill string and through the sub 14 into the cylinder 44.

Positioned proximate the lower end of the wash-barrel 38 is a removable extension member 47 in accordance with the present invention. The extension member is affixed to the wash barrel 38 in any suitable removable manner. In the presently preferred embodiment a threaded connection is used. As shown in FIGS. 6 and 7 the member 47 includes an internally threaded hub portion 48 with three equally circumferentially spaced cams 49, 50 and 51 extending radially therefrom. A plurality of friction fingers 52 extended downwardly from the hub and are so constructed that they frictionally engage a shoulder 53 formed proximate the lower end of the wash-barrel. Each of the cams contains an upper surface 54 which is a bearing surface in the retracted position of the tool. Each of the cams also defines a camming surface 55 and a load bearing surface 56, the relationships of which are described hereinafter. In the embodiment shown, each of the cams extends the same radial distance from the center line of the wash-barrel which is coincident with the longitudinal center line of the tool. The thickness of the cams, i.e., in the transverse direction, is such as to be matable with a pocket formed in the interior surface of the respective cutter arm as described more fully hereinafter.

Referring now particularly to FIGS. 4 and 5 an illustrative cutter arm is shown in cross section and in detail. As can be seen by reference to FIG. 2 the arm section of the cutter arm assembly is of uniform transverse width and is matable with a slot formed in the tool body which terminates in a circular opening into which a cutter cone is recessed in the retracted position of the cutter arm.

Referring now particularly to FIGS. 4 and 5 the arm section of the cutter arm assembly has formed in the interior surface a radially extending recess 60 with which the respective cam affixed to the wash barrel is matable when the cutter arm assembly is mounted upon the tool body. The recess is formed to define four operative surfaces. The first being a bearing shoulder surface 61 which is substantially horizontal when the cutter arm assembly is in the retracted position. A cam follower surface 62 extends radially, inwardly and downwardly. A cam bearing surface 63 is of greater inclination relative to the vertical than the cam follower section 62 and is such as to be substantially vertical when the cutter arm assembly is in the extended position as shown in FIG. 5. A fourth operative surface is a load bearing surface 64 which is radially outwardly and downwardly extending. The load bearing surface 64 meets with the cam loading surface 63 at an angle substantially less than 90 degrees. The angle of radially downward and outward inclination of the load bearing surface 64 is such that in the fully expanded position of the cutter arm assembly the surface 64 has a substantial radial outward and downward inclination. The transverse width of the pocket formed in the cutter arm is substantially equal to but greater than the transverse width of one of the cams 55 and is symmetrical about the longitudinal center line of the cutter arm.

The relative inclinations of the surfaces in the recess of the cutter arm can be best seen in connection with a description of the operation of the tool so far as the cam and cutter arm interrelationship is concerned. Thus, in the fully collapsed position of the tool the wash-barrel is in its uppermost position at which the upper surface 54 of each of the cams is in bearing contact with the surface 61 of the recess to thereby retain the cutter arm assembly in the retracted position and limit the upward travel of the wash-barrel. As the wash-barrel is forced downwardly to expand the cutter arm to its extended position the lowermost point 65 of the camming surface comes into engagement with the cam follower surface 62 of the cutter assembly. Since the cam follower surface is radially inwardly and downwardly inclined, as the wash-barrel and camming surface move downwardly along the cam follower surface the cutter arm assembly is forced to be swung outwardly.

As the cam point moves down the inwardly inclined cam follower surface 62 the cutter arm assembly is moved outwardly to the extended position until the cam point 65 passes the interface point 66 between the cam follower surface 62 and the cam bearing surface 63. By the time that this position is reached the cam bearing surface 63 is substantially vertical as shown in FIG. 5. The camming surface then moves down the cam bearing surface and holds the cutter arm assembly at the extended position. As the cam continues to move downwardly the radially inward and upward loading surface 56 of the cam comes into bearing contact with the load bearing surface 64 of the recess which is at substantially the same downwardly and outwardly directed angle as the load bearing face 56 of the cam. Thus the mating engagement of the caming surface 55 with the cam loading surface 63 of the cutter arm retains the cutter arm assembly at the desired extended radius while the bearing engagement of the load bearing surfaces 56 and 64 on the cam assembly and cutter arm respectively prevent the further outward movement of the cutter arm assembly. Thus, so long as the wash barrel remains in the downward position of FIG. 5 the cutter arm assembly is retained at the desired radius.

Referring now particularly to FIG. 7 it can be seen how the underreamer of the present invention is utilized to underream to different radii utilizing the same tool body and cutter arm assemblies by replacing only the extension member 47. In FIG. 7 there is shown in solid lines the cam which will extend the cutter arm assembly outwardly to a radius R1 whereas there is shown in broken lines the caming surfaces which will extend the cutter arm assembly outwardly to a radius R2 which is less than R1. As can be seen by the figure, the angles of the caming surface and the load bearing surface are interrelated and vary for each radius to which the cutter arm assembly is to be extended. The angle of the caming surface 55 is such that it is matable in surface contact with the cam bearing surface 63 of the cutter arm at the fully extended position of the arm assembly. Thus, the caming surface 55 is substantially vertical and to obtain a lesser radius of the cutter assembly arm the camming surface assumes a slight downward and inward radial inclination with respect to the vertical and with respect to the greater camming radius. Similarly the load bearing surface 56 of the cam is slightly more toward the vertical when a lesser radial extension of the cutter arm assembly is desired.

Three fluid passages 80 extend longitudinally through the tool body with fluid jets 81 positioned in the passages. The jet orifices are located as close as practical above the cutter cones and each jet orifice opens into a recess in the outer space of the body that is formed by a downwardly and outwardly extending guide surface. These jet guide surfaces 83 provide a convenient means for directing the jet flow of pressurized fluid in a downwardly and outwardly diverging stream. The fluid passages and jets are circumferentially disposed in the tool body 12 intermediate the cutter arm 16, 18 and 20. Thus, when the tool is rotated during the cutting operation to ream a portion of the hole to an enlarged bore as illustrated in FIG. 5, each of the cutting cones is lead by a jet stream which is directed generally into the region of the cutting plane and in this manner the jet stream will provide a full high-velocity washing flow directly in the region of the cutting ledge where it is most effective, the flow being unimpaired by any structure on the underreamer or by the ledge itself.

In the embodiment shown, each of the cutter arm assemblies is extendable to the same radii. However, as described hereinbefore, in one type of underreamer at least one of the cutter arms is extended to a lesser radius than the remaining two or all three are extended to different radii in order to provide what is termed a full-coverage underreamer. From the foregoing description, it can be seen that the variation of radii can be readily and easily achieved by means of the present invention by the simple variation of each of the cams on the extension member. That is, it is unnecessary in the present invention to vary the cutter arms or the camming recesses in the arms in order to obtain various radii of extension. It is necessary only to adapt the cams on the extension member to the configuration that is desired. On a single extension member the cams can be formed to extend each arm to a different radius or any predetermined combination of radii of the three arms in the manner discussed above in connection with FIG. 7.

In the inoperative or retracted position of the underreamer as it is being lowered through the hole to a desired region of operation, drilling fluid is not pumped through the drill string into the cylinder 44 and the biasing force of the spring 50 will hold the piston, wash barrel, and cams in their uppermost position as illustrated in FIGS. 1 and 4. In this inoperative or collapsed condition of the underreamer the three cutter arms are held in their retracted position by gravity and also by the spring bias engagement of the cams against shoulders 61 in the respective cutter arms.

When the tool is at the desired position in the hole, to commence reaming, the tool is rotated and drilling fluid is introduced under pressure through the sub into the cylinder 44. Some of the drilling fluid will pass on downwardly through the wash barrel 38 and thence through the hollow lower portion of the body 12 into the hole below the underreamer and the flow of this fluid back upwardly around the tool washes away the cuttings which are relatively free and which are freed by the jet streams provided from the orifices 81. Preferably there is a constriction in the wash pipe which serves to build up fluid pressure in the cylinder so as to more effectively actuate the cutters and provide high pressure and velocity to the jet streams from the orifices. The fluid pressure forces the piston 42 downwardly from the position of FIG. 1 to the position of FIG. 5. This in turn moves the wash barrel and cams downwardly so as to swing the respective cutter arms 16, 18 and 20 outwardly to their operative position.

While the present invention has been described in connection with a specific type of underreamer having roller cutters it can be seen from the foregoing that the invention is equally applicable to other oil drilling tools which are expanded in the hole and also to other types of cutters for underreamers.

Claims

What is claimed is:

1. An expandable bore hole enlarging tool which comprises an elongated, generally cylindrical tool body adapted to be suspended from and rotatably driven by a drill string;

cutter members mounted on said body in peripherally spaced relationship, said cutter member being selectively movable between an inoperative position generally retracted into said body and an operative position projecting generally radially outwardly from the body, said cutter members including respective cutter arms, said arms being arranged generally longitudinally of said body and being pivotally connected to the body adjacent their upper ends and supporting the respective cutters thereon adjacent their lower ends, said arms being pivotal between an inoperative position corresponding to said inoperative position of the cutters wherein said arms are generally recessed within elongated slots in the body and an operative position corresponding to said operative position of the cutters wherein the arms incline downwardly and radially outwardly from their pivotal connections with the body, the pivot axes of said arms being substantially horizontally coplanar and said arms having substantially the same length;

each of said arms defining a recess symmetrical with respect to the longitudinal centerline of the arm, a cam follower surface and cam bearing surface defined by said recess, said cam follower surface and said cam bearing surface being radially downwardly and inwardly inclined at the retracted position of said cutter arm;

a wash-barrel positioned within said tool body, said wash-barrel being movable from an upper position at which said cutter arms are retracted to a lower position at which said cutter arms are extended in response to fluid pressure on said wash-barrel;

an extension member removably connected to said wash-barrel, said extension member having a plurality of radially extending cams, each of which is matable with the recess in a respective one of said cutter arms, said cam and camming surfaces of said recess being interrelated such as to move said cutter arm from the retracted position to a radial extension at a predetermined radius upon downward movement of said cam, said extension member being removably affixed to said wash-barrel whereby different cams can be affixed to vary the radius to which each cutter arm is extended.

2. The apparatus as defined in claim 1 which also includes a stop means on said extension member for limiting the radially outward movement of said cutter arms.

3. The apparatus as defined in claim 2 in which the stop means comprises a radially outwardly and downwardly extending surface on each of said cams matable in bearing engagement with an outwardly and downwardly extending surface of said recess proximate the lower end of said recess when the cutter arm is extended.