US3145785A

US3145785A - Expansible drill collar stabilizer

Info

Publication number: US3145785A
Application number: US8789A
Authority: US
Inventors: Jackson M Kellner
Original assignee: Jersey Production Research Co
Current assignee: Jersey Production Research Co
Priority date: 1960-02-15
Filing date: 1960-02-15
Publication date: 1964-08-25
Anticipated expiration: 1981-08-25

Description

Aug. 25, 1964 J. M. KELLNER EXPANSIBLE DRILL CQLLAR STABILIZER 4 Sheets-Sheet 1 Filed Feb. 15, 1960 Inventor Jackson M. Kellner B %.-w0 2. LL Attorney Aug. 25, 1964 J. M. KELLNER 3,145,785

EXPANSIBLE DRILL COLLAR STABILIZER Filed Feb. 15, 1960 4 Sheets-Sheet 2 FIG. IA FIG. 3A

Jackson M. Kellner INVENTOR.

BY 2...) z. Q4. ATTORNEY Aug. 25, 1964 J. M. KELLNER EXPANSIBLE DRILL COLLAR STABILIZER 4 Sheets-Sheet 3 Filed Feb. 15, 1960 Ill FIG.

Inventor Jackson M. Kellner By a. Q....L Attorney Aug. 25, 1964 J. M. KELLNER EXPANSIBLE DRILL COLLAR STABILIZER 4 Sheets-Sheet 4 Filed Feb. 15. 1960 FIG. 5

Inventor 4 Jackson M. Kellner By 2%...) 2. Q)... Attorney United States Patent 3,145,785 EXPANSIBLE DRILL COLLAR STABILIZER Jackson M. Kelluer, Tulsa, Gkla, assignor to Jersey Production Research Company, a corporation of Delaware Filed Feb. 15, 1%0, Ser. No. 8,789 16 Claims. (Cl. 175-73) The present invention relates to apparatus useful for drilling boreholes in the earth and more particularly relates to an improved drill collar stabilizer for straightening crooked boreholes during rotary drilling operations. In still greater particularity, the invention relates to a drill collar stabilizer provided with a telescoping structure which permits expansion of the stabilzer ribs within the borehole.

It is conventional during the rotary drilling of oil wells, gas wells and similar boreholes in the earth to employ a series of heavy drill collars near the lower end of the rotary drill string in order to maintain high pressures between the drill bit and the formation beneath the bit and at the same time keep the relatively thin walled drill pipe in the upper part of the borehole in tension. This prevents buckling and flexing of the pipe and greatly increases the drilling effectiveness of the bit. The drill collars thus employed are normally positioned just above the bit and may extend several hundred feet up the drill string. Because they are under compression, the collars themselves tend to buckle, however, even though the drill pipe does not. This buckling action, coupled with the tendency of dipping, laminated strata to deflect the bit, often leads to the drilling of crooked, sloping boreholes. In such a borehole, the weight of the drill collars below the point of last contact with the borehole wall may be divided into two components: one acting along the axis of the collars and a second acting normal to the first toward the low side of the borehole. This second component is usually referred to as the pendulum force. The portion of the drill string above the point of last contact which is under compression results in an additional force which is transmitted axially by the drill collars to the bit and is in effect applied from the point of last contact at an angle to the vertical greater than the deviation angle. Ignoring effects due to the heterogeneity of the formation being drilled, the bit will advance in the direction of the resultant of the pendulum force and the forces transmitted axially to the bit by the drill collars. If the angle of this resultant to the vertical exceeds the deviation angle, continued drilling will result in an increase in deviation; whereas a decrease in deviation will occur with continued drilling if the angle of the resultant is less than the deviation angle. The angle which the resultant makes with the vertical can be reduced by changing the pendulum force, by changing the forces transmitted axially to the bit by the drill collars, or by changing the direction in which the axially-transmitted forces are applied to the bit.

The method generally employed for correcting deviation during a rotary drilling operation is to place a drill collar stabilizer in the drill string at a point some distance above the bit in order to hold the drill collars away from the borehole wall. This raises the point of contact between the drill string and wall and thus increases the magnitude of the pendulum force acting on the bit. It also decreases the angle to the vertical at which the forces transmitted axially by the drill collars are applied to the bit. The point at which the stabilizer should be placed for maximum effectiveness depends upon the angle of inclination of the borehole, the diameter of the borehole and drill collar, the weight on the bit, and the type of formation being drilled. Generally the distance between the stabilizer and bit ranges from about 30 to about 100 feet. The change in the forces acting on the bit when 3,145,785 Patented Aug. 25, 1964 the stabilizer is placed at the proper point counteracts the forces responsible for deviation of the borehole.

The conventional drill collar stabilizer employed for the purpose described above is generally a tubular sub provided with lateral projections or ribs which, when the stabilizer is connected between adjacent drill collars, will bear on the sloping borehole wall and hold the collars away from the wall. The outer diameter of the ribs of such a stabilizer must be slightly smaller than the diameter of the borehole in order to permit continuou downward movement of the drill string as the drilling operation progresses. The outer diameter should be as large as possible, on the other hand, so that the drill collars can be held a maximum distance away from the borehole wall. Stabilizers employed heretofore have generally had fixed projections or ribs made of rubber, steel or similar mate rial. Experience has shown that stabilizers of this type are not wholly satisfactory because the projections or ribs tend to scrape against and snag the Walls of the borehole during trips to and from the surface. This often results in damage to the borehole wall and in some cases may cause the drill string to become stuck in the borehole. In addition, shales tend to accumulate on the projecting ribs as the stabilizer is pulled out of the hole and as a result the ribs are frequently torn or badly worn.

The use of drill collar stabilizers provided with ribs or projections which will deflect upon contact with the borehole wall during trips into and out of the borehole has recently been suggested as a means for overcoming the difliculties encountered with conventional stabilizers having fixed ribs. It is diflicult to make the projections on such a stabilizer resilient enough to avoid damage to the borehole wall during trips into and out of the borehole and yet make them stiif enough to resist the weight of the drill collars against the wall of the sloping borehole. Moreover, problems due to the accumulation of shales which tend to tear and abrade the ribs during trips into and out of the borehole are encountered despite the resiliency of the ribs.

The present invention provides a new and improved drill collar stabilizer which avoids the difiiculties encountered with stabilizers available heretofore and thus makes the use of stabilizers more attractive for use in a variety of drilling operations where borehole deviations may be encountered. In accordance with the invention. the improved stabilizer thus provided utilizes a telescoping sub provided with elastic ribs which may be expanded or contracted in response to the motion of the sub. The weight of the drill collars below the sub is employed to hold the ribs in a retracted position during trips into the borehole. When this weight is taken up as the bit reaches the bottom of the hole and bears against the formation, the ribs are expanded and support the drill collars away from the borehole wall. Raising the drill string to withdraw it from the hole again retracts the ribs. The operation of the stabilizer is thus fully automatic and does not require back rotation of the drill string or similar manipulation. It has been found that the improved stabilizer permits rapid tripping into and out of the borehole, reduces stabilizer damage due to wear and abrasion during such tripping, and greatly decreases the likelihood of damage to the borehole wall.

The exact nature and objects of the invention can best be understood by referring to the following detailed description of several embodiments of the improved drill collar stabilizer and to the accompanying drawings, in which:

FIG. 1 is a partially-sectioned vertical view of one embodiment of the stabilizer of the invention utilizing resilient ribs mounted on the stabilizer sub so that the ribs are expanded as the effective length of the sub is reduced;

FIG. 1A is a fragmentary view showing in greater detail the splines or keys on the apparatus of FIG. 1;

FIG. 2 is a cross-sectional view of the stabilizer shown in FIG. 1 taken about the line 22;

FIG. 3 is a partially-sectioned vertical view of a stabilizer similar to that shown in FIG. 1 but provided with a hearing which reduces the necessity for lubricating the apparatus;

FIG. 3A is an enlarged view of the bearing sleeve utilized in the apparatus of FIG. 3;

FIG. 4 is a partially-sectioned vertical view of a further embodiment of the stabilizer of the invention which utilizes resilient ribs molded to expanded size, and

FIG. 5 is a cross-sectional view through the stabilizer of FIG. 4 taken about the line 5-5.

Referring first to FIG. 1 of the drawings, it will be seen that the stabilizer depicted therein includes a generally tubular mandrel 11 which has three distinct but integral sections. At the upper end of the mandrel is a piston section 12 of enlarged outer diameter upon which are mounted wiper and seal ring 13 and wiper ring 14. The rings may be made of rubber, plastic, hemp or similar material resistant to oil, water and other fluids which may be encountered or employed during rotary drilling operations. They are set in annular grooves in the outer surface of the piston and will normally be retained therein by their own elasticity. In some cases, however, non-resilient materials may be used for sealing purposes, in which event suitable retainer rings may be provided. Piston 12 is separated from the lower portion of mandrel 11 by an annular, downwardly facing shoulder 15.

Immediately below the piston section of the mandrel is an intermediate section 16 having a substantially uniform outer diameter somewhat smaller than the outer diameter of the piston.

Keys or splines 17 are positioned on the outer surface of intermediate section 16 near the upper end thereof and serve to transfer torque to the mandrel. The splines extend parallel to the longitudinal axis of the mandrel and are preferably spaced at intervals about the entire surface of the intermediate section. At the lower end of intermediate section 16 is tapered shoulder 18 which serves to seat the mandrel in an annular sleeve to be described hereafter.

Below tapered shoulder 18 on mandrel 11 is lower section 19 which has an outer diameter somewhat less than that of the intermediate section. The lower end of section 19 is provided with threads 20 for connecting the mandrel to a collar 21 fitted with a standard API tool joint pin 22. The upper rim of the collar surrounding the mandrel is provided with serrations 23 which, as will be explained hereafter, serve to restrict relative motion between the various parts of the stabilizer during washover operations. The mandrel contains an axial passage 24 for the circulation of fluids through the stabilizer.

The stabilizer assembly shown in FIG. 1 of the drawings is also provided with a supporting structure which includes an upper housing 26 into which the upper end of mandrel 11 extends. At the upper end of the housing is a standard API tool joint box 27 by means of which the stabilizer may be connected to a conventional drill collar or section of drill pipe. Below box 27 the internal diameter of the housing is enlarged to form shoulder 28 and cylinder 29. Piston 12 on the mandrel, including wiper and seal ring 13 and wiper ring 14, extends into the cylinder and is free to move axially with respect to the housing. The lower part of the housing is provided with internal threads 30.

Connected to housing 26 by means of threads 30 is an intermediate section of the supporting structure, splined sleeve 31 which contains splines 32. The splines mate with those on the mandrel 11 and provide a means for transferring torque from the housing and sleeve to the mandrel. The length of the splines on sleeve 31 is sufficient to permit axial movement of the piston section of the mandrel within the limits of cylinder 29. The splines are shown in greater detail in FIGURE 1A of the drawing.

Tapered sleeve 33 at the lower end of the supporting structure is connected to the lower end of splined sleeve 31 by means of threads 34. The internal diameter of the upper part of the tapered sleeve corresponds to that of the lower section of the splined sleeve. At an intermediate point on the tapered sleeve is internal shoulder 35, below which the inside diameter of the sleeve is reduced. The lower, outer edge of sleeve 33 is tapered as indicated by reference numeral 36.

Elastic sleeve 37 is supported on the intermediate section 16 of mandrel 11 and extends over the lower part of tapered sleeve 33 surrounding the mandrel. The elastic sleeve may be made of natural or synthetic rubber or similar elastic material and may be provided with reinforcing threads or filaments of nylon, rayon or the like.

Chloroprene and nitrile type synthetic rubbers are preferred because of their high resistance to deterioration in the presence of oils. Ribs 38 are molded or otherwise formed on the outer surface of the sleeve at spaced points about its circumference. The sleeve and rib configuration is shown more clearly in FIG. 2 of the drawings. At its lower end the elastic sleeve is connected to a lower sleeve 39 provided with an internal shoulder 40 corresponding to shoulder 18 on mandrel 11. The elastic sleeve and lower sleeve 39 may be interlocked as shown in FIG. 1 or may be connected by bands and rivets or the like. In some cases the sleeves may be bonded or cemented together. The lower edge of sleeve 39 is provided with serrations 41 which mate with serrations 23 on collar 21. The faces of the serrations on the collar and sleeve should be inclined so that the collar can rotate in a clockwise direction independently of the sleeve but will turn the sleeve when rotated counterclockwise.

In using the embodiment of the invention shown in FIG. 1 of the drawings, the stabilizer is generally inserted in the drill collar section of the rotary drill string at a point ranging from about 30 to about feet above the bit. The most effective distance will depend upon a number of factors, including the type of formation being drilled, the inclination of the borehole, the diameter of the bit and drill collars, and the weight to be used on the bit. It is generally preferred to survey the borehole just before the drill string is withdrawn, using an inclinometer or similar instrument, and then employ tables developed for that purpose to select the stabilizer position. Standard tables giving optimum stabilizer locations for various conditions have been published and will be familiar to those skilled in the art. After the stabilizer has been inserted at the proper place in the drill string, the string is lowered into the borehole.

During trips into and out of the borehole, the stabilizer is supported by the upper part of the drill string attached to housing 26. The weight of the drill collars and bit below the stabilizer hold mandrel 11 in a downward position in cylinder 29 so that shoulder 15 on the mandrel rests upon the upper edge of splined sleeve 31. The stabilizer ribs 38 remain in the retracted position shown in FIGS. 1 and 2 of the drawings. When the bit reaches the bottom of the hole, the weight of the mandrel, lower drill collars, and bit is transferred from housing 26 to the formation. This prevents further movement of the mandrel in a downward direction. Housing 26, splined sleeve 31 and tapered sleeve 33 continue to move downward, however, due to the weight of the drill collars above the stabilizer. The tapered end 36 of sleeve 33 is forced downwardly beneath elastic sleeve 37, moving rib 38 on the sleeve outwardly into an expanded position. The elastic sleeve is attached to sleeve 39 which bears against collar 21 on the mandrel and hence cannot move with the tapered sleeve. Downward movement of the housing and associated sleeve thus continues until shoulder 28 in the housing rests upon the top of piston 12 on the manin the art.

to the drill collars and bit below by splines 32 on the splined sleeve and matching'spline 17 on the mandrel. The outer diameter of the expanded stabilizer ribs is slightly less than the diameter of the bit and hence the stabilizer is free to slide along the walls of the borehole as the bit advances. Due to the absence of high contact pressures between the ribs and the wall of the hole and the force on the bit. This also reduces the angle to the vertical at which forces are transmitted axially by the drill collars to the bit. As a result, the bit tends to drill in a more vertical direction. The stabilizer thus corrects or controls the deviation of the borehole. More weight can be applied to the bit to increase drilling effectiveness than could beif a stabilizer were not used.

The stabilizer ribs 38 can readily be retracted to permit withdrawal of the drill string from the borehole. Raising the string from the surface causes housing 26 and

sleeves

31 and 33 to move upwardly with respect to the mandrel 11 in elastic sleeve 37. The lower edge of the tapered sleeve 33 is pulled upwardly with respect to the elastic sleeve. and the ribs are retracted. Thereafter, shoulder 15 engages the upper end of sleeve 31 and the entire stabilizer moves as a unit. Retraction of the ribs in this manner permits tripping without danger of damaging the borehole wall or injuring the stabilizer ribs. The likeli- -hood of the stabilizer becoming stuck in the borehole during tripping is greatly reduced.

In the event that the stabilizer should become stuck in the borehole, however, it can be removed by lowering a conventional washover tool over the drill string and milling off the ribs projecting from the surface to the stabilizer. A variety of washover tools suitable for this purpose are available and will be familiar to those skilled Rotation of the elastic sleeve on the mandrel during such a washover operation is prevented by serra- 'tions 23 on collar 21 and matching serrations 41 on lower sleeve 39. The serrations lock together and prevent clockwise rotation of the sleeve with respect to the mandrel but do not interfere with the normal rotation of the mandrel within the sleeve during drilling. The elastic sleeve must be replaced following such a washover operation but other parts of the stabilizer are normally not damaged. This minimizes the cost of the washover operation and makes the use of the improved stabilizer considerably more attractive from an economic standpoint than the use of stabilizers having fixed, integral ribs.

The ribs on the stabilizer shown in FIGS. 1 and 2 of the drawing tend to rotate with the tool because of friction between the tapered sleeve and the elastic sleeve, although this tendency can be reduced somewhat by the use of a lubricant between the two sleeves. The embodiment shown in FIG. 3 diifers from the earlier embodiment in that such rotation does not occur.

The stabilizer depicted in FIG. 3 is generally similar to that shown in FIGS. 1 and 2 but employs a bearing in the supporting structure to avoid friction between the tapered sleeve and the elastic sleeve. Mandrel 111 in FIG. 3 contains at its upper end piston section 112 upon which are mounted seal and wiper ring 113 and wiper ring 114. Intermediate mandrel section 115 below the piston section has an outer diameter somewhat less than that of the piston section. Splines 116 are located on the intermediate section near the upper end thereof. Lower man- 137 are molded integral with the elastic sleeve.

collar permits the circulation of drilling fluid through the stabilizer.

Cylindrical housing 124 at the upper end of the supporting structureon the stabilizer contains an API tool joint box 125 which communicates with a cylinder below shoulder 126 into which the piston section 112 of mandrel 111 extends. Splines 127 on the inner wall of the housing mate with splines 116 on the mandrel and permit the transmission of torque. Connecting sleeve 128 of the supporting structure into which splines 127 extend is attached to the lower end of the housing by means of threads 129. The connecting sleeve is in turn connected by threads 130 to bearing support 131 of the supporting structure. The bearing support contains an annular shoulder 132 which serves as the bearing surface.

Bearing sleeve 133 of the supporting structure, shown in greater detail in FIGURE 3A of the drawing, which may be made of brass, steel, rubber, or similar material, is retained on the bearing support over shoulder 132 and is free to rotate thereon. The bearing sleeve contains internal lands 133a provided with shoulders 133b which bear against the upper surface of shoulder 132 as the bearing sleeve turns with respect to the bearing support 131. Windows 1330 permit fluid to circulate between the lands to prevent the accumulation of solids in the sleeve. Tapered sleeve 134 at the lower end of the supporting structure is connected to the lower end of the bearing sleeve by threads 135. Elastic sleeve 136 is supported on the intermediate section of the mandrel and extends upwardly over the lower end of the tapered sleeve. Ribs Lower sleeve 138 is attached to the lower end of the elastic sleeve and contains an internal shoulder 139 which matches shoulder 118 on the mandrel. Serrations 140 are provided on the lower sleeve for locking the sleeve and collar 120 for counterclockwise rotation. The collar and mandrel are free to rotate in clockwise direction independently of the sleeve.

Operation of the stabilizer of FIG. 3 is similar to that of the embodiment depicted in FIGS. 1 and 2. The ribs 137 are expanded outwardly into the position shown in FIG. 3 by downward movement of tapered sleeve 134 beneath elastic sleeve 136. The bearing interconnecting the tapered sleeve and the upper assembly permits the tapered sleeve to remain stationary as the drill string is rotated and hence reduces friction on the elastic sleeve. Because of this reduced friction, lubrication of the stabilizer is unnecessary.

The embodiment of the invention shown in FIGS. 4 and 5 of the drawings differs somewhat from the earlier described embodiments in that the stabilizer ribs are molded to full or expanded size on the stabilizer sub and are retracted for tripping purposes in response to tension from the elastic sleeve.

Referring to FIG. 4, reference numeral 211 designates a stabilizer mandrel which contains an upper piston section 212 bearing wiper ring 213 and seal ring 214. Below the piston section, intermediate mandrel section 215 of reduced diameter carries splines 216 on the outer surface thereof. Lower mandrel section 217 is separated from the intermediate section by tapered shoulder 218. Threads 219 connect the mandrel to a collar 220 bearing an API tool joint pin 221 at its lower end. Serrations 222 are located on the upper rim of the collar for use during washover operations. Mandrel bore 223 permits the circulation of fluids through the apparatus.

Housing 224 of the supporting structure at the upper end of the stabilizer assembly contains API tool joint box 225 and bore 226 which communicates with the bore of mandrel 211. Tapered sleeve 227 at the lower and of the supporting structure is connected to the lower end of the housing by threads 228. The sleeve is provided with splines 229 that mate with those on the mandrel, the

latter being axially slidable in the sleeve. The outer diameter of the sleeve is reduced below an annular shoulder 230 located at an intermeidate point thereon. A secon shoulder 231 below shoulder 230 separates the intermediate section of the sleeve from a lower section of slightly larger outside diameter. The lower skirt of sleeve 227 is tapered toward the mandrel as indicated by reference numeral 232.

Upper sleeve 233 is positioned on tapered sleeve 227 between

shoulders

230 and 231 and is free to rotate and move axially thereon. Near its lower edge, sleeve 233 contains an integral shoulder 234 which engages shoulder 231 on sleeve 227 and restricts its downward movement. Elastic sleeve 235 of rubber or similar material is connected to the lower end of annular sleeve 233 and extends downwardly over tapered sleeve 227 below shoulder 231. Ribs 236 are molded into the elastic sleeve about solid inserts 237 spaced around the periphery of the stabilizer. The ribs are molded to the full or expanded size and are not bonded to the inserts. The cross-sectional area of the sleeve, including the ribs, should be essentially uniform over its length. FIG. 5 of the drawing shows the ribs and inserts in cross section. Lower sleeve 238 is attached to the lower edge of the elastic sleeve and is provided with an internal shoulder 239 which may seat against shoulder 218 on the mandrel. The lower edge of sleeve 238 contains serrations 240 which mate with those on collar 220 to permit clockwise rotation of the mandrel and collar independently of the elastic sleeve and upper and lower sleeves attached thereto and yet prevent independent rotation during washover operations. Resilient skirt 241 is positioned at the lower outer edge of sleeve 238 and bears upon the upper surface of collar 220 to prevent engagement of the serrations on the collar and sleeve in the absence of a downward force on the sleeve.

During trips into and out of the borehole with the stabilizer shown in FIGS. 4 and 5 of the drawings, the weight of the drill collars and bit below the stabilizer holds mandrel 211 in a downward position within the assembly. Shoulder 218 on the mandrel seats against shoulder 239 on lower sleeve 238 and hence the elastic sleeve is pulled downwardly with the mandrel. Ribs 236 and solid inserts 237 are held below the lower edge of tapered sleeve 227. Shoulder 231 on the tapered sleeve engages shoulder 234 on upper sleeve 233 and thus an upward force is exerted on the elastic sleeve. The

resulting elongation of the sleeve due to the tension reduces the ribs to the retracted diameter. Because of the uniform cross section of the elastic sleeve, the elongation is substantially uniform over its length. Since the inserts are not bonded to the sleeve, they do not interfere with elongation. With the ribs thus retracted, there is little danger of damage to the ribs or borehole walls and little opportunity for the stabilizer to become stuck in the borehole during tripping.

The stabilizer ribs are automatically expanded when the drill string reaches the bottom of the borehole. The weight of the string above the stabilizer causes the housing and tapered sleeve to move downwardly around the mandrel. This reduces the tension on the elastic sleeve so that the ribs can expand outwardly into their normal position. The tapered sleeve moves down beneath the elastic sleeve and ribs to support them. The rib inserts provide lateral strength to resist the contact pressure between the ribs and the borehole wall. In this expanded position, the elastic sleeve is not under radial tension and hence the mandrel and tapered sleeve can rotate within the sleeve without building up high friction forces. This reduces the lubrication requirements of the stabilizer and provides a more dependable tool than can otherwise be obtained.

It will be recognized that other modifications of the stabilizer of the invention can be made without departing from the scope of the invention. The ribs on the stabilizer depicted in FIGS. 1 and 2 of the drawings, for example, can be molded to expanded size. In this case, the ribs would not be retracted when the stabilizer sub is in the extended position shown in FIG. 1 of the drawings but would nevertheless be free to move inwardly in response to light radial loads such as might be encountered when passing a bridged section of the borehole during tripping. Movement of the tapered sleeve beneath the elastic sleeve would support the stabilizer ribs when the stabilizer is in use without requiring that the sleeve be in radial tension. This would reduce the friction between the elastic sleeve and tapered sleeve and avoid the problem of lubricating the sleeves.

What is claimed is:

1. A drill collar stabilizer comprising a tubular supporting structure having a tapered lower edge; a tubular mandrel having one end slidably positioned within said supporting structure and extending therefrom below said tapered edge in telescopic relationship to said supporting structure; means for limiting axial movement of said mandrel with respect to said supporting structure; an elastic sleeve having circumferentially-spaced ribs on the outer surface thereof, said elastic sleeve being rotatably mounted on said mandrel and extending upwardly over said tapered edge; means for limiting axial movement of said elastic sleeve with respect to said mandrel; and means for transmitting torque between said mandrel and said supporting structure.

2. A stabilizer as defined by claim 1 wherein said supporting structure includes an upper assembly, a lower sleeve, and a bearing section interconnecting said upper assembly and said lower sleeve.

3. A stabilizer as defined by claim 1 wherein rotatable upper and lower sleeves are mounted on said supporting structure and mandrel respectively and the upper and lower ends of said elastic sleeve are attached to said upper and lower sleeves respectively.

4. A stabilizer as defined by claim 1 wherein the normal inside diameter of the upper part of said elastic sleeve is greater than the outside diameter of the portion of said supporting structure over which said elastic sleeve extends.

5. A stabilizer as defined by claim 1 wherein rib inserts are positioned beneath said elastic sleeve and are supported by said supporting structure over which said elastic sleeve extends.

6. A drill collar stabilizer comprising a tubular supporting structure provided at the upper end thereof with means for connecting said supporting structure to a rotary drill string, said structure having a tapered lower edge; a tubular mandrel axially slidable within said supporting structure and extending below said tapered edge in telescopic relationship to said supporting structure, said mandrel including means for connecting the same to a rotary drill string below the mandrel; means interconnecting said mandrel and said supporting structure for the transfer of torque from said supporting structure to said mandrel; means for limiting axial movement of said mandrel with respect to said supporting structure; an elastic sleeve having integral ribs circumferentially spaced and extending longitudinally on the outer surface thereof, said elastic sleeve being rotatably mounted on said mandrel below said supporting structure and extending above the tapered edge thereof and said mandrel including means for limiting axial movement of said sleeve thereon; and means for limiting rotation of said elastic sleeve on said mandrel.

7. A stabilizer as defined by claim 6 wherein said means for limiting rotation of said elastic sleeve includes a rotatable sleeve mounted on said mandrel and provided with serrations which engage mating serrations on said mandrel and the lower end of said elastic sleeve is connected to said rotatable sleeve.

8. A stabilizer as defined by claim 6 wherein said tubular supporting structure includes a tubular upper assembly, a lower sleeve, and an annular bearing sleeve which is attached to said lower sleeve and rotatable on said upper assembly.

9. A stabilizer as defined by claim 6 wherein the normal inside diameter of said elastic sleeve is sufliciently large to permit rotation of said mandrel and the lower portion of said supporting structure therebeneath without radial tension in said sleeve.

10. A stabilizer as defined by claim 6 wherein a rotatable sleeve is mounted on said supporting structure above said tapered edge and is attached to the upper end of said elastic sleeve and means are provided for limiting axial movement of said rotatable sleeve on said supporting structure.

11. A drill collar stabilizer comprising a tubular supporting structure adapted at the upper end to be connected to a rotary drill string and having an elongated section of reduced outer diameter at the lower end, said supporting structure including internal splines; a tubular mandrel having external splines mating with said internal splines, said mandrel being axially slidable in said supporting structure and extending therefrom below said elongated section and including means for connecting the same to a rotary drill string below the mandrel and said supporting structure including means for limiting axial movement of said mandrel; a rotatable upper sleeve externally mounted and axially slidable on said elongated section of said supporting structure, said supporting structure including means for limiting axial movement of said upper sleeve; a rotatable lower sleeve externally mounted and axially slidable on said mandrel below said supporting structure, said mandrel including means for limiting axial movement of said lower sleeve; and an elastic sleeve rotatable over said mandrel and said elongated section of said supporting structure connected at one end to said upper sleeve and at the other end to said lower sleeve, said elastic sleeve having circumferentially-spaced external ribs beneath which said elongated section of said supporting structure extends when said mandrel is in an upper position with respect to said supporting structure and which are below said elongated section when said mandrel is in a lower position with respect to said supporting structure.

12. A stabilizer as defined by claim 11 including rigid rib inserts over which said ribs on said elastic sleeve extend.

13. A stabilizer as defined by claim 11 wherein said lower sleeve contains serrations on the lower edge thereof and said mandrel includes an upperwardly facing shoulder containing matching serrations, said serrations being adapted to prevent clockwise rotation of said lower sleeve on said mandrel when said lower sleeve is in the lowermost position thereon.

14. A drill collar stabilizer comprising a tubular upper assembly adapted at the upper end to be connected to a rotary drill string and having a section of reduced external diameter at the lower end, said upper assembly containing internal splines and said section of reduced diameter including an upwardly facing shoulder located near the lower end thereof; a tubular mandrel having external splines mating with said internal splines, said mandrel being axially slidable in said upper assembly and extending therefrom below said section of reduced external diameter, said upper assembly including means for limiting axial movement of said mandrel therein, and said mandrel including means near the lower end thereof for connecting the same to a drill string; an annular sleeve having an internal downwardly facing shoulder rotatably mounted on said section of reduced diameter on said upper assembly, said shoulder on said sleeve bearing against said shoulder on said section of reduced external diameter; an elongated sleeve rotatably mounted and axially slidable on said mandrel below said upper assembly, said elongated sleeve being connected to said annular sleeve on said upper assembly; a rotatable lower sleeve mounted and axially slidable on said mandrel below said elongated sleeve, said mandrel including means for limiting axial movement of said lower sleeve thereon; and an elastic sleeve rotatably mounted on said mandrel and extending upwardly over said elongated sleeve, said elastic sleeve being connected to said lower sleeve and having circumferentially-spaced external ribs beneath which said elongated sleeve extends when said mandrel is in an upper position with respect to said upper assembly and which are below said elongated sleeve when said mandrel is in a lower position with respect to said upper assembly.

15. A stabilizer as defined by claim 14 wherein said annular sleeve contains internal longitudinal grooves through which fluid may circulate between said sleeve and housing.

16. A drill collar stabilizer comprising a tubular upper assembly adapted at the upper end to be connected to a rotary drill string and having an elongated section of re duced external diameter at the lower end, said upper assembly having internal splines; a tubular mandrel having external splines mating with said internal splines in said upper assembly, said mandrel being axially slidable in said upper assembly and extending therefrom below said section of reduced external diameter, said upper assembly including means for limiting axial movement of said mandrel therein and said mandrel including means for connecting the same to a drill string below the mandrel; a rotatable sleeve mounted and axially slidable on said mandrel below said elongated section of reduced external diameter on said upper assembly, said mandrel including means for limiting axial movement of said rotatable sleeve thereon; and an elastic sleeve rotatably mounted on said mandrel and extending upwardly over said elongated section of reduced diameter on said upper assembly, said elastic sleeve being connected to said rigid sleeve and having circumferentially-spaced external ribs beneath which said elongated section of reduced diameter extends when said mandrel is in an upper position with respect to said upper assembly and which are below said elongated section of reduced diameter when said mandrel is in a lower position with respect to said upper assembly.

References Cited in the file of this patent UNITED STATES PATENTS 1,692,181 Machris Nov. 20, 1928 2,052,786 Meyer Sept. 1, 1936 2,173,309 Monroe Sept. 19, 1939 2,589,534 Buttolph Mar. 18, 1952 2,876,992 Lindsay Mar. 10, 1959 2,891,769 Page et a1. June 23, 1959