US 2754086 A
Description (OCR text may contain errors)
July 10, 1956 K. A. sUMMx-:Rs
TORQUE AND WEIGHT CONTROL. APPARATUS Filed Oct. 18, 1954 JNVENToR. KENNETH A.SUMMERS BY Mba a FIG. 1
2,754,086 TRQUE AND WEIGHT CONTROL APPARATUS Kenneth A. Summers, Los Angeles, Calif. Application October 18, 1954, Serial No. 462,700 1 Claim. (Cl. Z55- 28) This invention relates to an apparatus adapted to be inserted between a rotary driving means and a driven member for controlling the torque and axial force applied to the member. A preferred application of the invention is in controlling the torque and weight applied to a high speed drill bit in a bore hole drilling operation, and the apparatus will be described in this connection. It is to be understood, however, that the principles of operation are applicable to other types of rotary tools, such as drill pipe cutters, milling tools, and the like.
For maximum efficiency in a rotary drilling operation in a bore hole, it is important that the applied torque transmitted to the drill bit through rotation of the drill pipe string, be maintained substantially constant. If the applied torque is too small, the cutting blades of the drill bit will not be operating at maximum eiciency in cutting into the earth formations, and the drilling will be unnecessarily prolonged. On the other hand, if the applied torque exceeds a given value, the bit blades may be seriously damaged. In fact, if the resisting torque offered to the drill bit by a particularly hard formation is suliicient to hold the bit against rotation, the applied torque may increase to such a value as to twist ol'If the drill pipe string.
The problem of maintaining constant torque is particularly serious in the case of high speed drilling operations such as those using a diamond core bit. Too much torque on a bit of this type oftentimes results in the diamonds being broken loose from their settings, thereby necessitating costly replacements.
The desired value of the torque to be applied and maintained constant for maximum drilling efficiency, depends upon the type of drill bit used and the strength of the driving drill pipe string. For example, it may be found that the pipe string and bit may tolerate a torque suicient to result in three to four rotations of the upper end of the drill pipe before the drill bit at the lower end commences rotating. In this case, it is necessary to insure that the applied torque on the pipe string will not exceed this desired torque Value if twisting off' of the pipe string or damaging of the bit is to be avoided.
The applied torque on a drill bit is ordinarily controlled by the effective weight of the drill pipe string acting on the bit. This effective Weight is, in turn, controlled by the supporting traveling block at the surface of the bore hole. In an endeavor to maintain theapplied torque constant to attain maximum drilling eiciency and avoid broken bits and twisting off of ,drill pipe strings, a tension scale, interposed betweenjthe traveling block and pipe string, together With a suitable torque indicator, is carefully observed during -a drilling operation. If `the applied torque appears to be increasing ,beyondpagiven value, the effective .weight of the "drill-pipe -,string may be decreased by lifting up slightlyon the pipe string with the traveling block, thereby decreasing the'frictional force of the cutting blades againstthe formations. u I ftheltorque appears. to be decreasing, .more weight or axial force is applied to the bit byv lowering the traveling block.'
States Patent weight and torque control also exlsts 1n bore hole milling and cutting operations. In every instance, the operation is manually controlled from the surface of the bore hole and is, accordingly, subject to human error.
Bearing the above in mind, it is a primary object of the present invention to provide a tool in which the torque and weight on a drill bit or other member driven by a rotary driving means, is automatically controlled, whereby constant vigilance during a drilling operation is not necessary and the possibilities of damaged bits and twisted pipe strings are materially reduced.
More particularly, an object of the invention is to pro'- vide a tool for automatically maintaining the torque applied to a drill bit or cutting member substantially constant.
A further object is to provide a device ofthe above nature which is rugged and simple in construction, and which may be readily adapted to conventional bore hole drilling apparatus without modification of any of the existing equipment.
These and other objects and advantages of this invention are realized by providing a pair of telescoping elements adapted to be inserted between the rotary driving means and the driven member, such as a drill bit. These elements include means automatically responsive to an increase in the resistance to rotation of the bit beyond a given torque Value, for telescoping the elements together, whereby the bit is retracted slightly from the earth formations and the resisting torque is brought back to said given value. A further means is provided for maintaining the axial force or weight acting on the bit substantially constant so that the applied torque will not appreciably vary.
In a preferred form of the invention, one of the elements comprises a cylindrical section. The other element comprises a mandrel supporting the drill bit at its lower end and having its upper portion fitted partially within the cylindrical section for telescoping movement. The free end of the cylindrical section is secured to the end of a string of drill pipe. The mandrel is provided about its periphery with one or more grooves spiraling towards the drill bit end of the mandrel in the direction of normal rotation of the driving means. Cam means are stationarily secured to the cylindrical section and arranged to project into at least one of the grooves. Circulating mud pressure passing through the cylindrical section is preferably employed to control the axial force or weight applied to the drill bit. This control is accomplished by providing a restricting orilice in the mud passage passing through the mandrel so that a pressure differential exists between the upper and lower ends of the mandrel. This pressure differential will thus tend to normally urge the grooved mandrel axially from the section towards the earth formations. In certain types of operations, in which circulating mud is not available, the axial force or weight on the bit may be controlled by a compression spring disposed within the cylindrical section and normally acting between the mandrel and section to urge the mandrel outwards in the direction of the earth formations.
With the above described arrangement, an extraordinary resistance to rotation of thedrill bit will result in the bit being held rotationally stationary with respect to the rotatf ing pipe string and cylindrical section.` As a result, the cam means'will travel in the spiral groove, thereby tele-` scoping the grooved mandrel into the cylindrical section to retract the drill bit slightly from the formations. This retraction will decrease the resistance of the formation'sto rotation of the bit whereby the torque component of 1force applied to the grooved mandrel and bit by the cam means will be sutlicient to rotate the bit, and the drilling op'erajy tioncan continue. Y V f :"-i'
The problem of careful If the earth formations are exceedingly sott so that the resisting torque offered to the drill bit is decreased, the axial force exerted by the mud pressure or compression spring will urge the grooved mandrel and bit further in the formations until the resisting torqueV is in equilibrium with the applied torque component exerted on the mandrel by the cam means. Thus, regardless of the variations in resisting torque oiered by the formations, the axial weight or force and torque applied to the drill bit will be automatically adjusted to insure that the driving torque remains substantially constant.
A better understanding of the invention will be had by referring to the accompanying drawings in which:
Fig. l is an enlarged cuba-way perspective view showing the torque and force control apparatus of the invention in operative position between a drill pipe string and drill bit during a drilling operation; and,
Fig. 2 is an enlarged view of a portion of the apparatus looking in the direction of the arrow 2 of Fig. l.
Referring to Fig. l, there is shown a bore hole 19 containing a string of drill pipe 11 for rotating a high speed drilling bit 12. Interposed between the lower end of the drill pipe and bit there is provided, in accordance with the invention, a torque and weight control apparatus designated generally by the numeral 13. As shown, this apparatus comprises a pair of telescoping elements, respectively in the form of a cylindrical section 14 and mandrel 15. The upper end of the cylindrical section 14 is secured to the lower end of the drill pipe string 11 as by screw threads 16. The lower end of the cylindrical section, on the other hand, is provided with a collar 17 having a reduced diameter bore coaxially alined with the cylindrical section 14 and providing an inner annular shoulder 18.
The mandrel element is telescopically guided into and out of the cylindrical section by the collar 17. The upper end of the mandrel is provided with an enlarged head portion 19, having a diameter corresponding substantially t'o the inside diameter of the interior of the cylindrical section so that an annular seal between the head and interior walls of the cylindrical section is attained. The underside of the enlarged head 19 deiines a downwardly directed an nular shoulder 20 adapted to abut the shoulder 18 when the mandrel is in its lowermost position and thereby serve as a stop. The lower end of the mandrel is threadedly secured to the drill bit 12 as shown.
The main body portion of the mandrel 15 is provided with at least one peripheral groove 21 spiraling towards the drill bit in a direction corresponding to the direction of rotation of the drill pipe string 11. ln Fig. l this direction is clockwise as viewed looking down the bore hole from the top, and as indicated by the arrow. A projection 22, which may be in the form of an internal spline, integral with the collar 17, projects into the groove 21. With this arrangement, relative rotation between the mandrel and the cylindrical section will cause the projection 22 to ride in the spiral groove 21 and telescope the mandrel into and out of the cylindrical section.
ln the embodiment of Fig. l, there is shown a compression coil spring 23 positioned between the upper end of the mandrel head 19 and the top portion of the cylindrical section. This spring will normally urge the mandrel downwardly towards the earth formations. In drilling operations' such as illustrated in Fig. l, however, the principal axial force applied to the mandrel 15 is derived from the circulating mud pressure'. This mud ow generally passesdownwardly through the interior passage 24 of the drill pipe, through the hollow interior of the cylindrical section 14, through an internal bore v25 in the mandrel 15 and out the drill bit 12. The mud` then carries up chips and other debrischurned upV by the bit outside the drill pipevto the surface of the bore hole 10. ln order to employ the mud flow pressure for exerting an axial force onthe mandrel, there is provided a restricting oriiice 26 inthe-.boreZS of' the mandrelhad 19. There will then be established a pressure dilerential betweenthe upper and lower ends of the mandrel which may be varied by varying the mud pressure.
1n operation, the weight and torque control apparatus 13 and drill bit 12 are lowered into the bore hole 10 by the traveling block (not shown) in the conventional manner. During this lowering operation, the mandrel 15 is normally telescoped downwardly by the spring 23 or mud pressure until the shoulder 20 is seated against the shoulder 18. When the drill bit 12 engages the bottom of the bore hole, continued lowering of the pipe string will cause the cylindrical section 14 to telescope over the mandrel, and the entire pipe string and cylindrical section will rotate in a clockwise direction, and the projection 22 will downwardly spiral within the groove 21. When the mandrel head 19 reaches a substantially centered position within the hollow interior of the cylindrical section 14, the drill pipe string and cylindrical section are held against further movement in a vertical direction by the traveling block at the surface. The pipe string and cylindrical Section are then caused to rotate in a clockwise direction by the rotary table at the surface. This rotary motion is transmitted to the mandrel 15 and drill bit 12 by the cam means or projection 22 engaging the upper surface of the groove 21.
In order to understand the relationship between the various forces acting on the mandrel and drill bit, reference is had to Fig. 2. In this drawing, the projection 22, upon rotation of the cylindrical section 14, will be moving to the left andrthus bearing against the upper edge of the groove 21. The total force exerted by the projection against the groove 21 is indicated by the vector 27. This force will act in a direction normal to the tangential contact of the projection on the upper edge of the groove. Assuming the helix angle of the grooves to be 30 degrees, for example, the vector 27 will be at a 30 degree angle with respect to the vertical. This force vector may be divided into a horizontal force component 28 and a vertical force component 29. The vertical component 29 tends to lift the mandrel 15 up into the cylindrical section 14, while the horizontal component 28 tends to rotate the mandrel. This horizontal component therefore represents the torque applied to the mandrel and drill bit.
Under equilibrium conditions during a drilling operation, it will be clear that the axial force applied to the mandrel by the circulating mud pressure differential across the orifice 26, plus any axial force exerted by the compression spring 23, when such a spring is employed, exactly balances the upward component of force 29 resulting from the pressure of the projection 22 on the groove, plus the upward reaction force exerted by the formation on the drill bit. Also, it will be clear that the resistance to rotation of the drill bit by the formations will establish a reacting or resisting torque which will balance the horizontal torque component 28. The magnitude of the applied horizontal force component 28 may be controlledby the axial force brought to bear on the mandrel by the circulating mud pressure. For example, by increasing this axial force, the total contact force between the mandrel groove 21 and the projection 22 as represented by the vector 27 is increased. Correspondingly, the horizontal and vertical components 28 and 29 are increased. The increased vertical component balances the increase in the axial force so that there is no change in the axial force applied to the drill bit, while the increased horizontal component provides the desired increased torque. Since the vertical forces are in balance, themandrel and section will rotate as a unit.
With the mud pressure adjusted to provide a torque component 28 of desired value, the drilling progresses in the normal manner; Should the resistance to rotation of the drill bit increase suddenly as a result of a particularly hard formation, this increased resistance will tend to hold the mandrel rotationally stationary with respect to the rotating cylindrical section 14. As a result, the projection 22' will move in the groove 21 to the left,l
as viewed in Fig. 2, and thereby lift the mandrel into the section. This lifting action is a result of the increased tion. This telescoping movement in turn will retract the drill bit 12 slightly from the formations and thereby decrease the resisting torque offered to the bit by the formations. When this resisting torque has decreased to the desired torque value represented by the horizontal vector 28, the vertical force component 29 will again be in the axial force exerted on the mandrel by the mud pressure, and the mandrel and cylindrical section will again commence to rotate as a unit.
In the event the earth formations are unusually soft, the axially directed reacting force of the formation on the drill bit tending to urge Will decrease.
drilling operation regardless of variations in the hardness of the formations.
As the drilling progresses, it will be understood, of course, that the traveling block block 19 in a substantially centered position in the interior of the cylindrical section 14.
In certain drilling or cutting operations, circulating mud may not be available. In this instance, the compression spring 23 can be made suihciently strong to provide the desired axial force on the mandrel. An increase in this force will occur if the mandrel is telescoped any appreciable distance from its original position in the cylindrical section, but this increased force due to the characteristics of the spring will not be significant, provided the telescoping movements of the mandrel within the cylindrical section are only a small per cent of the total length of the spring.
In other instances, it may creased creased torque. In such cases, the helix angle could be changed to result in increased telescopic movements and the compression spring would then provide an increased torque component.
While the invention has been described with respect to a drilling operation, as mentioned previously, it is to be understood that the principles are applicable for controlling the torque and axial force applied to any member driven by a rotary driving means. The torque and force control apparatus is therefore not to be thought of as limited to the specific embodiment described and illustrated.
What is claimed is:
An apparatus for controlling the torque and weight applied to a driven member by a notary driving means in References Cited in the le of this patent