Xsill string stabilizer
US 3123162 A
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Description (OCR text may contain errors)
March 3, 1964 D. s. ROWLEY DRILL STRING STABILIZER Filed Aug. 4, 1961 DAVID S. ROWLEY INVENTOR.
BY Q L A T TORNEY United States Patent 0 3,123,162 BRILL STRiN-G TABlLlZER David S. Rowley, Tulsa, Shim, assignor to .lersey Productron Research Company, a corporation of Delaware Filed Aug, 4, 1961, Ser. No. 12?,281 3 Claims. (Cl. 175325) The present invention relates to apparatus for drilling boreholes in the earth and more particularly relates to an improved drill string stabilizer for controlling deviation during the rotary drilling of oil wells, gas wells and similar boreholes. In still greater particularity, the invention relates to a drill string stabilizer provided with cam-actuated ribs which are retracted into the body of the stabilizer during trips into and out of the borehole.
Efforts to achieve higher penetration rates and reduce costs during rotary drilling operations have focused increased attention upon borehole deviation problems in recent years. Experience has shown that an increase in the axial force or weight applied to the bit during rotary drilling will normally result in an increase in the drilling rate but that this increase is frequently accompanied by an increase in borehole deviation. Severe deviation, measured by the inclination of the borehole rom the vertical or by the rate of change of this inclination, may result in a failure to penetrate the geological structure of interest, may lead to sticking of the drill string in the borehole, may increase fatigue failure of pipe connections due to cyclic stresses generated as the string rotates in the crooked hole, may complicate the installation of casing and other equipment required to complete the well, and may give rise to later problems such as excessive wear of the sucker rods used to actuate the pump in the Well. In some cases deviation may also lead to legal problems because of inadvertent violation of regulations covering well spacing, proximity of the bottom of the borehole to lease lines, and the like. Recognition that these and similar difficulties are apt to accompany the use of increased bit weight has spurred interest in methods for minimizing deviation and its efiects.
Three basic methods have been used to combat borehole deviation in recent years. The first of these is predic-ated upon the tendency of a rotary bit to deviate in a direction perpendicular to the bedding planes in dipping formations, By purposely starting the borehole downdip, it is sometimes possible to compensate for deviation so that the borehole will reach the desired point at final depth. This may avoid certain problems associated with deviation but is not wholly satisfactory. A second method involves the use of large diameter drill collars to increase the effective rigidity of the drill collar assembly, particularly within about 90 to 120 feet of the bit. This reduces deflection of the bit axis under the influence of columnar forces in the collar to which the bit is at tached. Drill collar stabilizers or reamers may be used in combination with the large diameter collars to keep the collar axis centralized in the borehole and help increase effective column rigidity by preventing undue deflection of the drill string. Such packed hole techniques normally require that a stabilizer or reamer be placed between the bit and lowermost drill collar. Additional stabilizers may be located at higher points in the large-diameter drill collar assembly. The third method utilizes a stabilizer located a short distance above the bit to create a restoring force in response to the unsupported weight of the drill collars between the stabilizer and bit in the inclined borehole. Large diameter drill collars are preferably used.
To date the third method referred to above has been found to be the most effective means for coping borehole deviation problems. The installation of a stabilizer in the drill string about 40 to 60 feet or more above 3,l23,lb2 Patented Mar. 3, l fi i the bit centers the lower end of the string in the borehole and results in a change in the forces acting on the bit as long as the drill collars between the stabilizer and bit do not touch the borehole wall. The vector sum or resultant of these forces is shifted toward the vertical if the stabilizer is properly positioned in the rill string. Within limits, the drill bit tends to advance in the direction of this resultant force. Continued drilling with a stabilizer located at the proper point will therefore result in a reduction in deviation until a depth where the deviation angle corresponds to the angle between the resultant force and the vertical is reached. Thereafter, a change in the position fo the stabilizer in the drill string may permit a further decrease in deviation. Standard tables setting forth the optimum locations for the stabilizer under particular conditions have been published and will be familiar to those skilled in the art. The use of a stabilizer in this manner offsets the effect of increased bit weight by maintaining a more nearly vertical borehole and permits the application of more force to the drill bit for a given deviation angle than would otherwise be feasible.
The conventional drill string stabilizer is a tubular member provided with lateral projections or ribs which bear against the borehole wall when the stabilizer is connected in place between adjacent drill collars in a rotary drill string. The ribs, designed to support the drill collars ab ve the low side of the borehole, must have an outer diameter small enough to permit continuous downward movement of the stabilizer as the drill string advances and yet must be large enough to effect a change in the direction of the resultant force acting at the bit. Stabilizers employed heretofore have generally had fixed ribs of hard-surfaced steel which scrape along the borehole wall during drilling and during trips to and from the surface. On trips into the borehole, cuttings, shale fragments and other solids tend to accumulate on the ribs and may cause pressure surges sufficient to fracture the formation and create lost circulation problems. During trips out of the hole, solids may pack against the ribs until the drill string becomes wedged in place. These and similar diificulties frequently encountered with conventional stabilizers have discouraged their use in areas where problems such as caving and sloughing are encountered, despite the fact that the installation of a stabilizer in the drill string might otherwise permit a substantial reduction in total drilling costs.
It has been suggested that ditliculties due to sticking of the drill string and the creation of pressure surges as outlined above might be avoided by means of a stabilizer having retractable ribs which could be withdrawn into the body of the tool during trips into and out of the borehole. Etforts to develop such a tool have generally been unsuccessful. The use of mechanically retractable ribs normally requires that the retracting mechanism be actuated from the surface and poses serious design and operating problems. Ribs or pistons expanded by drilling fluid pressure present difiiculties because of problems in securing uniform expansion in a sloping borehole. Because of these and similar difiiculties, a satisfactory stabilizer having retractable ribs has not been available heretofore.
it is therefore an object of the present invention to provide an improved drill string stabilizer having ribs which can readily be retracted into the body of the tool during trips into and out of the borehole in order to reduce damage to the borehole wall, prevent sticking of the drill string in the borehole, and avoid fracturing of the formation. A further object is to provide a stabilizer including an improved means for extending and retracting the stabilizer ribs to permit trips to and from the surface.
arca es 3 Gther ob ects v 'll become more apparent as the inventi cr'bedin g eat rdetailhereaiter.
with the invention, it has now been illiculties encountered with drill string -e in the past can largely be avoided by in which cam-actuated ribs are exuded and retracted in response to displacement of a pring-loaded mandrel within the stabilizer. The pressure drop of the drill' -g fluid flowing through the bit no ed to the stabilizer mandrel and extend the ribs. The seals between the pressure-actuated mandrel and the body of the tool are exposed on one side to the fluid pre sure the annulus of the borehole and on the other side to hi h pressure within the central passageway in the drill collars and mandrel. When the flow of drilling fluid is interrupted, the mandrel returns to its normal position and the ribs are retracted. The ribs are automatically extended while fluid is circulated during drilling operations and are retracted when circulation is halted to permit trips into and out of the borehole. This eliminates the danger of sticking the drill string and creating pressure surges during tripping. Displacement of the mandrel by fiuid pressure and the use of cams to extend and retract the ribs avoid the necessity for manipulaion of the drill string to actuate the stabilizer and obviate difliculties encountered when fluid pressure is employed to inlate or extend elastic ribs or pistons. The result is a stabilizer which is considerably more dependable than tools available in the past.
The exact nature and objects of the invention can best be understood by referring to the following detailed description of a preferred embodiment of the improved drill collar stabilizer and to the accompanying drawing, in which:
FEGURE l is a partially sectioned vertical view of the stabilizer showing the ribs in the retracted position;
FIGURE 2 is an enlarged cross-section taken about line 22 in FIGURE 1;
FEGURE 3 is a partially sectioned vertical view of the tool with the ribs in the extended position; and,
FZGURE 4 is an enlarged cross-section taken about the line in PPGURE 3.
As can be seen from FZGURE l of the drawing, the im roved drill string stabilizer of the invention includes elongated housi g 13, a mandrel assembly 2b which moves downwardly within the housing when drilling fluid is passed through the tool, a series of cam members 4i) attached to the mandrel assembly, ribs 45 which are actuated by the cam members, and a spring 33 for returning the mandrel to its initial position in the housing when the flow of fluid through the tool is interrupted.
The housing 11 is a generally cylindrical member of steel or similar material provided with connecting means for attaching the stabilizer in a rotary drill string. The connecting means will normally consist of a standard API tool joint box 12 at the upper end of the housing and a corresponding tool joint pin 13 at the lower end of the tool. An axial passageway 14 extends through the housing for the circulation of drilling mud or other fluid from the drill string above the tool to the drill collar or other component below it. Internal shoulders 1:7, 16 and 17 the upper end of the tool are located respectively elow box 12-, at an intermediate point in the hous- .nd just above pin 13. Elongated openings 18 exr 1 gh the housing wall between internal shoulders The tool depicted contains 6 of these open ings arranged in opposed lateral pairs and staggered at 6 intervals around the housing. Not all of the openings can be seen in the drawing. An internal shoulder 19 at each end of the openings faces toward the interior of the housing. A greater or lesser number of opnings arranged in a somewhat di erent pattern may be utilized if desired.
The mandrel assembly 2% employed in the stabilizer is made up of three tubular steel sections. Upper section 29A fits into and slides within passageway 14 above internal shoulder The upper section contains an outer shoulder which faces the lower end of the tool and seats against shoulder 15 when the assembly is in its lo; "rrnost position. Internal shoulders 22 and 23 on the upper section bear against center mandrel section 2533 to which the upper section is connected by threads 24. Spanner wrench sockets 25 permit threading of the. two sections together in the housing. A set screw 26 which extends through the upper section and is tightened against the center section prevents loosening of the threaded joint due to vibration. Packing 27 of rubber, plastic, hemp or a similar material is positioned between the lower end of upper section 23A and an external shoulder 23 on center section 268 to provide a seal between the mandrel and the housing near the upper end of the tool. The mandrel and housing do not rotate with respect to one another and hence maintaining the seal presents little difiiculty. The outer surface of the center mandrel section contains longitudinally grooved recesses 29 at points adjacent the lateral openings in housing ll. The grooves 39 are shown more clearly in FEGURE 2 of the drawing. Each recess is slightly longer than the corresponding opening in the housing. An external shoulder 31 near the lower end of center section 2% seats against housing shoulder 16 when the mandrel is in its lowermost position. Below shoulder 31, a lower mandrel section 29C is connected to the center section by threads 32. Internal shoulder 33 on the center section bears against the upper end of the lower section 26C. Packing is retained between external shoulders 35 and 36 on the center and lower sections respectively to effect a seal between the housing and mandrel near the lower end of the tool. A set screw or similar locking means, not shown in the drawing, may be provided in order to prevent loosening of the threaded joint connecting the two sections. Helical spring 38 surrounds the lower section of the mandrel be ween lower shoulder 17 of the housing and external shoulder 39 of the mandrel. The entire mandrel assembly is free to slide downwardly in the housing in response to the difiference in force exerted by the drilling fluid pressure downwardly agaibst the upper seal and upwardly against the lower seal, since the effective area of the upper seal is greater. The mandrel is returned to its initial upward position in the housing by the helical spring when the force exerted by the fluid pressure is reduced.
Cam members 49 of steel or other metal are mounted within recesses 29 on center mandrel section ZilB and extend parallel to the longitudinal axis of the stabilizer. The cam members are held in place by bolts 41 threaded into holes in the mandrel. The bolts are countersunk below the outer surface of the cam members and are secured in place by lock nuts 42. Splines 43 on the lower surfaces of the cam members seat in grooves 36 on the mandrel in order to reduce shearing stresses in the bolts. Slots 44- extend laterally through the cam members. Each slot originates at a point near the inner surface of the cam member, extends parallel to the longitudinal axis of the tool for a short distance, slopes outwardly toward the upper end of the stabilizer, again extends a short distance parallel to the tool axis, and terminates at a point near the outer surface of the cam member. The slots in the cam members may slope at an angle of from about 10 to about 45 to the longitudinal axis of the tool, depending upon the size of the stabilizer and the pressure differential available to actuate it. An angle between about 25 and about 35 is generally preferred. Each cam memher as shown contains two slots but in some cases a single slot will sufiice.
Steel ribs 45 are slidably connected to the cam members by pins 46 which extend through slots 44. The ribs and pins are shown more clearly in FEGURES 2 and 4 of the drawing. Each rib is an elongated member containing an inner recess 47 within which the corresponding cam member sets when the rib is retracted. The ribs are provided with external shoulders 48 at their upper and lower ends. These shoulders seat against internal shoulders 19 within the openings in the housing to retain the ribs in place and prevent their over-extension. Ports extend radially through the ribs to permit access to lock nuts 42 and bolts 41 when the ribs are retracted. The access ports are closed by threaded plugs 5%. The outer surface of each rib is covered with a layer of hard surfacing material 51, cemented tungsten carbide chips supported in a copper-nickel alloy matrix for example. The hard surfacing material reduces wear of the ribs as the tool rotates in contact with the borehole wall but permits their removal by milling ofi of the steel behind it should this become necessary during a drilling or fishing operation. The leading edge of each rib is rounded to provide a wedge of drilling fluid and filter cake between the rib and the borehole wall as the stabilizer is rotated during rotary drilling. This reduces friction between the ribs and borehole wall and prevents the accumulation of cuttings against the leading surfaces of the ribs.
The stabilizer of the invention is assembled by first positioning helical spring 38 on shoulder 17 in lower part of housing ll. Cam members 40 are placed in recesses 5 7 in ribs 45. Pins 46 are inserted through the ribs and cam members to hold them together. The assembled ribs, cam members and pins are positioned in openings 15 in the housing wall and wedged outwardly so that the cam members clear the inner wall of the housing. Lower mandrel section ZtlC and center section 21GB are threaded together. Packing 34 is positioned between shoulders 35 and 35 on the mandrel. The assembled sections 293 and 28C are then inserted into the housing so that the lower section extends downwardly within helical spring 38. Packing 27 is placed on shoulder 28 about the upper end of the mandrel. Upper section 23A is threaded over this center section and tightened in place with a spanner wrench. Set screw 26 is threaded in place. The ribs and cam members are freed and positioned so that the access ports align with the bolt holes in the cam members and mandrel. Bolts 41 and lock nuts 42 are inserted to secure the cam members to the mandrel. Plugs 50 are then inserted in the access ports to close them. Assembly of the stabilizer is then complete and the tool is ready for use.
in utilizing the stabilizer, the tool is generally inserted in the drill string between drill collars at a point from about 30 to about 90 feet above the bit. The most effective location will depend upon a number of factors, including the dip of the formation being drilled, the inclination of the borehole, the diameter of the bit and drill collars, and the weight to be used in drilling. The borehole will normally be surveyed with an inclinometer or similar instrument before the drill string containing the stabilizer is lowered in place. 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 the trip into the borehole, the drilling fluid circulation pumps on the surface are normally shut down and hence no fluid flows through the stabilizer. Helical spring 33 therefore holds the mandrel assembly 2% in an upward position within housing ii. The stabilizer ribs are held in the re racted position shown in FIGURE 1 of the drawing. After the bit has reached the bottom of the borehole, the circulation of fluids through the drill string is commenced. Fluid flowing tlnough the stabilizer and the bit nozzles below it exerts pressure against upper mandrel section 29A suflicient to force the mandrel assembly downwardly within the housing against spring 38. The cam members move downwardly with the mandrel, forcing the ribs outwardly as the slots in the cam members move with respect to the pins extending through them. The shoulders at each end of the ribs and housing openings limit extension of the ribs. The internal shoulders in the housing restrict the downward movement of the mandrel assembly. FlGURE 3 of the drawing depicts the tool in operating position. As the drill string is rotated to turn the bit, the entire stabilizer assembly rotates. The stabilizer ribs bear against the borehole wall and hold the drill collars below the stabilizer away from the wall. This moves the resultant force acting on the bit toward the vertical and thus tends to reduce deviation of the borehole. The rounded leading edges of the stabilizer ribs force fluid between the ribs and borehole wall as the stabilizer rotates. This reduces friction between the ribs and the wall. The abrasion-resistant outer surfaces of the ribs thus rotate against and slide along the wall of the borehole as the drill string advances. Relatively little wear of the rib surfaces occurs because contact stresses are small.
When it becomes necessary to withdraw the drill string from the borehole, the drilling fluid circulating pumps at the surface are normally stopped. The pressure differential across the stabilizer thereupon decreases to zero. The force exerted by the compressed stabilizer spring moves the mandrel assembly upwardly within the stabilizer housing. Movement of the cam members with respect to the ribs pulls the ribs into the retracted position shown in FIGURE 1 of the drawing. The drill string can then be withdrawn from the borehole just as though the stabilizer were not present. The ribs do not extend into the annulus surrounding the drill collars and hence there is little or no danger of damaging the borehole wall or sticking of the drill string during the trip to the surface. Wear and abrasion of the rib surfaces and operating mechanism during tripping is precluded. Continned use of the stabilizer in this manner will correct excessive borehole deviation and permit the use of more weight on the drill bit than would otherwise be feasible.
In the event that the drill string should for some reason become stuck in the borehole during tripping, it is often possible to free the string by resuming the circulation of drilling fluid and thus extending the stabilizer ribs. The pressure exerted by the ribs against the wall will tend to force the string away from the wall. The pressure differential across the stabilizer and bit permits extension of the ribs regardless of the position of the drill string in the borehole. Should it become necessary to mill olf the ribs, a conventional milling tool can be lowered over the drill string and employed in the usual manner. The milling tool will cut through the steel behind the hard surfacing material of the rib surfaces and hence the milling operation can be completed relatively rapidly.
What is claimed is:
1. A drill string stabilizer which comprises an elongated tubular housing containing a plurality of lateral openings and including means for connecting said housing in a drill string; a tubular mandrel positioned within said housing and axially slidable therein; sealing means between said mandrel and housing above and below said lateral openings; a plurality of slotted cam members mounted in fixed position on the outer surface of said mandrel and extending outwardly within said lateral openings; a pinrality of rib members positioned in said lateral openings over said cam members; cam pins attached to said rib members and extending through said slotted cam members, said pins and the slots in said cam members being positioned so that said rib members are forced outwardly as said cam members and mandrel slide downwardly with respect to said housing and said pins bearing against vertical surfaces on said cam members when said rib members are in the expanded position; and a spring in said housing biasing said mandrel in a normally upward position with respect to said housing.
2. A stabilizer as defined by claim 1 wherein the slots in said cam members extend at an angle between about 25 and about 35 to the longitudinal axis of the stabilizer. 3. A drill string stabilizer which comprises a tubular,
27 generally cylindrical housing provided with means for connecting said housing at an intermediate point in a rotary drill string, said housing including a plurality of elongated lateral openings spaced at intermediate points therein; an elongated tubular mandrel positioned within said housing and axially slidable in response to the passage of fluid through said housing and mandrel; sealing means between said housing and mandrel above and below said lateral openings in said housing; a plurality of cam members mounted in fixed position on the outer surface of said mandrel and extending into said lateral openings in said housing, each of said cam members containing a slot including upper and lower sections extending parallel to the axis of said stabilizer and a center section which slopes outwardly toward the upper end of said housing; a plurality of rib members fitting over said cam members wi hin said lateral openings; cam pins attached to said rib members and extending through said slots in said cam members, said pins and the slots in said cam members being positioned so that said rib members are extended as said cam members and mandrel move downwardly with respect to said housing; and a helical spring in lower portion of said housing against which said mandrel bears, said spring urging said mandrel in a normally upward position with respect to said housing.
1,671,474 Jones May 29, 1928 1,878,260 Buniter Sept 20, 1932 2,427,052 Grant Sept. 9, 1947 2,630,390 Emanuel Mar. 3, 1953 2,657,907 Cochran et a1. Nov. 3, 1953