-by-

Daniel A. Marson

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Appl. 62 /174,809, filed 12- JUN-2015, which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

[0002] While drilling a borehole, operators attempt to maintain an optimum weight on the drill bit used to penetrate the earth formation. In general, too little weight on the drill bit does not effectively drill the borehole. Meanwhile, depending on the type of drilling system used, too much weight on the drill bit can cause damage, produce unwanted counter-torque, increase wear, stall drilling, etc.

[0003] For example, some drilling systems use a rotary drilling system in which a rotary rig imparts rotation to a drill string having the drill bit on its distal end. Other drilling system use a downhole mud motor on the drill string to impart rotational torque to the drill bit. The mud motor can rotate the drill bit while the drill string is not rotated, or both the drill string and the motor can impart rotation to the drill bit.

[0004] When a mud motor is used, drilling mud pumped through the drill string drives the motor, which rotates the drill bit. Stalling of the mud motor can occur due to debris near the drill bit, resistance to motor rotation, etc. As will be appreciated, motor stalling can damage the mud motor.

[0005] When the drilling string is rotated in a rotary system, variations in torque along the extensive length of drill string can produce various vibrations and oscillations. For instance, the different frictional conditions encountered along the drill string, the changes in drilling through formations of different hardness, etc. can produce the variations in torque. In the end, the vibrations and oscillations can considerably strain the drill string, prematurely wear the drill bit, damage downhole electronics on the drill string, etc. In particular, the drill bit may encounter a section of the formation that is difficult to penetrate, and the drill bit jams or stalls. Yet, the rotary drive continues to impart rotation to the drill string from the surface. The drill string builds up torsional energy that then suddenly releases and can damage the downhole components. [0006] To control drilling and to monitor for such jamming or stalling, operators can monitor a number of parameters. For example, a weight indicator reading at the surface can be used to monitor weight on the drill bit. Pump pressure at the surface can also be monitored to detect issues when the readings exceed certain thresholds. Although these forms of monitoring can be effective in some cases, problems can still occur downhole.

[0007] Regardless of whether a mud motor or a rotary drilling system is used, once drilling jams or stalls, operators need to decrease the weight on the drill bit by lifting the drill string to resume rotation, relieve counter-torque, etc. Operators can then place weight again on the drill bit to resume drilling. As expected, needing to lift the drill string can be time consuming and can slow down the drilling process.

[0008] There are some ways to deal with torque and other forces during drilling. For example, a torque absorber for a downhole drilling motor is known in the art as described in US 7,044,240. The torque absorber is disposed on a drill string near the motor and automatically adjusts the weight on the drill bit to reduce the likelihood of motor stall caused by resistance to the drill bit's rotation. To do this, the torque absorber includes upper and lower unit assemblies. The lower unit assembly can rotate in response to back torque using a lead screw and ball bearings, while the upper unit assembly remains stationary. A spring applies a force on the lower unit assembly.

[0009] In another example, a dynamic damper for a drill string is known in the art as described in US 7,578,360. The damper reduces the risk of jamming a drill bit. To do this, the damper has outer and inner string sections that are supported concentrically and interconnected through a helical threaded connection. Relative rotation between the sections caused by torque give an axial movement that lifts and loosens the drill bit from the bottom of the hole when jamming occurs. A spring maintains the outer string section in an axial position, and communication of trapped oil through narrow bores between oil- filled volumes in the damper produce a hydraulic damping effect on the axial movements.

[0010] Although such techniques to detail with torque and other forces may be effective, techniques are needed to better account for various situations encountered downhole during operations. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.

SUMMARY OF THE DISCLOSURE

[0011] According to the present disclosure, a limiter is used with a work string and a cutting tool in a method to drill a borehole, mill downhole, clean casing, under-ream a borehole, etc. The method involves pumping fluid through the work string to the cutting tool, imparting rotation to at least the cutting tool, and applying weight on the cutting tool. To impart the rotation to at least the cutting tool, the work string can be rotated, and/or the cutting tool can be rotated with a mud motor operated by the pumped fluid.

[0012] Displacement of the cutting tool is adjusted relative to the work string in response to variation in torque between the work string and the cutting tool. To do this, the displacement of the cutting tool is biased relative to the work string with the limiter, and the displacement is controlled (guided) both longitudinally and rotationally with mating profiled sections disposed inside the limiter.

[0013] The displacement of the cutting tool can be mechanically and hydraulically biased relative to the work string. For example, mechanically biasing the displacement of the cutting tool relative to the work string with the limiter can involve biasing a shaft of the limiter relative to a housing of the limiter with a biasing element disposed between the shaft and the housing.

[0014] At least a portion of the pumped fluid can be diverted to a space of the limiter between the mating profiled sections. Therefore, to hydraulically bias the displacement of the limiter, the diverted fluid can act against a piston area of the limiter before being expelled from the limiter to the borehole. The diverted portion of the pumped fluid can act against a piston area of a shaft disposed in a housing, and the diverted portion of the pumped fluid can be expelled from a space between the shaft and the housing to the borehole.

[0015] To adjust the displacement of the cutting tool relative to the work string and control (guide) the movement, an inner member of the limiter can move with longitudinal and rotational displacement relative to an outer member of the limiter against the bias in response to a level of weight on the cutting tool and a level of the torque on the cutting tool. For example, the level of the weight on the cutting tool can be reduced by moving the inner member further into the outer member in response to an increase in the level of the torque on the cutting tool.

[0016] The limiter can be lubricated with the diverted portion of the pumped fluid, and about 10% or less of a total of the pumped fluid for the cutting tool can be diverted. In the diversion, a pressure drop can be produced in the diverted fluid by restricting passage of the diverted fluid through the limiter. A pressure drop in the flow passing from the work string, through the limiter, and to the cutting tool can also be produced by operating a mud motor disposed at a point between the cutting tool and the limiter.

[0017] According to the present disclosure, an apparatus is coupled between a work string and a cutting tool in a borehole and is used in drilling the borehole, milling downhole, cleaning casing, under-reaming the borehole, etc. The apparatus includes a limiter comprising an outer member, an inner member, and a biasing element. The outer member couples adjacent to one of the work string and the cutting tool, while the inner member couples adjacent to the other of the work string and the cutting tool. The outer member defines an internal profiled section therein, and the inner member has an external profiled section thereon. The external profiled section is movably disposed at least partially relative the internal profiled section of the outer member [i.e., the external and internal profiled sections mate with one another and allow for relative movement therebetween). The biasing element biases between the outer member and the inner member. The internal and external profiled sections control (guide) longitudinal and rotational movement of the inner and outer members relative to one other in response to variation in torque between the work string and the cutting tool. At least one of the internal and external profiled sections has a layer of elastomer disposed thereon.

[0018] The apparatus defines a through-bore for fluid flow passing from the workstring to the cutting tool. To adjust to weight and torque on the cutting tool, the apparatus diverts at least a portion of the fluid flow for the though-bore to a space between the internal and external profiles and expels the diverted fluid flow from the space to the borehole. The surface area in the apparatus, such as the interface of the profiles with the diverted portion of the fluid flow, produces a longitudinal force that tends to extend the inner member relative to the outer member.

[0019] The biasing element can include a plurality of conical washers stacked between the outer member and the inner member. The external profiled section can include a first helical profile defined about an exterior portion of the inner member, and the internal profiled section can include a second helical profile defined about an internal portion of the outer member. The first and second helical profiles can have a same number of lobes.

[0020] To divert the portion of the fluid flow for the though-bore to the space between the internal and external profiled sections and to expel the diverted fluid flow from the space to the borehole, the apparatus includes a flow inlet and a flow outlet. The flow inlet is disposed between the inner and outer members and diverts the portion of fluid flow for the though-bore to the space between the internal and external profiled sections. The flow outlet is disposed between the inner and outer members and expels the diverted fluid flow from the space to the borehole.

[0021] In general, the flow inlet includes an outer cylindrical portion or outer sleeve disposed in the outer member and includes an inner cylindrical portion or inner sleeve disposed on the inner member. The inner sleeve is in communication with the through- bore. The inner and outer sleeves are longitudinally and rotationally movable relative to one another and define an inlet flow passage or annular gap therebetween for diverting the portion of the flow to the space. The flow inlet tends to lubricate the space between the internal and external profiled sections with the diverted portion of the fluid flow, and the flow inlet may divert about 10% or less of a total of the fluid flow for the through-bore.

[0022] In general, the flow outlet in communication with the space includes an outer cylindrical portion or outer sleeve disposed in the outer member and includes an inner cylindrical portion disposed on the inner member. The inner and outer cylindrical portions are longitudinally and rotationally movable relative to one another and define an outlet flow passage or another annular gap therebetween for expelling the diverted portion of the flow from the space to the borehole.

[0023] The apparatus further comprises a flow restrictor disposed at a point between the cutting tool and the inner and outer members. The flow restrictor produces (or increases) a pressure drop in the fluid flow passing from the workstring, through the apparatus, and to the cutting tool. For example, the internal and external profiled sections disposed with one another can act to restrict passage of the diverted portion of the fluid flow.

Additionally, the flow inlet and the flow outlet can produce a pressure drop in the portion of the fluid flow for the though-bore diverted to the space between the internal and external profiled sections.

[0024] In various arrangements, the outer member couples adjacent to a motor, and the inner member couples adjacent to a rotary steerable tool. Alternatively, the outer member can couple adjacent to the work string, and the inner member can couple adjacent to an assembly having a motor and a rotary steerable tool. In another alternative, the outer member couples adjacent to a drill string as the work string, and the inner member couples adjacent to a drill bit as the cutting tool. In this way, the apparatus can adjust a weight on the drill bit while drilling the borehole. [0025] In one arrangement, the apparatus includes a rotary steerable tool disposed at a point between the cutting tool and the inner and outer members. The rotary steerable tool directs the cutting tool in the borehole. For example, the rotary steerable tool can be coupled between the inner member and a drill bit as the cutting tool and can be operable to change a direction of the drill bit.

[0026] In another arrangement, the apparatus includes a mud motor disposed at a point between the cutting tool and the inner and outer members. The mud motor imparts rotation to the cutting tool in response to the fluid flow from the through-bore of the inner member. Moreover, by virtue of its operation, the mud motor produces a pressure drop in the fluid flow passing from the work string, through the apparatus, and to the cutting tool.

[0027] In a similar arrangement, the outer member can instead couple adjacent to the work string, and the inner member can couple adjacent to a motor for imparting rotation to the cutting tool. In this case, the apparatus can adjust a weight on the cutting tool while milling with the cutting tool.

[0028] In yet another arrangement, the outer member couples adjacent to an under- reamer on the work string, and the inner member couples adjacent to the cutting tool. During operation, the apparatus can then balance a force between the cutting tool and the under-reamer.

[0029] The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 illustrates a bottom hole assembly having a torque limiter according to the present disclosure.

[0031] FIG. 2 illustrates a cross-sectional view of an embodiment of a torque limiter in an assembled state.

[0032] FIG. 3A illustrates a cross-sectional view of an outer member or housing of the disclosed torque limiter.

[0033] FIG. 3B illustrates an end view of the limiter's outer housing showing the lobes of the internal profiled section.

[0034] FIG. 4 illustrates a cross-sectional view of an inner member or shaft of the disclosed torque limiter.

[0035] FIG. 5 illustrates a cross-sectional view of a portion of a biasing element of the disclosed torque limiter. [0036] FIGS. 6A-6C illustrate cross-sectional views of the torque limiter during stages of operation.

[0037] FIGS. 7A-7C illustrate drilling systems having the disclosed torque limiter and a rotary steerable tool.

[0038] FIG. 8 illustrates a milling system having the disclosed torque limiter.

[0039] FIG. 9 illustrates a drilling system having the disclosed torque limiter and a reamer.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0040] Turning to FIG. 1, a system 10 has a bottom hole assembly 50 deployed on a work string 22. Depending on the type of system 10 involved, the work string 22 may use coiled tubing, threaded drill pipe, or the like. The bottom hole assembly 50 has a torque limiting apparatus 100 and a cutting tool 28.

[0041] As shown, the system 10 can be a drilling system 10 for drilling a borehole 12. Accordingly, the work string 22 can be a drill string [i.e., coiled tubing or drill pipe), and the cutting tool 28 can be a drill bit for drilling the borehole 12. Also as shown, the assembly 50 can have a flow restrictor 30 to restrict flow and/or can have a mud motor 40 to provide torque to the drill bit 28. The assembly 40 can also include additional components 45, such as discussed below.

[0042] The torque limiter 100 can be placed at any desired location within the drill string 22, not just attached near the drill bit 28 or the mud motor 40. For example, the assembly 50 may include other components 45, such as LWD subs, stabilizers, under-reamer, etc., which can be attached to one end or the other adjacent the torque limiter 100.

[0043] Although the system 10 can be a drilling system and the cutting tool 28 can be a drill bit as shown, the torque limiter 100 may be used with systems other than drilling systems, such as milling system, rotary steerable systems, under-reaming systems, etc. Examples of these are described much further below.

[0044] During operations, the drilling system 10 can use a rotary drilling rig 20 at the surface to rotate (Rs) the drill string 22 connected to the bottom hole assembly 50. A mud system 25 can circulate drilling fluid or "mud" through the drill string 22 to the bottom hole assembly 50. As the drill string 22 rotates, the torque limiter 100, the drill bit 28, and any drill collars 26 or other components also rotate. The mud exits the drill bit 28 to carry away cuttings as the borehole 12 is formed. [0045] For an arrangement of the system 10 having a mud motor 40, the pumped drilling mud operates the mud motor 40 to rotate (RB) and provide torque to the drill bit 28 either while the drill string 22 is rotated or not. (For example, if the bottom hole assembly 50 is run on coiled tubing for the string 22, then rotation may only imparted to the drill bit 22 using the mud motor 40 and not by a rotary drilling rig.) Eventually, the mud exits through the drill bit 28 and returns to the surface via the annulus.

[0046] During drilling, the drill string 22, the bottom hole assembly 50, the drill bit 28, and other components can suffer from undesirable oscillations and vibrations depending on conditions and the like. The resulting motion from these oscillations and vibrations can be extremely damaging and hard to control. To alleviate these issues, the bottom hole assembly 50 uses the torque limiter 100 to actively adjust the weight on the drill bit 28 in response to stalling, jamming, or the like.

[0047] The torque and the longitudinal force transferred to the torque limiter 100 are depicted schematically in FIG. 1 by arrows A and T. The uphole end of the torque limiter 100 is attached to the drill string 22 with a threaded connection or the like, which transfers the forces to the torque limiter 100. For example, when the drill string 22 is rotated in a rotary system, the drill string 22 imparts rotation and torque from uphole to the torque limiter 100. When the drill string 22 is not rotated, however, torque is not imparted from uphole. In either case, longitudinal force A from the surface is applied from uphole as weight on the drill bit 28 through the torque limiter 100.

[0048] The downhole end of the torque limiter 100 is attached with a threaded connection or the like to one or more of a drill collar 26, a mud motor 40, a drill bit 28, a restrictor 30, etc., depending on the arrangement. This connection transfers forces to the torque limiter 100. For example, when the drill string 22 is rotated in a rotary system, the drill string 22 imparts rotation and torque through the torque limiter 100 to the drill collar 26, drill bit 28, etc. Counter-torque due to stalling, jamming, sticking, resistance, etc. of the drill bit 28 is applied to the downhole end of the torque limiter 100. When the drill string 22 is not rotated, however, counter-torque can still be imparted from downhole from operation of the mud motor 40 and stalling, jamming, etc. of the drill bit 28. In either case, longitudinal force A from the drill bit 28 and the like is applied to the downhole end of the torque limiter 100.

[0049] As drilling of the borehole is performed, the torque limiter 100 can prevent stalling or jamming from developing and evolving into other uncontrolled motions. To do this, the torque limiter 100 automatically adjusts the weight on the drill bit 28 during drilling and reduces the likelihood that counter-torque will build up, that the mud motor 40 will stall, etc. when rotation of the drill bit 28 is unduly resisted.

[0050] Turning to FIG.2, an embodiment of a torque limiter 100 according to the present disclosure is illustrated in a cross-sectional view of an assembled state. Meanwhile, FIGS. 3A through 5 show the separate components of the torque limiter 100 in isolated cross- sectional views. In particular, FIG. 3A illustrates a cross-sectional view of an outer member 110 of the disclosed torque limiter 100, and FIG. 3B illustrates an end view of the limiter's outer member 110 showing lobes of its internal profiled section. FIG.4 illustrates a cross- sectional view of an inner member 150 of the disclosed torque limiter 100, and FIG. 5 illustrates a cross-sectional view of a portion of a biasing element 120 of the disclosed torque limiter 100.

[0051] The outer member 110 is a housing, which can couple at the limiter's uphole end 102 to the drill string (22: Fig. 1) or some other intermediate component. The outer housing 110 defines an interior 112, and an internal profiled section 114 is formed partially inside the interior 112 of the outer housing 110.

[0052] For its part, the inner member 150 is a shaft, which couples at the limiter's downhole end 104 to a drill collar (26), the drill bit (28), or some other intermediate component, as discussed later. The inner shaft 150 is movably disposed at least partially in the interior 112 of the outer housing 110, and an exterior 152 of the inner shaft 150 defines a space (S) with the housing's interior 112. The exterior 152 of the inner shaft 150 also has an external profiled section 154 thereon that is disposed with the internal profiled section 114 of the outer housing 110.

[0053] The biasing element 120 is disposed in the interior 112 of the outer housing 110 and biases against the inner shaft 150 at least partially disposed in the interior 112. In particular, the biasing element 120 fits onto an extension 153 of the inner shaft 150. One end of the biasing element 120 engages against an end ring 125a (Fig. 3A) disposed inside the housing's interior 112, and an opposite end of the biasing element 120 engages against another end ring 125b (Fig.4) disposed on the shaft 150 inside the housing's interior 112. This end ring 125b has angled flow ports 127. During operations, the bypass flow flows through the gap between the inside diameter of the biasing element 120 [e.g., washers 122) and the outside of the extension 153. Then, the flow ports 127 in the end ring 125b enable the flow to pass into the region of a flow restriction 162. [0054] As shown in the present configuration, the biasing element 120 can include a plurality of conical washers 122 stacked between the housing's interior 112 and the inner shaft 150. In fact, the conical washers 122 can be disposed about the inner shaft's extension 153 and can bias against a main shaft 151a. As shown in Fig. 5, the biasing element 120 preferably includes a stack of opposing conical disc spring washers, such as Belleville springs. However, other types of biasing elements may be used that are known to those skilled in the art.

[0055] As best shown in Fig. 2, the inner shaft 150 and the outer housing 110 are engaged through their profiled sections 114, 154 so that relative rotation of these components produces relative axial or longitudinal movement between them. The pre-tension of the biasing element 120 as well as other operating parameters as disclosed herein dictate how much the torque (T) combined with the axial force (A) must exceed a given limit before relative movement between the inner shaft 150 and outer housing 110 occurs.

[0056] The external profiled section 154 on the shaft 150 can have a number of splined, spiraled, or contoured shapes to produce concurrent longitudinal and rotational movement. As shown in Fig.4, the external profiled section 154 can uses a first helical profile defined about a first portion of the exterior 152 of the inner shaft 150. To match this profile 154, the internal profiled section 114 of the housing 110 as shown in Fig. 3A can have a second helical profile defined about a second portion of the interior 112 of the outer housing 110. Other profiles could be used.

[0057] The first and second helical profiles 114, 154 of the torque limiter 100 can have the same number of lobes. Such an arrangement is contrary to what is conventionally used in a power section of a mud motor, for example, in which a rotor and a stator having different numbers of lobes. By having the same number of lobes here, however, the disclosed torque limiter 100 acts as a helical spline. Therefore, as the torque limiter 100 torques up, it decreases in length, maintaining a more consistent depth of cut at the bit (28).

[0058] Although the same number of lobes can be used for the profiles 114, 154, this is not strictly necessary because other configurations can be used. In fact, a helical spline can include one or more lobes missing on the shaft's profile 154, although accommodating space for the missing lobe would be included on the shaft's exterior 152. The

accommodating space from the missing lobes can create a larger flow path, but the profiles 114, 154 can still operate as a helical spline. [0059] Overall, the torque limiter 100 defines a through-bore for the passage of fluid flow from the workstring (22) to the cutting tool (28). This through-bore is at least partially defined by portion of the interior 112 of the housing 110 and the though-bore 155 of the shaft 150 that allows flow from one end 102 of the limiter 100 to the other end 104. The limiter 100 is mud lubricated with approximately 5%-10% of the total flow bypassing through the internals of the torque limiter 100. The bypass rate is dictated by four flow restrictors 160-166 within the torque limiter 100. Flow enters the top of the torque limiter 100 at high pressure (bore pressure). A majority of the flow continues on through the limiter 100 to other downhole components, such as the drill bit (28). However, a portion of the flow enters the space (S) between the inner and outer members 110, 150 of the limiter 100 and eventually exits to the annulus at the downhole end of the torque limiter 100.

[0060] The flow restrictors 160-166 inside the torque limiter 100 have a pressure drop across them that urges the torque limiter 100 to extend (assisting the biasing element 120). In general then, the inner member 150 defines a piston area (by virtue of various surfaces and the like) against which the diverted fluid flow acts and assists the bias of the biasing element 120. In this way, the greater the pressure drop across the torque limiter 100 is, then the stiffer the torque limiter 100 becomes.

[0061] In particular, a flow inlet 160 (Fig. 2) is disposed between the inner and outer members 110, 150 toward the uphole end 102 of the limiter 100. Likewise, a flow outlet 166 (Fig. 2) is disposed between the inner and outer members 110, 150 toward the downhole end 104 of the limiter 100. During operations, the majority of the fluid flow of drilling fluid from the drill string (22) passes from the uphole end 102 into the limiter 100 and then passes through the limiter 100 to the downhole end 104 where the drill collar (26) and the like are coupled. The flow inlet 160 diverts at least a portion of this fluid flow for the though-bore 155 instead to the space (S) between interior 112 and exterior 152 of the housing 110 and the shaft 150. (To deal with debris, grit, etc. in the fluid flow, a screen (not shown) can be disposed at or near the flow inlet 160 to filter the diverted fluid flow. Any suitable type of filtering media can be used for such a screen.) The flow outlet 166 then expels the diverted fluid flow from the space (S) to the borehole.

[0062] The flow inlet 160 for diverting the fluid flow through the limiter 100 can take a number of forms. As shown in Fig. 3A, for example, an outer sleeve or bushing 170 is disposed on the interior 112 of the outer housing 110, such as at the end coupling 111a. An inner sleeve portion of the shaft's extension 153 of Fig.4 is disposed inside this bushing 170. As the inner shaft 150 moves relative to the outer housing 110, the extension 153, which has the form of a sleeve, can longitudinally and rotationally move relative to the bushing 170 while a flow passage is defined in the annular gap therebetween to permit a bypass of fluid flow into the inlet 160.

[0063] The flow outlet 166 can have a comparable configuration. As shown in Fig. 3A, an outer sleeve portion or bushing 176 is disposed on the interior 112 of the outer housing 110 at its downhole end 104. An outer sleeve portion or bushing 178 in Fig.4 can be disposed on the inner shaft 150 at this bushing 176. These can longitudinally and rotationally move relative to one another and define a flow passage in the annular gap therebetween for bypassed flow to exit the limiter 100 from the outlet 166.

[0064] During operations, the flow inlet 160 and the flow outlet 166 produce a pressure drop as the portion of the fluid flow for the though-bore 155 is diverted to the space (S) between interior 112 and exterior 152. The level of pressure drop between the inlet 160 and outlet 166 is governed by the pressure drop downhole of the torque limiter 100 due to a flow restriction in the form of the bit (28), the motor (40), the restrictor (30), choke sub, or any combination of these and other elements (45). The pressure drop is therefore dictated by the surrounding environment on the assembly 50, and the bypass flow rate through the limiter 100 is dictated by the clearances for the restrictions 160-166 within the limiter 100.

[0065] The diverted portion of the fluid flow lubricates the space (S) between the interior 112 and exterior 152. In general, the diverted portion of the fluid flow can be about 10% or less of a total of the fluid flow for the through-bore 155. In addition to providing lubrication, the diverted portion of the fluid flow creates a longitudinal force tending to extend the inner shaft 150 relative to the outer housing 110. To be precise, the fluid flow does not strictly create the longitudinal force. The pressure drop in the assembly 50 creates the force, and the flow is a byproduct. Thus, more bypass flow through the torque limiter 100 does not necessarily equate to more longitudinal force. Instead, a greater pressure drop in the assembly 50 more properly equates to more longitudinal force.

[0066] Additional restrictions can be formed in the space (S) between the housing 110 and the shaft 150. For example, a restriction 162 (Fig.2) can be defined between a bushing 172 on the housing 110 and a portion of the main shaft 151a to restrict passage of the diverted portion of the fluid flow from the flow inlet 160 to the flow outlet 166. Moreover, the internal and external profiled sections 114, 154 disposed with one another will tend to form a restriction 164 that restricts passage of the diverted fluid flow from the flow inlet 160 to the flow outlet 166.

[0067] When the torque limiter 100 retracts, the volume inside the tool decreases, and fluid has to exit the torque limiter 100 via the flow restrictors 160-166. Therefore, the flow restrictors' clearances not only affect the bypass flow rate but also the damping

characteristics of the torque limiter 100. Tight-fitting restrictors 160-166 produce less bypass flow but create more damping. By corollary, loose fitting restrictors 160-166 produce more bypass flow but create less damping. These variables can be configured for a particular implementation.

[0068] In addition to the mud lubrication reducing friction, a thin layer of elastomer 115 shown in the end view of Fig. 3B can be disposed at the profiled section 114 to avoid metal- to-metal contact. Here, only the internal profiled section 114 is shown having the elastomer 115. In general, one or both of the profile sections can have elastomer or other material coated therein. The compliance of such an elastomer 115, for example, will provide additional vibration damping. The thickness and hardness for the elastomer 115 can be configured for different applications. The elastomer 115 allows for easy repair, and once the elastomer 115 is worn, it can be easily stripped out and replaced.

[0069] As will be appreciated, the components of the limiter 100 can comprise several interconnecting elements to facilitate assembly. Thus, the outer housing 110 as shown in Fig. 3A generally includes a coupling sub 111a, a cylindrical housing 113a, an intermediate coupling 111b, an internally profiled housing 113b, and an end piece 113c.

[0070] In a similar fashion, the inner shaft 150 as shown in Fig.4 includes the extension 153 coupled to the main shaft 151a by a coupling 151b. An adapter 151c connects to the opposite end of the main shaft 151a, and a coupling 151d connects to the adapter 151c and to other downhole components, such as a drill collar (26). Various connections, seals, threads, bushings, etc. may be used for the torque limiter 100 and are not explicitly discussed herein, but will be appreciated by one skilled in the art.

[0071] Having an understanding of the disclosed torque limiter 100, discussion now turns to FIGS. 6A-6C, which illustrate cross-sectional views of the torque limiter 100 during stages of operation. Fig. 6A shows the torque limiter 100 in its assembled state with the shaft 150 and housing 110 fully extended relative to one another by the bias of the biasing element 120. As such, a stop 180 engages between shoulders on the main shaft 150 and the housing 110, and the profiled sections 114, 154 can be matched. FIG.6A specifically shows the torque limiter 100 prior to imposing weight on drill string (22) and with the biasing element 120 is in its fully extended position.

[0072] In use, drilling operations flow fluid through the torque limiter 100. The pressure drop between the flow inlet 160 and the flow outlet 166 causes a portion of the total flow to bypass through the limiter 100 for lubrication and creates a force tending to extend the limiter 100, assisting the biasing element 120. The flow rate of this bypassed, diverted fluid is throttled by the flow restrictions 160-166 formed at the flow inlet, bushings, profile sections, and flow outlet.

[0073] As shown in Fig. 6B, the torque limiter 100 will partially compress by virtue of weight and torque applied to the drill bit (28) during drilling. FIG. 6B shows a partially contracted position. This position could occur due to weight being applied in a downward direction to drill string (22) from the surface. In response to the weight, the inner shaft 150 moves with longitudinal and rotational displacement relative to the outer housing 110 against the bias of the biasing element 120 in response to a level of weight on the drill bit (28) and a level of torque on the drill bit (28). The movement of the inner shaft 150 relative to the outer housing 110 is controlled (guided) by the internal and external profiled sections 114, 154 and is dampened by the bias of the biasing element 120 and the diverted fluid flow.

[0074] FIG. 6B may be a normal drilling position. If the drill bit (28) encounters resistance against rotation, the counter torque on the limiter 100 increases. As shown in Fig. 6C, the increase in the level of the torque on the drill bit (28) may occur during operations, producing counter torque. This causes the limiter 100 to more fully compress as the inner shaft 150 displaces further relative to the outer housing 110 (i.e., rotates in a counterclockwise direction and advances upwards relative to housing 110). The decrease in the longitudinal length of the limiter 100 from its partial state of Fig. 6B lifts the drill bit (28) upward slightly and will cause a reduction of the level of the weight of the drill bit (28). In turn, this action will reduce the counter torque on the drill bit (28) and will improve drilling efficiency and operation.

[0075] The amount that the bit (28) gets lifted up can be very small. Yet, when the weight reduces, the entire drill string (22) tends to get longer, and the torque limiter 100 has to accommodate this lengthening. Depending on the over length of the string (22), borehole friction, and other factors, this lengthening can be an order of magnitude greater than the amount the bit (28) actually gets lifted. [0076] Eventually, the weight and torque on the drill bit (28) may reach more preferred levels so that the limiter 100 reverts to its partially compressed state of Fig. 6B. In particular, the biasing element 120 and the diverted fluid flow applies a greater force on the inner shaft 150, causing it to rotate back downward to the position of FIG. 6B once the counter-torque on the drill bit (28) reduces. The adjustments and displacements such as discussed above can occur repeatedly during drilling as operations warrant, and the operators may continue to apply the same weight-on-bit (WOB) at surface during the relative movement of the torque limiter 100.

[0077] The maximum displacement can be controlled (limited) by the stops (180: Fig. 6A) and (182: Fig. 6B), and the amount of displacement during operations accounts for the bias of the biasing element 120, the bypass flow rate, the weight on bit, the torque on bit, etc. Varying parameters of the biasing element 120 (stack length, washer thickness, and stack configuration) can produce different bias rates. The bias is assisted by the internal pressure exerted by the diverted drilling fluid pressure, which can be configured with the restrictions 160-166 and other ways. The effective piston area of the inner shaft 150 can be changed to alter the force applied, and thus an optimal force at a given pump rate, torque, and applied weight can be achieved.

[0078] In one embodiment, the torque limiter 100 can be used alone on the drill string (22) with the drill bit (28) and any drill collars (26), stabilizers, etc. In a second

embodiment, a flow restrictor can be disposed at a point between the drill bit (28) and the torque limiter 100. The flow restrictor produces a pressure drop in the fluid flow passing from the drill string (22), through the torque limiter 100, and to the drill bit (28).

[0079] For example, a restrictor sub (30: Fig. 1) can be run below the torque limiter 100 depending on the application to alter the pressure drop characteristics and resulting stiffness of the torque limiter 100. For example, a drilling application that is expected to involve high weight-on-bit (WOB) and high torque-on-bit (TOB) may include a 500-psi restrictor sub 30 run below the torque limiter 100 to effectively stiffen the limiter 100.

[0080] In another example, a drilling application that is expected to involve low WOB and low TOB may not include a restrictor sub (30), making the limiter 100 more compliant. If the bottom hole assembly 50 has a mud motor 40 below the torque limiter 100, then a restrictor sub (30) may not be used on the assembly 50 because the motor 40 itself may provide an appreciable pressure drop. Finally, the restrictor sub 30 can have a fixed restriction. Alternatively, the restrictor sub 30 can have a variable or a controllable restriction to change the stiffness of the torque limiter 100 while drilling. Various types of drilling devices (valves, chokes, clutches, pulsers, etc.) can be used for such a purpose.

[0081] In a third embodiment, a mud motor (40: Fig. 1) can be disposed at a point between the drill bit 28 and the torque limiter 100. The mud motor 40 imparts rotation to the drill bit 28 in response to the fluid flow from the through-bore 155 of the inner member 150. Moreover, by virtue of its operation, the mud motor 40 produces a pressure drop in the fluid flow passing from the drill string 22, through the torque limiter 100, and to the drill bit 28.

[0082] The mud motor 40 disposed on the drill string 22 is powered by drilling fluid from the surface and rotates the bit 28. The mud motor 40 can rotate the bit 28 while the drill string 22 remains stationary, or the mud motor 40 can add additional rotation to the bit 28 while the drill string 22 rotates. In general, the mud motor 40 has a stator with a rotor passing therethrough. Drilling fluid pumped down through the space (S) between the stator and rotor imparts rotation to the drill bit 28 operatively connected to the rotor.

[0083] FIG. 7 A illustrates another drilling system 10 having the disclosed torque limiter 100. In this drilling system 10, the bottom hole assembly 50 includes a rotary steerable system or tool 60 operable to push or point the drill bit 28. One type of rotary steerable system is disclosed in U.S. Pat. No.6,116,354, which is incorporated herein by reference. The assembly 50 is also shown with stabilizers 52, which may be located as shown or located elsewhere on the assembly 50.

[0084] FIG. 7B illustrates an alternative having the torque limiter 100 coupled adjacent to a mud motor 40, which in turn is coupled adjacent to a rotary steerable tool 60. In this arrangement, the limiter's outer member 110 couples adjacent to the work string 22. The limiter's inner member 150 couples adjacent to the motor's stator 42. In turn, the motor's rotor 44 couples to an inner shaft 64 of the rotary steerable tool 60, which can rotate inside an outer non-rotating sleeve 62.

[0085] FIG. 7C illustrates yet another alternative having the mud motor 40 coupled adjacent to the torque limiter 100, which in turn is coupled adjacent to the rotary steerable tool 60. In this arrangement, the motor's stator 42 couples to the work string (22), and the rotor 44 couples to the limiter's outer member 110. The limiter's inner member 150 couples adjacent to the inner shaft 64 of the rotary steerable tool 60, which can rotate inside the outer non-rotating sleeve 62. [0086] The arrangement of FIG. 7B uses the torque limiter 100 in a motorized rotary steerable system where the limiter 100 is above the bottom hole assembly of the motor 40 and steerable tool 60. The arrangement of FIG. 7C uses the torque limiter 100 in a motorized rotary steerable system where the limiter 100 is positioned between the motor 40 and the steerable tool 60 on the bottom hole assembly 50. As these examples shown, the torque limiter 100 can be used in these and other arrangements of drilling systems having a motor, rotary steerable tool, and/or other components known in the art.

[0087] As noted previously, the torque limiter 100 can be used with drilling system or other types of systems, such as those used for milling, reaming, cleaning, etc. For example, the bottom hole assembly 50 can be a milling or other type of assembly so that other drilling or milling tools may be used. In fact, torque control can be an issue in wellbore cleaning operations, such as operation involving dressing a polished bore receptacle (PBR), scraping casing, etc. In milling operations, such as milling a window or grinding through a bridge plug, torque control is also an issue. Therefore, the torque limiter 100 can be useful in these and other types of systems having a work string 22 and a cutting tool 28.

[0088] For example, FIG. 8 illustrates a system having the disclosed torque limiter 100 used for milling operations. The limiter 100 is deployed as part of an assembly 50 on a work string (not shown) from surface and connects to a motor 40 of the assembly 50.

During operations, the motor 40 rotates a cutting tool 28 to mill out a plug P disposed in the casing 12 between perforations 13 of a formation's zones Z. The torque limiter 100 can automatically adjust the weight on the cutting tool 28 to reduce the likelihood of motor stall caused by resistance to the tool's rotation and other related issues.

[0089] As another example, FIG.9 illustrates a system having the disclosed torque limiter 100 and an under-reamer 70. The torque limiter 100 is positioned between a cutting tool or drill bit 28 and the under-reamer 70 on the assembly 50. During operations, the limiter 100 can balance a force between the drill bit 28 and the under-reamer 70 [i.e., balance the weight applied to each of the drill bit 28 and the under-reamer 70). For example, if the drill bit 28 takes too much weight (and torques up), then the torque limiter 100 will shorten. This in turn will apply more weight to the under-reamer 70.

[0090] The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.

[0091] In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.