BACKGROUND

[0001] The following descriptions and examples do not constitute an admission as prior art by virtue of their inclusion within this section.

[0002] Drilling motors are commonly used to provide rotational force to a drill bit when drilling earth formations. Drilling motors used for this purpose are typically driven by drilling fluids pumped from surface equipment through a drill string. This type of motor is commonly referred to as a mud motor. In use, the drilling fluid is forced through the mud motor, which extracts energy from the flow to provide rotational force to a drill bit located below the mud motor. There are two primary types of mud motors: positive displacement motors ("PDM") and turbodrills. The following disclosure focuses primarily on turbodrills; however, one of ordinary skill in the art will appreciate that balance drums disclosed herein may be similarly used in PDMs.

[0003] Figure 1 illustrates a cross-sectional view of a turbodrill 100 in connection with implementations of various techniques described herein. A housing 1 10 includes an uphole connection 1 15 to connect to the drill string. Turbine stages 120 are disposed within the housing 1 10 and may be used to rotate a shaft 130. At a downhole end portion of the turbodrill 100, a drill bit (not shown) may be attached to the shaft 130 by a downhole connection 125. In addition, stabilizers (not shown) may be disposed on the housing 1 10 to help keep the turbodrill centered within the wellbore.

[0004] The turbodrill 100 may use turbine stages 120 to provide rotational force to the drill bit. The turbine stages 120 may consist of one or more non-moving stator vanes and a rotor assembly having rotating vanes mechanically linked to the shaft 130. The turbine stages 120 may be designed such that the vanes of the stator stages direct the flow of drilling fluid into corresponding rotor blades to provide rotation to the shaft 130, where the shaft 130 ultimately connects to and drives the drill bit. Thus, the high-speed drilling fluid flowing into the rotor vanes may cause the rotor and the drill bit to rotate with respect to the housing 1 10. The turbine stages 120 may also include radial bearings provided between the shaft 130 and the housing 1 10.

[0005] While providing rotational force to the shaft 130, the turbine stages 120 may also produce a downhole axial force, or thrust, from the drilling fluid. The downhole thrust, however, may produce a higher weight on bit (WOB) than required for operation of the turbodrill 100. To mitigate the effects of excess thrust in the turbodrill 100, thrust bearings 140 may be provided. The thrust bearings 140 may include steel roller bearings, polycrystalline diamond compact ("PDC") surface bearings, or any other implementation known to those skilled in the art.

[0006] The excess downhole thrust produced from the drilling fluid may also cause damage to the hard materials of the thrust bearings 140, thereby reducing the life of the thrust bearings 140. A balance drum (not shown) may be used in a turbodrill to reduce axial loading on thrust bearings resulting from the downhole thrust, where the balance drum may be coupled to an uphole end portion of the shaft.

SUMMARY

[0007] Described herein are implementations of various technologies for a turbodrill using a balance drum. In one implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include a compliant mounting disposed between the balance drum assembly and the housing, where the compliant mounting is configured to allow displacement of the balance drum assembly within the housing.

[0008] In another implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include an elastomeric mounting disposed between the balance drum assembly and the housing, where the elastomeric mounting is configured to allow displacement of the balance drum assembly within the housing.

[0009] In yet another implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include a compliant rod mechanism coupled to an uphole end portion of the balance drum assembly, where the compliant rod mechanism is configured to allow displacement of the balance drum assembly within the housing.

[0010] In another implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include a rod with one or more compliant joints coupled to an uphole end portion of the balance drum assembly, where the rod with one or more compliant joints is configured to allow displacement of the balance drum assembly within the housing.

[0011] In another implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include a flex shaft having an uphole end portion coupled to the balance drum assembly and a downhole end portion coupled to the rotatable shaft, where the flex shaft is configured to allow displacement of the balance drum assembly within the housing.

[0012] In yet another implementation, the turbodrill may include a housing having an upper end portion that is configured to be coupled to a drill string. The turbodrill may also include a rotatable shaft having a lower end portion configured to be coupled to a drill bit. The turbodrill may further include a balance drum assembly coupled to the shaft within the housing. In addition, the turbodrill may include a spherical bearing assembly disposed between the balance drum assembly and the housing, where the spherical bearing assembly is configured to allow displacement of the balance drum assembly within the housing.

[0013] The above referenced summary section is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section. The summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Implementations of various techniques will hereafter be described with reference to the accompanying drawings. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various techniques described herein.

[0015] Figure 1 illustrates a cross-sectional view of a turbodrill in connection with implementations of various techniques described herein.

[0016] Figure 2 illustrates a cross-sectional view of a turbodrill using a balance drum assembly.

[0017] Figures 3-5 illustrate a cross-sectional view of a turbodrill using a balance drum assembly with a coil spring in accordance with implementations of various techniques described herein.

[0018] Figure 6 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with one or more Belleville springs and one or more rotational inhibitors in accordance with implementations of various techniques described herein.

[0019] Figure 7 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with a rubber mounting in accordance with implementations of various techniques described herein. [0020] Figure 8 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with a spherical bearing assembly in accordance with implementations of various techniques described herein

[0021] Figure 9 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with an axial bearing cage and one or more rotational inhibitors in accordance with implementations of various techniques described herein.

[0022] Figure 10 illustrates a cross-sectional view of a turbodrill, using a balance drum assembly with an axial bearing cage, a spring mechanism, and one or more rotational inhibitors in accordance with implementations of various techniques described herein.

[0023] Figure 1 1 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with a flex rod and a rod retainer in accordance with implementations of various techniques described herein.

[0024] Figure 12 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with a rod, a lower universal joint, and an upper universal joint in accordance with implementations of various techniques described herein.

[0025] Figure 13 illustrates a cross-sectional view of a turbodrill using a balance drum assembly with an internal flex shaft in accordance with implementations of various techniques described herein.

[0026] Figure 14 illustrates a cross-sectional view of the turbodrill using a balance drum assembly with an external flex shaft in accordance with implementations of various techniques described herein.

[0027] Figure 15 illustrates a cross-sectional view of the turbodrill using the balance drum assembly with the internal flex shaft in accordance with implementations of various techniques described herein.

DETAILED DESCRIPTION

[0028] The discussion below is directed to certain specific implementations. It is to be understood that the discussion below is only for the purpose of enabling a person with ordinary skill in the art to make and use any subject matter defined now or later by the patent "claims" found in any issued patent herein.

[0029] It is specifically intended that the claimed invention not be limited to the implementations and illustrations contained herein, but include modified forms of those implementations including portions of the implementations and combinations of elements of different implementations as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the claimed invention unless explicitly indicated as being "critical" or "essential."

[0030] It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first object or step could be termed a second object or step, and, similarly, a second object or step could be termed a first object or step, without departing from the scope of the invention. The first object or step, and the second object or step, are both objects or steps, respectively, but they are not to be considered the same object or step.

[0031] As used herein, the terms "up" and "down"; "upper" and "lower"; "upwardly" and downwardly"; "below" and "above"; and other similar terms indicating relative positions above or below a given point or element may be used in connection with some implementations of various technologies described herein. However, when applied to equipment and methods for use in wells that are deviated or horizontal, or when applied to equipment and methods that when arranged in a well are in a deviated or horizontal orientation, such terms may refer to a left to right, right to left, or other relationships as appropriate. [0032] The following paragraphs provide a brief summary of various technologies and techniques directed at a turbodrill using a balance drum in accordance with various implementations described herein.

[0033] In one implementation, the turbodrill may use a balance drum assembly with a compliant mounting, where the compliant mounting may be a spring mechanism, such as a coil spring. A balance drum assembly may be disposed within a main flow area of the turbodrill and may include a drum stator and a drum rotor. The drum stator may also include a cap and a sleeve, where the drum rotor may be movably disposed within the sleeve. The balance drum assembly may be coupled to the coil spring, which may in turn be coupled to the housing. Space may exist between the cap and an inner wall of the housing such that the coil spring may allow for a lateral displacement and an angular displacement of the balance drum assembly within the housing. The lateral and angular displacement via coil spring may reduce the likelihood of point loading caused by canting within the balance drum assembly, thereby avoiding wear along {e.g., in the vicinity of) a radial gap formed between an inner diameter of the sleeve and an outer diameter of the drum rotor.

[0034] In another implementation, the spring mechanism may be one or more Belleville springs. Further, one or more rotational inhibitors may be used to resist rotation of the drum stator within the housing in response to the flow of drilling fluid. The rotational inhibitors may be coupled to an inner wall of the housing and may be linked to the cap such that rotation of the drum stator is restrained.

[0035] In yet another implementation, the turbodrill may use a balance drum assembly with a compliant mounting, which may be constructed of a solid material. As an example, the compliant mounting may be an elastomeric mounting. The balance drum assembly may be coupled to the elastomeric mounting, which may in turn be coupled to the housing. The elastomeric mounting may include a top portion coupled to a bottom portion. The top portion may be disposed between an inner wall of the housing and the cap. The bottom portion may be disposed between an inner shoulder of the housing and the downhole end portions of the cap and the top portion. The top portion and the bottom portion of the elastomeric mounting may possess sufficient flexibility to allow for a lateral displacement and an angular displacement of the balance drum assembly within the housing.

[0036] In still another implementation, the turbodrill may use a balance drum assembly with axial bearings, such as an axial bearing cage, and one or more rotational inhibitors. The balance drum assembly may rest on the axial bearing cage, where the axial bearing cage may also rest on an inner shoulder of the housing. The one or more rotational inhibitors may be used to resist rotation of the drum stator within the housing in response to a flow of drilling fluid. Bearings of the axial bearing cage may freely rotate and allow for the lateral displacement of the balance drum assembly within the housing.

[0037] In still yet another implementation, the turbodrill may use a balance drum assembly with axial bearings, a spring mechanism, and one or more rotational inhibitors. The balance drum assembly may rest on the axial bearing cage, where the axial bearing cage may rest on a spring mechanism. In turn, the spring mechanism may rest on an inner shoulder of the housing. The one or more rotational inhibitors may be used to resist rotation of the drum stator within the housing in response to a flow of drilling fluid. Bearings of the axial bearing cage may freely rotate and allow for the lateral displacement of the balance drum assembly within the housing. The spring mechanism may also allow for the lateral and angular displacement of the balance drum assembly.

[0038] In still yet another implementation, the turbodrill may use a balance drum assembly with a compliant rod mechanism, where the compliant rod mechanism may include a flex rod and rod retainer. The balance drum assembly may be coupled to the flex rod, where the flex rod is coupled to the rod retainer. Essentially, the balance drum assembly hangs from the rod retainer via the flex rod. The flex rod may allow for a lateral displacement and an angular displacement of the balance drum assembly within the housing.

[0039] In another implementation, the turbodrill may use a balance drum assembly with a compliant rod mechanism, where the compliant rod mechanism may include a rod and one or more compliant joints. In such an implementation, the one or more compliant joints may include a universal joint. The balance drum assembly may be coupled to the rod via a lower universal joint, where the rod is coupled to the rod retainer via an upper universal joint. Essentially, the balance drum assembly hangs from the rod retainer via the rod, the lower universal joint, and the upper universal joint. Lateral and angular displacement of the balance drum assembly may be performed via the lower universal joint and the upper universal joint.

[0040] In another implementation, the turbodrill may use a balance drum assembly with a compliant rod mechanism, where the compliant rod mechanism may include a flex shaft. A drum rotor may be coupled to an uphole end portion of an internal flex shaft, such that the drum rotor may be configured to rotate in conjunction with the internal flex shaft. In particular, the internal flex shaft may be coupled to the drum rotor within a drum rotor annulus and within a sleeve. The internal flex shaft may be coupled to the main shaft, where the main shaft may extend in a downhole direction through the turbodrill. The internal flex shaft may allow for the lateral and angular displacement of the main shaft via binding of the internal flex shaft.

[0041] Various implementations described above will now be described in more detail with reference to Figures 2-15.

Balance Drum Assembly

[0042] Figure 2 illustrates a cross-sectional view of a turbodrill 200 using a balance drum assembly 210 in connection with implementations of various techniques described herein. In one implementation, the turbodrill 200 may include a housing 202, where the housing 202 may have an upper connection 204 for engaging with uphole members of a drill string.

[0043] The housing 202 may further include turbine stages 240, which may be used to rotate a shaft 230 using a flow of drilling fluid. Drilling fluid may include drilling mud or any other implementation known to those skilled in the art. In particular, the turbodrill 200 may use turbine stages 240 to provide rotational force to a drill bit (not shown). The turbine stages 240 may include one or more stator components, rotor components, radial bearings, or any other implementation known to those skilled in the art. At a downhole end portion of the turbodrill 200, the drill bit (not shown) may be attached to the shaft 230 by a downhole connection 250. In addition, stabilizers (not shown) may be disposed on the housing 202 to help keep the turbodrill 200 centered within a wellbore.

[0044] To reduce axial loading resulting from the flow of drilling fluid, one or more thrust bearings 260 may be disposed proximate to the downhole end portion of the turbodrill 200. The thrust bearings 260 may be coupled to the housing 202 and the shaft 230. The thrust bearings 260 may include various components, such as steel roller bearings, polycrystalline diamond compact ("PDC") surface bearings, or any other implementation known to those skilled in the art.

[0045] The balance drum assembly 210 may be disposed within a main flow area 220 of the turbodrill 200 and may include a drum stator 212 and a drum rotor 214. The drum stator 212 may include a cap 215 fixed to an inner wall of the housing 202 and have one or more flow ports 224, where the one or more flow ports 224 allow drilling fluid to pass through the main flow area 220. The drum stator 212 may also include a sleeve 217 descending from the cap 215 in a downhole direction 201 , where the drum rotor 214 may be movably disposed within the sleeve 217. The drum rotor 214 may define a microannulus 219 within the sleeve 217. The drum stator 212 may be stationary within the housing 202. [0046] In one implementation, the drum rotor 214 may be hollow and configured to rotate within the housing 202. Specifically, the drum rotor 214 may be configured to rotate within the sleeve 217. The drum rotor 214 may be coupled to an uphole end portion of shaft 230, such that the drum rotor 214 may be configured to rotate in conjunction with the shaft 230. The shaft 230 may also be hollow such that a channel 232 may be formed with the drum rotor 214, where the channel 232 may begin at the microannulus 219 and terminate at a vent 234 of the shaft 230 proximate to a downhole end portion of the shaft 230. In one implementation, the vent 234 may open to the main flow area 220 at a location between the turbine stages 240 and the thrust bearings 260. In another implementation, the vent 234 may open to the main flow area 220 at a location downhole from the thrust bearings 260.

[0047] In operation, the turbodrill 200 may receive drilling fluid 270 from an uphole member of the drill string, where the drilling fluid 270 may pass downhole through the one or more flow ports 224. Most of the drilling fluid 270 may pass through the turbine stages 240, whereby the drilling fluid 270 may lose fluid pressure as it reaches a portion of the main flow area 220 proximate to the vent 234. A small amount of the drilling fluid 270 may leak through a channel or microannulus 219 formed by a radial gap 280 between an inner diameter of the sleeve 217 and an outer diameter of the drum rotor 214. Thus, the radial gap 280 provides a channel or microannulus 219 for the drilling fluid 270 to leak from the main flow area 220 into the channel 232. Further, a leak flow path may be defined from main flow area 220 through the microannulus 219, through the channel 232 and through the vent 234. In one implementation, the radial gap 280 may have a maximum width and a minimum width.

[0048] The radial gap 280 may also be of a width such that there is a fluid pressure differential across the microannulus 219 between the channel 232 and the main flow area 220 outside of the sleeve 217. In particular, the radial gap 280 may be of a size such that the drilling fluid 270 is inhibited from exerting significant downhole thrust on an uphole end portion of the shaft 230. Thus, the fluid pressure inside the channel 232 may be nearly equal to the fluid pressure of the portion of the main flow area 220 proximate to the vent 234, thereby producing the fluid pressure differential across the microannulus 219 between the channel 232 and the main flow area 220 outside of the sleeve 217. This fluid pressure differential may cause an uphole axial force to act on the shaft 230, offsetting the downhole thrust, and thereby approximately balancing an axial load applied to the shaft 230. Essentially, by reducing an amount of downhole thrust acting on the shaft 230, the balance drum assembly 210 may reduce axial loading on the thrust bearings 260.

[0049] In one implementation, the one or more radial bearings and/or the one or more thrust bearings 260 may each have a clearance with the shaft 230 that is greater than the radial gap 280. For example, each radial bearing and each thrust bearing 260 may have a clearance with the shaft 230 of about 0.004-0.005 inches, while the radial gap 280 may be about 0.001 inches.

[0050] During directional drilling, the turbodrill 200 may be forced to flex, such as when it passes through high doglegs. This flexing may force the components of the balance drum assembly 210 to behave as a bearing, such as by inducing a load within the drum stator 212 and possibly canting the drum rotor 214 within the drum stator 212. The drum rotor 214 and/or the drum stator 212 may then wear due to friction, causing the balance drum assembly 210 to lose effectiveness in maintaining the fluid pressure differential across the microannulus 219 between the channel 232 and the main flow area 220 outside of the sleeve 217. Various implementations may be used to minimize the canting of the drum rotor 214 within the drum stator 212.

Balance Drum Assembly with a Compliant Mounting

[0051] Figures 3-8 illustrate a cross-sectional view of a turbodrill using a balance drum assembly with a compliant mounting in accordance with implementations of various techniques described herein. The compliant mounting may allow for some movement of the balance drum assembly.

Spring Mechanism

[0052] In this implementation, the turbodrill may use a balance drum assembly with a compliant mounting, where the compliant mounting may be a spring mechanism. The spring mechanism may be a coil spring, one or more Belleville springs, a machine spring, a wave spring, or any other spring mechanism known to those skilled in the art.

[0053] Figure 3 illustrates a cross-sectional view of a turbodrill 300 using a balance drum assembly 310 with a coil spring 390 in accordance with implementations of various techniques described herein. The turbodrill 300 may include a housing 302, where the housing 302 may have an upper connection for engaging with uphole members of a drill string.

[0054] The balance drum assembly 310 may be similar to the balance drum assembly 210, where the balance drum assembly 310 may be disposed within a main flow area 320 of the turbodrill 300 and may include a drum stator 312 and a drum rotor 314. The drum stator 312 may also include a cap 315 having one or more flow ports 324, where the one or more flow ports 324 allow drilling fluid to pass through the main flow area 320. The drum stator 312 may also include a sleeve 317 descending from the cap 315 in a downhole direction 301 , where the drum rotor 314 may be movably disposed within the sleeve 317.

[0055] Similar to the drum rotor 214, the drum rotor 314 may be hollow and configured to rotate within the housing 302. Specifically, the drum rotor 314 may be configured to rotate within the sleeve 317. The drum rotor 314 may be coupled to an uphole end portion of a shaft (not shown), such that the drum rotor 314 may be configured to rotate in conjunction with the shaft. The shaft may also be hollow such that a channel 332 may be formed with the drum rotor 314. A radial gap 380 similar to the radial gap 280 may be formed between an inner diameter of the sleeve 317 and an outer diameter of the drum rotor 314. In one implementation, the radial gap 380 may be about 0.001 inches to about 0.01 inches.

[0056] In contrast to the balance drum assembly 210, the balance drum assembly 310 may not be fixed to the housing 302. Instead, the balance drum assembly 310 may be coupled to the coil spring 390, where the coil spring 390 may be coupled to the housing 302. In particular, a downhole end portion of the cap 315 may be coupled to an uphole end portion of the coil spring 390. The cap 315 may be coupled to the coil spring 390 through bonding, clamping, bolting, or any other implementation known to those skilled in the art. In turn, a downhole end portion of the coil spring 390 may be coupled to an inner shoulder 360 of the housing 302. The coil spring 390 may be coupled to the inner shoulder 360 through bonding, clamping, bolting, or any other implementation known to those skilled in the art. In one implementation, the inner shoulder 360 may include an internal nut, bolt, or screw attached to the housing 302.

[0057] In another implementation, an outer diameter of the cap 315 may be less than an internal diameter of the main flow area 320. An outer diameter of the coil spring 390 may also be less than the internal diameter of the main flow area 320. In particular, space may exist between the cap 315 and an inner wall of the housing 302 such that the coil spring 390 may allow for a lateral displacement and an angular displacement of the balance drum assembly 310 within the housing 302.

[0058] In one implementation, lateral displacement of the balance drum assembly 310 may occur when a central axis of the balance drum assembly 310 is misaligned from a central axis of the housing 302 by a uniform distance. In such an implementation, the coil spring 390 may allow for the lateral displacement of the balance drum assembly 310 via lateral shifting of coils in the coil spring 390. In another implementation, angular displacement of the balance drum assembly 310 may occur when the central axis of the balance drum assembly 310 is misaligned from the central axis of the housing 302 by nonuniform distances, such that the central axis of the balance drum assembly 310 forms an angle with the central axis of the housing 302. In such an implementation, the coil spring 390 may allow for the angular displacement of the balance drum assembly 310 by compressing one side of the coil spring 390 more than the other. [0059] In the cases of directional drilling or curved drilling tools, the lateral and angular displacement via coil spring 390 may lessen the likelihood of point loading due to canting within the balance drum assembly 310, thereby avoiding wear along the radial gap 380. In one implementation, the turbodrill 300 may allow for up to about 10 millimeters in lateral displacement of the balance drum assembly 310 within the housing 302. In another implementation, the turbodrill 300 may allow for up to about 10 degrees of angular displacement of the balance drum assembly 310 within the housing 302.

[0060] In a further implementation of the balance drum assembly 310, the cap 315 and the coil spring 390 may be designed such that they are placed further downhole along the sleeve 317. For example, Figures 4 and 5 illustrate cross-sectional views of the turbodrill 300 using the balance drum assembly 310 with the coil spring 390, where the caps 315 and the coil springs 390 are placed further downhole along the sleeve 317 in comparison to Figure 3.

[0061] In another implementation, referring back to Figure 3, the cap 315 may be coupled to the coil spring 390 such that torsion of the coil spring 390 resists rotation of the drum stator 312 within the housing 302 in response to a flow of the drilling fluid. In such an implementation, while the drum rotor 314 may rotate in conjunction with the shaft, the drum stator 312 may remain largely stationary within the housing 302. The coil spring 390 may also be configured to resist a downhole thrust resulting from the flow of the drilling fluid.

Spring Mechanism with Rotational Inhibitors

[0062] In this implementation, the turbodrill may use a balance drum assembly having one or more rotational inhibitors in addition to the spring mechanism. As previously mentioned, the spring mechanism may be a coil spring, one or more Belleville springs, a machine spring, a wave spring, or any other spring mechanism known to those skilled in the art.

[0063] Figure 6 illustrates a cross-sectional view of a turbodrill 600 using a balance drum assembly 610 with one or more Belleville springs 690 and one or more rotational inhibitors 695 in accordance with implementations of various techniques described herein. The turbodrill 600 may include a housing 602, where the housing 602 may have an upper connection for engaging with uphole members of a drill string. The balance drum assembly 610 may include the same/similar components and configuration as the balance drum assembly 310 described with reference to Figure 3, e.g., a drum rotor 614, a drum stator 612 having a cap 615 and a sleeve 617.

[0064] In one implementation, the balance drum assembly 610 may rest on the one or more Belleville springs 690, which in turn rest on an inner shoulder 660 of the housing 602. In particular, a downhole end portion of the cap 615 may rest on an uphole end portion of the one or more Belleville springs 690. In turn, a downhole end portion of the one or more Belleville springs 690 may rest on the inner shoulder 660 of the housing 602. It should be understood that the inner shoulder 660 is similar to the inner shoulder 360. The one or more Belleville springs 690 may be configured to resist a downhole thrust resulting from a flow of drilling fluid.

[0065] One or more rotational inhibitors 695 may be used to resist rotation of the drum stator 612 within the housing 602 in response to the flow of drilling fluid. The rotational inhibitors 695 may be coupled to an inner wall of the housing 602 and may be linked to the cap 615 such that rotation of the drum stator 612 is restrained. In one implementation, the rotational inhibitors 695 may include one or more pins or springed pins having a first end portion coupled to the housing 602 and a second end portion engaging the cap 615, e.g., resting within a respective gap of the cap 615. The turbodrill 600 may be configured such that each pin or springed pin would rest within a particular gap of the cap 615. Upon an application of rotational force on the drum stator 612, the cap 615 may rotate a minimal distance until a pin or springed pin comes into contact with an edge of its particular gap. In another implementation, the rotational inhibitors 695 may include one or more cables having a first end portion coupled to the housing 602 and a second end portion coupled to the cap 615. Rotation of the cap 615 would be limited by a length of the one or more cables. In a further implementation, the one or more cables may be made using steel or any other implementation known to those skilled in the art.

[0066] In a further implementation, a lateral displacement and an angular displacement of the balance drum assembly 610 within the housing 602 may be achieved similarly to the lateral displacement and the angular displacement of the balance drum assembly 310 within the housing 302, as the rotational inhibitors 695 may be configured to offer no resistance to the lateral and angular displacement of the balance drum assembly 610. Similar to the coil spring 390, the lateral and angular displacement via the one or more Belleville springs 690 may lessen the likelihood of point loading caused by canting within the balance drum assembly 610, thereby avoiding wear along a radial gap formed between the inner diameter of the sleeve 617 and the outer diameter of the drum rotor 614.

[0067] In particular, in one implementation, lateral displacement of the balance drum assembly 610 may occur when a central axis of the balance drum assembly 610 is misaligned from a central axis of the housing 602 by a uniform distance. In such an implementation, the one or more Belleville springs 690 may allow for the lateral displacement of the balance drum assembly 610 via lateral shifting of springs in the one or more Belleville springs 690. In another implementation, angular displacement of the balance drum assembly 610 may occur when the central axis of the balance drum assembly 610 is misaligned from the central axis of the housing 602 by non-uniform distances, such that the central axis of the balance drum assembly 610 forms an angle with the central axis of the housing 602. In such an implementation, the one or more Belleville springs 690 may allow for the angular displacement of the balance drum assembly 610 by compressing one side of the one or more Belleville springs 690 more than the other.

Compliant Mounting of Solid Material

[0068] In this implementation, the turbodrill may use a balance drum assembly with a compliant mounting constructed of a solid material. In such an implementation, the compliant mounting may be an elastomeric mounting, such as a rubber mounting, a mounting composed of polytetrafluoroethylene (PTFE), or any other elastomeric mounting known to those skilled in the art.

[0069] Figure 7 illustrates a cross-sectional view of a turbodrill 700 using a balance drum assembly 710 with an elastomeric mounting 790 in accordance with implementations of various techniques described herein. In one implementation, the elastomeric mounting 790 may be composed of rubber. The turbodrill 700 may include a housing 702, where the housing 702 may have an upper connection for engaging with uphole members of a drill string. The balance drum assembly 710 may include the same/similar components and configurations as the balance drum assembly 310, e.g., a drum rotor 714 and a drum stator 712 having a cap 715 and a sleeve 717.

[0070] The balance drum assembly 710 may be coupled to the elastomeric mounting 790, where the elastomeric mounting 790 is coupled to the housing 702. In one implementation, the elastomeric mounting 790 may include a top portion 791 coupled to a bottom portion 792. The elastomeric mounting 790 may be oriented such that the top portion 791 is uphole relative to the bottom portion 792. The top portion 791 may be disposed between an inner wall of the housing 702 and the cap 715. The top portion 791 may be coupled to the housing 702 and to the cap 715 using a bonding or any other implementation known to those in the art.

[0071] The bottom portion 792 may be disposed between an inner shoulder 760 of the housing 702 and the downhole end portions of the cap 715 and the top portion 791 . A downhole end portion of the bottom portion 792 may be coupled to the inner shoulder 760, and an uphole end portion of the bottom portion 792 may be coupled to the downhole end portions of the cap 715 and the top portion 791 . The bottom portion 792 may be coupled using a bonding or any other implementation known to those in the art. The coupling of the top portion 791 and the bottom portion 792 to the cap 715 may help resist rotation of the drum stator 712 within the housing 702 in response to a flow of drilling fluid.

[0072] In one implementation, the top portion 791 may have more compliance and/or flexibility than the bottom portion 792. In another implementation, the top portion 791 and the bottom portion 792 may constitute one piece and may consist of material having the same compliance and/or flexibility. In yet another implementation, the inner shoulder 760 may include an internal nut, bolt, or screw attached to the housing.

[0073] The top portion 791 and the bottom portion 792 of the elastomeric mounting 790 may possess sufficient compliance and/or flexibility to allow for a lateral displacement and an angular displacement of the balance drum assembly 710 within the housing 702. Similar to the coil spring 390, the lateral and angular displacement via the elastomeric mounting 790 may lessen the likelihood of point loading caused by canting within the balance drum assembly 710, thereby avoiding wear along the radial gap. [0074] In particular, in one implementation, lateral displacement of the balance drum assembly 710 may occur when a central axis of the balance drum assembly 710 is misaligned from a central axis of the housing 702 by a uniform distance. In such an implementation, the elastomeric mounting 790 may allow for the lateral displacement of the balance drum assembly 710 via compression of the top portion 791 and/or the bottom portion 792. In another implementation, angular displacement of the balance drum assembly 710 may occur when the central axis of the balance drum assembly 710 is misaligned from the central axis of the housing 702 by non-uniform distances, such that the central axis of the balance drum assembly 710 forms an angle with the central axis of the housing 702. In such an implementation, the elastomeric mounting 790 may allow for the angular displacement of the balance drum assembly 710 by compressing one side of the top portion 791 and/or the bottom portion 792 more than the other.

Spherical Bearing Assembly

[0075] In this implementation, the turbodrill may use a balance drum assembly with a compliant mounting, where the compliant mounting is a spherical bearing assembly. The spherical bearing assembly may be constructed of steel, or any other implementation known to those skilled in the art.

[0076] Figure 8 illustrates a cross-sectional view of a turbodrill 800 using a balance drum assembly 810 with a spherical bearing assembly 890 in accordance with implementations of various techniques described herein. The turbodrill 800 may include a housing 802, where the housing 802 may have an upper connection for engaging with uphole members of a drill string. The balance drum assembly 810 may include the same/similar components and configurations as the balance drum assembly 310, e.g., a drum rotor 814 and a drum stator 812 having a cap 815 and a sleeve 817. In one implementation, a ring 851 and/or a snap ring 852 may be coupled to an inner wall of the housing 802, and may be positioned uphole relative to the cap 815 such that uphole movement of the drum stator 812 may be relatively minimized within the housing 802.

[0077] In one implementation, the spherical bearing assembly 890 may include a top spherical seat 891 configured to mate to a bottom spherical seat 892. The top spherical seat 891 has an uphole end portion which may couple with the downhole end portion of the cap 815. The top spherical seat 891 has an outer diameter which may be smaller than an inner diameter of the housing 802, such that a clearance 871 may be formed. The top spherical seat 891 may be coupled to the cap 815 using threads or any other coupling means known to those skilled in the art. In another implementation, the top spherical seat

891 and the cap 815 may constitute one piece and may be composed of the same material. In yet another implementation, the top spherical seat 891 may also have a portion which may be disposed between the inner wall of the housing 802 and the cap 815.

[0078] A downhole end portion of the top spherical seat 891 may be generally convex in shape and may be configured to mate with an uphole end portion of the bottom spherical seat 892, where the uphole end portion of the bottom spherical seat 892 may be generally concave in shape. A downhole end portion of the bottom spherical seat 892 may rest on an inner shoulder 860 of the housing 802. An outer diameter of the bottom spherical seat

892 may be smaller than the inner diameter of the housing 802, such that a clearance 872 may be formed. In one implementation, the clearance 872 may range from about .03 inches to .05 inches.

[0079] Lateral displacement of the balance drum assembly 810 may occur when a central axis of the balance drum assembly 810 is misaligned from a central axis of the housing 802 by a uniform distance. In such an implementation, clearance 872 may allow for the lateral displacement of the balance drum assembly 810 via lateral movement of the spherical bearing assembly 890. In particular, the bottom spherical seat 892 may be configured to move laterally along the inner shoulder 860, thereby allowing the spherical bearing assembly 890 and the balance drum assembly 810 to also move laterally. In one implementation, the outer diameter of the bottom spherical seat 892 may be larger than the outer diameter of the top spherical seat 891 , such that lateral displacement of the top spherical seat 891 and the balance drum assembly 810 may be limited to the lateral displacement experienced by the bottom spherical seat 892.

[0080] Angular displacement of the balance drum assembly 810 may occur when the central axis of the balance drum assembly 810 is misaligned from the central axis of the housing 802 by non-uniform distances, such that the central axis of the balance drum assembly 810 forms an angle with the central axis of the housing 802. In such an implementation, the convex shape of the downhole end portion of the top spherical seat 891 and the concave shape of the uphole end portion of the bottom spherical seat 892 may allow for the angular displacement of the balance drum assembly 810. In particular, the top spherical seat 891 and the bottom spherical seat 892 may be configured to rotate with respect to one another, thereby allowing for angular displacement of the balance drum assembly 810.

Balance Drum Assembly with Axial Bearings

[0081] Figures 9-10 illustrate a cross-sectional view of a turbodrill using a balance drum assembly with axial bearings in accordance with implementations of various techniques described herein.

Axial Bearings with Rotational Inhibitors

[0082] In this implementation, the turbodrill may use a balance drum assembly with axial bearings and one or more rotational inhibitors. The axial bearings may be configured in an axial bearing cage having ball bearings, spherical contact bearings, tungsten carbide bearings, brass bearings, PDC surface bearings, or any other axial bearings known to those skilled in the art.

[0083] Figure 9 illustrates a cross-sectional view of a turbodrill 900 using a balance drum assembly 910 with an axial bearing cage 985 and one or more rotational inhibitors 995 in accordance with implementations of various techniques described herein. The turbodrill 900 may include a housing 902, where the housing 902 may have an upper connection for engaging with uphole members of a drill string. The balance drum assembly 910 may include the same/similar components and configurations as the balance drum assembly 310 described in Figure 3, e.g., a drum rotor 914 and a drum stator 912 having a cap 915 and a sleeve 917.

[0084] In one implementation, the balance drum assembly 910 may rest on the axial bearing cage 985, where the axial bearing cage 985 may also rest on an inner shoulder 960 of the housing 902. In particular, a downhole end portion of the cap 915 may rest on an uphole end portion of the axial bearing cage 985. In turn, a downhole end portion of the axial bearing cage 985 may rest on the inner shoulder 960 of the housing 902. In addition, the sleeve 917 may pass through an inner ring 986 of the axial bearing cage 985, such that the inner ring 986 may be in contact with the sleeve 917.

[0085] Similar to the rotational inhibitors 695, one or more rotational inhibitors 995 may be used to resist rotation of the drum stator 912 within the housing 902 in response to a flow of drilling fluid. The rotational inhibitors 995 may be coupled to an inner wall of the housing 902 and may be linked to the cap 915 such that rotation of the drum stator 912 is restrained. In one implementation, the rotational inhibitors 995 may include one or more pins or springed pins having a first end portion coupled to the housing 902 and a second end portion engaging the cap 915, e.g., resting within a respective gap of the cap 915. In another implementation, the rotational inhibitors 995 may include one or more cables having a first end portion coupled to the housing 902 and a second end portion coupled to the cap 915.

[0086] In one implementation, lateral displacement of the balance drum assembly 910 may occur when a central axis of the balance drum assembly 910 is misaligned from a central axis of the housing 902 by a uniform distance. In such an implementation, bearings of the axial bearing cage 985 may freely rotate and allow for the lateral displacement of the balance drum assembly 910 within the housing 902. Similar to the rotational inhibitors 695, the rotational inhibitors 995 may be configured to offer no resistance to the lateral displacement of the balance drum assembly 910. However, the arrangement of the axial bearing cage 985 and the inner shoulder 960 may prevent angular displacement of the balance drum assembly 910 within the housing 902. The lateral displacement via the axial bearing cage 985 may still lessen the likelihood of point loading resulting from canting within the balance drum assembly 910.

Axial Bearings with Rotational Inhibitors and Spring Mechanism

[0087] In this implementation, the turbodrill may use a balance drum assembly with axial bearings, a spring mechanism, and one or more rotational inhibitors. The axial bearings may be configured in an axial bearing cage having ball bearings, tungsten carbide bearings, brass bearings, PDC surface bearings, or any other axial bearings known to those skilled in the art. The spring mechanism may be a coil spring, one or more Belleville springs, a machine spring, a wave spring, or any other spring mechanism known to those skilled in the art.

[0088] Figure 10 illustrates a cross-sectional view of a turbodrill 1000, using a balance drum assembly 1010 with an axial bearing cage 1085, a spring mechanism 1090, and one or more rotational inhibitors 1095 in accordance with implementations of various techniques described herein. The turbodrill 1000 may include a housing 1002, where the housing 1002 may have an upper connection for engaging with uphole members of a drill string. The balance drum assembly 1010 may include the same/similar components and configurations as the balance drum assembly 310 described in Figure 3, e.g., a drum rotor 1014 and a drum stator 1012 having a cap 1015 and a sleeve 1017.

[0089] In one implementation, the balance drum assembly 1010 may rest on the axial bearing cage 1085, where the axial bearing cage 1085 may rest on a spring mechanism 1090. In turn, the spring mechanism 1090 may rest on an inner shoulder 1060 of the housing 1002. In particular, a downhole end portion of the cap 1015 may rest on an uphole end portion of the axial bearing cage 1085. A downhole end portion of the axial bearing cage 1085 may rest on an uphole end portion of the spring mechanism 1090, where a downhole end portion of the spring mechanism 1000 may rest on the inner shoulder 1060 of the housing 1002. In addition, the sleeve 1017 may pass through an inner ring 1086 of the axial bearing cage 1085, such that the inner ring 1086 may be in contact with the sleeve 1017.

[0090] Similar to the rotational inhibitors 695, one or more rotational inhibitors 1095 may be used to resist rotation of the drum stator 1012 within the housing 1002 in response to a flow of drilling fluid. The rotational inhibitors 1095 may be coupled to an inner wall of the housing 1002 and may be linked to the cap 1015 such that rotation of the drum stator 1012 is restrained. In one implementation, the rotational inhibitors 1095 may include one or more pins or springed pins having a first end portion coupled to the housing 1002 and a second end portion engaging the cap 1015, e.g., resting within a respective gap of the cap 1015. In another implementation, the rotational inhibitors 1095 may include one or more cables having a first end portion coupled to the housing 1002 and a second end portion coupled to the cap 1015. [0091] In one implementation, lateral displacement of the balance drum assembly 1010 may occur when a central axis of the balance drum assembly 1010 is misaligned from a central axis of the housing 1002 by a uniform distance. In such an implementation, bearings of the axial bearing cage 1085 may freely rotate and allow for the lateral displacement of the balance drum assembly 1010 within the housing 1002. In another implementation, the spring mechanism 1090 may allow for the lateral displacement of the balance drum assembly 1010 via lateral shifting of springs in the spring mechanism 1090. Similar to the rotational inhibitors 695, the rotational inhibitors 1095 may be configured to offer little or no resistance to the lateral displacement of the balance drum assembly 1010.

[0092] In another implementation, angular displacement of the balance drum assembly 1010 may occur when the central axis of the balance drum assembly 1010 is misaligned from the central axis of the housing 1002 by non-uniform distances, such that the central axis of the balance drum assembly 1010 forms an angle with the central axis of the housing 1002. In such an implementation, the spring mechanism 1090 may allow for the angular displacement of the balance drum assembly 1010 by compressing one side of the spring mechanism 1090 more than the other. The lateral and angular displacement via the spring mechanism 1090 and/or the axial bearing cage 1085 may lessen the likelihood of point loading caused by canting within the balance drum assembly 1010, thereby avoiding wear along the radial gap.

Balance Drum Assembly with Compliant Rod Mechanism

[0093] Figures 1 1 -15 illustrate a cross-sectional view of a turbodrill using a balance drum assembly with a compliant rod mechanism in accordance with implementations of various techniques described herein. The compliant rod mechanism may allow for some movement of the balance drum assembly.

Flex Rod and Rod Retainer

[0094] In this implementation, the compliant rod mechanism includes a flex rod and rod retainer. Figure 1 1 illustrates a cross-sectional view of a turbodrill 1 100 using a balance drum assembly 1 1 10 with a flex rod 1 190 and a rod retainer 1 191 in accordance with implementations of various techniques described herein. The turbodrill 1 100 may include a housing 1102, where the housing 1102 may have an upper connection for engaging with uphole members of a drill string.

[0095] A balance drum assembly 1110 may be disposed within a main flow area 1120 of the turbodrill 1100 and may include a drum stator 1112 and a drum rotor 1114. The drum rotor 1114 may be movably disposed within the drum stator 1112. The drum rotor 1114 may also be hollow and configured to rotate within the housing 1102. Specifically, the drum rotor 1114 may be configured to rotate within the drum stator 1112. The drum rotor 1114 may be coupled to an uphole end portion of a shaft (not shown), such that the drum rotor 1114 may be configured to rotate in conjunction with the shaft. The shaft may also be hollow such that a channel 1132 may be formed with the drum rotor 1114. A radial gap 1180 similar to the radial gap 280 may be formed between an inner diameter of the drum stator 1112 and an outer diameter of the drum rotor 1114.

[0096] In contrast to the balance drum assembly 210, the balance drum assembly 1110 may not be fixed to the housing 1102. Instead, the balance drum assembly 1110 may be coupled to the flex rod 1190, where the flex rod 1190 is coupled to the rod retainer 1191. Essentially, the balance drum assembly 1110 hangs from the rod retainer 1191 via the flex rod 1190. In particular, a downhole end portion of the flex rod 1190 may be coupled to an uphole end portion of the drum stator 1112. The flex rod 1190 may be coupled to the drum stator 1112 through bonding, clamping, bolting, welding, threading, pinning, or any other implementation known to those skilled in the art.

[0097] In turn, an uphole end portion of the flex rod 1190 may be coupled to a downhole end portion of the rod retainer 1191. The flex rod 1190 may be coupled to the rod retainer 1191 through bonding, clamping, bolting, welding, threading, or any other implementation known to those skilled in the art. Like the cap 315, the rod retainer 1191 may have one or more flow ports 1124 for allowing drilling fluid to pass through the main flow area 1120. The downhole end portion of the rod retainer 1191 may be disposed on an inner shoulder 1160 of the housing 1102. The inner shoulder 1160 may include an internal nut, bolt, or screw attached to the housing 1102.

[0098] In one implementation, an outer diameter of the drum stator 1112 may be less than an internal diameter of the main flow area 1120. In particular, space may exist between the drum stator 1 1 12 and an inner wall of the housing 1 102 such that the flex rod 1 190 may allow for a lateral displacement and an angular displacement of the balance drum assembly 1 1 10 within the housing 1 102. The flex rod 1 190 may be a cable attachment, a coil spring, a rod composed of titanium, flexible steel, or any other compliant material known to those skilled in the art which would allow displacement of the balance drum assembly 1 1 10 within the housing 1 102. In one implementation, in order to maximize compliance and/or flexibility of the flex rod 1 190, the flex rod 1 190 may be designed to be as long and as thin as allowed under the design constraints for the turbodrill 1 100.

[0099] As mentioned above, lateral displacement of the balance drum assembly 1 1 10 may occur when a central axis of the balance drum assembly 1 1 10 is misaligned from a central axis of the housing 1 102 by a uniform distance. Accordingly, the flex rod 1 190 may allow for the lateral displacement of the balance drum assembly 1 1 10 via bending of the flex rod 1 190.

[00100] Likewise, angular displacement of the balance drum assembly 1 1 10 may occur when the central axis of the balance drum assembly 1 1 10 is misaligned from the central axis of the housing 1 102 by non-uniform distances, such that the central axis of the balance drum assembly 1 1 10 forms an angle with the central axis of the housing 1 102. Accordingly, the flex rod 1 190 may allow for the angular displacement of the balance drum assembly 1 1 10 via bending of the flex rod 1 190. In the cases of directional drilling or curved drilling tools, the lateral and angular displacement via the flex rod 1 190 may lessen the likelihood of point loading caused by canting within the balance drum assembly 1 1 10, thereby avoiding wear along the radial gap 1 180.

[00101] In one implementation, torsion of the flex rod 1 190 may resist rotation of the drum stator 1 1 12 within the housing 1 102 in response to a flow of the drilling fluid. In addition, the rod retainer 1 191 may be largely stationary within the housing 1 102. In such an implementation, while the drum rotor 1 1 14 rotates in conjunction with the shaft, the drum stator 1 1 12 may remain largely stationary within the housing 1 102. The flex rod 1 190 may also be configured to handle a downhole thrust resulting from the flow of the drilling fluid. In implementations where the flex rod 1 190 may be of a lower torsion, one or more rotational inhibitors, such as those discussed with respect to Figure 6, may be used to restrain rotation of the drum stator 1 1 12.

Rod with Compliant Joints

[00102] In this implementation, the compliant rod mechanism includes a rod, a rod retainer, and one or more compliant joints. In such an implementation, the one or more compliant joints may include a universal joint, a constant-velocity (CV) joint, or any other compliant joint known to those skilled in the art.

[00103] Figure 12 illustrates a cross-sectional view of a turbodrill 1200 using a balance drum assembly 1210 with a rod 1290, a lower universal joint 1293, and an upper universal joint 1295 in accordance with implementations of various techniques described herein. The turbodrill 1200 may include a housing 1202, where the housing 1202 may have an upper connection for engaging with uphole members of a drill string.

[00104] The balance drum assembly 1210 may be disposed within the housing 1202, and may include a drum rotor 1214 and a drum stator 1212. It should be understood that the housing 1202 is similar to the housing 1002, and the balance drum assembly 1210 is similar to the balance drum assembly 1010. In particular, the drum rotor 1214 is similar to the drum rotor 1 1 14, and the drum stator 1212 is similar to the drum stator 1 1 12. The turbodrill 1200 may also include a rod retainer 1291 similar to the rod retainer 1 191 .

[00105] The balance drum assembly 1210 may be coupled to the rod 1290 via the lower universal joint 1293, where the rod 1290 is coupled to the rod retainer 1291 via the upper universal joint 1295. Essentially, the balance drum assembly 1210 hangs from the rod retainer 1291 via the rod 1090, the lower universal joint 1293, and the upper universal joint 1295. In particular, a downhole end portion of the rod 1290 may be coupled to an uphole end portion of the drum stator 1212 via the lower universal joint 1293.

[00106] In turn, an uphole end portion of the rod 1290 may be coupled to a downhole end portion of the rod retainer 1291 via the upper universal joint 1295. The downhole end portion of the rod retainer 1291 may also be disposed on an inner shoulder 1260 of the housing 1202. In one implementation, the inner shoulder 1260 may be similar to the inner shoulder 1 160. In a further implementation, the rod 1290 may be composed of any material known to those skilled in the art which would support the configuration of the balance drum assembly 1210 within the housing 1202 as described herein.

[00107] As previously mentioned, lateral displacement of the balance drum assembly 1210 may occur when a central axis of the balance drum assembly 1210 is misaligned from a central axis of the housing 1202 by a uniform distance. Accordingly, the balance drum assembly 1210 may be laterally displaced through pivoting of both the lower universal joint 1293 and the upper universal joint 1295.

[00108] Likewise, angular displacement of the balance drum assembly 1210 may occur when the central axis of the balance drum assembly 1210 is misaligned from the central axis of the housing 1202 by non-uniform distances, such that the central axis of the balance drum assembly 1210 forms an angle with the central axis of the housing 1202. Accordingly, the balance drum assembly 1210 may be angularly displaced through pivoting of either the lower universal joint 1293 or the upper universal joint 1295. In the cases of directional drilling or curved drilling tools, the lateral and angular displacement via the lower universal joint 1293 and the upper universal joint 1295 may lessen the likelihood of point loading caused by canting within the balance drum assembly 1210, thereby avoiding wear along the radial gap formed between an inner diameter of the drum stator 1212 and an outer diameter of the drum rotor 1214.

[00109] In one implementation, the rod 1290, the lower universal joint 1293, and the upper universal joint 1295 may be configured to resist rotation of the drum stator 1212 within the housing 1202 in response to a flow of the drilling fluid. The rod 1290, the lower universal joint 1293, and the upper universal joint 1295 may also be configured to handle a downhole thrust resulting from the flow of the drilling fluid.

Flex Shaft

[00110] In this implementation, the turbodrill may use a balance drum assembly with a compliant rod mechanism, where the compliant rod mechanism may include a flex shaft. Figure 13 illustrates a cross-sectional view of a turbodrill 1300 using a balance drum assembly 1310 with an internal flex shaft 1390 in accordance with implementations of various techniques described herein. The turbodrill 1300 may include a housing 1302, where the housing 1302 may have an upper connection for engaging with uphole members of a drill string.

[00111] A balance drum assembly 1310 may be disposed within a main flow area 1320 of the turbodrill 1300 and may include a drum stator 1312 and a drum rotor 1314. The drum stator 1312 may include a cap 1315 and a sleeve 1317 descending from the cap 1315 in a downhole direction 1301 . An uphole end portion of the cap 1315 may have openings for one or more flow ports 1324, where the one or more flow ports 1324 allow drilling fluid to pass in the downhole direction 1301 through one or more channels in the sleeve 1317 and to the main flow area 1320.

[00112] The drum stator 1312 may be largely stationary within the housing 1302. In particular, a downhole end portion of the sleeve 1317 may be disposed on an inner shoulder 1360 of the housing 1302. In one implementation, the inner shoulder 1360 may include an internal nut, bolt, or screw attached to the housing 1302. The drum rotor 1314 may be movably disposed within the sleeve 1317, where the drum rotor 1314 may be hollow and configured to rotate. Specifically, the drum rotor 1314 may be configured to rotate within the sleeve 1317. Further, a radial gap 1380, similar to the radial gap 280, may be formed between an inner diameter of the sleeve 1317 and an outer diameter of the drum rotor 1314.

[00113] The drum rotor 1314 may be coupled to an uphole end portion of the internal flex shaft 1390, such that the drum rotor 1314 may be configured to rotate in conjunction with the internal flex shaft 1390. In particular, the uphole end portion of the internal flex shaft 1390 may be coupled to the drum rotor 1314 within a drum rotor annulus 1318 and within the sleeve 1317, where the drum rotor annulus 1318 may be defined by an inner bore of the drum rotor 1314.

[00114] In turn, a downhole end portion of the internal flex shaft 1390 may be coupled to an uphole end portion of a main shaft 1330, where the main shaft 1330 may extend in a downhole direction 1301 through the turbodrill 1300 and may be coupled to a drill bit (not shown). In addition, the internal flex shaft 1390 and the main shaft 1330 may both be hollow such that a channel 1332 may be formed with the drum rotor 1314. The internal flex shaft 1390 may be configured to rotate in conjunction with the main shaft 1330. In another implementation, the internal flex shaft 1390 may be coupled to the main shaft 1330 and to the drum rotor 1314 using threads, screws, bolts, or any other coupling mechanism known to those skilled in the art.

[00115] In one implementation, space may exist within the main flow area 1320 and/or the drum rotor annulus 1318 such that the internal flex shaft 1390 may allow for a lateral displacement and an angular displacement of the main shaft 1330 within the housing 1302. As mentioned above, lateral displacement of the main shaft 1330 may occur when a central axis of the main shaft 1330 is misaligned from a central axis of the housing 1302 by a uniform distance. In such an instance, the internal flex shaft 1390 may allow for the lateral displacement of the main shaft 1330 via bending of the internal flex shaft 1390.

[00116] Likewise, angular displacement of the main shaft 1330 may occur when the central axis of the main shaft 1330 is misaligned from the central axis of the housing 1302 by non-uniform distances, such that the central axis of the main shaft 1330 forms an angle with the central axis of the housing 1302. In such an instance, the internal flex shaft 1390 may allow for the angular displacement of the main shaft 1330 via bending of the internal flex shaft 1390. In the cases of directional drilling or curved drilling tools, the lateral and angular displacement via the internal flex shaft 1390 may lessen the likelihood of point loading caused by canting within the balance drum assembly 1310, thereby avoiding wear along the radial gap 1380. In one implementation, the bending of the internal flex shaft 1390 may occur within the drum rotor annulus 1318.

[00117] In one implementation, the flex shaft may be coupled to the drum rotor 1314 further downhole along the turbodrill 1300. For example, Figure 14 illustrates a cross- sectional view of the turbodrill 1300 using the balance drum assembly 1310 with an external flex shaft 1490 in accordance with implementations of various techniques described herein. In such an implementation, an uphole end portion of the external flex shaft 1490 may be coupled to a downhole end portion of the drum rotor 1314 located outside of the sleeve 1317. In a further implementation, the flex shafts 1390 and 1490 may be composed of titanium, flexible steel, or any other compliant material known to those skilled in the art which would allow displacement of the main shaft 1330 within the housing 1302. [00118] In another implementation, one or more vents 1334 may be placed proximate to the balance drum assembly 1310. For example, Figure 15 illustrates a cross-sectional view of the turbodrill 1300 using the balance drum assembly 1310 with the internal flex shaft 1390 in accordance with implementations of various techniques described herein. The vents 1334 may be positioned along the housing 1302, such that the vents open to an area outside of the turbodrill 1300. In particular, this area is formed by an outer diameter of the housing 1302 and an inner wall of a borehole in which the turbodrill 1300 is placed. This area may have lower fluid pressure relative to a main flow area 1320 of the turbodrill 1300.

[00119] The vents 1334 may be connected to a channel 1333 formed within the cap 1315 of the drum stator 1312, leading to a microannulus 1319. The microannulus 1319 may be similar to the microannulus 219, and may be defined by the drum rotor 1314 within the sleeve 1317. In operation, drilling fluid may leak from the main flow area 1320, through the radial gap 1380, and into the microannulus 1319. However, while in the microannulus 1319, the drilling fluid may be prevented from exerting significant downhole thrust on an uphole end portion of the internal flex shaft 1390 due to the connection between the vents 1334 and the microannulus 1319. Essentially, the connection to the lower pressure area outside of the turbodrill 1300 may mitigate downhole thrust acting on the internal flex shaft 1390, and therefore, the balance drum assembly 1310 may reduce axial loading on any thrust bearings. In a further implementation, the internal flex shaft 1390 and/or the main shaft 1330 (not pictured) may be composed of solid material, such that, unlike shaft 230 of Figure 2, the internal flex shaft 1390 and/or the main shaft 1330 may not be hollow.

[00120] The turbodrills and their respective balance drum assemblies described above with respect to Figures 1 -15 allow for the turbodrills to follow angular deflections of the shaft, whether from a curved design or from directional drilling. The lateral and angular displacement used in the turbodrills above may lessen the likelihood of point loading due to canting within the balance drum assemblies. The turbodrills above are also arranged and designed to handle a downhole thrust resulting from a flow of drilling fluid through the tools.

[00121] While the foregoing is directed to implementations of various techniques described herein, other and further implementations may be devised without departing from the basic scope thereof. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.