Background

[0001] This disclosure relates to the field of motors used in wellbore drilling and completion operations. More particularly, the disclosure relates to fluid operated motors that can be selectively lock to facilitate extraction of a stuck drill bit or similar drill string component operated by the motor.

[0002] Well drilling motors such as drilling fluid operated ("mud") motors comprise a housing that is coupled to a drill string suspended in a wellbore. Such motors comprise a housing coupled to the drill string and a drive shaft rotated by means of drilling fluid flow. The well is drilled by means of a drill bit rotated by the motor. Some mud motors comprise a bend in the housing to enable use in directional drilling.

[0003] Mud-motors most commonly used are one of two types. One type comprises an eccentric rotor disposed inside a corresponding stator inside the motor housing. Such motors comprise positive displacement motors (PDMs), wherein fluid chambers are displaced axially along the interior of the motor by rotation of the rotor in the stator. The other commonly used type of motor is an axial reaction turbine motor. One or more sets of turbine blades are coupled to the motor output shaft ("drive shaft"); the interior of the housing may comprise one or more stator blade sets. The drive shaft is not rotationally directly connected to the housing to ensure that the drill string above the mud motor can be rotated independently from the surface by equipment such as a top drive on a drilling unit or "rig."

[0004] During the process of drilling potential problems may arise by reason of drilled formation anomalies. One such problem includes sticking of the drill bit in a formation. A stuck bit may be caused by, e.g., tectonic stresses in the formations, wellbore debris (e.g., drill cuttings) accumulating behind the drill bit, differential pressure between the well drilling fluid and fluid pressure in the pore space of permeable formations, and directional drilling factors such as excessive change in trajectory of the well (dogleg severity). The torque required to release a stuck bit is variable, and is related to the severity of the stuck bit condition. In order to overcome a stuck bit condition a number of solutions exist, for example, dropping of metallic balls in the drill string to reach the predefined cavities in a PDM and help braking the connection between the motor and a bottom hole assembly (BHA) to retrieve the BHA except the downhole motor or selected portion of the drill string, which is either fished from the well or left behind in the well depending on existing conditions, in order to continue drilling. However, due to the widespread use of measurement while drilling (MWD) instruments in directional BHAs that have limited internal open area, using locking balls is not possible in such cases.

[0005] Another method to free a stuck drill bit is to apply additional torque to the bit, which is not possible when using mud motors because the drive shaft has a higher counter torque than the input torque. Additional torque could be applied by rotating the drill string from the surface thus applying additional torque, however due to absence of any direct connection between the motor housing and the drive shaft in typical mud motors, this is impractical.

[0006] Mechanisms known in the art for applying drill string torque to the drive shaft from the surface include devices such as centrifugal clutch systems and similar friction type locking mechanism. Both the prior art mechanisms rely on various locking components to engage with housing of the mud motor. Limitations of such devices include limited torque transfer capability due to the limited strength and frictional type torque transmission of the locking mechanism. Other limitations include that torque transfer between the housing and the drive shaft may be limited to one rotational direction, mud flow induced erosion of internal components of the mud motor as well as radial bearing wear resulting in shorter life span and complexity of the locking mechanism.

[0007] What is needed is a motor having the capacity for high torque transfer between the housing and drive shaft for the freeing of a stuck bit. The motor locking mechanism should be selectively releasable to enable drilling to resume after the bit is freed, with effectiveness not being reduced by mud flow erosion on the clutch elements or by internal radial bearings wear, and thereby maintain useful life of the mud motor and the locking mechanism.

Brief Description of the Drawings

[0008] FIG. 1 shows a cut away view of portions of a turbine motor according to the present disclosure.

[0009] FIGS. 1A and IB show enlarged views of portions of the motor shown in FIG. 1.

[0010] FIGS. 2A and 2B, respectively, show the motor of FIG. 1 in the unlocked and locked positions.

Detailed Description

[0011] FIG.1 shows a cut away view of a drilling motor 20. The motor 20 may comprise a housing 2 that has features (not shown) for connection of the housing 2 to a drill string (not shown). Such features may include, for example, industry standard tapered threads. A drive shaft 1 is rotatably supported inside the housing 2. A longitudinal end of the drive shaft 1 may comprise a thread coupling called a "bit box" (24 in FIGS. 2A and 2B) to which may be coupled a drill bit 22. Fluid, e.g., drilling mud, flowing through the housing 2 acts on a power section comprising components, e.g., a turbine or a positive displacement motor (not shown in the Figures) to cause the drive shaft 1 to rotate, thus rotating the drill bit 22 to drill through subsurface formations. The housing 2 may be straight or may have a bend therein, the latter type of housing being used in directional drilling methods known in the art.

[0012] Referring to the inset FIGS. 1A and IB the components of a locking mechanism that selectively locks the drive shaft 1 rotationally to the housing 2 may be better understood. A biasing element 10 such as an array of springs, for example, bellville springs, disposed in a spring housing 4 may urge the lower drive shaft 1 compressively toward an upper drive shaft assembly in order to selectively engage the lower drive shaft 1 with active components (the "power section") of the turbine or positive displacement motor (not shown) through male and female elements 5, 6 respectively of a conically shaped coupling 3 and drive and driven elements, 7 and 8, respectively of the coupling 3.

[0013] Locking engagement of the lower drive shaft 1 with the housing 2 using respective splines 11 and 12 may be located at the lower end of lower drive shaft 1, close to drill bit connection (bit box 24 in FIGS. 2A and 2B). Splines 11, 12 are only shown as one example of the locking mechanism, and other types of locking mechanism will occur to those skilled in the art. This may help to ensure that the drive shaft assembly and components do not undergo excessive torsional stress when the housing 2 is rotated from the surface in order to free the drill bit (22 in FIG. 1) However the positions of the foregoing components may vary based on the intended application of the locking mechanism in other embodiments.

[0014] Still with reference to FIGS. 1A and IB, just below the biasing element 10, the conically shaped coupling 3 may maintain connection between the power section (through an upper drive shaft) and the lower drive shaft 1. The conically shaped coupling 3 may comprise male 5 and female 6 tapered components, that can be engaged with a combination of axial compressive load from the biasing element 10 and a selected axial force acting on the drill bit (2 in FIG. 1) resulting in contact pressure between the joining surfaces of the male 5 and female 6 components. The conically shaped coupling 3, by reason of coaxial arrangement of the components 5, 6 as well as the above mentioned splines 7, 8 ensure to that drive torque is transferred from the power section to the lower drive shaft 1 and thus in turn to the drill bit (22 in FIG. 1).

[0015] The conically shaped coupling 3 is engaged in normal operation of the motor 20 due to axial force exerted by springs in the biasing element 10. This also means that the adjacent splines 7, 8 are in an engaged position 9 irrespective of whether the locking mechanism (explained below) is engaged or not, as the splines 7, 8 are disposed above the conically shaped coupling 3 and have an effective engagement length that is within the limits of longitudinal movement of the lower drive shaft 1 within the housing 2.

[0016] Referring now to FIG. 2 A, an example embodiment of the locking mechanism may be observed. External splines 11 may be disposed the lower end of the lower drive shaft 1, proximate to the bit box 24. Internal splines 12 may be formed in the internal bore of the bottom of the housing 2. During ordinary operation of the motor 20, the biasing element 10 and axial loading during drilling urge the lower drive shaft 1 upwardly such that the external splines 11 on the lower drive shaft 1 and the internal splines 12 on the housing 2 are disengaged. In this configuration, the power section (not shown) rotates the drive shaft 1 to effect rotation of the drill bit (22 in FIG. 1) while transferring axial loading of the drill string (not shown) to the drill bit (22 in FIG. 1) because the drive shaft 1 is moved to its inwardmost limit of longitudinal movement and axial force is transferred through the thrust bearing (not shown) to the drive shaft 1 from the housing 2.

[0017] If the drill bit (22 in FIG. 1) becomes stuck in a formation, the drilling unit operator may lift the drill string. Referring to FIG. 2B, when the drill string is lifted, the housing 2 is lifted along with the drill string. Because the drill bit is stuck, the lower drive shaft 1 will ordinarily be stuck rotationally and axially along with the drill bit. Thus, when the housing 2 is lifted, the relative longitudinal position of the lower drive shaft 1 changes with reference to the housing 2. During such lifting, the biasing element 10 is compressed. As the housing 2 is lifted with respect to the lower drive shaft 1, the external splines 11 on the drive shaft become longitudinally collocated with the internal splines 12 on the housing 2. Thus, any rotation applied to the housing 2 through the drill string from the surface will be transferred to the lower drive shaft 1.

[0018] The distance of travel of the lower drive shaft 1 with reference to the housing 2 may be equal to the distance traveled by the internal splines 12. This distance (i.e.. pull load) may be selected to ensure that maximum contact between the splines 11, 12 is ensured. The absence of any other direct contact between the housing 2 and the lower drive shaft 1 enable the housing 2 to move up and connect the splines 11, 12 without the need for frictional engagement of components or restriction of movement.

[0019] A mechanical stop feature limiting the maximum axial travel distance and ensuring maximum engagement of splines 11 with splines 12 also may prevent any dampening effect on the operation of a drilling jar (not shown) whenever fired in upward action.

[0020] The generated displacement results in engagement of the splines 11, 12, as shown in FIG. 2B. Engagement of the splines 11, 12 can be used to transfer the surface drive torque exerted by a kelly and rotary table or by a top drive (whichever is used on the particular drilling rig). Such devices are capable of generating torque which is of several orders of magnitude larger than the torque that a fluid driven drilling motor is capable of producing. When the drill bit is free, the biasing element 10 lifts the drive shaft 1 back into its ordinary position for drilling using power from the power section (not shown).

[0021] A drilling motor according to the present disclosure may have one or more of the following advantages. The locking mechanism is fully reversible, allowing re- engagement of the lower drive shaft with the power section enabling drilling to resume as many times as necessary after freeing a stuck drill bit. The locking mechanism engagement allows transmitting both right hand and left torque. The locking mechanism allows rotationally locking the drill string for back off procedure and partial string and BHA recovery without use of metallic locking balls and similar devices and components being dropped through the drill string (allowing rotational lock when MWD is present in BHA).

[0022] While the invention has been described with respect to a limited number of embodiments, those skilled in the art having the benefit of the present disclosure will readily devise other embodiments which to not depart from the scope of the present disclosure. The scope of invention is accordingly limited only by the attached claims.