BACKGROUND OF THE PRESENT INVENTION

1. Field of the Invention

The present invention pertains to downhole drilling equipment for wells penetrating subterranean formations including, without limitation, oil and gas wells. More particularly, the present disclosure pertains to a drive shaft assembly for use with a downhole motor. More particularly still, the present invention pertains to a drive shaft assembly that efficiently and effectively transfers torque forces, rotation and thrust loads between downhole drilling equipment situated within a wellbore.

2. Description of Related Art

In many cases, wells drilled into subterranean formations can be deviated from a purely vertical path or orientation. Such wells can have at least one curved or bent section, sometimes referred to as a “dog leg.” Frequently, conventional drilling methods are unable to create such curved portion(s) of the borehole and steer a wellbore in desired direction(s). Thus, downhole mud motors are frequently used to drill curved portions of a wellbore, and such mud motors typically include a bent or curved segment as part of the bottom hole assembly.

In most cases, downhole mud motors typically consist of three major components: a power section (typically consisting of a rotor and a stator); a bearing assembly; and a drive shaft assembly that connects said power section to said bearing assembly. Generally, the power section converts fluid pressure from pumped drilling fluid into mechanical (typically rotational) energy; said drilling fluid acts on said rotor, causing the rotor to rotate or spin within the surrounding stator. The drive shaft is typically operationally connected to said rotor, and must transfer torque forces and rotation from the rotor to said bearing assembly, while also accommodating downhole thrust loads encountered during the drilling process. Such thrust loads include axial forces that are generally aligned with the longitudinal axis of section of a wellbore.

Said drive shaft is frequently encased within a surrounding housing. In many cases, said housing can be bent or curved in order to facilitate drilling of a curved or deviated wellbore section. As a result, the drive shaft (contained within said housing) must also accommodate said bend in the housing. In such cases, the drive shaft must be sufficiently strong to withstand—and transfer—torque forces generated by the power section, while accommodating the (frequently eccentric) rotation of the rotor and the bend in said drive shaft housing.

It is often beneficial to utilize longer power sections in order to generate greater torque forces; as the rotors and stators in power sections are lengthened, such power sections produce greater torque forces. The torque force output of power sections has increased to the point that drive line failures are being experienced with the use of conventional drive shafts.

Thus, there is a need for an improved drive shaft capable of withstanding the torque forces generated by power sections of modern downhole drilling devices, without being susceptible to the negative effects of these torque demands, or from high temperatures, high pressures, and other factors associated with a mud motor in a downhole drilling environment.

SUMMARY OF THE INVENTION

The present invention comprises a drive shaft assembly—sometimes referred to as a drive line—for use with downhole mud motors and well drilling operations. The drive shaft assembly of the present invention is capable of handling greater torque and thrust forces than conventional drive shaft assemblies.

In a preferred embodiment, the drive shaft assembly of the present invention comprises an elongated central drive shaft and at least one end housing; said end housing(s) can optionally be disposed at one or both ends of said central drive shaft. In a preferred embodiment, said central drive shaft has a substantially cylindrical shape with opposed first and second ends. Each end of said central drive shaft that is equipped with an end housing defines a rounded or partially-spherical outer end surface. Further, each end housing has a substantially concave interior surface defining a seat for receiving a rounded end surface of said central drive shaft. Said shaft and seat assemblies facilitate omnidirectional pivotal movement between said shaft and each of said end housings.

A plurality of elongate protrusions or “keys” extend radially outward from the exterior surface of the shaft at each of said rounded or partially-spherical end surface. Additionally, a plurality of circumferentially spaced axial keyways is provided in the interior surface of each of the end housings; said keyways are adapted to receive and engage with said keys of said shaft in mating relationship. Each of said keys has opposed sides, opposed ends, a rear face and a front face. The front face is radiused to facilitate omnidirectional, pivotal movement of said shaft relative to the adjoining housing(s). Said elongate keys (including, without limitation, the dimensions and geometry thereof) greatly increases the surface contact area and cross sectional shear area thereof, thereby increasing the torque load capacity of the drive line.

The driveline assembly of the present invention can be beneficially housed within an outer housing assembly. Said outer housing assembly can comprise a bend with each opposing end set at a different axis angle relative to the opposing end. Said housing assembly can also be optionally configured such that each opposing end is aligned (i.e., straight). The drive shaft assembly of the present invention allows for articulation in virtually any radial direction relative to its central longitudinal axis, while also permitting transfer of rotational and thrust forces across said drive shaft assembly. Further, the drive shaft assembly of the present invention is capable of handling greater torque and thrust forces than conventional drive shaft assemblies.

