Patent Application
20150176342
Directional drilling subassemblies have some specific drive requirements which are problematic. Two examples are the movements inherent in progressive cavity mud motor rotors of the driving end of the rotor, which must be connected to the rotating bit which it is meant to drive, and the off-set or angle between elements of the bottom-hole assembly (such as the motor and the bit assembly) in an adjustable or bent-housing used in directional drilling. To accommodate these differences in angular alignment between rotating parts of the equipment, various types of universal joint and similar drive arrangements have been used. The invention addresses certain shortfalls in the prior art, and aims to provide a novel drive shaft for use between a progressive cavity or similar mud motor and the downhole portion of the drilling equipment, namely a rotating bit or similar driven equipment. As will be familiar to those skilled in the art, in addition to accommodating the variable angular differences in the driving and driven equipment, these drive-shafts must also be capable of sustaining large longitudinal loads (along their length) whether in vertical or deviated postures within the wellbore, and whether in compression or in tension.
In directional drilling settings, as opposed to vertical drilling, in particular in oil and gas exploration and production wells, given the depths and formations through which wells are bored, it is impractical to drive rotating drill bits from surface by rotating the entire drill string by forces applied at surface in order to rotate the bit attached in a rigid way to the string's bottom end. It is therefore typical now to place a motor at or near the bottom of the drill-string which can be driven by forces applied at surface which do not involve rotating the entire drill-string most commonly by pumping drilling fluid (mud) under pressure with sufficient flow rates and force to cause the motor to rotate. The motor is attached at its bottom end to a rotating drill. The motor will typically be a progressive cavity motor, with a fixed outer body or stator and a moving, rotating rotor. To develop the torque forces required to drive the drill bit, as the wellbore's size (diameter) decreases, the motor's length increases. Perversely, the length of the motor in a small diameter bore will decrease the ability of the motor and bit assembly to deviate much from linear drilling operations, and so it is desirable to be able to bend the assembly along its length to accommodate a tighter turning radius in a directional or deviated drilling operation. In addition, the mud motor will operate with better efficiency and less wear if the rotor is permitted to turn and at the same time deviate from rotating around a strictly centred axis within its stator's body. Generally, torque transfer capacity depends in most machines on so the radius of the rotating member; again perversely, when the radius of the wellbore is reduced, the outside diameter of downhole equipment must also be reduced and the torque transfer within the universal joint(s) on a drive shaft between an eccentrically rotating rotor of a mud motor, and the driven downhole equipment (such as a rotating bit) become extreme with small diameter rotating travel. Universal joints experience extreme loading, and wear quickly.
These conditions (the rotor's rotation not being centred, and the desire to bend the bottom hole assembly between the motor and the bit) can be accommodated with an intermediate drive-shaft between the motor's rotor and the bit assembly with what amounts to universal joints or constant-velocity joints at either end of the drive-shaft. Problematically, the shaft and the rotating bendable joints must also be capable of bearing longitudinal forces of compression and tension downhole, as well as high torque forces.
Several examples of prior art drive-shafts and bearing assemblies exist. Two which are of relevance are described below.
U.S. Pat. No. 4,904,228 to Frear (US '228) shows an improved universal ball joint adapted for use in high-torque situations such as downhole drilling. It includes a shaft with a ball end on one shaft received in a mating housing on another shaft (one being driven, the other driving). Opposed surfaces of the ball and the mating receptacle include axially extending grooves of essentially the same depth and length forming a plurality of chambers around the ball's circumference, each chamber to receive a pin which is tapered at both ends and forms the driving connection between the shafts.
U.S. Pat. No. 8,033,917 to Prill (US '917) provides a similar universal ball joint, but instead of the groove-pin-groove driving connection between similar ball-receiver assembly between two shafts, '917 provides for two or four pivoting drive keys mounted in the ball-end shaped to facilitate rotation of one shaft's axis with respect to the other shaft's axis (length-wise) while stopping rotation of one shaft's rotation about its axis with respect to the rotation of the other shaft about its own axis (thus providing a drive link between the two shafts).
The improved drive shaft and bearing assembly of this invention provides a shaft with a parabolic shaped or rounded ball end received in a mating housing or retaining bonnet attached to another component of a drill-string's downhole assembly for transmitting rotational force (torque) from a motor to a drilling assembly at the bottom of the drill-string. The mating housing may have a drive seat with a parabolic pocket which mates with the outer surface of the end of the shaft's parabolic ball end, against which the shaft pivots during articulation of the joint between the shaft (and attached equipment) and the mating housing (and attached equipment). The opposing surfaces of the shaft's ball end and the receiver housing are provided with shaped mating voids forming chambers deployed about the ball end's circumference and within the receiver housing's inner mating circumference to receive elliptically shaped rollers. The rollers outer contact surface (except the rollers' ends) has a radius which maximizes the surface area of the roller which engages with the surface area of the mating voids on the driven and driving components (ball end and receiver housing), when the shaft is deviated from the components attached to the housing. Similar bearing arrangements are typically deployed at both ends of a drive shaft which is between a motor's drive (rotor) and a drill assembly downhole, and which can accommodate deviations encountered in bent shaft arrangements used in deviated drilling operations.
A drive-shaft assembly with two universal joint style thrust bearing assemblies for attachment between a progressive cavity type mud motor's rotor and driven downhole componentry in a bottom-hole assembly for deviated drilling is shown in
At the other, lower ball-end of the shaft 27, rollers 26 are similarly fitted to ball-end receptacles 301, which are fitted to a bonnet 22 with roller receptacles 401, and the bonnet 22 on the lower-end of the shaft 27 is attached to driven equipment lower in the drillstring (for instance, a bearing drive shaft 19 within a bent housing 20 for directing the direction of a drill-bit at the bottom of the string).
There may or may not be a seat in the bearing adapter or bonnet 22 at either or both ends. The putative circumference of the outer surface of each barrel-shaped roller 26 is designed to minimize point-loading between the roller and the roller receptacles 301, 401 when mated and under torque forces when the angle between the longitudinal axis of the shaft 27 and the equipment on either side of the shaft to which each bonnet 22 is attached changes. Angles of up to or greater than 3 degrees can be accommodated without serious point loading at the rollers' outer surface.
The roller 26 may be made of flexor metal, for example 4330 vanadium steel, and should be heat treated or otherwise treated to have a hardness of around 650 Rockwell. Pockets in the shaft 301 and housing receptacles 401 may be electrically hardened to similar Rockwell numbers on their mating surfaces.
These bearings and shaft assemblies are preferably used in 5″ or 6½″ drill strings. They may be sealed and bathed in lubricant, or may be mud lubricated and unsealed, operating bathed in drilling fluid.
It will be apparent to those skilled in the art that the embodiment described above is illustrative of the principle elements and operation of the invention as claimed, and that the claims are not limited by the example of the description, but by the terms of the claims themselves.
| Number | Date | Country | |
|---|---|---|---|
| 61885819 | Oct 2013 | US |
