Directional drilling apparatus

[0001] This invention pertains to apparatus for use in the bottom hole assembly of a drill string to influence the direction of the bore of a well being drilled. Further, it pertains to apparatus that disables a drilling motor to permit rotary, straight hole drilling, and enables the motor and deflects the housing for directional drilling.

[0002] Directional drilling usually involves down-hole drill bit driving drilling motors. The motors are usually powered by the drilling mud flowing down the drill string bore. The motors are usually of the positive displacement type. Such motors are currently limited in terms of drilling fluid pressure drop through the motor. Motor output power is proportional to the pressure drop. The acceptable pressure drop is usually much less than the available pressure that the surface pumps could supply. Drilling motors seldom deliver the maximum available horsepower to the drill bit.

[0003] The pressure drop through the motor is proportional to motor output torque, and modern drill bits are often capable of using more torque than drilling motors can provide. In many such cases, the common rotary practice can drill hole more economically without the motor. The motor, however, may be essential to well bore direction control.

[0004] If directional control is necessary, a down hole assembly often has to have steerable rotary apparatus or a motor with a bore deflecting ability. Either choice adds a technical and economical burden to the drilling activity.

[0005] There is a need for rotary drilling assembly that can accommodate a down hole motor. The motor is needed periodically to provide a hole direction influence. The motor needs to be capable of efficient activation and de-activation so that optimum rotary practice can be applied most of the drilling time.

[0006] If the drilling motor is used a small percentage of the drilling time, it can be made somewhat smaller than greater dependence upon the motor would allow. By reducing the motor size, the wall thickness of the motor housing can be thickened to accept greater rotary torque. Overall benefit is realized from the ability to readily switch from one mode of drilling to another.

[0007] When the motor is activated, it is advantageous to deflect the drilling assembly, ideally with the same down link command. That can be accomplished if the motor drives the deflection apparatus. While the motor runs, then, the deflection is effective. While the motor is disabled, then, the rotary system drives the drill bit in the straight hole drilling mode.

[0008] While the motor is activated, the progressing well bore needs directional control. Such control, in terms of orientation, can be provided by Measurement While Drilling (MWD) apparatus. The MWD apparatus, currently available, does not control drill string deflecting apparatus. To get the best use of drill string deflecting apparatus, there is a need for some form of down link command that is reliable and simple to exercise. In addition to down link command, there is a need to have some form or reaction feedback that indicates, in real time, that the command is being carried out.

[0009] To accomplish down link command control, the apparatus responds to alternate onsets of drilling fluid flow. For instance, on even actuations, it may cause deflection and direct drilling fluid flow through the motor. On odd actuations, the apparatus may open drilling fluid by-pass channels, weakening the drilling motor torque. The drill string rotary drive acts through a one-way clutch to mechanically by-pass the motor and drive the drill bit from drill string delivered torque. The general apparatus housing is divided but the upper housing and the lower housing are connected by a tilted deflector bearing assembly. The rotation of the drill string is conducted through the upper housing to the deflector bearing, and drill bit rotation resistance causes the lower housing to rotate, a limited amount, counterclockwise to the straight configuration allowing straight drilling rotary practice independently of the motor.

[0010] When the motor by-pass channel is closed (the drill string rotation may be stopped) the motor acts through a resisting one-way clutch to rotate the lower housing clockwise to the deflected configuration. The lower housing carries the output shaft bearings and controls deflection of the drill bit from the center line of the upper housing. The deflected drill bit changes the direction of the evolving well bore. Because of the simplicity of the change in configuration, frequent small corrections become possible. Severe changes in well bore direction can be reduced.

[0011] The by-pass channel has minimized pressure loss, in contrast to the motor driving pressure drop. When changing to the rotary, straight hole, drilling mode the stand pipe pressure at a selected flow rate is reduced and the reduction is an indication that the straight rotary mode is in effect down hole. This is a feed-back signal that leaves no doubt about the mode in effect down hole. Changing from the rotary drilling mode has the opposite, detectable, effect.

[0012] These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.

[0032] The overall apparatus includes a mode selector, a motor connected to the final output shaft, a motor by-pass valve responsive to the mode selector, a general housing with an upper housing and a lower housing connected by a tilted bearing allowing limited rotation of the lower housing relative to the upper housing, and a one-way resisting clutch which allows the drill string to drive the drill bit clockwise but allows the motor, when activated, to first rotate the lower housing clockwise to the deflected configuration, then drive the drill bit clockwise for drilling while the drill string does not rotate.

[0033] FIGS. 1 and 2 show upper housing 1 connected to lower housing 15 by tilted bearing 8. Motor 5 is connected to output shaft 13 by shaft 7 by way of couplings 6 and 9. Mode selector 2 acts to control by-pass valve 3 which opens or closes channel 4. Channel 4 extends through the bore in the motor rotor. Bearing 10 has radial and thrust bearings to position the output shaft 13 within the lower housing 15. One-way clutch 11 is biased against interdigitating teeth 12 to resist, but allow, rotation of the output shaft relative to the lower housing 15. Fluid channel 4, and fluid passing through the motor passes through channel 14 to flush the drill bit (not shown). FIG. 2 shows the apparatus in the deflected configuration. Lower housing 15 has been rotated relative to the upper housing by the motor that is made operational by the actuation of mode selector 2, closing by pass valve 3 to cause most of the drilling fluid to pass through the motor. The deflection is shown as angle b relating the upper housing and the lower housing. Clutch 11 is spline connected to the lower housing and may be dis-engaged from the output shaft.

[0034] FIGS. 3 and 4 show clutch 11 connecting the lower housing 15 and output shaft 13. Output shaft 13 is supported in the lower housing by bearing assembly 10 which includes thrust bearing 10a and radial bearing sleeves 10b and 10c. Clutch 11 includes spring 11a which urges clutch element 11b, with splines 11c and clutch teeth 12 into engagement with clutch grooves 13a on the output shaft 13. The clutch is dis-engaged in FIG. 3 and is engaged in FIG. 4. Resistance of the clutch will rotate housing 15 clockwise to deflect the lower housing in response to rotation of the output shaft. It is not yet shown deflected. When the motor is not driving the output shaft, and the drill string rotates the upper housing, the clutch will engage and resistance of the drill bit (not shown) will cause the lower housing to rotate counterclockwise relative to the upper housing, to limits, and straighten the overall housing. In addition to drill bit rotation resistance, any stabilizers present on the lower housing will add rotation resistance to urge the lower housing to the straight configuration.

[0035] FIG. 5 shows grooves 13a on output shaft 13.

[0036] FIG. 6 shows clutch teeth 12 engaging teeth 13a of the output shaft 13.

[0037] FIG. 7 shows mode selector 2 urged to a first position by spring 2f. By-pass valve 3 is urged open by spring 3a and drilling fluid flows through channel FC, weakening the motor output torque. Pins 2e engage serpentine grooves 2d and stop movement of the armature 2b short of the valve on alternate rightward excursions. The rightward excursions are induced by drilling fluid flow through resistance ports 2a and 2c.

[0038] FIG. 8 shows the mode selector moved rightward by an alternate onset of drilling fluid flow. When arbor 2b engages the valve 3, it is urged to closure. The valve 3 is driven closed by fluid pressure and moves some amount after the arbor 2b is stopped by travel limits, avoiding continuous engagement between stationary and rotating parts.

[0039] FIG. 9 shows the relationship between pins 2e and arbor 2b.

[0040] FIG. 10 is a surface development of the serpentine grooves 2d which cause the arbor to rotate during excursions. This is the usual configuration of walk-around mode selectors now in common use in down hole tools.

[0041] FIGS. 11 and 12 show the preferred form of rotation limiting elements between upper housing 1 and lower housing 15. The drive shaft 7 of the motor rotates as shown by arrow d and the clutch, see FIGS. 3 and 4, drives the lower housing 15 as shown by arrow e. Slot 8b permits lug 8a to move a limited amount. The tilted bearing of FIG. 13 causes that amount of rotation to deflect the lower housing 15 a pre-selected amount relative to upper housing 1.

[0042] FIG. 13 shows the tilted bearing assembly 8 connecting upper housing 1 and lower housing 15. Bearing balls 8d and 8e and related races are situated on an axis BCL which is tilted angle a relative to the upper housing centerline HCL. Rotation of the lower housing relative to the upper housing causes the pre-selected amount of deflection of the lower housing. Seals s permit access to the lug 8a from outside the general housing.

[0043] FIG. 14 shows the mechanism of resistance to initial relative rotation of the output shaft 13 relative to the lower housing. The teeth are biased into engagement and are engaged at an angle. To dis-engage the clutch, torque has to be applied to separate the teeth. Once separated, the teeth do not re-engage readily because of fluid damping common to moving elements in a down hole situation.

[0044] FIG. 15 shows the teeth 12 riding over the crests of the teeth between grooves 13a. Grooves 13a move in the direction of arrow g. The crests of the teeth are slightly angled at a pre-selected angle f and thrusts the teeth apart at a rate that is compatible with the fluid damped movement of the clutch toward engagement. While movement exists, the teeth do not engage. When the motor is disabled and the housing transmits drill string rotation to the output shaft, teeth 12 move in the direction of arrow g and the teeth freely engage. The drill string can then drive the drill bit. Teeth 12 cannot rotate relative to the lower housing. The torque that drives the drill bit rotates the lower housing to urge it to the straight configuration. Rotary drilling practices then continue without regard to the idle motor.

[0045] FIGS. 16 and 17 show an alternate routing for by-pass of drilling fluids. Motor M has an outer jacket 21 that fits in the bore of the upper housing, with fluid channels 21a situated between the housing bore and the jacket. The rotor R has a bore with restrictor 16 at the entry end. Tubular valve element 20 moves downward, opposed by spring 20a, to occlude the peripheral by-pass openings. Mode selector 2 is unchanged.

[0046] With the peripheral by-pass channels, the rotor bore is not required. If the rotor bore is present, the valve plug 3 of FIG. 7 can be carried by the element 20 of FIG. 16 to control greater by-pass channel capacity.

[0047] From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

[0048] It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims.

[0049] As many possible embodiments may be made of the apparatus of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.