BACKGROUND OF THE DISCLOSURE

The present disclosure relates generally to the field of drilling wells and more particularly to steerable drilling tools.

In deviated and horizontal drilling applications it is advantageous to use rotary steerable systems to prevent pipe sticking in the deviated and horizontal sections. It is ad vantageous to have the drill string rotating to prevent differential sticking and to reduce friction with the borehole wall. The rotar steerable system may have a housing that is substantially non-rotating. The present disclosure describes a downhole adjustable bent housing for rotary steerable drilling.

Directional drilling involves varying or controlling the direction of a wellbore as it is being drilled. Usually the goal of directional drilling is to reach or maintain a position within a target sabterranean destination or formation with the drilling string. For instance, the drilling direction may be controlled to direct the wellbore towards a desired target destination, to control the wellbore horizontall to maintain it within a desired payzone or to correct for unwanted or undesired deviations from a desired or

predetermined path.

Thus, directional drilling may be defined as deflection of a wellbore along a predetermined or desired path in order to reach or intersect with, or to maintain position withi ;, a specific subterranean formation or target. The predetermined path typically includes a depth where initial deflection occurs and a schedule of desired deviation angles and directions over the remainder of the wellbore. Thus, deflection is a change in the direction of the wellbore from the current wellbore path.

i t is often necessary to adjust the direction of the wellbore frequently w hite directional drilling, either to accommodate a planned change in direction or to

compensate for unintended or unwanted deflection of the wellbore. Unwanted deflection may result from a variety of factors, including the characteristics of the formation being dri lled, the makeup of the bottomhole drilling assembly and the manner in which the wellbore is being drilled.

Deflection is measured as an amount of deviation of the wellbore from the current wellbore path and is expressed as a deviation angle or hole angle. Commonly, the initial wellbore path is in a vertical direction. Thus, initial deflection often signifies a point at which the wellbore has deflected off vertical. As a result, deviation is commonly expressed as an angle in degrees from the vertical.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a drilling system;

FIG .2 A shows a steerable drilling assembly;

FIG. 2B shows the steerable drilling assembly of PIG .2 with a deviated steering shaft for altering the drilling direction;

FIG. 3A shows a section of the steerable assembly with the steering shaft aligned with the housing;

FIG. 333 shows an end view of the assembly of FIG. 3A;

FIG. 4A shows the section of the steerable assembly of FIG. 3A with the rotation of the orienting assemblies and the orienting sleeve to create a deviation angle between the steering shaft and the housing;

FIG. 4B is an end view of the assembly of FIG. 4A; and

FIG. 5 is a block diagram of one embodiment of a steerable drilling apparatus.

While the disclosed embodiments are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail it should be understood, however, that the drawings and detailed description herein are not intended to limit the disclosed subject matter to the particular form(s) disclosed, but on die contrary, the intention is to cover all modifications, equivalents and alternatives failing within the scope of the present disclosure as defined by the appended claims.

DETAILED DESCRIPTION

The illustrative embodiments described below are meant as examples and not as limitations on the claims that follow.

FIG. I show's a schematic diagram of a drilling system 1 10 having a downhole assembly according to one embodiment of the present disclosure. As shown, the system 1 10 includes a conventional derrick 1 1 1 erected on a derrick floor 1 12, which supports a

7 rotary table 1 14 that is rotated by a prime mover (not shown) at a desired rotational speed. A drill siring 120 that includes a drill pipe section 122 extends downward from rotary table 1 14 into a directional borehole 126, also called a weUhore. Borehole 126 may travel in a three-dimensional path. The three-dimensional direction of the bottom 151 of borehole 126 is indicated by a pointing vector 152, A drill bit 150 is attached to the downhole end of drill string 120 and disintegrates the geological formation 123 when drill bit 150 is rotated. The drill string 120 is coupled to a drawworks 1 0 via a keily joint 121, swivel 128, and line 129 through a system of pulleys (not shown). During the drilling operations, drawworks 130 may be operated, to control the weight on hit 150 and the rate of penetration of drill string 120 into borehole 126. The operation of drawworks 130 is well known in the art and is thus not described in detail herein.

Daring drilling operations a suitable drilling fluid (commonly referred to in the art as "mud") 131 from a mud pit 132 is circulated under pressure through drill string 120 by a mud pump 134. Drilling fluid 131 passes from mud pump 1.34 into drill string 1.20 via fluid line 138 and keily joint 121 , Drilling fluid 131 is discharged at the borehole bottom 151 through an opening in drill bit 150, Drilling fluid 131 circulates uphole through the annular space 127 between drill string 120 and borehole 126 and is discharged into mud pit 132 via a return line 135. A variety of sensors (not shown) may be appropriately deployed on the surface according to known methods in the art to provide information about various drilling-related parameters, such as fluid flow rate, weight on bit, hook load, etc.

A surface control unit 140 may receive communications, via a telemetry link, from downhole sensors and devices. The communications ma be detected by sensor 143 placed in fluid line 138 and processed according to programmed instructions provided to surface control unit 140. Surface control unit 140 may display desired drilling parameters and other information on a display/monitor 1 2 which ma be used by an operator to control the drilling operations. Surface control unit 140 may contain a computer, memory for storing data and instructions, a data recorder and other peripherals. Surface control unit 140 may also include well plan and evaluation models and may process data according to programmed instructions, and respond to user commands entered through a suitable input device, such as a keyboard (not shown). In one example, a steerable drilling bottom hole assembly (BHA) 159 may comprise dill collars and/or drill pipe, a measurement while drilling system 158, and a steerable assembly 160. MWD system 358 comprises various sensors to provide information about the formation 123 and downhole drilling parameters. MWD sensors 164 in BHA 159 may include, but are not limited to, a device for measuring the formation resistivity near the drill bit gamm ray device for measuring the formation gamma ray intensity, devices for determining the inclination and azimuth of the drill siring, and pressure sensors for measuring drilling fluid pressure downhole. The above-noted devices may transmit data to a downhole transmitter 133, which in turn transmits the data uphole to the surface control unit 140, via sensor 143. In one embodiment, a mud pulse telemetry technique may be used to communicate dat from downhole sensors and devices during drilling operations. A pressure transducer 143 placed in the mud supply line .138 detects mud pulses representative of the data transmitted b the downhole transmitter 133,

Transducer 143 generates electrical signals i response to the mud pressure variations and transmits such signals to surface control unit 140. Alternatively, other telemetry

techniques such as electromagnetic and/or acoustic techniques or any other sui table technique known in the art may be utilized. In one embodiment, hard-wired drill pipe may be used to communicate between the surface and downhole devices. In one example, combinations of the techniques described may be used, in one embodiment, a surface transmitter 180 transmits data and/or commands to the downhole tools using any of the transmission techniques described, for example a mud pulse telemetry technique. This may enable two-way communication between surface control unit 140 and a downhole controller 601 described below.

BHA 159 may also comprise a steerable assembly 160 for directing a steering shaft 75 attached between the rotating BHA 159 and bit. 150 along the desired direction to steer the path of the well.

Referring to FIGS. 2A-2B, a steerable drilling apparatus 160 is positioned near bit .150 in BHA 159, Steerable drilling assembly 160 comprises rotatable drive shaft 195 coupled to a rotating member 191 of drill string 120, Rotatable drive shaft 1 5 is coupled to a rotating steering shaft 75 by a coupling member 80. Rotating steering shaft 75 is, in turn, coupled to drill bit 150 for drilling the wellbore 126, As such, rotation of rotating member 191 causes drill it 150 to rotate, n one example, rotating member 1 1 may be a drill string component that rotates at the same speed as the drill siring. Alternatively, rotating member 191 may be the output shaft of a. drilling motor disposed in drill string 120, such that rotating member 191 rotates at an increased RPM equal to the motor output RPM plus the drill, string RPM

As shown, orienting sleeve 50 is rotatably supported between a first orienting assembly 220A and a second orientmg assembly 220B disposed within a substantially tubular housing 46. Housing 46 is substantially rotationally stationary in the wellbore during drilling, Rotatabie steering shaft 75 is rotatably supported in orienting sleeve 50. Orienting sleeve 50 is also rotatabie with respect to each orienting assembly 220A,B by actuation of orienting sleeve actuator 226. Actuation of first orienting assembl 220A, second orienting assembly 22ΘΒ, and orienting sleeve actuator 226 acts to orient steering shaft 75 and bit 150 in a desired three dimensional direction 252 to control the path of borehole 126.

First orienting assembly 220A and second orienting assembly 220B are disposed within housing 46 for controlling orienting sleeve 50. Steering shaft 75 rotates within orienting sleeve 50. Orienting sleeve 50 may be oriented to change the direction of steering shaft 75. Orienting sleeve 50 may provide contact hearing support to steering shaft 75 to limit the bending and bending stresses imposed on steering shaft 75, as described below.

With reference to FIGS. 3A-4B, orienting assembly 220 A comprises a circular outer ring 45A that is rotatably supported by bearings 59, on a circular inner peripheral surface 51 of housing 46. Note in FIGS. 36 and 4B that the bearings 59 are omitted for clarity. Outer ring 45 A has a circular inner peripheral surface 56A that is eccentric with respect to inner peripheral surface 51 of housing 46. Circular inner peripheral surface 56A of outer ring 45 A rotatably supports orienting sleeve 50 through bearings 59.

Similarly, orienting assembly 220B comprises a circular outer ring 45B that is rotatably supported by bearings 59, on circular inner peripheral surface 51 of housing 46. Oute ring 45B has a circular inner peripheral surface 568 that is eccentric with respect to inner peripheral surface 5.1 of housing 46, Circular inner peripheral surface 56B of outer ring 45B rotatably supports orienting sleeve 50 through bearings 59. Orienting sleeve 50 has an inner peripheral surface 65 that defines an. angled longitudinal circular bore 65 which has a centerime CLj that, is angled with respect to a centerline C L? defined by the outer peripheral surface 66 of orienting sleeve 50 by a predetermined angle, Θ (shown in FIG. 4A). By rot ting outer rings 45A,B and the orienting sleeve 50 relative to each other, and relative to housing 46, shaft 75 may be inclined by angle, Θ, such that bit 150 drills in a direction 1.52' with respect to the borehole centerline, CLj, of housing 46. In the embodiment shown, orienting assemblies 220A,B also comprise a motors 25A,B driving a spur gears 2?A,B that engages ring gears 26A,B, Ring gears 26A,B are attached to outer rings 45A,B and controllably drive outer rings 45A,B under the direction of a downhole controller 601 , discussed below.

Orienting sleeve 50 may be control!ably rotated relative to housing 46 and each outer ring 45A,B by orienting sleeve actuator 226, Orienting sleeve actuator 226 comprises a motor 30 driving a spur gear 31 that is operatively engaged with a ring gear 32 attached to outer peripheral surface 66 of orienting sleeve 50. Motor 30 controilab!y rotates deflection sleeve 50 under the control of controller 601. Motors 25 A, 25B, and 30 may be electric motors, hydraulic motors, or combinations thereof Such motors may incorporate rotational sensors, 607, 608, and 615, respectively, for accurate determination of the rotational angular orientation of the outer rings 45AJB and defleciion sleeve 50 relative to housing 46.

The rotational orientation of drilling shaft 75 may be referenced as a tooiface angle with respect to the gravitational high side of an inclined wellbore. Alternatively, in a substantially vertical wellbore, the reference may be to a north reference, for example magnetic, true, or grid. north. As used herein, the tooiface angle is the angle between the discussed reference, high side or north, and the plane containing the angled drilling shaft

As indicated above, orienting sleeve 50 may provide contact bearing support to steering shaft 75 to limit, the bending and bending stresses imposed on steering shaft 75. In one example, the inner peripheral surface 65 of orienting sleeve 50 may be coated with an abrasion resistant coating 95 to act as a wear resistant bearing surface. Such a coating 95 may extend over the entire length of orienting sleeve 50, Alternatively, the coating 95 may extend over predetermined portions of inner peripheral surface 65. Abrasion resistant coating 95 may comprise at least one of, a natural diamond coating, a synthetic diamond coating, a tungsten coating, a tungsten carbide coating, and combinations thereof. Similarly, at least some portions of steering shaft 75 may be coated. For example, the peripheral surface of steering shaft 75 may be coated where they are operationally juxtaposed with coated bearing surfaces on the inner peripheral surface of 65 of orienting sleeve 50,

Downhole controller 601, see FIG . 5, may be located in housing 46 to control the operation of steerabie assembly 1 0, Controller 601 may comprise processor 695 in data communications with any of the orienting assemblies 220A,B and 226 described above. In one embodiment, the deviation angle of drilling shaft 75 may be controlled by rotating the orientation sleeve 50 described above, and the toolface angle of drilling shaft 75 may be controlled with respect to the housing 46 by the proper rotation of outer rings 45A,B, thus orienting the drill bit 150 to drill along a desired path.

In one example well trajectory models 697 may be stored in a memory 696 that is in data communications with a processor 695 in the electronics 601 , Directional sensors 692 may be mounted in housing 46 or elsewhere in the BHA, and may be used to determine the inclination, azimuth, and highside of the steering assembly 160. Directional sensors may include, but are not limited to: azimuth sensors, inclination sensors, gyroscopic sensors, magnetometers, and three-axis accelerometers. Depth measurements may be made at the surface and/or downhole for calculating the location of steering assembly 160 along the we ^' llbore 26, If depth measurements are made at the surface, they ma be transmitted to the downhole assembly using surface transmitter 180 described above with reference to FIG. 1 , In operation, electronic interface circuits 693 may distribute power from power source 690 to one, or more, of directional sensors 692 , processor 695, downhole transmitter 133, first orienting assembly 220, second orienting assembly 225, and deflection sleeve actuator assembly 226. In addition, electronic interface circuits 693 may transmit and/or receive data and command signals from directional sensors 692, processor 695, and telemetry system 691. Angular rotation sensors 607, 608 and 615 may be used to determine the rotational positions of outer ring 45A, outer ring 45B, and orienting sleeve 75 relative to housing 46. Power source 690 may comprise batteries, a downhole generator/alternator, and combinations thereof. In one embodiment, models 697 may comprise directional position models to control the steering assembly to control the direction of the wellhore al ong a predetermined trajectory. The predetermined trajectory may be 2~dimensional and or 3~dimensionaL In. addition models 69? may comprise instructions that evaluate the readings of the directional sensors to determine when the well path has deviated from the desired trajectory. Models 697 ay calculate and control corrections to the ioolface and drilling shaft angle to make adjustments to the well path based on the detected deviations. In one example, models 697 may adjust the well path direction to move back to an original planned predetermined trajectory. In another, example, models 697 ma calculate a new trajectory from the deviated position to the target; and control the steering assembly to follow the new path, in one example, the measurements, calculations, and corrections are autonomously executed do nhole. Alternatively, direction sensor data may be transmitted to the surface, corrections calculated at the surface, and commands from the surface may be transmitted to the downhole tool to alter the settings of the steering assembly.

Numerous variations and modifications will become apparent to those skilled in the art. It is intended that the following claims be interpreted to embrace all such variations and modifications.