Patent Publication Number: US-11028646-B2

Title: Hybrid rotary steerable system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. National Stage of Application No. PCT/US2018/012471, filed on Feb. 23, 2018, which claims the benefit of Chinese Patent Application No. 20170111732.1, filed on Feb. 28, 2017, the disclosures of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention generally relates to a directional drilling system and method, and in particular, to a hybrid rotary steerable system and method that fuse point-the-bit and push-the-bit functions. 
     BACKGROUND OF THE INVENTION 
     An oil or gas well often has a subsurface section that needs to be drilled directionally. Rotary steerable systems, also known as “RSS,” are designed to drill directionally with continuous rotation from the surface, and can be used to drill a wellbore along an expected direction and trajectory by steering a collar while it&#39;s being rotated. Thus rotary steerable systems are widely used in such as conventional directional wells, horizontal wells, branch wells, etc. Typically, there are two types of rotary steerable systems: “push-the-bit” systems and “point-the-bit” systems. 
     In the point-the-bit system, the point direction of the drill bit is changed by bending the bit shaft relative to the rest of the bottom hole assembly (BHA). In an idealized form, the drill bit of the point-the-bit system is not required to cut sideways because the bit axis is continually aligned with the direction of the wellbore being drilled. 
     In the push-the-bit system, the drilling direction is changed by applying a lateral force (a force in a steering direction that is at an angle with respect to the direction of wellbore propagation) to the collar to push the drill bit to deviate from the wellbore center. The lateral force usually is applied to the collar by an actuating unit, such as one or more pads. In an idealized form, the drill bit of the push-the-bit system is required to cut sideways in order to change the drilling direction. 
     Generally, the push-the-bit system has a high build-up rate but forms an unsmooth drilling trajectory and rough well walls, whereas the point-the-bit system forms relatively smoother drilling trajectory and well walls, but has a relatively lower build-up rate. How to improve the efficiency, build-up rate and wellbore quality in directional drilling for oil &amp; gas exploitation is always a big challenge. 
     SUMMARY OF THE INVENTION 
     A rotary steerable drilling system includes a collar, a drill bit, and a bit shaft connecting the drill bit to the collar. The bit shaft is coupled to the collar through a joint capable of transmitting a torque from the collar to the bit shaft, and is swingable with respect to the collar around the joint. The rotary steerable drilling system further includes a first eccentric wheel and a second eccentric wheel coupled to the bit shaft and rotatable to swing the bit shaft with respect to the collar around the joint, a controller for controlling the first and second eccentric wheels to harmoniously rotate such that the swing of the bit shaft with respect to the collar substantially compensates rotation of the collar, and an active stabilizer mounted on the bit shaft and capable of pushing the bit shaft to deviate to cause a lateral displacement and a tilt angle of the drill bit to change a drilling direction. 
     A rotary steerable drilling method includes drilling a borehole with a drill bit coupled to a collar via a bit shaft, while rotating the collar, the bit shaft and the drill bit. The method further includes rotating a first eccentric wheel and a second eccentric wheel coupled to the bit shaft, to swing the bit shaft with respect to the collar around a joint adapted to connect the bit shaft to the collar and transmit a torque from the collar to the bit shaft. The method further includes controlling the first and second eccentric wheels to harmoniously rotate such that the swing of the bit shaft with respect to the collar substantially compensates rotation of the collar, and pushing the bit shaft to deviate to cause a lateral displacement of the drill bit, to change a drilling direction while the drilling, via an active stabilizer mounted on the bit shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic longitudinal section view of a portion of a hybrid rotary steerable system in accordance with one embodiment of the present disclosure, which shows a drill bit and a bottom hole assembly (BHA) of the hybrid rotary steerable system. 
         FIG. 2  is an enlarged view of the portion A as shown in  FIG. 1 . 
         FIG. 3  is a schematic cross section view of the BHA of  FIG. 1  taken along line B-B. 
         FIG. 4  is an enlarged view of the portion C as shown in  FIG. 1 . 
         FIG. 5  is a schematic view illustrating interaction of two eccentric wheels of the hybrid rotary steerable system of  FIG. 1 . 
         FIG. 6  is a schematic cross section view of the BHA of  FIG. 1  taken along line D-D. 
         FIG. 7  is a schematic view illustrating a status of the hybrid rotary steerable system of  FIG. 1  when it is used to steer to establish or change curvature during drilling. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more embodiments of the present disclosure will be described below. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. The terms “first,” “second,” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “or” is meant to be inclusive and mean any, some, or all of the listed items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The term “coupled” or “connected” or the like includes but is not limited to being connected physically or mechanically, and may be connected directly or indirectly. 
     Embodiments of the present disclosure relate to a rotary steerable drilling system and method and particularly a hybrid rotary steerable system and method for directional drilling a borehole or wellbore. The hybrid rotary steerable system and method incorporate point-the-bit and push-the-bit steering modes into a single scheme, and can greatly improve the build-up rate. 
       FIG. 1  is a schematic longitudinal section view of a portion of a hybrid rotary steerable system  100 , which shows a bottom hole assembly (BHA)  101  and a drill bit  103  of the hybrid rotary steerable system  100 . The drill bit  103  is coupled with a drill string (collar)  105  via a bit shaft  107 . The bit shaft  107  is coupled with the collar  105  through a joint  108 , around which the bit shaft  107  is swingable relative to the collar  105 . The joint  108  may be a flexible joint such as a universal joint. Through such a flexible joint, the bit shaft  107  is swingable but not rotatable relative to the collar  105 , and a torque can be transferred from the collar  105  to the bit shaft  107 . In some embodiments, the bit shaft  107  has a longitudinal tubular shape, and includes an upper section  111  above the joint  108  and a lower section  113  below the joint  108 . The joint  108  between the upper section  111  and the lower section  113  is coupled to the collar  105  near a front end  115  of the collar  105 , having the upper section  111  within the collar  105  and the lower section  113  outside the collar  105 . The swing of the bit shaft  107  relative to the collar  105  can cause the drill bit  103  tilted in a desired direction as in a point-the-bit system. 
     In addition, the hybrid rotary steerable system  100  further includes an active stabilizer  141  for pushing the bit shaft  107  and the collar  105  to deviate to generate a lateral displacement of the drill bit  103 , like in a push-the-bit system. A combination of the tilt and the lateral displacement of the drill bit  103  increases the offset of the drill bit  103  to improve the build-up rate, comparing with a pure point-the-bit or push-the-bit system. 
       FIG. 2  is an enlarged view of the portion A as shown in  FIG. 1 . As shown in  FIG. 1  and  FIG. 2 , there are at least two motors  121  and  123  installed in the BHA  101 . Each of the motors  121  and  123  may have an encoder (not shown) that converts mechanical motion into an electrical signal for motor speed and/or position measure and control. The two motors  121  and  123  rotate two eccentric wheels  125  and  127 , respectively. In some embodiments, rotary axes of the eccentric wheels  125  and  127  are substantially in parallel with each other. Specifically, the first motor  121  drives the first eccentric wheel  125  to rotate, through a first gear drive train  160  including, for example, gears  161  and  163 , and the second motor  123  drives the second eccentric wheel  127  to rotate, through a second gear drive train  170  including, for example, gears  171 ,  173 ,  175  and  177 . In some embodiments, the first gear drive train  160  includes at least one gear fixed with the first eccentric wheel  125 , and the second gear drive train  170  includes at least one gear fixed with the second eccentric wheel  127 . As used herein, “fixed with the first or second eccentric wheel” means being one-piece formed with the first or second eccentric wheel, or being fixed to the first or second eccentric wheel via one or more fasteners such as bolts. As shown in  FIG. 1  and  FIG. 2 , the gear  163  in the first gear drive train  160  is one-piece formed with the first eccentric wheel  125 , and the gear  177  in the second gear drive train  170  is one-piece formed with the second eccentric wheel  127 . The first motor  121  drives the gear  161  to drive the gear  163  fixed with the first eccentric wheel  125  and thereby drives the first eccentric wheel  125  to rotate, and the second motor  123  drives the gear  171  to drive the gear  173  and the gear  175  fixed with the gear  173 , and the gear  175  drives the gear  177  fixed with the second eccentric wheel  127  and thereby drives the second eccentric wheel  127  to rotate. In a specific embodiment as shown in  FIG. 1  and  FIG. 2 , the gear  173  is one-piece formed with the gear  175  and supported by a support  180  via a bearing  131 . The support  180  is fixed with the collar  105 . 
     In some embodiments, the two eccentric wheels  125  and  127  are coupled to the upper section  111  of the bit shaft  107 , and particularly, are coupled to an upper axial end  118  of the bit shaft  107 , whereas the drill bit  103  is coupled to the lower section  113  of the bit shaft  107 , and particularly, is coupled to a lower axial end  119  of the bit shaft  107 . In some specific embodiments, the drill bit  103  is fixed at the lower axial end  119  of the bit shaft  107 . 
     As shown in  FIG. 1  and  FIG. 2 , the eccentric wheels  125  and  127  are coupled to the bit shaft  107  through bearings around the upper end  118  of the bit shaft  107 . In some embodiments, the two eccentric wheels  125  and  127  are coupled between the collar  105  and the bit shaft  107 , wherein the eccentric wheel  125  is coupled between the eccentric wheel  127  and the collar  105  and the eccentric wheel  127  is coupled between the bit shaft  107  and the eccentric wheel  125 . There is a first bearing  135  between the eccentric wheel  125  and the collar  105 , a second bearing  137  between the two eccentric wheels  125  and  127 , and a third bearing  139  between the eccentric wheel  127  and the bit shaft  107 . By rotating the two eccentric wheels  125  and  127 , the bit shaft  107  can be pushed to swing around the joint  108  to change the point direction of the drill bit  103 , which makes the hybrid rotary steerable system  100  act as a point-the-bit system. The swing of the tubular bit shaft  107  can change the bit shaft  107  from being coaxial with the collar  105  to being uncoaxial with the collar  105 . 
     In some embodiments, as illustrated in  FIG. 3 , the joint  108  is a ball-shape universal joint including a plurality of small balls  117 . These small balls  117  transfer the torque from the collar  105  to the bit shaft  107 , such that the collar  105  can rotate the bit shaft  107  and the drill bit  103  to cut rock while drilling. As illustrated in  FIG. 1 , each of these small balls  117  is contained in a space defined between the collar  105  and the bit shaft  107 . In some embodiments, as illustrated in  FIG. 4 , there is a groove  109  defined in the collar  105  and a cavity  110  defined in the bit shaft  107  corresponding to each of the small balls  117 , and the groove  109  and the cavity  110  together form a closed space for accommodating the small ball  117 . The closed space is surplus for the ball  117  along an axial direction of the collar  105 , to allow the bit shaft  107  to swing relative to the collar  105  around the joint  108 . In some specific embodiments, the cavity  110  defined in the bit shaft  107  conforms to the size and shape of the ball  117 , whereas the groove  109  defined in the collar  105  is surplus for the ball  117  along the axial direction of the collar  105 . 
     Returning to  FIG. 1  and  FIG. 2 , while directional drilling, the two motors  121  and  123  drive the eccentric wheels  125  and  127  to tilt the bit shaft  107  with respect to the collar  105  at the joint  108 , to generate a tilt angle between the collar  105  and the bit shaft  107  around the joint  108 . There is at least one measurement module such as a measurement while drilling (MWD) module (not shown) and at least one controller (not shown) in the hybrid rotary steerable system  100 . The measurement module may be used to measure rotation and gesture parameters of the collar  105  and the bit shaft  107  in real-time. Based on the measured parameters, the controller can control the two motors  121  and  123  to harmoniously rotate the two eccentric wheels to push the bit shaft  107  to swing in a manner that the swing substantially compensates the rotation of the collar  105  to keep the drill bit  103  stably pointing to a desired direction, like in a point-the-bit system. Specifically, the bit shaft  107  swings to make sure the tilt of the drill bit  103  is actively maintained in the desired direction with respect to the formation being drilled, as in a point-the-bit system. 
     In some embodiments, the swing of the bit shaft  107  is controlled via movements of the first and second eccentric wheels  125  and  127 . As illustrated in  FIG. 5  and  FIG. 1 , O 1  is the center of the collar  105  or the bearing  135  (also the rotary axis of the first eccentric wheel  125 ), O 2  is the center of the bearing  137  (also the rotary axis of the second eccentric wheel  127 ), and O 3  is the center of the bearing  139  (also the center of the upper end  118  of the bit shaft  107 ). O 1 XY is a coordinate system coupled to the collar through O 1 . But the coordinate system does not rotate along with the collar. θ 1  is an angle between line O 1 O 2  and the X axis, and θ 2  is an angle between line O 1 O 2  and line O 2 O 3 . 
     During drilling, the collar  105  rotates with an angular speed Ω. The first eccentric wheel  125  rotates with an angular speed ω with respect to collar  105 . If Ω is equal to ω but with an inverse direction, the first eccentric wheel  125  can keep stationary to the fixed coordinate system O 1 XY. So the first eccentric wheel  125  has no rotation to the well. Further, the second motor  123  can be controlled to keep the θ 2  substantially constant, for example, by rotating the second motor  123  with respect to collar  105  at a controlled speed, such that the active stabilizer bias displacement and the point direction of the drill bit  103  can be kept stable. Thus, the system can stably drill the borehole. 
     In some embodiments, a distance between O 1  and O 2  is substantially equal to a distance between O 2  and O 3 . When θ 2  is equal to 180 degree, O 3  overlaps with O 1 , the bit shaft  107  is not tilted with respect to the collar  105  and the bit shaft  107  has no bias displacement, thus the drill bit drills along a straight line. When O 3  doesn&#39;t overlap with O 1 , the active stabilizer  141  can keep a bias displacement that is proportional to a distance between O 1  and O 3  (O 1 O 3 ), and particularly is very close to the distance O 1 O 3 . Therefore, when O 3  doesn&#39;t overlap with O 1 , and O 1  and O 2  are kept substantially constant, the drill bit drills along an arc trajectory and the build-up rate is kept stable. 
     In some specific embodiments, w is kept to be equal to Ω with an inverse direction during drilling. By controlling θ 1  and θ 2 , the drilling direction can be continuously changed and the drill bit can move forward along an expected trajectory. 
       FIG. 6  illustrates a cross section view of the active stabilizer  141  taken along line C-C in  FIG. 1 . In some embodiments, as illustrated in  FIG. 1  and  FIG. 6 , the active stabilizer  141  is fixed on the upper section  111  of the bit shaft  107  near the upper end  118  of the upper section  111  (which also is the upper end of the bit shaft  107 ), and has an outer surface  143  for contacting an inner surface of a borehole (not shown in  FIG. 1  and  FIG. 6 ) drilled by the drill bit. There are ribs  145  passing through the collar  105  and extending between an outer surface of the upper section  111  and the outer surface  143  of the active stabilizer  141 . In particular, the outer surface  143  is an annular surface supported by the ribs  145 , and there may be grooves on the annular surface for mud to pass through. When rotating the two eccentric wheels  125  and  127 , the active stabilizer  141  is constrained by the borehole and its outer surface  143  abuts on the inner surface of the borehole and applies a lateral force to the inner surface of the borehole. The counterforce of the lateral force applied to the active stabilizer  141  and the bit shaft  107  fixed with the active stabilizer  141  pushes the collar  105  via the joint  108  to deviate to generate a lateral displacement, which makes the hybrid rotary steerable system  100  act as a push-the-bit system. At the same time, the lateral displacement of the collar  105  at the joint  108  causes a tilt angle between the collar  105  and the bit shaft  107 , which makes the hybrid rotary steerable system act as a point-the-bit system. 
       FIG. 7  illustrates a status of the hybrid rotary steerable system  100  when it steers to change the drilling direction while drilling a well  200 . As shown in  FIG. 7 , the hybrid rotary steerable system  100  further includes one or more fixed stabilizers (only the fixed stabilizer  151  closest to the active stabilizer  141  is shown) fixed on the collar  105 . When the hybrid rotary steerable system  100  steers to change the drilling direction, the motors  121  and  123  (shown in  FIG. 1 ) and the active stabilizer  141  cooperatively drive the bit shaft  107 , the drill bit  103  fixed on the bit shaft  107 , and a section  153  of the collar  105  that is between the joint  108  and the fixed stabilizers  151  closest to the active stabilizer  141 , to gradually deviate to generate a deviating angle β between the rotation axis of the collar section  153  and an axis of the well  200  near the fixed stabilizers  151 . The motors  121  and  123  and the active stabilizer  141  also cooperatively drive the bit shaft  107  to tilt around the joint  108  with respect to the collar section  153  with a tilt angle α between a rotation axis of the bit shaft  107  (which is also the rotation axis of the drill bit  103 ) and a rotation axis of the collar section  153 . 
     The dual effect makes an angle γ between the rotation axis of the drill bit  103  and the axis of the well  200  near the fixed stabilizers  151  approximately equal to a sum of α and β, i.e., γ≈α+β. It can be seen that, the angle between the rotation axis of the drill bit  103  and the axis of the well  200  near the fixed stabilizers  151  significantly increases comparing with a pure point-the-bit or push-the bit system of the prior art, which means that the build-up rate is significantly improved. In addition, due to the active stabilizer and the stable control, the drilling trajectory can be more smooth and the well quality can be improved. 
     The hybrid rotary steerable system as described herein above steers in a hybrid manner incorporating point-the-bit and push-the-bit steering modes. The fused point-the-bit and push-the-bit functions can improve the build-up rate as the bit shaft  107  is pushed to generate a lateral displacement and a tilt angle of the drill bit  103  in a same direction by the active stabilizer  141  and the two eccentric wheels  125  and  127 . 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.