Abstract:
The invention provides rotary steerable devices and methods for use of rotary steerable devices. One aspect of the invention provides a rotary steerable device including: a cylinder configured for rotation in a wellbore, the cylinder having a slot and a gauge; and at least one cam received in the slot. The cam is configured for selective actuation between a first position, wherein the cam lies within the gauge of the cylinder, and a second position, wherein the cam is displaced out of the gauge of the cylinder.

Description:
TECHNICAL FIELD 
       [0001]    The invention provides rotary steerable devices and methods for use of rotary steerable devices. 
       BACKGROUND 
       [0002]    Controlled steering or directional drilling techniques are commonly used in the oil, water, and gas industry to reach resources that are not located directly below a wellhead. The advantages of directional drilling are well known and include the ability to reach reservoirs where vertical access is difficult or not possible (e.g. where an oilfield is located under a city, a body of water, or a difficult to drill formation) and the ability to group multiple wellheads on a single platform (e.g. for offshore drilling). 
         [0003]    With the need for oil, water, and natural gas increasing, improved and more efficient apparatus and methodology for extracting natural resources from the earth are necessary. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides rotary steerable devices and methods for use of rotary steerable devices. 
         [0005]    One aspect of the invention provides a rotary steerable device including: a cylinder configured for rotation in a wellbore, the cylinder having a slot and a gauge; and at least one cam received in the slot. The cam is configured for selective actuation between a first position, wherein the cam lies within the gauge of the cylinder, and a second position, wherein the cam is displaced out of the gauge of the cylinder. 
         [0006]    This aspect can have several embodiments. The cam can be utilized in displacing the cylinder for steering the rotary steerable device. The rotary steerable device can include an actuator configured to actuate the cam. The actuator can be a low power actuator. The actuator can be an electric motor. The actuator can be a hydraulic actuator. The rotary steerable device can include a controller configured to control actuation of the cam by the actuator. 
         [0007]    The rotary steerable device can include a drill bit. The drill bit can be substantially adjacent to the cam. The cam can rotate in a first direction about a rotational axis. The cam can be configured to rotate in a second direction about the rotational axis after contact with the wellbore. The cylinder can rotate in a direction opposite to the first direction of rotation of the cam. The cam can be configured for actuation to an angle at which a non-slip condition occurs when the cylinder is rotated. 
         [0008]    The rotary steerable device can include a cam shaft extending from the cam along the rotational axis of the cam. The rotary steerable device can include a plurality of bearings for supporting the cam shaft. The rotary steerable device can include a wear ring external to the cylinder. The wear ring can be configured for displacement when contacted by the cam. The cylinder can include a plurality of slots. A cam can be received in each slot. 
         [0009]    Another aspect of the invention provides a rotary steerable device including: a cylinder configured for rotation in a wellbore, the cylinder having a slot; and a plurality of cams received in the slot. Each cam is configured for selective actuation between a first position wherein at least one of the cams lies within a gauge of the cylinder, and a second position, wherein at least one of the cams is displaced out of a gauge of the cylinder. 
         [0010]    Another aspect of the invention provides a method of steering a bottom hole assembly. The method includes: providing a bottom hole assembly including a cylinder configured for rotation in a wellbore, the cylinder having a slot, and at least one cam received in the slot, the cam configured for selective actuation from a first position, wherein the cam lies within a gauge of the cylinder, and a second position, wherein the cam is displaced out of a gauge of the cylinder; rotating the cylinder; and selectively actuating the cam to steer the bottom hole assembly. 
         [0011]    This aspect can have several embodiments. The bottom hole assembly can include a wear ring external to the cylinder. The wear ring can be configured for displacement when contacted by the cam. 
         [0012]    Another aspect of the invention provides a wellsite system including: a drill string; a kelly coupled to the drill string; a rotary steerable device coupled to the drill string; and a drill bit coupled to the drill string. The rotary steerable device includes: a cylinder configured for rotation in a wellbore, the cylinder having a slot and a gauge; and at least one cam received in the slot, the cam configured for selective actuation between a first position, wherein the cam lies within the gauge of the cylinder, and a second position, wherein the cam is displaced out of the gauge of the cylinder. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference characters denote corresponding parts throughout the several views and wherein: 
           [0014]      FIG. 1  illustrates a wellsite system in which the present invention can be employed. 
           [0015]      FIG. 2A  illustrates a rotary steerable device in a side and cross-sectional view according to one embodiment of the invention. 
           [0016]      FIG. 2B  illustrates another embodiment of the invention that includes a continuous slot. 
           [0017]      FIGS. 3A-3F  illustrates the operation of a rotary steerable device within a borehole to steer a drill bit coupled to the rotary steerable device according to one embodiment of the invention. 
           [0018]      FIG. 4  illustrates a model of the interaction between a cam and a borehole according to one embodiment of the invention. 
           [0019]      FIG. 5  illustrates a profile of an exemplary cam for incorporation within a rotary steerable device according to one embodiment of the invention. 
           [0020]      FIG. 6  illustrates a rotary steerable device including a wear ring surrounding a plurality of cams according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The invention provides rotary steerable devices and methods for use of rotary steerable devices. Some embodiments of the invention can be used in a wellsite system. 
       Wellsite System 
       [0022]      FIG. 1  illustrates a wellsite system in which the present invention can be employed. The wellsite can be onshore or offshore. In this exemplary system, a borehole  11  is formed in subsurface formations by rotary drilling in a manner that is well known. Embodiments of the invention can also use directional drilling, as will be described hereinafter. 
         [0023]    A drill string  12  is suspended within the borehole  11  and has a bottom hole assembly (BHA)  100  which includes a drill bit  105  at its lower end. The surface system includes platform and derrick assembly  10  positioned over the borehole  11 , the assembly  10  including a rotary table  16 , kelly  17 , hook  18  and rotary swivel  19 . The drill string  12  is rotated by the rotary table  16 , energized by means not shown, which engages the kelly  17  at the upper end of the drill string. The drill string  12  is suspended from a hook  18 , attached to a traveling block (also not shown), through the kelly  17  and a rotary swivel  19  which permits rotation of the drill string relative to the hook. As is well known, a top drive system could alternatively be used. 
         [0024]    In the example of this embodiment, the surface system further includes drilling fluid or mud  26  stored in a pit  27  formed at the well site. A pump  29  delivers the drilling fluid  26  to the interior of the drill string  12  via a port in the swivel  19 , causing the drilling fluid to flow downwardly through the drill string  12  as indicated by the directional arrow  8 . The drilling fluid exits the drill string  12  via ports in the drill bit  105 , and then circulates upwardly through the annulus region between the outside of the drill string and the wall of the borehole, as indicated by the directional arrows  9 . In this well known manner, the drilling fluid lubricates the drill bit  105  and carries formation cuttings up to the surface as it is returned to the pit  27  for recirculation. 
         [0025]    The bottom hole assembly  100  of the illustrated embodiment includes a logging-while-drilling (LWD) module  120 , a measuring-while-drilling (MWD) module  130 , a roto-steerable system and motor, and drill bit  105 . 
         [0026]    The LWD module  120  is housed in a special type of drill collar, as is known in the art, and can contain one or a plurality of known types of logging tools. It will also be understood that more than one LWD and/or MWD module can be employed, e.g. as represented at  120 A. (References, throughout, to a module at the position of  120  can alternatively mean a module at the position of  120 A as well.) The LWD module includes capabilities for measuring, processing, and storing information, as well as for communicating with the surface equipment. In the present embodiment, the LWD module includes a pressure measuring device. 
         [0027]    The MWD module  130  is also housed in a special type of drill collar, as is known in the art, and can contain one or more devices for measuring characteristics of the drill string and drill bit. The MWD tool further includes an apparatus (not shown) for generating electrical power to the downhole system. This may typically include a mud turbine generator (also known as a “mud motor”) powered by the flow of the drilling fluid, it being understood that other power and/or battery systems may be employed. In the present embodiment, the MWD module includes one or more of the following types of measuring devices: a weight-on-bit measuring device, a torque measuring device, a vibration measuring device, a shock measuring device, a stick slip measuring device, a direction measuring device, and an inclination measuring device. 
         [0028]    A particularly advantageous use of the system hereof is in conjunction with controlled steering or “directional drilling.” In this embodiment, a roto-steerable subsystem  150  ( FIG. 1 ) is provided. Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction. 
         [0029]    Directional drilling is, for example, advantageous in offshore drilling because it enables many wells to be drilled from a single platform. Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer length of the wellbore to traverse the reservoir, which increases the production rate from the well. 
         [0030]    A directional drilling system may also be used in vertical drilling operation as well. Often the drill bit will veer off of a planned drilling trajectory because of the unpredictable nature of the formations being penetrated or the varying forces that the drill bit experiences. When such a deviation occurs, a directional drilling system may be used to put the drill bit back on course. 
         [0031]    A known method of directional drilling includes the use of a rotary steerable system (“RSS”). In an RSS, the drill string is rotated from the surface, and downhole devices cause the drill bit to drill in the desired direction. Rotating the drill string greatly reduces the occurrences of the drill string getting hung up or stuck during drilling. Rotary steerable drilling systems for drilling deviated boreholes into the earth may be generally classified as either “point-the-bit” systems or “push-the-bit” systems. 
         [0032]    In the point-the-bit system, the axis of rotation of the drill bit is deviated from the local axis of the bottom hole assembly in the general direction of the new hole. The hole is propagated in accordance with the customary three-point geometry defined by upper and lower stabilizer touch points and the drill bit. The angle of deviation of the drill bit axis coupled with a finite distance between the drill bit and lower stabilizer results in the non-collinear condition required for a curve to be generated. There are many ways in which this may be achieved including a fixed bend at a point in the bottom hole assembly close to the lower stabilizer or a flexure of the drill bit drive shaft distributed between the upper and lower stabilizer. In its idealized form, the drill bit is not required to cut sideways because the bit axis is continually rotated in the direction of the curved hole. Examples of point-the-bit type rotary steerable systems, and how they operate are described in U.S. Patent Application Publication Nos. 2002/0011359; 2001/0052428 and U.S. Pat. Nos. 6,394,193; 6,364,034; 6,244,361; 6,158,529; 6,092,610; and 5,113,953. 
         [0033]    In the push-the-bit rotary steerable system there is usually no specially identified mechanism to deviate the bit axis from the local bottom hole assembly axis; instead, the requisite non-collinear condition is achieved by causing either or both of the upper or lower stabilizers to apply an eccentric force or displacement in a direction that is preferentially orientated with respect to the direction of hole propagation. Again, there are many ways in which this may be achieved, including non-rotating (with respect to the hole) eccentric stabilizers (displacement based approaches) and eccentric actuators that apply force to the drill bit in the desired steering direction. Again, steering is achieved by creating non co-linearity between the drill bit and at least two other touch points. In its idealized form, the drill bit is required to cut side ways in order to generate a curved hole. Examples of push-the-bit type rotary steerable systems and how they operate are described in U.S. Pat. Nos. 5,265,682; 5,553,678; 5,803,185; 6,089,332; 5,695,015; 5,685,379; 5,706,905; 5,553,679; 5,673,763; 5,520,255; 5,603,385; 5,582,259; 5,778,992; and 5,971,085. 
       Rotary Steerable Devices 
       [0034]      FIG. 2A  depicts a rotary steerable device  200   a  in a side and cross-sectional view according to one embodiment of the invention. The invention includes a cylinder  202   a  having a gauge  204   a  and a slot  206   a.  A cam  208   a  is received within the slot  206   a.  The cam  208   a  can rotate about a pin  210   a,  as depicted by the dashed lines. 
         [0035]      FIG. 2B  depicts another embodiment of the invention that includes a continuous slot  206   b.  Four cams  208   a,    208   b,    208   c,    208   d  are received within slot  206   b.    
         [0036]    In some embodiments, steering device  200  includes between three and five cams  208 . Although cams  208   a,    208   b,    208   c,  and  208   d  are arranged in a single plane in  FIG. 2B , the invention is not limited to such an embodiment. Rather, multiple cams  208  can be arranged in adjacent planes. 
         [0037]      FIGS. 3A-3F  depict the operation of the rotary steerable device  200   a  within a borehole  11  to steer a drill bit coupled to the rotary steerable device  200   a  in a negative x direction. In  FIG. 3A , cylinder  202   a  is rotated in a clockwise direction, while cam  208   a  rotates in a counterclockwise direction. In  FIG. 3B , as the cylinder  202   a  and the cam  208   a  continue to rotate in their respective directions cam,  208   a  is brought into contact with the borehole  11 . Although the cam  208   a  may initially slide against the borehole  11 , at a certain point, the angle of cam  208   a  with respect to the borehole  11  increases so that a “non-slip” condition is created and the cam “grips” the borehole  11 . In  FIG. 3C , cam  208   a  is rotated to a fully extended position while the cam still grips the borehole  11 . The rotational inertia of the steering device  200  and the BHA causes the cam  208   a  to rotate around its center of rotation (i.e. the point of contact with the borehole  11 ), which pushes the rotary steerable device  200   a  and a drill bit coupled to the rotary steerable device  200   a  in a negative x direction. In  FIGS. 3D-3F , the cylinder  202   a  and the cam  208   a  continue to rotate in their respective directions before returning to position depicted in  FIG. 3A . 
         [0038]      FIG. 4  depicts a model of the interaction between the cam  208  and borehole  11 . W represents the weight applied through the center of rotation of the cam  208 . T A  represents the friction force. N A  represents the normal force. F B  represents the force on the on the center of rotation of the cam  208 . θ represents the angle between the force vector Wand the line formed between the point of contact A (between the cam  208  and the borehole  11 ) and the rotational axis of cam  208 . L represents the distance between the point of contact A (between the cam  208  and the borehole  11 ) and the rotational axis of cam  208  (i.e. the distance between points A and B). 
         [0039]    Forces W and N A , and forces T A  and F B  balance each other. The moment of equilibrium about point B can be expresses as follows: 
         [0000]        T   A   L  cos θ− N   A   L  sin θ=0. 
         [0000]    Rearranging for T A  and substituting W for N A  yields: 
         [0000]      T A =W tan θ. 
         [0040]    According to Coulombs&#39;s Friction Law, a non-slip condition will occur when T A &lt;μN A  and a slip condition will occur when T A =μN A , wherein μ is the coefficient of friction between the borehole  11  and the cam  208 . Accordingly, an angle that will produce a non-spip condition, i.e., an angle at which the cam  208  grips the borehole  11 , can be calculated as follows: 
         [0000]      W tan θ≦μN A    
         [0000]      tan θ≦μ 
         [0000]      θ grip ≦tan −1  μ. 
         [0041]    This model predicts that the grip angle is dependent on the coefficient of friction between the cam  208  and borehole  11 . The greater the coefficient of friction, the greater the angle through which the cam will grip the formation. The grip angle could be improved by adding teeth or other aggressive structures or surfaces (e.g. roughened, milled, knurled surfaces) to the cam  208  to better grip the borehole  11 . Additionally or alternatively, a layer of non-slip and/or compressive materials (e.g. rubber) can be applied to the contacting surface of the cam. 
         [0042]    The profile of the cam and the distance of the cam&#39;s rotational axis from the rotational axis of the steering device  200  (and the BHA) will determine the distance that the steering device  200  (and the BHA) is displaced due to the cam deployment. The profile of the cam will also determine the time that the BHA is displaced. Ideally, the displacement time is maximized while the displacement acceleration (and therefore shock loading) is minimized. 
         [0043]      FIG. 5  depicts a profile of an exemplary cam  502  for incorporation within the rotary steerable device  200 . The cam  502  has a long top dwell section  504  to maximize the displacement time and smooth rise and fall sections  506 ,  508  to reduce the acceleration imparted on the BHA. While smaller cams will allow a greater cross sectional area however, larger cams will allow greater BHA displacement time windows which will ultimately provide greater steering performance. 
         [0044]    Each cam  208  is coupled with a pin  210 . The cam  208  and pin  210  can be machined from a single piece of material. Alternatively, the cam  208  and pin  210  can be joined by a key, a Woodruff key, a spline, welding, brazing, adhesive, mechanical fasteners, bolts, screws, nails, press fitting, friction fitting, and the like. As will be appreciated, the pin  210  will be loaded in shear, and therefore should of a sufficient material and dimension to withstand such forces. Suitable materials for the cam  208  and/or pin  210  include steel, “high speed steel”, carbon steel, brass, copper, iron, polycrystalline diamond compact (PDC), hardface, ceramics, carbides, ceramic carbides, cermets, and the like. 
         [0045]    In some embodiments, slot  206  is dimensioned to minimize the clearance between the edges of the slot and cam  208 . A minimal clearance will reduce the accumulation of drilling cuttings in the slot and reduce the occurrence of jamming. 
         [0046]    In a neutral mode, the cam(s)  208  remains within the gauge  204  of the rotary steerable device  200 . The cam  208  can be held by some mechanism so that it will not be deployed by mud flow as the rotary steerable device  200  rotates with the rest of the BHA. The cam  208  can be actuated by electrical, mechanical, electromechanical, hydraulic, and/or pneumatic devices, and the like. For example, a mud motor can generate electricity and/or mechanical force to rotate the pin(s)  210  and cam(s)  208 . 
         [0047]    Rotary steerable device  200  can further include a control unit (not depicted) for selectively actuating steering devices cam(s)  208 . Control unit maintains the proper angular position of the cam(s)  208  relative to the cylinder  202  and/or subsurface formation of the borehole  11 . In some embodiments, control unit is mounted on a bearing that allow control unit to rotate freely about the axis of the cylinder  202 . The control unit, according to some embodiments, contains sensory equipment such as a three-axis accelerometer and/or magnetometer sensors to detect the inclination and azimuth of the bottom hole assembly. The control unit can further communicate with sensors disposed within elements of the bottom hole assembly such that said sensors can provide formation characteristics or drilling dynamics data to control unit. Formation characteristics can include information about adjacent geologic formation gathered from ultrasound or nuclear imaging devices such as those discussed in U.S. Patent Publication No. 2007/0154341, the contents of which is hereby incorporated by reference herein. Drilling dynamics data can include measurements of the vibration, acceleration, velocity, and temperature of the bottom hole assembly. 
         [0048]    In some embodiments, control unit is programmed above ground to following an desired inclination and direction. The progress of the bottom hole assembly can be measured using MWD systems and transmitted above-ground via a sequences of pulses in the drilling fluid, via an acoustic or wireless transmission method, or via a wired connection. If the desired path is changed, new instructions can be transmitted as required. Mud communication systems are described in U.S. Patent Publication No. 2006/0131030, herein incorporated by reference. Suitable systems are available under the POWERPULSE™ trademark from Schlumberger Technology Corporation of Sugar Land, Tex. 
         [0049]    The rotary steerable device  200  is ideally positioned in close proximity to drill bit  105 . For example, the rotary steerable device  200  can be integrated with either drill bit  105  or roto-steerable subsystem  150  as depicted in  FIG. 1 . Positioning the rotary steerable device  200  close to the drill bit  105  maximizes the steering force on drill bit  105  to more effectively “push the bit”. 
         [0050]    Referring to  FIG. 6 , another embodiment of the invention provides a rotary steerable device  600  including a wear ring  612  surrounding cams  608   a,    608   b,    608   c,    608   d.  Wear ring  612  allows for continuous and/or increased contact with borehole  11 . Suitable materials for the wear ring include steel, “high speed steel”, carbon steel, brass, copper, iron, polycrystalline diamond compact (PDC), hardface, ceramics, carbides, ceramic carbides, cermets, and the like. 
         [0051]    Wear ring  612  can be rigid or flexible. A rigid ring can, for example, be fabricated by molding, casting, machining, and the like. A flexible ring can be flexible due to the nature of the material (e.g. rubber, para-arimid fabrics) or can be flexible due to the design of the wear ring (e.g. a wear ring having a plurality of hinged links). 
         [0052]    Wear ring  612  can minimize wear of cams  608   a,    608   b,    608   c,    608   d  and can minimize the infiltration of drilling cuttings into slot  606 . To further inhibit the infiltration of drilling cuttings, the volume defined by wear ring  612  can be packed with a grease. Additionally or alternatively, a gasket (e.g. a rubber gasket) can be attached to the exterior of cylinder  602  and wear ring  612  to prevent infiltration of drilling cuttings and/or maintain proper lubrication of cams  608   a,    608   b,    608   c,    608   d.    
         [0053]    The invention provided herein represents a significant improvement over conventional steering devices. The rotary steerable devices provided herein utilize relatively low amounts of power, which can easily be generated in the bottom hole assembly. Moreover, most of the force utilized to steer the bottom hole assembly is generated by the rotational forces of the bottom hole assembly. 
         [0054]    Finally, modeling of invention suggests that small deflections provide very effective steering when the rotary steerable device is located near the drill bit. According to one model, a displacement of a cam out of gauge by 0.2 mm will produce a dogleg of 10.8 degrees over 30 meters. 
       INCORPORATION BY REFERENCE 
       [0055]    All patents, published patent applications, and other references disclosed herein are hereby expressly incorporated by reference in their entireties by reference. 
       EQUIVALENTS 
       [0056]    Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents of the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.