Abstract:
According to one embodiment of the invention, a rotary steerable tool includes a drive shaft having an upper portion configured to be coupled to a drill string and a lower portion configured to be coupled to a drilling tool. The drive shaft has a middle portion disposed between the upper and lower portions, the middle portion having a smaller diameter than each of the upper and lower portions. The tool further includes a housing rotatably coupled externally to the drive shaft at an axial location corresponding to the middle portion of the drive shaft, the housing formed from at least two housing segments configured to be coupled to each other substantially parallel to a longitudinal axis of the housing.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 60/479,608, filed Jun. 17, 2003, entitled SPLIT HOUSING FOR ROTARY STEERABLE TOOL. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of drilling systems and, more particularly, to a split housing for a rotary steerable tool.  
         BACKGROUND OF THE INVENTION  
         [0003]    Drilling well bores in the earth, such as well bores for oil and gas wells, is an expensive undertaking. One type of drilling system used is rotary drilling, which consists of a rotary-type rig that uses a sharp drill bit at the end of a drill string to drill deep into the earth. At the earth&#39;s surface, a rotary drilling rig often includes a complex system of cables, engines, support mechanisms, tanks, lubricating devices, and pulleys to control the position and rotation of the bit below the surface. Underneath the surface, the drill bit is attached to a long drill string that transports drilling fluid to the drill bit. The drilling fluid lubricates and cools the drill bit and also functions to remove cuttings and debris from the well bore as it is being drilled.  
           [0004]    Directional drilling involves drilling in a direction that is not necessarily precisely vertical to access reserves. Directional drilling involves turning of the drill bit while within the well bore. Offshore drilling often involves directional drilling because of the limited space beneath the offshore platform, although directional drilling is also vastly used onshore.  
           [0005]    Various types of directional drilling tools exist. One type of directional drilling involves rotary steerable directional drilling, in which the drill string continues to rotate while steering takes place. Typically, a plurality of steering ribs are associated with the rotary steerable directional drilling tool to facilitate the steering. The ribs are disposed outwardly from a sleeve, inside of which is disposed a rotating shaft associated with the drill string. In one type of rotary steerable directional drilling tool, the outer sleeve rotates and in another the outer sleeve does not rotate. In the type in which the outer sleeve does not rotate, bearings allow relative movement between the outer sleeve and the rotating shaft. High axial and torsional forces are often encountered during this type of drilling.  
         SUMMARY OF THE INVENTION  
         [0006]    According to one embodiment of the invention, a rotary steerable tool includes a drive shaft having an upper portion configured to be coupled to a drill string and a lower portion configured to be coupled to a drilling tool. The drive shaft has a middle portion disposed between the upper and lower portions, the middle portion having a smaller diameter than each of the upper and lower portions. The tool further includes a housing rotatably coupled externally to the drive shaft at an axial location corresponding to the middle portion of the drive shaft, the housing formed from at least two housing segments configured to be coupled to each other substantially parallel to a longitudinal axis of the housing.  
           [0007]    Some embodiments of the invention provide numerous technical advantages. Other embodiments may realize some, none, or all of these advantages. For example, according to one embodiment, a smaller diameter rotary steerable tool may be utilized without having to worry about breakage of the rotary steerable tool due to torsional forces during drilling operations. A smaller diameter rotary steerable tool, with its associated small diameter drill string, may not only be used to drill small diameter bore holes, but may be easily insertable into existing larger diameter bore holes so that new large diameter bore holes do not have to be drilled. In one embodiment, the smaller diameter rotary steerable tool is facilitated by a split housing (i.e., a housing formed from more than one segment) that allows the driveshaft to have a smaller diameter at an intermediate portion as well as to be formed from one piece, which aids in reducing the torsional stress on the driveshaft.  
           [0008]    Other advantages may be readily ascertainable by those skilled in the art from the following figures, description, and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic diagram of a drilling rig in accordance with one embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a functional block diagram of a rotary steerable tool associated with a drill string of the drilling rig of FIG. 1 in accordance with one embodiment of the present invention;  
         [0011]    [0011]FIG. 3 is a partially exploded perspective view of an example rotary steerable tool in accordance with one embodiment of the present invention; and  
         [0012]    [0012]FIG. 4 is a partial cross-sectional view of the rotary steerable tool of FIG. 3 illustrating an example steering system according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0013]    The following description is directed to a rotary steerable tool associated with a drill string. In one embodiment, such a rotary steerable tool facilitates, among other things, more efficient and cost-effective drilling of well bores, especially small diameter well bores. In one embodiment of the invention, as described below, a smaller diameter rotary steerable tool may be utilized without having to worry about drilling problems, such as breakage of the rotary steerable tool, due to torsional forces encountered when drilling. This is facilitated, in one embodiment, by cylindrical housing formed from multiple arcuate housing segments that allow the drive shaft of the rotary steerable tool to have a smaller diameter at an intermediate portion compared to the end portions of the drive shaft.  
         [0014]    [0014]FIG. 1 illustrates a drilling rig  10  in accordance with one embodiment of the present invention. In this embodiment, rig  10  is a conventional rotary table/kelley drive; however, the present invention contemplates other suitable drive devices for drilling rigs, such as top drive, power swivel, and down hole motor. Non-land rigs, such as jack up rigs, semi-submersibles, drill ships, mobile offshore drilling units (MODUs), and other suitable drilling systems that are operable to bore through the earth to resource-bearing or other geologic formations are also useful with the invention.  
         [0015]    In the illustrated embodiment, rig  10  includes a mast  12  supported above a rig floor  14 . A lifting gear associated with rig  10  includes a crown block  16  mounted to mast  12  and a travelling block  18 . Crown block  16  and travelling block  18  are coupled by a cable  20  that is driven by draw works  22  to control the upward and downward movement of travelling block  18 .  
         [0016]    Travelling block  18  carries a hook  24  from which is suspended a swivel  26 . Swivel  26  supports a kelley  28 , which in turn supports a drill string, designated generally by the numeral  30 , in a well bore  32 . A blow out preventor (BOP)  35  is positioned at the top of well bore  32 . Drill string  30  may be held by slips  58  during connections and rig-idle situations or at other appropriate times.  
         [0017]    Drill string  30  includes a plurality of interconnected sections of drill pipe  34 , one or more stabilizers  37 , a rotary steerable tool  36 , and a rotary drilling tool  40 , which may be a drill bit. Drill pipe  34  may be any suitable drill pipe having any suitable diameter and formed from any suitable material. Rotary steerable tool  36 , which is described in greater detail below in conjunction with FIGS. 2 through 4, generally functions to control the drilling direction of drilling tool  40 . Rotary drilling tool  40  functions to bore through the earth when drill string  30  is rotated and weight is applied thereto. Drill string  30  may include different elements or more or fewer elements than those illustrated depending on the type of drilling system. For example, drill string  30  may also include drill collars, measurement well drilling (MWD) instruments, and other suitable elements and/or systems.  
         [0018]    Mud pumps  44  draw drilling fluid, such as mud  46 , from mud tanks  48  through suction line  50 . A “mud tank” may include any tank, pit, vessel, or other suitable structure in which mud may be stored, pumped from, returned to, and/or recirculated. Mud  46  may include any suitable drilling fluids, solids or mixtures thereof. Mud  46  is delivered to drill string  30  through a mud hose  52  connecting mud pumps  44  to swivel  26 . From swivel  26 , mud  46  travels through drill string  30  and rotary steerable tool  36 , where it exits drilling tool  40  to scour the formation and lift the resultant cuttings through the annulus to the surface. At the surface, mud tanks  48  receive mud  46  from well bore  32  through a flow line  54 . Mud tanks  48  and/or flow line  54  include a shaker or other suitable device to remove the cuttings.  
         [0019]    Mud tanks  48  and mud pumps  44  may include trip tanks and pumps for maintaining drilling fluid levels in well bore  32  during tripping out of hole operations and for receiving displaced drilling fluid from the well bore  32  during tripping-in-hole operations. In a particular embodiment, the trip tank is connected between well bore  32  and the shakers. A valve is operable to divert fluid away from the shakers and into the trip tank, which is equipped with a level sensor. Fluid from the trip tank may then be directly pumped back to well bore  32  via a dedicated pump instead of through the standpipe.  
         [0020]    Drilling is accomplished by applying weight to drilling tool  40  and rotating drill string  30 , which in turn rotates drilling tool  40 . Drill string  30  is rotated within well bore  32  by the action of a rotary table  56  rotatably supported on the rig floor  14 . Alternatively, or in addition, a down hole motor may rotate drilling tool  40  independently of drill string  30  and the rotary table  56 . As previously described, the cuttings produced as drilling tool  40  drills into the earth are carried out of well bore  32  by mud  46  supplied by pumps  44 . To direct or “steer” drilling tool  40  in a desired direction, drill string  30  includes rotary steerable tool  36  adjacent to drilling tool  40 .  
         [0021]    [0021]FIG. 2 is a functional block diagram of rotary steerable tool  36  illustrating some of the components of rotary steerable tool  36  in accordance with one embodiment of the present invention. As illustrated, rotary steerable tool  36  includes an electrical system  202 , a hydraulic system  210 , a steering system  212 , solenoid valves  214 , and a data pulser  216 .  
         [0022]    Electrical system  202  includes a generator  204 , a plurality of sensors  206 , and a controller  208 . Generally, generator  204  provides the electrical power for rotary steerable tool  36 . A separate power source (not shown) may also be provided in addition to generator  204  to provide additional power or to provide backup power to rotary steerable tool  36 . Generator  204  may also be used to provide power to other elements, components, or systems associated with either rotary steerable tool  36  or drill string  30 .  
         [0023]    Sensors  206  may include any suitable sensors or sensing systems that are operable to monitor, sense, and/or report characteristics, parameters, and/or other suitable data associated with rotary steerable tool  36 , drilling tool  40 , or the conditions within well bore  32 . For example, sensors  206  may include conventional industry standard triaxial magnetometers and accelerometers for measuring inclination, azimuth, and tool face parameters. The sensed characteristics, parameters, and/or data is typically automatically sent to controller  208 ; however, sensors  206  may send the characteristics, parameters, and/or data to controller  208  in response to queries by controller  208 .  
         [0024]    Generally, controller  208  provides the “brains” for rotary steerable tool  36 . Controller  208  is any suitable down hole computer or computing system that is operable to receive sensed characteristics or parameters from sensors  206  and to communicate the sensed characteristics or parameters to the surface so that drilling personnel may monitor the drilling process on a substantially real-time basis, if so desired. The data communicated to the surface may be processed by controller  208  before communication to the surface or may be communicated to the surface in an unprocessed state. Controller  208  communicates data to the surface using any suitable communication method, such as controlling data pulser  216 .  
         [0025]    Data pulser  216  may be any suitable transmission system operable to generate a series of mud pulses in order to transmit the data to the surface. Typically, mud pulses are created by controlling the opening and closing of a valve associated with data pulser  216 , thereby allowing a small volume of mud to divert from inside drill string  30  into an annulus of well bore  32 , bypassing drilling tool  40 . This creates a small pressure loss, known as a “negative pulse” inside drill string  30 , which is detected at the surface as a slight drop in pressure. The controlling of the valve associated with data pulser  216  is controlled by controller  208 . In this manner, data may be transmitted to the surface as a coded sequence of pressure pulses. Alternate types of pulses that may be used momentarily restrict mud flow inside the pipe. This type is referred to as a “positive pulse.” 
         [0026]    Hydraulic system  210  generally functions to provide hydraulic pressure to steering system  212  SO that arched spring members associated with steering system  212  may be actuated in a predetermined manner to facilitate the steering of drilling tool  40 . The arched spring members, which are described in greater detail below in conjunction with FIG. 4, are part of steering system  212  along with associated pistons that function to “push out” a respective arched spring member when a respective solenoid valve  214  is opened by electrical system  202 . Solenoid valves  214  may be any suitable solenoid valves that are operable to allow hydraulic fluid to pass through hydraulic passages for the purpose of actuating arched spring members via pistons. Controller  208  may function to control the opening and closing of solenoid valves  214 .  
         [0027]    [0027]FIG. 3 is a partially exploded perspective view of an example rotary steerable tool  36  in accordance with one embodiment of the present invention. In the illustrated embodiment, rotary steerable tool  36  includes a rotating shaft  300 , generally referred to as the “drive shaft,” rotatably coupled within a non-rotating housing  302 , a head end  304 , a box end  306 , and a saver sub  308 .  
         [0028]    Rotating shaft  300  is a hollow shaft having any suitable diameter and formed from any suitable material that is coupled to drill pipe  34  via head end  304  and coupled to drilling tool  40  (not explicitly shown) via saver sub  308 . In one embodiment, rotating shaft  300  is formed from non-magnetic alloy, such as Monel or Inconel, so that magnetometers used with rotary steerable tool  36  operate properly. Rotating shaft  300  may be formed integral or may be formed from any number of separate pieces. If formed integral, as illustrated, then rotating shaft  300  does not utilize a cross-over sub.  
         [0029]    According to one embodiment of the invention, rotating shaft  300  has a variable diameter along its length with its smallest diameter being associated with an intermediate portion of rotating shaft  300 . In other words, a middle portion  320  of rotating shaft  300  has a smaller diameter than end portions  321 ,  322  of rotating shaft  300 . This facilitates a smaller diameter rotary steerable tool  36  because, as described in more detail below, housing  302  may have a smaller diameter if middle portion  320  of rotating shaft  300  has a smaller diameter. One reason end portions  321 ,  322  of rotating shaft  300  may have a larger diameter than middle portion  320  is so that drilling problems, such as breakage of rotary steerable tool  36 , due to torsional forces encountered during drilling may be avoided.  
         [0030]    Housing  302  houses many of the components of electrical system  202 , hydraulic system  210 , steering system  212 , and data pulser  216 , as well as solenoid valves  214 . Housing  302  may be formed from any suitable material, usually non-magnetic. Some components associated with housing  302  may be adversely affected by magnetic fields; therefore, the material used to house these elements, such as the elements of electrical system  202 , are preferably made of a non-magnetic material, such as Monel or other suitable non-magnetic material.  
         [0031]    As described above, a smaller diameter housing  302  may result by providing middle portion  320  of rotating shaft  300  with a smaller diameter than end portions  321 ,  322  of rotating shaft  300 . Solely as examples, housing  302  may have an outside diameter of approximately 4¾ inches or approximately 3½ inches.  
         [0032]    As illustrated in FIG. 3, housing  302  is formed from multiple arcuate housing segments  310 . The present invention contemplates any number of housing segments; however, based on the relatively small diameter of housing  302 , two or three housing segments are preferred. Use of the term “arcuate” means that housing segments  310  are curved in such a manner that, when coupled together, they form a generally cylindrical housing. One technical advantage of having housing  302  formed from multiple arcuate housing segments  310  is that this allows driveshaft  300  to be formed from one piece of material, which aids in reducing the torsional stress on driveshaft  300 , and to have a diameter of middle portion  320  smaller than end portions  321 ,  322 .  
         [0033]    Housing segments may be coupled to one another in any suitable manner. In the illustrated embodiment, housing segments are coupled together with fasteners  350 , which may be any suitable fasteners, such as bolts, screws, rivets, and the like. In this embodiment, each housing segment  310  includes one or more protrusions  352  on one longitudinal side and one or more notches  354  on the opposite longitudinal side. Protrusions  352  on one housing segment  310  match up with a particular notch  354  on an adjacent housing segment  310  such that a fastener  350  may be inserted into appropriate fastening holes  356  in order to couple housing segments together.  
         [0034]    Housing segments  310  may, in one embodiment, function to house the components of electrical system  202 , hydraulic system  210 , solenoid valves  214 , and other suitable components that allow rotary steerable tool  36  to be utilized for directional drilling. For example, the directional sensing electronics may be disposed within one of the housing segments  310 , while the hydraulic system and related components may be disposed within another of the housing segments  310 . In one embodiment, electromagnetive inductive coupling is utilized to get power to the electronic components housed within any of the housing segments  310 . However, other coupling techniques, such as the use of slip rings, may be utilized.  
         [0035]    Head end  304  may be coupled to drill pipe  34  in any suitable manner, such as by a screwed connection.  
         [0036]    Box end  306  couples to rotating shaft  300  in any suitable manner. In a particular embodiment, box end  306  is formed integral with rotating shaft  300 . With reference to FIG. 4, box end  306  has internal threads  316  that function to accept external threads  317  of saver sub  308  in order to couple saver sub  308  to box end  306 . Saver sub  308  functions to couple drilling tool  40  thereto and protects box end  306  from damage arising from repeated threading/unthreading of drilling tool  40 .  
         [0037]    Although any suitable steering system may be utilized in conjunction with rotary steerable tool  36 , FIG. 4 is a partial cross-sectional view of rotary steerable tool  36  illustrating an example steering system  212  according to an embodiment of the present invention.  
         [0038]    Steering system  212 , according to one embodiment, includes a spring member  402  having a bearing surface  401 , a pair of mounting pins  406  coupling spring member  402  to housing  302 , and a piston  404 . Generally, steering system  212  functions to steer drilling tool  40  in a desired direction when arched spring member  402  of steering system  212  is actuated radially by a respective piston  404  such that bearing surface  401  applies a force to the wall of well bore  32 . Although bearing surface  401  may have any suitable profile, including a flat surface, bearing surface  401  preferably has a curved profile that substantially matches the profile of the wall of well bore  32  SO that an evenly distributed load may be applied thereto.  
         [0039]    Spring member  402  is coupled to housing  302  via pins  406 . In one embodiment, either one or both pins  406  are disposed within slots formed within the wall of housing  302  to allow for axial movement when piston  404  is actuated. However, spring member  402  may be coupled to housing  302  in other suitable manners.  
         [0040]    In one embodiment, there are four steering systems  212  spaced approximately an equal circumferential distance apart around housing  302 ; however, any number of steering systems  212  may be used.  
         [0041]    To drill well bore  32 , weight is applied to drilling tool  40  and drilling commences by rotating drill pipe  34 , which rotates head end  304 , rotating shaft  300 , box end  306 , saver sub  308 , and drilling tool  40  (not explicitly shown). Concurrently, drilling fluid, such as mud  46 , is circulated down through drill pipe  34 , rotating shaft  300 , and saver sub  308  before exiting drilling tool  40  and returning to the surface in the annulus formed between the wall of well bore  32  and the outside surfaces of rotary steerable tool  36  and drill pipe  34 . Rotating shaft  300  is able to rotate within housing  302  by utilizing one or more bearings  310 . Any suitable bearings  310  may be utilized, such as roller bearings, journal bearings, and the like.  
         [0042]    Although embodiments of the invention and their advantages are described in detail, a person of ordinary skill in the art could make various alterations, additions, and omissions without departing from the spirit and scope of the present invention as defined by the appended claims.