Abstract:
A technique facilitates drilling applications by providing a unique flex joint. In one embodiment, the flex joint has an adjustable bending stiffness while being much more compact than conventional flex joints. The flex joint also may be designed to de-couple bending moments from the tool joints and, in some applications, can operate as an active vibration and shock control sub by incorporating suitable sensors and a hydraulic actuator system. The design also enables incorporation of other features, such as electrical insulation features disposed above and/or below the flex joint. In some applications, the flex joint also may have an electrical feed through.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present document is based on and claims priority to U.S. Provisional Application Ser. No.: 61/356,462, filed Jun. 18, 2010, incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In downhole drilling applications, flex joints are sometimes used to facilitate directional drilling. The flex joints can be useful in steerable drilling applications to provide a bottom hole assembly with sufficient flexibility to allow deflection of the borehole. Conventional flex joints are long, necked-down sections of pipe having a lower bending stiffness than other components of the bottom hole assembly. 
       SUMMARY 
       [0003]    In general, the present invention provides a flex joint having substantially improved capabilities for use in a wider variety of drilling applications. In one embodiment, the flex joint has an adjustable bending stiffness while being much more compact than conventional flex joints. The flex joint also may be designed to de-couple bending moments from the tool joints and, in some applications, can operate as an active vibration and shock control sub by incorporating suitable sensors and a hydraulic actuator system. The design also enables incorporation of other features, such as electrical insulation features disposed above and/or below the flex joint. In some applications, the flex joint also may have an electrical feed through. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0005]      FIG. 1  is a schematic illustration of a flex joint incorporated into a drill string to facilitate directional drilling, according to an embodiment of the present invention; 
           [0006]      FIG. 2  is a flowchart illustrating an embodiment of a methodology for utilizing the flex joint in controlling detrimental drilling effects, according to an embodiment of the present invention; and 
           [0007]      FIG. 3  is a schematic illustration of a drilling system incorporating the flex joint to facilitate directional drilling, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0009]    The present invention generally relates to a system and methodology to facilitate directional drilling by incorporating a flex joint into a drill string. The flex joint may be used to provide a bottom hole assembly with a sufficient flexibility to better allow deflection of the wellbore being drilled. The flex joint may be designed to provide variable stiffness in a compact structure. In some embodiments, the flex joint may be adjusted to vary the allowed angle of deflection. In other embodiments, the flex joint may comprise an in-line integrated stabilizer. Additionally, the flex joint may be employed in a variety of rotary steerable drilling applications to facilitate directional drilling. 
         [0010]    Referring generally to  FIG. 1 , an embodiment of a flex joint  20  is illustrated as coupled into a drill string  22  which may comprise a bottom hole assembly  24  located on a downhole side of flex joint  20 . In drilling applications, the bottom hole assembly  24  may comprise a rotary steerable system for steering a drill bit. In the illustrated example, flex joint  20  comprises a first component  26  coupled to a second component  28  via a universal joint  30 , such as a Hooke&#39;s Joint type of universal joint. The first component  26  may be pivoted with respect to the second component  28  about the universal joint  30  to form a bend angle. The design of the flex joint  20  and universal joint  30  provided a solid joint which may be subjected to high loading. 
         [0011]    In the embodiment illustrated, the flex joint  20  incorporates an internal, adjustable spring assembly  32 , which may be adjusted to provide a variable bending stiffness of the first component  26  relative to the second component  28 . For example, spring assembly  32  may comprise a plurality of bow springs  34  which may be selectively adjusted by an external adjustment mechanism  36  to vary the bending stiffness. However, spring assembly  32  also may utilize other types of springs, e.g. torsion springs, coil springs, or tension springs. 
         [0012]    The flex joint  20  may further comprise a sleeve  38  connected to one of the components  26 ,  28  and extending past the universal joint  30  to shield the universal joint. By way of example, sleeve  38  may be rigidly connected to second component  28  at a position which allows the sleeve to extend past the universal joint  30  and to cover a portion of the first component  26 . This allows sleeve  38  to be used to limit the maximum offset/bend angle of the flex joint. In fact, adjustment mechanisms  40 , such as split rings, can be mounted to sleeve  38  to limit the pivotable travel of the first component  26  with respect to the second component  28  and to thus selectively adjust the maximum offset/bend angle of the flex joint  20 . The external sleeve  38  may be run into a wellbore  42  slick or it may incorporate stabilizers  44 , such as stabilizer blades, to help center the flex joint  20  in the wellbore  42 . 
         [0013]    In the embodiment illustrated, the spring assembly  32  is located inside external sleeve  38  between an interior surface of the sleeve and the portion of the first component  26  covered by the external sleeve  38 . The preload on spring assembly  32  may be selectively adjusted to change the bending stiffness of the flex joint. For example, if the spring assembly comprises bow springs  34 , the preload on the bow springs may be externally adjusted to vary the bending stiffness of first component  26  relative to second component  28 . 
         [0014]    Depending on the specifics of a given application, additional features may be incorporated into the flex joint  20  such as an electrical feed through  46  positioned within flex joint  20 . By way of example, the feed through  46  may comprise a local tool bus (LTB) connection or a multi-pin rotary connection at the top and bottom of the sub forming the flex joint. Additionally, an insulation feature  48 , such as an insulation coating, may be applied to first component  26  and second component  28  in a manner which provides electrical insulation between tools or other components above and below the flex joint  20 . 
         [0015]    The design of the flex joint  20  enables a relatively short profile which helps reduce bending loads on rotary connections above and below the flex joint at high dogleg severities (DLS). This characteristic facilitates running an otherwise DLS-limited tool at a higher DLS. Additionally, the flex joint  20  may be used in both rotating and sliding drilling modes. 
         [0016]    Another feature which may be incorporated into flex joint  20  is an actuator or actuators  50 , such as a hydraulic actuator or actuators, which cooperate with one or more sensors  52 . The sensors  52  may be designed and positioned to sense shock and vibration and to provide data to a control system  54 . For example, the sensors  52  may be positioned to sense relative motion, e.g. vibrations, between the first component  26  and the second component  28 . The control system  54  also is designed to control hydraulic actuators  50  in a manner which actively reduces vibration and shock during, for example, a drilling operation. The one or more hydraulic actuators  50  may be positioned between external sleeve  38  and the portion of first component  26  covered by sleeve  38 . 
         [0017]    The sensors  52  also may be selected and utilized to optimize drilling conditions in a manner which proactively reduces shock, vibration, and/or other detrimental effects. In one embodiment, for example, sensors  52  transmit data to control system  54  at a surface location. The data may be transmitted uphole by a suitable telemetry system, such as a measurement-while-drilling type system or a wired drill pipe system. The data from sensors  52  is then processed and evaluated via control system  54  to improve/optimize conditions so as to mitigate shock and vibration. Examples of conditions which may be optimized to proactively reduce detrimental effects include torque, drilling RPM, weight on bit, flow rate, and/or other conditions. 
         [0018]    Referring generally to  FIG. 2 , a flowchart is provided to illustrate one embodiment of a methodology for utilizing controlled actuators  50  in cooperation with the flex joint  20  to limit or reduce detrimental effects of a drilling operation. As illustrated by flowchart block  56 , drill string  22  includes and is operated with flex joint  20  in a drilling application. One or more sensors  52  is employed to sense relative motion between flex joint components, such as between first component  26  and second component  28 , as represented by block  58 . However, sensors  52  may be provided on, between, or in proximity to additional or alternate components depending on the structure of the drill string and on the specific parameter or parameters being monitored. 
         [0019]    The motion data from sensors  52  is transmitted to control system  54 , as represented by block  60 . The control system  54  may be located downhole in the drill string  22 , or the control system  54  may be located at the surface or at another suitable location. Regardless, the control system  54  is programmed to process the sensor data, as represented by block  62 , to facilitate control of the undesirable effect, e.g. vibration and/or shock caused by the drilling operation. Based on the processed data, the control system  54  is employed to send control signals to actuators  50 , as represented by block  64 . The control signals are designed to operate the one or more actuators  50  in a manner which helps optimize drilling by reducing or eliminating the undesirable effect, e.g. the vibration and/or shock, as represented by block  66 . In some embodiments, the actuators  50  comprise hydraulic actuators; however other types of actuators, e.g. electro-mechanical actuators, piezo-electric actuators, may be employed for a given application. 
         [0020]    The flex joint  20  may be utilized in a variety of drilling systems to facilitate many types of drilling operations. In  FIG. 3 , for example, the drilling system comprises drill string  22  deployed in a lateral wellbore or a multilateral wellbore drilling application. In this example, the drill string comprises bottom hole assembly  24  having a rotary steerable system  68  designed to facilitate drilling of one or more lateral wellbores  70 . The rotary steerable system  68  may be any of a variety of types known to those of ordinary skill in the art, and the system  68  is used to orient a drill bit  72  for drilling the lateral wellbore  70  to a desired target. 
         [0021]    In this particular example, a plurality of sensors  52  is used to provide data to control system  54  which, in turn, directs control signals to a plurality of hydraulic actuators  50  to reduce the vibration and shock loads that would otherwise result during the lateral wellbore drilling operation. As illustrated, the control system  54  may be positioned at a surface location; however other control system locations may be used and may be selected according to the design of the drilling system and the parameters of a given drilling application. Signals may be communicated between the flex joint  20  and control system  54  via a communication line  74 . The communication line  74  may comprise a hardwired line, such as a cable, or a wireless communication line employing a wireless communications methodology, such as mud pulse telemetry. 
         [0022]    Although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.