Abstract:
A tool and associated methods for transmitting electromagnetic data telemetry from a downhole sensor during drilling operations. The tool may include a pressure housing, the pressure housing including an EM transmitter, receiver, or transceiver. A conductive element electrically coupled to the EM transmitter, receiver, or transceiver is positioned between an upper and a lower signal conductor positioned coaxially around the conductive element. The upper and lower signal conductors support the pressure housing and conductive element within the inner diameter of a drill collar and provide electrical connection between the conductive element and a section of the drill collar on either side of an insulated gap. In some embodiments, the conductive element is tensioned between the upper and lower signal conductors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from provisional U.S. Patent Application Ser. No. 61/706,030, filed Sep. 26, 2012. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to the collection of data from sensors within a drill collar as part of a bottom hole assembly near the lower ends of a drill pipe stand while said pipe is in use in a downhole environment. 
       BACKGROUND 
       [0003]    Downhole logging aids in determine the structural, physical and chemical properties of a formation being penetrated. Data is collected in the borehole. Traditionally Logging While Drilling (LWD) operations were recorded for later analysis while Measurement While Drilling (MWD) operations were transmitted to the surface to provide more immediate feedback. In many operations today the difference between the two has blurred, with tools which commonly log and transmit data to allow immediate feedback and still avoid data loss. For purposes of this discussion, the term MWD will be utilized and should be interpreted to indicate: MWD, LWD, and/or MWD+LWD. 
         [0004]    Methods of transmission known to those skilled in the arts, may include but are not limited to: wireline transmission, modulated pressure waves/mud pulsing, and electromagnetic (EM) signal, wired drill pipe (i.e. intellipipe). Methods for transmitting data to the surface depend on the formation and drilling techniques utilized in a specific situation. For example, if compressible fluids are used for drilling, mud pulse telemetry data is lost in deeper wells. EM MWD technology may utilize earth formation as the medium to propagate a communications signal for the bottom of a wellbore to the surface. EM MWD may allow large quantities of real time data about a wellbore to be gathered during drilling operations. EM may be useful in environments where substantially incompressible drilling mud cannot be utilized for various reasons, which prevents to use of mud pulse telemetry as a data propagation medium. 
         [0005]    Reliability of an EM MWD tool and specifically the communications system to the surface may be a significant factor in the effectiveness of the tool. A major application of EM MWD technology may involve wells where it is not possible to use liquid (termed drilling fluid or “mud”) to flush cuttings to surface. In such environments compressed gas or foam is used in place of the mud. EM MWD may be useful in such situations due to the absence of mud as a transition medium to the surface for data. However, drilling mud may provide a significant dampening of shock and vibration in traditional well operations. Drilling without mud causes the levels of shock and vibration in the BHA to be significantly higher. 
         [0006]    Typically EM systems may be considered to be more reliable and faster than mud pulse telemetry for transmission of down-hole data to surface, assuming the formations outside the wellbore are suitable for EM transmission. However, in rough drilling conditions where high levels of shock and vibration are present, standard narrow probe systems with rubber centralizers or metal spring loaded centralizers are inadequate to maintain the required reliability of the down-hole tool and communications channel for the length of the operation. 
       SUMMARY 
       [0007]    This disclosure provides for a tool for transmitting electromagnetic data telemetry from a downhole sensor during drilling operations. The tool may include a pressure housing, the pressure housing including an EM transmitter, receiver, or transceiver; a conductive element electrically coupled to the EM transmitter, receiver, or transceiver; a lower signal conductor positioned coaxially around the conductive element, the lower signal conductor supporting the pressure housing and conductive element within the inner diameter of a drill collar and providing electrical connection between the conductive element and a section of the drill collar on one side of an insulated gap; and an upper signal conductor positioned coaxially around the conductive element, the upper conductor supporting the conductive element within the inner diameter of the drill collar and providing electrical connection between the conductive element and a section of the drill collar on the other side of the insulated gap. 
         [0008]    This disclosure also provides for a tool for transmitting electromagnetic data telemetry from a downhole sensor during drilling operations. The tool may include a drill collar, the drill collar including a first and second tubular, the first and second tubulars formed from an electrically conductive material and coupled by an insulated gap; a pressure housing, the pressure housing including an EM transmitter, receiver, or transceiver; a conductive element electrically coupled to the EM transmitter, receiver, or transceiver; a lower hanger rigidly coupled to the first tubular, the lower hanger positioned coaxially around the conductive element, the lower hanger supporting the pressure housing and conductive element within the inner diameter of the first tubular and providing electrical connection between the conductive element and the first tubular; and an upper hanger rigidly coupled to the second tubular, the upper hanger positioned coaxially around the conductive element, the upper hanger supporting the conductive element within the inner diameter of the second tubular and providing electrical connection between the conductive element and the second tubular. 
         [0009]    This disclosure also provides for a tool for transmitting electromagnetic data telemetry from a downhole sensor during drilling operations. The tool may include a drill collar, the drill collar including a first and second tubular, the first and second tubulars formed from an electrically conductive material and coupled by an insulated gap; a pressure housing, the pressure housing including an EM transmitter, receiver, or transceiver; a conductive element electrically coupled to the EM transmitter, receiver, or transceiver; a lower hanger rigidly coupled to the first tubular, the lower hanger positioned coaxially around the conductive element, the lower hanger supporting the pressure housing and conductive element within the inner diameter of the first tubular and providing electrical connection between the conductive element and the first tubular; and an upper signal conductor, the upper signal conductor positioned coaxially around the conductive element, the upper signal conductor providing electrical connection between the conductive element and the second tubular. 
         [0010]    This disclosure also provides for a method for providing improved reliability of electromagnetic (EM) data telemetry to the well site surface from downhole EM sensors in a tool assembly during drilling of a well. The method may include providing a pressure housing, the pressure housing including an EM transmitter, receiver, or transceiver; electrically coupling a conductive element to the EM transmitter, receiver, or transceiver; and tensioning the conductive element between an upper hanger and a lower hanger, the upper hanger and lower hanger positioned within a drill collar, the drill collar including a first and second conductive tubular, the tubulars separated by an insulating gap. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0012]      FIGS. 1A-1C  are partial cross sections of an EM MWD/LWD system consistent with at least one embodiment of the present disclosure. 
           [0013]      FIG. 2  is a partial cross section of the EM MWD/LWD system of  FIG. 1   
           [0014]      FIG. 3  is a continuation of the partial cross section of  FIG. 2 . 
           [0015]      FIG. 4  is a continuation of the partial cross section of  FIG. 3 . 
           [0016]      FIG. 5  is a continuation of the partial cross section of  FIG. 4 . 
           [0017]      FIG. 6  is a continuation of the partial cross section of  FIG. 5 . 
           [0018]      FIG. 7  is a continuation of the partial cross section of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0020]    Disclosed herein is a configuration of an EM MWD/LWD system which may improve communication reliability through more secure contact between the probe and the drill collar. Further, the configuration may improve reliability by increasing shock and vibration tolerance, and increasing electrical isolation between upper and lower units to avoid signal shorting and attenuation found in earlier derivations. Additionally, the disclosed configuration may be optimized for shipping and movement between a rig site and off-site maintenance and repair facilities to minimize rig downtime and allow for service and maintenance in more optimal and controlled conditions. The configuration may be utilized with multiple fluid drilling configurations, including but not limited to mud, air, and foam drilling. 
         [0021]    In one embodiment, the MWD tool assembly is kept to the minimum length possible. The MWD tool has multiple positive electrical contacts both above and below the electrical isolation in a Gap Sub via electrical conduction springs and solid metal centralizers which may also may be further sealed against drilling fluid flow by O-rings between the solid metal centralizers and the inside diameter (ID) of the drill collar. Openings through the metal centralizers allow fluid to flow past connection points without interfering with the electrical connection. Additionally, the MWD tool involves placing the components in either tension or compression to help ensure the system is rigid and resistant to movement during shock and vibration of the BHA with respect to the EM tool assembly. By adjusting the tension of the system, the natural frequency of the EM tool assembly can be adjusted to avoid common frequencies and harmonics found in drilling operations. 
         [0022]      FIGS. 1A-1C  depict an EM MWD system  101  consistent with at least one embodiment of the present disclosure installed in a collar assembly  102 . Here, collar assembly  102  is depicted as a four collar set including an upper hanger collar  103 , gap sub  105  (also called the upper to lower isolation), sensor collar  107 , and lower sub  109  (also called orientation collar). In at least one embodiment, all electronics of MWD tool  101  and specifically the EM Transmitter are installed in a pressure housing  113 . In some embodiments, pressure housing  113  may be approximately 3¼″ in diameter, and approximately 5.4 feet in length. One having ordinary skill in the art with the benefit of this disclosure will understand that differing diameters and lengths may be utilized depending on the size, shape, and configuration of the EM transmitter. Although discussed herein as a transmitter, one having ordinary skill in the art with the benefit of this disclosure will understand that EM MWD system  101  could likewise be used to receive signals from the surface within the scope of this disclosure. 
         [0023]    By selecting the OD and length of pressure housing  113 , pressure housing  113  may be of a sufficient stiffness to counteract the potential of pressure housing  113  contacting the wall of sensor collar  107  during a mechanical shock event. Additionally, higher stiffness may also increase the resonant frequency of EM MWD system  101 . When the resonant frequency is increased, the chances of causing EM MWD system  101  to oscillate at its natural frequency may be reduced, and the potential for extremely high levels of vibration may be lowered. 
         [0024]    Pressure housing  113  is sealed both above and below the electronics with end caps (coil housing  115 , tail  117 ) as shown in  FIGS. 6 and 7  respectively. Tail  117  may include a flow diverter  119  to re-direct the drilling fluid from between pressure housing  113  and the ID of Sensor Collar  107  to the ID of lower sub  109 . Tail  117  may also include a lower signal conductor  121  coupled to lower sub  109 .  FIG. 7  depicts lower signal conductor  121  as an external tapered thread for interfacing with an internal tapered thread of lower sub  109 . This connection constitutes one of two potential locations EM MWD system  101  is electrically connected to collar assembly  102  wall below gap sub  105  and the rest of the BHA (not shown) through this metal to metal mounting. Tail  117  may include rubber spacers  123  between the ID of sensor collar  107  and the OD of tail  117  to, for example, buffer EM MWD system  101  against shock. 
         [0025]    Pressure housing  113 , as depicted in  FIGS. 5 ,  6 , also includes coil housing  115 . Coil housing  115  may in some embodiments include a transformer coil (not shown) positioned between the transmitter of EM MWD system  101  and conductive element  139 . Coil housing  115  may be connected to lower hanger  125 . Lower hanger  125  may have an OD just under the ID of sensor collar  107 . Lower hanger  125  and coil housing  115  are conductive and may be utilized to transfer an electrical signal from EM MWD system  101  to a second point on collar assembly  102 . Lower hanger  125  may include seals  127 ,  129  between the OD of lower hanger  125  and the ID of sensor collar  107  to form a sealed portion  131  from drilling fluid present in collar assembly  102 . Seals  127 ,  129  are depicted in  FIG. 5  as  0  rings, but one having ordinary skill in the art with the benefit of this disclosure will understand that any suitable seal may be utilized within the scope of this disclosure. 
         [0026]    In sealed portion  131 , at least one toroidal contact spring  133  electrically couples the body of lower hanger  125  and sensor collar  107  in the absence of drilling fluid, foam, gas, or other invasive medium. In some embodiments, two such toroidal contact springs  133  are utilized, but one skilled in the art would appreciate that other numbers of contact springs may be utilized. A plurality of contact springs  133  may decrease the chance of contact loss. One skilled in the art would appreciate additional materials may be utilized to establish reliable electrical contact in the space between lower hanger  125  and sensor collar  107 . For example, when a nonconductive fluid is utilized, fluid, or nonconductive contaminants could lodge between a conducting member and the collar wall in the absence of seals  127 ,  129 , causing an electrical disconnection. 
         [0027]    Lower hanger  125  may thus serve as a contact from EM MWD system  101  to the collars below gap sub  105 . Isolating toroidal contact springs  133  from fluid invasion may help ensure the designed contact point stays consistent in electrical conductivity throughout the operation of EM MWD system  101  regardless of the drilling fluid utilized. Lower hanger  125  may also serve as a centralizer and support point for pressure housing  113 . Sensor collar  107  is installed around lower hanger  125 . Sensor collar  107  may be threaded onto lower sub  109  at the same location the tapered thread on tail  117  mates to lower sub  109  from the ID. 
         [0028]    Coupling EM MWD system  101  to the collars below gap sub  105  at both lower hanger  125  and tail  117  may increase resilience of the electrical connection by providing two paths to make electrical contact. This redundancy may reduce the possibility of losing contact with the wall of the collars below gap sub  105  under severe shock and vibration. 
         [0029]    Lower hanger  125  is coupled to a probe isolation component  135 , which serves to electrically isolate pressure housing  113  and lower hanger  125  from antenna housing  137  on the other end of probe isolation component  135  utilizing an internal non-conductive material. 
         [0030]    A sheathed wire (not shown) is run internally from coil housing  115  through probe isolation component  135  and connected to conductive element  139  located within antenna housing  137  (see  FIG. 4 ), allowing the electronics to induce an electrical signal across probe isolation component  135  and eventually gap sub  105  via upper hanger  141  shown in  FIG. 2 . Conductive element  139  includes an electrical conductor  140  which is surrounded by a non-conductive sleeve  143 . One having ordinary skill in the art with the benefit of this disclosure will understand that electrical conductor  140  may be any suitable conductive structure, including but not limited to a wire, rod, cable, etc. In some embodiments, sleeve  143  is formed from fiberglass. Sleeve  143  prevents conductive fluids from allowing signal leakage between electrical conductor  140  and collar assembly  102 . Sleeve  143  also eliminates the need to align probe isolation component  135  with gap sub  105  to avoid shorting or signal attenuation. 
         [0031]    At one or more locations along sleeve  143 , a centralizer  145  is used to support conductive element  139  and help minimize movement with respect to collar assembly  102 . Centralizer  145  may be constructed from a hard, nonconductive material. In some embodiments, centralizer  145  is formed from fiberglass. In at least one embodiment, multiple centralizers  145  are positioned as close as possible to, for example, prevent vibration of conductive element  139 , and provide adequate support for horizontal operations. Centralizers  145  may also be spaced enough to eliminate needless turbulence in the fluid flow which may add to wear on sleeve  143  and centralizers  145 . 
         [0032]    In some embodiments, centralizers  145  could be lengthened to the point that one or more run the length of conductive element  139 , serving the function of both centralizer  145  and sleeve  143 . In such a configuration, care would need to be taken to orient wings or protrusions  147  on centralizer  145  with respect to an abutting centralizer to avoid fluid turbulence or blockage. 
         [0033]    In at least one embodiment, both centralizer  145  and sleeve  143  are sealed to solid conductor  140  of conductive element  139  with the use of O-rings or other sealing systems to further prevent exposure of large areas of conductor  140  to the invasive medium at high pressure. Ideally spacers and sleeves are also abutted in such a manner as to create an additional seal between the neighboring spacers/sleeves. 
         [0034]    By creating a non-conducting sleeve  143  around conductive element  139 , the system can be assembled within varying lengths of collars without the need to adjust the placement of the probe isolation components  135 . Without non-conducting sleeve  143 , if the probe isolation components  135  are not aligned with gap  149  of gap sub  105 , the annular space between conductive element  139  OD and collar assembly  102  ID could carry conductive drilling fluid which could shunt the EM signal across the fluid. Any shunting may, for example, reduce the effectiveness of the system by applying additional load to the transmitting system. Furthermore, any signal shunted across the conductive fluid would not aid in transmitting the EM signal from down hole to surface. 
         [0035]    In addition, the use of a hard centralizer  145  compared with current technology&#39;s use of rubber or spring loaded metal may increase the rigidity of conductive element  139  by rigidly coupling it to the surrounding collar assembly  102 . Thus, shock resulting from hard impacts may be reduced, and vibration may be dampened. Reduction in shock and vibration to pressure housing  113  and conductive element  139  may lead to improved reliability. 
         [0036]    Gap Sub  105  is threaded onto sensor collar  107  around conductive element  139 . In some embodiments, compression stack  151  may be positioned within sensor collar  107 , such that compression stack  151  is compressed between the pin of gap sub  105  and the top of lower hanger  125  as gap sub  105  is screwed into sensor collar  107  ( FIG. 5 ). Compression stack  151  may include a hard rubber body positioned to, for example, dampen shock and vibration to EM MWD system  101  while retaining it within sensor collar  107 . 
         [0037]    In some embodiments, as depicted in  FIG. 2 , upper hanger collar  103  is coupled to gap sub  105 . Upper hanger  153  is installed in upper hanger collar  103 , and may be secured in place with hanger retention nut  155  to the ID of upper hanger collar  103 . Upper hanger  153  has a center hole (not shown) to accommodate conductive element  139 , which may traverse through upper hanger  153 . Conductive element  139  may be secured to upper hanger  153  by conductive element tensioning nut  157 . Conductive element tensioning nut  157  may serve to tension conductor  140  by pulling it against lower hanger  125 . At the same time, sleeve  143  is put in compression as it is pinched between upper and lower hangers  131 ,  153 . 
         [0038]    Applying tension on conductor  140  may add to the stiffness of conductive element  139 . Increased tension may also increase the fundamental harmonic frequency of conductive element  139 , thereby reducing the chance for high levels of vibration caused by resonance. Compression of sleeve  143  may amplify this effect. 
         [0039]    Upper hanger  153 , similarly to lower hanger  125 , may also utilize two seals  159 ,  161  to seal a section  163  of the OD of upper hanger  153  from the drilling fluid, or other invasive medium. In some embodiments, at least one toroidal contact spring  165  is positioned to electrically couple upper hanger  153  to upper hanger collar  103 . As with lower hanger  125 , making electrical contact in an uncontaminated location ensures continuous conduction across the contact in the presence of drilling fluid within the collar. 
         [0040]    In at least one embodiment, upper hanger  153  is installed directly into Gap Sub  105 . The length of conductive element  139  may be less than 36 inches in length. Conductive element  139  may be supported at the midpoint, whereby conductive element  139  is supported at approximate 18 inch increments with a hard non-conductive centralizer  145 . The drawings included in this disclosure illustrate an embodiment which utilizes an upper hanger collar  103  to allow testing of various gap subs without modification of the gap sub body itself. One having ordinary skill in the art with the benefit of this disclosure will understand that any length conductive element may be substituted without deviating from the scope of this disclosure, and that stabilizer positioning may be carried as previously discussed and otherwise. 
         [0041]    In at least one other embodiment, conductive element  139  is not rigidly coupled to upper hanger collar  103  by an upper hanger. Instead, conductive element  139  is electrically coupled to upper hanger collar  103  by a traditional connection such as, for example and without limitation, a bow spring, wire, or bolt. Conductive element  139  is thus held rigidly to collar assembly  102  by lower hanger  125 . In certain embodiments, conductive element  139  may be held in tension by compressing sleeve  143 . 
         [0042]    Due to the nature of this assembly, it may be desirable that EM MWD system  101  be assembled in a shop as opposed to the rig floor. For example, excessive rig down time may not be required while the system is installed in the collar on the rig floor, since EM MWD system  101  may be inserted as a complete unit into the bottom hole assembly as it is made up on the rig floor. Additionally, the shop assembly process may be easier to accomplish with better quality control than is possible using the rig floor assembly process. 
         [0043]    The diagrams provided are in accordance with exemplary embodiments of the disclosure, and are provided as examples. They should not be construed to limit other embodiments within the scope of the disclosure. For instance, the size of certain sections should not be taken as absolutes with respect to other elements. Additional element may be added or subtracted from the configuration illustrated. Further some elements may vary in count, orientation, or position within the scope of the disclosure. Further, plurality of elements rendered as separate elements may be joined into single elements, and elements illustrated individually may be divided into a plurality of sub-elements. Further yet, specific numerical data values (such as specific quantities, numbers, categories, etc.) or other specific information should be interpreted as illustrative for discussing exemplary embodiments. Such specific information is not provided to limit the disclosure. 
         [0044]    The diagrams in accordance with exemplary embodiments of the present disclosure are provided as examples and should not be construed to limit other embodiments within the scope of the disclosure. For instance, heights, widths, and thicknesses may not be to scale and should not be construed to limit the disclosure to the particular proportions illustrated. Additionally some elements illustrated in the singularity may actually be implemented in a plurality. Further, some element illustrated in the plurality could actually vary in count. Further, some elements illustrated in one form could actually vary in detail. Further yet, specific numerical data values (such as specific quantities, numbers, categories, etc.) or other specific information should be interpreted as illustrative for discussing exemplary embodiments. Such specific information is not provided to limit the disclosure. 
         [0045]    Multiple figures have been provided for many pieces, the views, sizes, and angles of the illustrations may vary, such variance should not be construed in a manner that is would limit the disclosure. Where multiple views, illustrations, photographs, renderings, or drawings have been provided of a single piece, any inconsistencies should be interpreted as different embodiments of the disclosure. 
         [0046]    The above discussion is meant to be illustrative of the principles and various embodiments of the present disclosure. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.