Abstract:
The present disclosure is directed to an antenna for transfer of information along a drill string. The antenna has an antenna coil having a long side and short side. The antenna coil is adapted to be affixed to the drill string such that the long side of the antenna coil is along the longitudinal axis of the drill string, and the short side is perpendicular to the longitudinal axis of the drill string.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from provisional application Ser. No. 60/657,628, filed Feb. 28, 2005. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0002]    1. Field 
         [0003]    This disclosure relates to communication from downhole tools to the surface and among different sections of the bottom hole assembly (BHA). 
         [0004]    2. Background Discussion 
         [0005]    Directional drilling uses a BHA in the drill string, which typically includes a drill bit, stabilizers, bent subs, drill collars, rotary steerable and/or a turbine motor (mud motor) that is used to turn the drill bit. In addition to the BHA, a set of sensors and instrumentation, known as a measure while drilling system (MWD), is normally required to provide information to the driller that is necessary to guide and safely drill the borehole. Due to the mechanical complexity and the limited space in and around the BHA, the MWD is typically placed some distance from the bit above the motor assembly. A communication link to the surface is typically established by the MWD system using one or more means such as a wireline connection, mud pulse telemetry or electromagnetic wireless transmission. Because of the lag between the bit location and the sensors monitoring the progress of the drilling, the driller at the surface may not be immediately aware that the bit is deviating from the desired direction or that an unsafe condition has occurred. For this reason, drilling equipment providers have worked to provide a means of locating some or all of the sensors and instrumentation in the limited physical space in or below the motor assembly and therefore closer to the drill bit while maintaining the surface telemetry system above the motor assembly. These sensors generate near-bit data that is typically communicated to the MWD section to be transmitted to the surface. 
       SUMMARY 
       [0006]    One embodiment of present disclosure is directed to an antenna for transfer of information along a drill string. The antenna has an antenna coil having a long side and short side. The antenna coil is adapted to be affixed to the drill string such that the long side of the antenna coil is along the longitudinal axis of the drill string, and the short side is perpendicular to the longitudinal axis of the drill string. 
         [0007]    Another embodiment of the present disclosure is directed to a system for communication in a borehole. The system includes a first cross-coil antenna with an antenna coil having a long side and short side. The antenna coil is affixed to a drill string. The drill string includes a mud motor and a drill bit. The long side of the antenna coil is along the longitudinal axis of the drill string, and the short side is perpendicular to the longitudinal axis of the drill string. The system further includes an insulated gap electrode, toroidal antenna, a band electrode, or a second cross-coil antenna. 
         [0008]    In still another embodiment, a method of borehole communication is disclosed. The method includes providing a first cross-coil antenna comprising an antenna coil having a long side and short side. The antenna coil is affixed to a drill string and the drill string includes a mud motor and a drill bit. The long side of the antenna coil is along the longitudinal axis of the drill string, and the short side is perpendicular to the longitudinal axis of the drill string. The method further includes providing a voltage source in electrical communication with the first cross-coil antenna and providing an insulated gap electrode, toroidal antenna, a band electrode, or a second cross-coil antenna. The method also includes actuating the voltage source to produce an electrical current in the first cross-coil antenna and inducing a magnetic field to form a current on the drill string. The current is used to transmit data along the drill string and the data is received at the insulated gap electrode, toroidal antenna, band electrode, or second cross-coil antenna. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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 reduced for clarity of discussion. 
           [0010]      FIG. 1  is a depiction of a well installation consistent with certain embodiments of the present disclosure; 
           [0011]      FIG. 2  is a depiction of a cross-coil antenna consistent with certain embodiments of the present disclosure; 
           [0012]      FIG. 3  depicts the electric current lines consistent with certain embodiments of the present disclosure; 
           [0013]      FIG. 4  depicts the placement of a cross-coil antenna consistent with certain embodiments of the present disclosure; 
           [0014]      FIG. 5  depicts a multi-node bottom hole assembly communication consistent with certain embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. 
         [0016]      FIG. 1  depicts diagrammatically a typical, non-limiting example of a rotary drilling installation of a type in which certain embodiments of the present disclosure may be used. The BHA includes drill bit  1  connected to the lower end of drill string  2  which is rotatably driven from the surface by rotary table  3  on drilling platform  4 . A suitable drilling fluid, generally referred to as mud, may be pumped downward through the interior of drill string  2  to assist in drilling and to flush cuttings from the drilling operation back to the surface in annular space  2   a  outside of drill string  2 . Rotary table  3  is driven by drive motor  5 . Raising and lowering of drill string  2 , and application of weight-on-bit, is under the control of draw works  6 . Drill bit  1  may alternatively be rotated by a mud-motor, contained within apparatus  7 , located in drill string  2 . 
         [0017]      FIG. 2  is a depiction of a cross-coil antenna consistent with certain embodiments of the present disclosure. A section of drill string  2  is shown with drill string collar  100 . Drill string  2  has drill string axis  102 . Cross-coil antenna  104  is shown within drill collar cutout  106 . 
         [0018]    Cross-coil antenna  104  as shown in  FIG. 2  is rectangular, with cross-coil sides  110  being longer than cross-coil cross sides  112 . Cross-coil antenna  104  may have multiple windings  108 . The longer side of cross-coil windings  108  may run essentially parallel with drill string axis  102 . The number of windings may be between 1 and 300, alternatively between 5 and 75, or between 10 and 40. In other embodiments of the present disclosure cross-coil antenna geometries can include, but are not limited to, circles, ovoids, squares, and other polygons. When cross-coil antenna  104  is rectangular, as depicted in  FIG. 2 , cross-coil sides  110  may be considerably longer than that of cross-coil cross sides  112 . In certain non-limiting embodiments, the ratio of cross-coil side length to cross-coil cross side length can range from 1:1 to 1000:1 or from 10:1 to 100:1 or from 20:1 to 200:1. When the cross-coil side length exceeds that of the cross-coil cross side length, cross-coil antenna  104  is an elongated rectangle. The elongated rectangle form allows cross-coil antenna  104  to have a larger area while in place within drill collar cutout  106  than if the cross-coil side length  110  was less than or equal to that of cross-coil side length  112 . Cross coil sides  110  may run essentially parallel with longitudinal drill string axis  102 . Cross-coil sides  112  may be essentially perpendicular to coil sides  110 . “Essentially perpendicular” allows orientation of the cross-coil sides  112  to be rotated about cross-coil side  110  by as much as about 50°. 
         [0019]    In certain embodiments, cross-coil antenna  104  may have a ferrite or ferromagnetic core. When cross-coil antenna  104  has a ferrite or ferromagnetic core it may be desirable to cover the core with protective insulating material along the entire length of cross-coil antenna  104  in order to prevent the ingress of mud and water and to prevent mechanical damage. The type of insulating material is not critical and any suitable material may be used. In other embodiments, cross coil antenna may have an insulating material as a core. In those embodiments, the resistivity may be more than 10 Ohm m, 100 Ohm m, 1000 Ohm m or 10 15  Ohm m. In still other embodiments, cross-coil antenna  104  may be formed entirely of an electrically insulating material. 
         [0020]    Cross-coil antenna  104  is electrically connected to a voltage source (not shown) sufficient to impart a current to cross-coil antenna  104 , generating a magnetic field. When an alternating voltage source is activated, cross-coil antenna  104  forms a magnetic field which is capable of inducing a current in drill string  2 . In some embodiments, the frequency range of the excitation of cross-coil antenna  104  is from 10 Hz to 100 kHz or from 100 Hz to 10 kHz or from 400 Hz to 4 kHz. Without wishing to be bound by theory, an alternating magnetic field is created by an alternating current (AC) signal made to flow through an appropriate inductor, typically a coil of wire, mounted on or around the drill pipe, thereby creating a magnetic flux. The presence of a highly permeable material such as ferrite or ferromagnetic material has the effect of increasing the effective area of the inductor, and correspondingly increasing the magnetic flux. Lines of flux are thus concentrated by the ferrite or ferromagnetic material, which acts as a conduit for the alternating magnetic field. 
         [0021]    Cross-coil antenna  104  is also capable of detecting an alternating current on drill string  2 . An AC current on the drill string  2  creates an alternating magnetic field in cross-coil antenna  104  that induces a voltage across the cross-coil antenna  104  ends. In certain embodiments of the present disclosure, one end of the cross coil antenna  104  may be connected to the drill string or the sensor package. 
         [0022]      FIG. 3  depicts the current flow lines  200  generated by certain embodiments of the present disclosure. When the voltage source is activated, cross-coil antenna  104  generates a magnetic field and thus is inducing a current through the drill string  2  and the formation. 
         [0023]    Cross-coil antenna  104  may transmit signals to a gap electrode, a band electrode, a toroidal antenna, or to another cross-coil antenna. Examples of gap electrodes and band electrodes may be found in U.S. patent application Ser. No. 7,518,528, which is fully incorporated herein by reference. An example of a toroid antenna may be found in U.S. patent application Ser. No. 5,160,925, which is fully incorporated herein by reference. 
         [0024]      FIG. 4  depicts a particular embodiment of the present disclosure. Lower downhole assembly  500  includes drill bit  510 , bit box  520 , near-bit sub  530 , mud motor  540 , a string of subs and collars  550  that may include a mud pulser, an MWD sensor, and electric field transmitter to surface with its control subs  560  below an insulated gap electrode  570  in drill string  2 . 
         [0025]    Cross-coil antenna  104  is further depicted in  FIG. 4  on near-bit sub  530  at a lower location below mud motor  540  or other mechanical means  550  and an insulating gap type electrode  570  on sub  401  above such a motor or mechanical means. In the embodiment depicted in  FIG. 4 , insulating gap electrode  570  can serve as both the upper electrical contact for the short hop communication link of one embodiment of the present disclosure and as the lower terminus of a surface link. In an alternative embodiment, surface communication link can be accomplished by mud pulse type. In this alternative embodiment, insulated gap electrode  570  may be accompanied by a mud pulser, not shown. The upper electrical contact for the short hop communication link could also be a toroidal antenna, a band electrode, or another cross-coil antenna. 
         [0026]    In certain embodiments, in particular when oil-based-mud is in use, a cross-coil antenna may be used as a transmitter, with the receiver being a toroid antenna, insulating gap type electrode, or another cross-coil antenna. 
         [0027]    In another embodiment, a cross-coil antenna may be used as part of a multipoint communication network in the bottom hole assembly and drill string wherein a transceiver for each node in the system is utilized.  FIG. 5  schematically shows one such multipoint communication network. Numeral  800  designates the bottom hole assembly of the drilling assembly. Mounted within this assembly as a sonde, or built integrally into the drill collars, are an MWD system  801  and a formation resistivity sensor  802 . Numeral  803  depicts a rotary steerable device and  804  shows a near bit sensor, located just above the bit  806 . Sensor  804  may include devices such as a natural gamma ray sensor, inclinometer or other sensors used in logging or geo steering of boreholes. Four uses of cross-coil antennas  104  are shown, Data communicated between these nodes can be used by the rotary steerable device  803  to adjust the course of the drilling or can be transmitted to the surface by the MWD system  801  for analysis by the directional driller. The invention in this case enables the wireless means for these independent sensors to share information and use that information to change events in the process of drilling a borehole. In other embodiments, one or more of the cross-coil antennas  104  may be replaced with a toroid antenna, insulating gap type electrode, or band electrode. 
         [0028]    The foregoing outlines features of several embodiments so that a person of ordinary skill in the art may better understand the aspects of the present disclosure. Such features may be replaced by any one of numerous equivalent alternatives, only some of which are disclosed herein. One of ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. One of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 
         [0029]    The Abstract at the end of this disclosure is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 
         [0030]    Moreover, it is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the word “means” together with an associated function.