Abstract:
A system and method for transmitting mud pulse signals in a downhole environment is disclosed. In one embodiment, a mud pulser system includes a valve ( 32 ), a wire ( 26 ) comprising shape memory alloy (SMA), and operable to have a first shape at a first temperature and a second shape at a second temperature; a thermal energy source ( 18 ) to heat the wire ( 26 ) from the first temperature to the second temperature; and a valve poppet ( 32 ) coupled to the wire, wherein the valve poppet is extended to close the valve when the wire is in the first shape and wherein the valve poppet is retracted to open the valve when the wire is in the second shape.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Application Ser. No. 60/990,210, filed Nov. 26, 2007. This provisional application is incorporated by reference herein in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates in general to equipment for drilling operations and more specifically, but not by way of limitation to a mud pulsing actuation device and method for doing same. 
       BACKGROUND OF INVENTION 
       [0003]    Conventional mud pulsing devices generate a pressure pulse by inserting a poppet which can be actuated either directly or by means of a hydraulic ram into an orifice. The drawbacks of conventional methods of actuating the pulser orifice include high electrical current demands and high maintenance costs due to the number of moving parts. Accordingly and for the aforementioned reasons, there is a need for a cheaper mud pulsing device that can generate mud pulses at relatively low power and over several cycles. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to systems and methods for transmitting mud pulse signals in a downhole environment. In one embodiment, a mud pulser system is disclosed. The mud pulser system includes a valve; a wire comprising shape memory alloy (SMA) and operable to have a first shape at a first temperature and a second shape at a second temperature; a thermal energy source to heat the wire from the first temperature to the second temperature; and a valve poppet coupled to the wire, wherein the valve poppet is extended to close the valve when the wire is in the first shape and wherein the valve poppet is retracted to open the valve when the wire is in the second shape. 
         [0005]    According to another embodiment, a method for generating a mud pulse signal is disclosed. The method includes the steps of providing a mud pulser tool having a valve poppet; providing a SMA wire coupled to the valve poppet; positioning the mud pulser tool into the downhole environment; heating the SMA wire from a first temperature to second temperature, transitioning the wire transitions from a first shape to a second shape; and retracting the valve poppet to open the valve. 
         [0006]    The foregoing has outlined some of the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features of the invention will be described herein after which form the subject of the claims of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A more complete understanding of the system of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein: 
           [0008]      FIG. 1  shows an illustrated embodiment of Measurement While Drilling (MWD) mud pulsing data transmission system of the present invention. 
           [0009]      FIG. 2  shows a cross-section of the mud pulser or wireline tool of the present invention. 
           [0010]      FIG. 3  shows a different illustration of the cross-section of the mud pulser or wireline tool of the present invention as outlined in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is understood that the various embodiments of the invention, although different, are not mutually exclusive. For example, a particular, feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with a full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views. 
         [0012]    A mud pulser device is used in conjunction with a MWD system to provide relevant information about wellbore features without halting regular drilling operations. The pulser receives parameters from the attached sensors and creates a series of pressure pulses which can be observed from the surface receiver connected to the drill pipe assembly. Based on the timing of the pulses, statistics such as temperature, gamma ray count rate, or inclination and azimuth may be decoded. 
         [0013]    Given the high costs associated with this data transmission process, existing MWD mud pulsers use a pilot valve to operate a large hydraulic ram as a means of conserving power. The hydraulic ram forces a choke into an orifice as it extends and retracts, partially restricting the flow of the drilling fluid. This main poppet which can be actuated either directly or by means of a hydraulic ram creates the pulses in the drilling pipe which are decoded on the surface. 
         [0014]    There are, however, different actuation methods for the operation of the pilot valve. One design involves the pilot valve being operated by solenoid such that the linear motion of the solenoid directly opens and closes the pilot valve. Another design involves a rotary motor and gearing system that implements a ball screw to convert the rotary motion to linear motion. Another similarly designed alternative incorporates an oil-submersed brushless DC motor. The drawbacks of these conventional methods of actuating the pulser orifice include high electrical current demands and high maintenance costs due to the number of moving parts. Accordingly, for the aforementioned reasons, there is a need for a cheaper mud pulsing device that can generate mud pulses at relatively low power and over several cycles. 
         [0015]    One of the major contributors to downhole failure of pulsers is the breakdown of pulser components. Motors, bearings, gearboxes, ball-screws, and other friction items are difficult to replace and add considerable expense to the operating cost of a tool. In addition, motor suppliers cannot easily and economically meet the reliability requirements desired for downhole usage. The presently disclosed embodiments of a mud pulser actuation system use a SMA wire to actuate the pilot valve of the mud pulser. Accordingly, the mud pulser actuation system provides a more direct and efficient method of linear actuation because the servo/pilot valve extension rod actuated by a compression spring and variable length SMA wire. In addition, the disclosed embodiments of the mud pulser system utilize relatively lower power and fewer moving parts than conventional designs. 
         [0016]      FIG. 1  shows an example of a system for transmitting MWD data, indicated generally by the numeral  2 . System  2  includes rig  4  to suspend or position tool  6  within borehole  8  formed within earth formation  10 . Tool  6  may be a mud pulser, MWD tool, logging-while-drilling (LWD) tool or similar downhole device for generating mud pulse signals. Tool  6  may be a wireline tool (e.g., positioned via wireline  5 ). Alternatively, tool  6  may be a generator or battery operated tool. Tool  6  may be seated in a mule shoe in a landing sub. System  2  includes mud pump  12  to circulate drilling mud  14  within borehole  8 . System  2  includes surface device  16  to receive mud pulse signals transmitted by Tool  6 . 
         [0017]      FIG. 2  shows a cross-section of an embodiment of Tool  6 . Tool  6  includes pulser electronics  18 , which may include power supply, sensors, processors, and other electronic devices. Tool  6  includes wire  26 . Wire  26  is coupled to pulser electronics  18  via electrical connectors  22  via high-pressure electrical pass-through bulkhead  20 . Wire  26  is coupled to servo/pilot valve poppet  32 . Spring  28  is coupled to poppet  32 . Wire  26 , electrical connectors  22  and spring  28  are positioned within chamber  24 , which is oil-filled and pressurized. Tool  6  includes compensation bladder  30 , pulser flow screens  34 , piston unit  36  and valve seat  38 . Valve seat  38  is a cylindrical orifice. 
         [0018]    Wire  26  comprises SMA material, smart alloy, memory metal, muscle wire, or any similar material that, through a memory effect, including without limitation, the one-way and two-way memory effects, can regain or be returned to its original geometry, e.g., crystallographic composition, after being deformed, e.g., by applying heat to the alloy. SMA material repeatedly switches between austenite and martensite phases at a prescribed temperatures and applied stress. When formed as wire, SMA materials will change length significantly at a specified temperature. For example, heating the SMA component of wire  26  causes wire  26  to contract while cooling wire  26  along with a minimal deformation force will allow wire  26  to return to its elongated position. As long as the stress levels remain sufficiently low, this process can be repeated for a substantial number of cycles, e.g., for as many as a million cycles. 
         [0019]    An example of suitable material for wire  26  includes ‘Flexinol’ produced by Dynalloy in California. Flexinol is a Nickel Titanium (NiTi) shape memory alloy commonly referred to as Nitinol. Nitinol wire like other SMAs has a high electrical resistance such that the resistance of the wire to electric current quickly generates sufficient heat (ohmnic heating) to bring the wire through its transition temperature and cause the wire to contract. Exploitation of such pseudo-elastic properties of SMA materials therefore, results and depends on temperature dependant reactions which alter the properties of the compound from martensite to austenite and vice-versa. Other examples of suitable materials include, without limitation, CuSn, InTi, TiNi, and MnCu. 
         [0020]    Wire  26  is deformed by the application of heat and, as wire  26  cools down, wire  26  may recover its original shape with the help of a counter-force which resets or stretches the wire back to its original length. The temperatures at which wire  26  changes shape, e.g., the transformation temperature, is based on the composition and tempering of the SMA of wire  26 . For example, wire  26  could comprise material with a transition temperature range of approximately 140-220° C. This is sufficiently high enough to allow cooling downhole via the typical 125-150° C. mud flow. If direct electrical current is used, it could provide adequate heating to cause the wire to contract to 1.5-2% strain. Wire  26  may be selected or processed to meet specific qualifications for length, diameter, tensile strength, and transition temperature, among other parameters. 
         [0021]    In one embodiment, tool  6  electrically heats wire  26  with an electrical current generated by thermal energy source  18  and delivered to wire  26  via connectors  22 . Thermal energy source  18  may comprise pulser electronics and connectors  22  may comprise electrical connectors. Alternatively, thermal energy source  18  can comprise other electrical sources to generate heat such as batteries, a generator or even a capacitor bank. In other examples, thermal energy source  18  may comprise a heat pump, combustion device or any other source of thermal energy conveyed by radiation or convection. As wire  26  is heated to the transformation temperature, wire  26  undergoes macroscopic deformation that is manifested as a contraction or strain. As wire  26  contracts due to heating, wire  26  displaces poppet  32  from its default position (e.g., displacing poppet  32  such that valve seat  38  is opened). As wire  26  cools and returns to its original length, poppet  32  may return to its default position (e.g., allowing poppet  32  to close the valve by blocking valve seat  38 ). Rapid cooling can be achieved by means of agitator  40  near wire  26 . 
         [0022]    Accordingly, Tool  6  uses electrically heated wire  26  to mechanically actuate a valve to generate mud pulses. Wire  26  may act to replace traditional mechanical linkages such as a motor, gearbox, and ball screw. Wire  26  may be used to operate either a pilot valve or the main valve of an MWD system. In the example shown in  FIG. 2 , wire  26  actuates a pilot valve (which includes poppet  32  and valve seat  38 ). 
         [0023]    In one example, shown in  FIG. 2 , spring  28  supplies force contrary to the direction of the force of the contraction of wire  26 . For instance, spring  28  may be a pre-loaded compression spring that will be compressed as wire  26  is heated. In this example, spring  28  provides the closing force for the valve and the contracted wire  26  provides the opening force. For example, as shown in  FIG. 2 , the default (off) pilot valve position is closed. When wire  26  is heated wire  26  will contract, compressing spring  28  and moving poppet  32  to open valve seat  38 , up to the maximum strain of wire  26 . A single contraction of wire  26  may produce sufficient force to overcome spring  28  and move poppet  32 , e.g., open valve seat  38  for 1-2 seconds to produce a mud pulse signal. As wire  26  is re-cooled spring  28  will deform wire  26  and push poppet  32  back to its default position to close the pilot valve. For example, when the pulser is configured to give a servo poppet travel of ⅛ of an inch, the SMA wire with an operating range of 140-220° C. will produce a strain of up to 2%. A 6.25 inch length of wire will yield a strain of about 0.125 inches, adequate to actuate the poppet while six wires in parallel will produce a max pull force of 46 lbf. Additionally, a spring force of approximately 20 lbs will adequately close the poppet and allow compression from the SMA wire. 
         [0024]    The mud pulser and method of actuation as disclosed herein, may be more efficient than other conventional actuation tools and methods because it reduces the number of moving parts and reduces the chance of mechanical failure, thus providing improved tool reliability. The disclosed mud pulser tool may also be more efficient than convention tools because the SMA wire directly activates the valve with no friction losses from bearings and gearings or moving parts. Additionally, there is a substantial cost benefit to using an SMA actuated pulser. An SMA wire only costs a few dollars compared to the several thousand dollars needed for a motor/ball-screw system. Furthermore, with motors having a short operating life of about 500 hours, the savings on parts and services for operating a single pulser each year, also amounts to several thousand dollars. 
         [0025]    Other examples of the disclosed mud pulser actuation system may use different arrangements or configurations of the SMA wire with respect to the valve to fit the needs of the particular device or application. Other examples include: contraction of the SMA wire to oppose a compression spring, contraction of the SMA wire to oppose an extension spring, alternate contraction of the SMA wire to facilitate bi-directional motion, using fluidic forces to create the default closing/opening force and the SMA wire to create unidirectional opening/closing force only, or an SMA wire wrapped around a circular element to create rotational motion/force. 
         [0026]    Although the disclosed system and method has been described in connection with a mud pulser device, one of ordinary skill in the relevant arts will recognize that the disclosed system and method may be used in any system where a valve is opened or closed by linear motion from an electrical signal. 
         [0027]    From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a mud pulser actuation system and method that is novel has been disclosed. Although specific examples have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed examples without departing from the spirit and scope of the invention as defined by the appended claims which follow.