Patent Publication Number: US-10760378-B2

Title: Pulser cleaning for high speed pulser using high torsional resonant frequency

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The disclosure relates generally to systems and methods for cleaning stator-rotor assemblies. 
     2. Description of the Related Art 
     Drilling fluid telemetry systems, generally referred to as mud pulse systems, are particularly adapted for telemetry of information from the bottom of a borehole to the surface of the earth during oil well drilling operations. The information telemetered may include, but is not limited to, parameters of pressure, temperature, direction and deviation of the well bore. Other parameters include logging data such as resistivity of the various layers, sonic density, porosity, induction, and pressure gradients. Valves that use a controlled restriction placed in the circulating mud stream are commonly referred to as positive pulse systems, for example see U.S. Pat. No. 3,958,217. 
     One type of positive pulser are oscillating shear valves as described in U.S. Pat. No. 6,626,253, the contents of which are incorporated by reference for all purposes. One illustrative system is an oscillating shear valve that comprises a non-rotating stator and a rotationally oscillating rotor. The stator and rotor may have a plurality of length wise flow passages for channeling the flow. The rotor may be connected to a drive shaft disposed within a pulser housing and driven by an electrical motor. The motor may be powered and controlled by an electronics module. The rotor may be powered in a rotationally oscillating motion such that the rotor flow passages are alternately aligned with the stator flow passages and then made to partially block the flow from the stator flow passages thereby generating pressure pulses in the flowing drilling fluid. 
     The flow passages may in certain situation become clogged with debris or other materials entrained in the circulating mud. This disclosure provides, in part, pulsers that are not susceptible to clogging from such entrained material. 
     SUMMARY OF THE DISCLOSURE 
     In aspects, the present disclosure provides an apparatus for generating pressure pulses in a fluid flowing in a downhole tool. The apparatus may include a stator, a rotor, a motor, and an electronics module. The stator and the rotor each have one or more flow passages. The motor oscillates the rotor relative to the stator to align and misalign the flow passage(s) of the stator and the rotor to thereby generate the pressure pulses. The electronics module drives the motor using at least a first signal and a second signal. The motor causes the rotor to have an information-transmitting oscillation in response to the first signal and a cleaning oscillation in response to the second signal. 
     It should be understood that examples of certain features of the disclosure have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and further aspects of the disclosure will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
         FIG. 1  is an isometric view of a pulser in accordance with one embodiment of the present disclosure; 
         FIG. 2A , B illustrate embodiments of a stator and rotor, respectively, in accordance with embodiments of the present dislcosure; 
         FIG. 3  illustrate an oscillation of a pulse generator during signal transmission in accordance with one embodiment of the present disclosure; 
         FIG. 4  illustrates an oscillation of a pulse generator during cleaning in accordance with one embodiment of the present disclosure; 
         FIG. 5  illustrate an oscillation of a pulse generator that combines cleaning and signal transmission in accordance with one embodiment of the present disclosure; and 
         FIG. 6  schematically illustrate a drilling system that may use a pulse generator in accordance with one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to devices and methods for enabling communication via pressure variations in a flowing fluid. Illustrative embodiments of systems and related methods for generating pressure pulses in a fluid circulated in a wellbore are discussed below. Advantageously, the disclosed pulse generating devices are less susceptible to clogging and impaired operation if the fluid includes or is replaced with a fluid that includes entrained solids. While the present disclosure is discussed in the context of a hydrocarbon producing well, it should be understood that the present disclosure may be used in any borehole environment (e.g., a geothermal well). 
     Referring to  FIG. 1 , there is schematically illustrated a pulser assembly  100 , also called an oscillating shear valve, that may utilize the teachings of the present disclosure. The pulser assembly  100  may be positioned in an inner bore  102  of a tool housing  104 . The housing  104  may be a section of a bottom hole assembly  14  ( FIG. 6 ) or a separate housing adapted to fit into a drill collar bore (not shown). A drilling fluid  11  flows through a stator  120  and a rotor  122  and passes through an annulus  126  between a pulser housing  130  and an inner diameter of the tool housing  104 . 
     Referring to  FIGS. 1 and 2A , B, the stator  120  may be fixed with respect to the tool housing  104  and to the pulser housing  130 . In one arrangement, the stator  120  has a plurality of radially elongated flow passages  131 . The rotor  122  may be disk shaped and have circumferentially distributed blades  132  separated by flow passages  134 . The flow passages  134  may be similar in size and shape to the flow passages  131  in the stator  120 . Alternatively, the flow passages  131  and  134  may be holes through the stator  120  and the rotor  122 , respectively. The stator passages  131  and the rotor passages  134  may be angularly aligned to create a flow path that presents the smallest relative flow resistance to the flowing fluid  11 . 
     The rotor  122  may be configured to rotationally oscillate such that an angular displacement of the rotor  122  with respect to the stator  120  changes the effective flow area, which then creates pressure fluctuations in the circulated mud. A pressure cycle may be generated by opening and closing the flow channel by changing the angular positioning of the rotor blades  134  with respect to the stator flow passage  131 . This can be done with an oscillating movement of the rotor  122 . The rotor blades  132  may be rotated in a first direction until the flow area is fully or partly restricted. This creates a pressure increase. They are then rotated in the opposite direction to open the flow path again. This creates a pressure decrease. It should be understood that it is not necessary to completely block the flow to create a pressure pulse and therefore different amounts of blockage, or angular rotation, create different pulse amplitudes. 
     Referring to  FIG. 1 , the rotor  122  may be attached to a drive shaft  140 . The drive shaft  140  is connected to an electrical motor  142 , which may be a reversible brushless DC motor, a servomotor, or a stepper motor. The motor  142  may be electronically controlled by circuitry in the electronics module  150 . The electronics module  150  may include processors, memory modules, circuitry, and programmed algorithms that allow the rotor  122  to be precisely driven in either direction. Also, precise control of the position of the rotor  122  can enable specific shaping of the generated pressure pulse. The electronics module  150  may be preprogrammed to transmit data utilizing any of a number of encoding schemes which include, but are not limited to, Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), or Phase Shift Keying (PSK) or the combination of these techniques. As used herein, the term “signal” refers to a command sent by the electronics module  150  to the motor  142  to control the rotary output of the motor  142 . 
     In embodiments, the motor  142  may include a shaft  144 . One end of the motor shaft  144  is attached to drive shaft  140  and the other end of the motor shaft  144  may be attached to a torsion spring  170 . The torsion spring  170  may be directly or indirectly anchored to the pulser housing  130 . The torsion spring  170  along with the drive shaft  140  and the rotor  120  comprise a mechanical spring-mass system. The torsion spring  170  may be designed such that this spring-mass system is at its natural frequency at, or near, the oscillating pulse frequency of the pulser  100  used while transmitting signals/information. The methodology for designing a resonant torsion spring-mass system based on a torsional resonant frequency is well known in the mechanical arts and is not described here. The advantage of a resonant system is that once the system is at resonance, the motor  142  only has to provide power to overcome external forces and system dampening, while the rotational inertia forces are balanced out by the resonating system. 
     As noted previously, the drilling fluid  11  may intentionally or unintentionally include entrained particles. One non-limiting example of intentional entrained particles are lost circulation materials (LCM). LCM may include cotton-like or fiber weave materials or natural materials such as nut plug that can seal a borehole wall. Unintentional particles include sand and other small, hard particulates. Both such materials can clog, to varying degrees, the passages,  131 ,  134  of the stator  120  and rotor  122 , respectively. 
     Embodiments of the present disclosure provide techniques and methods for maintaining stator  120 , the rotor  122 , and associated passages  131 ,  134  free of such materials and/or removing such materials if they accumulate on the surfaces of the features. The action of preventing the accumulation of entrained materials and/or removing accumulated entrained materials will collectively be referred to as “cleaning.” In embodiments, the cleaning of the stator  120  and rotor  122  is effectuated by a high-frequency rotational oscillation of the rotor  122 . In some embodiments, the high-frequency oscillation may be at a torsional resonant frequency of the pulser assembly  130 . For convenience, the torsional resonant frequency used for cleaning will be referred to as the second torsional resonant frequency whereas the torsional frequency used for signal/information transmission will be referred to as the first torsional resonant frequency. 
     The methodology for cleaning the stator  120  and/or the rotor  122  using high-frequency oscillations will be described with reference to  FIGS. 3-5 , all of which graphically illustrate the oscillatory motion of the rotor  122  ( FIG. 1, 2B ) during operation. In these Figures, time is along the “X” axis  160  and angular displacement is along the “Y” axis  162 . 
     In  FIG. 3 , in response to control signals from the electronics module, the rotor  122  oscillates at a frequency and amplitude selected to impart pressure pulses in the drilling fluid that transmit information. For convenience, this type of oscillation will be referred to as an information-transmitting oscillation  190 . During such oscillations, the rotor  122  rotates such that the flow passages  131 ,  134  of the stator  120  and the rotor  122 , respectively, are partially or completely misaligned, which causes a flow restriction. The magnitude of the flow restriction is sufficient to generate a pressure pulse that can be detected at a remote location, e.g., at the surface. The oscillation frequency may be at a first torsional resonant frequency of the pulser assembly  130 . 
     In  FIG. 4 , in response to control signals from the electronics module  150 , the rotor  122  oscillates at a frequency and amplitude selected to mechanically dislodge materials from the stator  120  and/or rotor  122 . For convenience, this type of oscillation will be referred to as cleaning oscillations  200 . During such oscillations, the rotor  122  rotates at a frequency that is sufficiently high to clean the stator  120  and/or rotor  122 . The frequency may be a second torsional resonant frequency of the pulser assembly  130 . The amplitude of the rotation is sufficiently low as to not generate a pressure pulse that can be detected at a remote location, e.g., at the surface. Additionally, the relatively smaller degree of rotation reduces power demands by the motor. As compared to the  FIG. 3  pulser movement, the  FIG. 4  pulser movement has a significantly higher frequency and a significantly lower amplitude. In embodiments, the frequency of the cleaning oscillation may be greater than 500 HZ, greater than 1000 HZ, or greater than 1200 HZ. In some embodiments, the frequency may be between 1000 HZ and 1400 HZ. 
     In arrangements, the cleaning oscillation may have frequency that is at least twice that of the information-transmitting signal. In other arrangements, the cleaning oscillation may have frequency that is at least five times, at least ten times, or at least twenty times greater than that of the information-transmitting signal. Likewise, in arrangements, the cleaning oscillation may have an amplitude that is no greater than half that of the information-transmitting signal. In other arrangements, the cleaning oscillation may have an amplitude that is no greater than a fifth, a tenth, or a twentieth of the amplitude of the information-transmitting signal. Also, both the cleaning oscillation and the information-transmitting oscillation may use torsional resonant frequencies, which are different from one another. 
       FIG. 5  illustrates one non-limiting technique of using the  FIG. 3  cleaning oscillation  200 . In embodiments, the electronics module  150  drives the motor  142  with the cleaning oscillation  200  superimposed on the information-transmitting oscillation  190 . Thus, in a sense, the rotor  122  has a macro-oscillation that imparts pressure pulses in the drilling mud  11  and a micro-oscillation that supplies kinetic energy used to dislodge materials from the stator  120  and/or rotor  122 . That is, the “back and forth” micro movement of the rotor  122  may shake or scrape debris and particles from inside the passages of the stator  120  and/or rotor  122 . 
     The cleaning oscillation  200  may be used in numerous variations. In some embodiments, the cleaning oscillation  200  may be superimposed on the information-transmitting oscillation  190 . In other embodiments, the cleaning oscillation  200  may be used independently of the information-transmitting oscillation  190 . Also, the cleaning oscillation  200  may be used continually, periodically, and/or “on demand.” For example, the cleaning oscillation  200  may be periodically applied for a defined duration (e.g., one minute every five minutes). Other methods may use a control signal sent from a remote location (e.g., the surface) that instructs the electronics module  130  to begin or end use of the cleaning signal. Still other methods may apply the cleaning oscillation  200  based on a measured parameter. For instance, increased power usage by the motor  142  may indicate the presence of clogging, which can be used to start use of the cleaning signal. Other measured parameters may be pressure, flow rate, temperature, etc. The parameter(s) may be measured downhole and/or at the surface. Also, the electronics module  150  may be programmed to operate in a closed loop fashion based on the measured parameter(s) and/or in response to an received command signal. 
     Referring now to  FIG. 6  there is schematically illustrated a drilling system  10  that may include a pulser  100  according to aspects of the present disclosure. A pulser  100  may be used to generate pressure pulses in a fluid circulating in a borehole  12 . While a land system is shown, the teachings of the present disclosure may also be utilized in offshore or subsea applications. A drilling system  10  may have a bottom hole assembly (BHA) or drilling assembly  14  is conveyed via a string  16  (or ‘drill string’) into the borehole  12 . The tubing  16  may include a rigid carrier, such as jointed drill pipe or coiled tubing, and may include embedded conductors for power and/or data for providing signal and/or power communication between the surface and downhole equipment. The BHA  14  may include a drilling motor  18  for rotating a drill bit  30 . The BHA  14  includes hardware and software to provide downhole “intelligence” that processes measured and preprogrammed data and writes the results to an on-board memory and/or transmits the results to the surface. Processors disposed in BHA  14  may be operatively coupled to one or more downhole sensors that supply measurements for selected parameters of interest including BHA  14  or drill string  16  orientation, formation parameters, and borehole parameters. In one arrangement, the drilling system  10  may include a pulse detector  40  at a surface location. The pulse detector  40  may include a fluid and pressure sensor (not shown) in fluid communication with the fluid being circulated into the borehole  12  and/or flowing out of the borehole  12 . The pulse detector  40  may also include a suitable processor and related electronics for decoding the sensed pressure pulses. 
     In one non-limiting mode of operation, that BHA  14  operates to drill the borehole  12 . During this time, the drilling fluid, such as drilling mud, is circulated through the drill string  16 . The pulser  100  may transmit communication uplinks as needed to convey information to the surface or another downhole location. 
     In one operating mode, the cleaning oscillation  200  is continually superimposed on the information-transmitting oscillation  190  at any time the pulser  100  is operating to transmit the communication uplinks, which yields an oscillation pattern similar to that shown in  FIG. 5 . In another operating mode, the cleaning oscillation  200  is used when the pulser  100  is not operating, which yields an oscillation pattern similar to that shown in  FIG. 4 . 
     As noted previously, the cleaning oscillation  200  may be applied periodically and/or “on demand.” For instance, the cleaning oscillation  200  may be periodically applied for a defined duration (e.g., one minute every five minutes). Other methods may use a control signal sent from a remote location (e.g., the surface) that instructs the electronics module to begin or end use of the cleaning signal. Still other methods may apply the cleaning oscillation based on a measured parameter. For instance, increased power usage by the motor may indicate the presence of clogging, which can be used to start use of the cleaning signal. Other measured parameters may be pressure, flow rate, temperature, etc. The parameter(s) may be measured downhole and/or at the surface. Also, the electronics module may be programmed to operate in a closed loop fashion based on the measured parameter(s) and/or in response to an received command signal. 
     In some situations, the BHA  14  may penetrate into a weak formation. Such a formation can draw drilling fluid out of the borehole  12 , thereby causing an undesirable loss of drilling fluid. To remedy such a situation, LCM may be circulated into the borehole  12  via the drill string  16 . The loss situation material may include solids of much larger size than the solids present in conventional drilling fluid. The lost circulation material penetrates into the weak formation and forms a seal along a borehole wall at the weak formation. The lost circulation material being circulated in the borehole  12  may flow through the pulser  100 . Advantageously, the pulser  100  may use the cleaning oscillation as described above to minimize the accumulation of entrained particles in the stator  120  and/or the rotor  122 . 
     The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure and is not intended to limit the disclosure to that illustrated and described herein.