Patent Publication Number: US-9850754-B1

Title: High speed telemetry signal processing

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of telemetry systems, and more particularly, but not by way of limitation, to signal processing systems for use in connection with acoustic signal generators deployed in wellbore drilling operations. 
     BACKGROUND 
     Wells are often drilled for the production of petroleum fluids from subterranean reservoirs. In many cases, a drill bit is connected to a drill string and rotated by a surface-based drilling rig. Drilling mud is circulated through the drill string to cool the bit as it cuts through the subterranean rock formations and to carry cuttings out of the wellbore. 
     As drilling technologies have improved, “measurement while drilling” techniques have been enabled that allow the driller to accurately identify the location of the drill string and bit and the conditions in the wellbore. MWD equipment often includes one or more sensors that detect an environmental condition or position and relay that information back to the driller at the surface. This information can be relayed to the surface using acoustic signals that carry encoded data about the measured condition. 
     Systems for emitting these acoustic signals make use of wave generators that create rapid changes in the pressure of the drilling mud. The rapid changes in pressure create pulses are carried through the drilling mud to receivers located at or near the surface. Pressure pulse generators include the use of rotary “mud sirens” and linearly-acting valves that interrupt the flow of mud through the pulse generator. The temporary flow disruption can be used to create a pattern of pressure pulses that can be recorded, interpreted and decoded at the surface. 
     The MWD signal is typically received by one or more transducers located on a standpipe on the surface. The MWD signals contain multiple frequencies and these signals may overlap with other sources of noise in the wellbore. Mud pumps and other drilling equipment may produce noise that frustrates the process of extracting the MWD signal. Additionally, as the MWD travels through the wellbore and standpipe, the MWD signal may reflect off of tubing and equipment (such as the mud pump). Depending on the signal strength, frequency and location of the recording transducers, the reflected signal may partially or entirely cancel the primary MWD signal. There is, therefore, a need for an improved method and system for recording MWD signals that alleviates the deficiencies experienced in the prior art. 
     SUMMARY 
     In various embodiments, the present invention includes a drilling system that includes a sensor, an encoder operably connected to the sensor and a pressure pulse generator operably connected to the encoder. The pressure pulse generator is configured to produce a primary signal in response to input from the encoder. The drilling system further includes a primary transducer, a reference transducer and a signal processor connected to the primary transducer and the reference transducer. The signal processor includes a two-stage filter that is configured to extract the primary signal from noise observed at the primary transducer. 
     In another embodiment, the present invention includes a receiver system for use in receiving and decoding a primary pressure pulse signal generated by a measurement-while-drilling (MWD) tool. The MWD tool can be used in a drilling system that includes a mud pump that is a source of pressure pulse signal noise. The receiver system includes a primary transducer, a reference transducer and a signal processor. The primary transducer produces an electric signal in response to the measurement of the primary pressure pulse signal and the pressure pulse signal noise. The reference transducer produces an electric signal in response to the measurement primarily of the pressure pulse signal noise. 
     The signal processor includes an adaptive filter and a low pass filter. The adaptive filter produces a first-filtered electric signal from the electric signals produced by the primary transducer and reference transducer. The low pass filter produces a second-filtered electric signal from the first filtered-electric signal. The second-filtered electric signal represents the recovered primary signal. 
     In another aspect, the present invention includes a method for processing a primary pressure pulse signal generated by a measurement-while-drilling (MWD) tool that is used in a drilling system. The method begins with the steps of producing a reference electric signal in response to the measurement primarily of the pressure pulse signal noise and producing a primary electric signal in response to the measurement of the primary pressure pulse signal and the pressure pulse signal noise. The method continues with the step of applying an adaptive filter to the reference electric signal and the primary electric signal to produce a first-filtered electric signal. Next, the method includes the step of applying a low pass filter to the first-filtered electric signal to produce a second-filtered electric signal. The method continues with the step of decoding the primary electric signal from the second-filtered electric signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a drilling system constructed in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagrammatic depiction of the MWD signal processor of the present invention. 
         FIG. 3  is a process flow diagram depicting a method of processing the MWD signal. 
     
    
    
     WRITTEN DESCRIPTION 
     In accordance with an embodiment of the present invention,  FIG. 1  shows a drilling system  100  in a wellbore  102 . The drilling system  100  includes a drill string  104 , a drill bit  106  and a MWD (measurement while drilling) tool  108 . It will be appreciated that the drilling system  100  will include additional components, including drilling rigs, mud pumps and other surface-based facilities and downhole equipment. Although the embodiments of the present invention are disclosed in connection with a measurement-while-drilling (MWD) tool  108 , it will be appreciated that the present invention will also find utility in logging-while-drilling (LWD) techniques. Accordingly, references to MWD should be understood to broadly refer to any applications or techniques that involve the use of pressure pulse signal telemetry from the wellbore  102 . 
     The MWD tool  108  includes one or more sensors  110 , an encoder module  112  and a pressure pulse generator  114 . It will be appreciated that the MWD tool  108  may include additional components, such as centralizers. The sensors  110  are configured to measure a condition on the drilling system  100  or in the wellbore  102  and produce a representative signal for the measurement. Such measurements may include, for example, temperature, pressure, vibration, torque, inclination, magnetic direction and position. The signals from the sensors  110  are encoded by the encoder module  112  into command signals delivered to the pressure pulse generator  114 . 
     Pressurized drilling mud is provided to the drilling system  100  by a mud pump  116  through a standpipe  118 . The standpipe  118  and mud pump  116  may be located on the surface or below the platform of a drilling rig. Based on the command signals from the encoder module  112 , the pressure pulse generator  114  controllably adjusts the flow of drilling mud or other fluid through the pressure pulse generator  114 . The rapid variation in the size of the flow path through the pressure pulse generator  114  increases and decreases the pressure of drilling mud flowing through the MWD tool  108 . The variation in pressure creates acoustic pulses that include the encoded signals from the sensors  110 . 
     The original signal generated by the pressure pulse generator  114  is referred to herein as the “primary” signal. Extraneous noise within the wellbore  102  and standpipe  118  is referred to herein as “noise.” Noise includes pressure pulses generated by equipment other than the pressure pulse generator  114 , environmentally-produced pulses and reflections from the primary signal. The primary signals and noise are transmitted through drilling mud, equipment and tubing in the wellbore  102  and standpipe  118 . 
     A receiver system  120  records the pressure pulses within the standpipe and isolates the primary signal from the noise. In exemplary embodiments, the receiver system  120  includes a primary transducer  122 , a reference transducer  124  and a signal processor  126 . The reference transducer  124  is positioned in the standpipe  118  in relative close proximity to the mud pump  116 . In this position, the noise created by the mud pump  116  dominates the pressure pulses recorded by the reference transducer  124 . In this location, the reference transducer  124  is therefore configured to produce an electric signal that is largely reflective of the noise created by the mud pump  116  and noise reflected off the mud pump  116 . 
     The primary transducer  122  is positioned within the standpipe at a spaced-apart distance from the mud pump  116  and reference transducer  124 . The primary transducer  122  is positioned within the standpipe  118  at a location which minimizes the extent of reflected signals. The primary transducer  122  is configured to produce an electric signal that is responsive to the measurement of the primary signal and noise within the standpipe  118 . 
     The signals produced by the primary transducer  122  and reference transducer  124  are provided to the signal processor  126 . Although the signal processor  126  is depicted as a standalone component, it will be appreciated that the signal processor  126  can be incorporated within a computer or computer network used in conjunction with the drilling or logging process. Generally, the signal processor  126  is configured to extract and isolate the primary signal from the noise in the standpipe  118  and wellbore  102  in real-time with little or no delay. Effective and rapid isolation of the primary signal from the noise enlarges the bandwidth of the telemetry from the MWD tool  108  to the surface and permits the transmission of a primary signal with increased spectral density. 
     Turning to  FIG. 2 , shown therein is a diagrammatic depiction of a two-stage filter  128  used to extract the primary signal from the combination of the primary signal and noise. The two-stage filter  128  is incorporated as a computer program running within the signal processor  126 . In the first stage, the output from the primary transducer  122  and reference transducer  124  are fed into an adaptive filter  130 . The adaptive filter  130  produces a first-filtered electric signal. In the second stage, the output from the adaptive filter  130  is provided to a low pass filter  132 . The low pass filter  132  produces a second-filtered electric signal that represents the recovered primary signal. The recovered primary signal is provided by the low pass filter  132  to a display  134  or other output device for displaying the recovered signal to an operator or for sending the recovered signal to automated controls associated with the drilling process. 
     In exemplary embodiments, the adaptive filter  130  is a least means squares (LMS) adaptive filter. The adaptive filter has a step size of from about 0.0001 to about 0.00001 and a filter length of from about 500 to about 10,000. These values are selected to provide rapid and reliable convergence within the adaptive filter  130 . In some embodiments, the adaptive filter  130  has a step size of about 0.00003 and a filter length of about 5000. These settings can be adjusted by the operator or automatically by the signal processor  126  in response to convergence or divergence results. The adaptive filter  130  uses the reference signal provided primarily by the reference transducer  124  to remove noise from the signal provided by the primary transducer  122 . 
     The signal extracted by the adaptive filter  130  is presented to the low pass filter  132 , where high frequency noise is reduced. In exemplary embodiments, the low pass filter  132  is a finite impulse response (FIR) filter that is configured to permit passage of only the lower frequency signals associated with the known spectra of the primary signal generated by the MWD tool  108 . In other embodiments, the low pass filter is a Hamming window FIR filter or a Kaiser window FIR filter. The output of the low pass filter  132  represents the recovered primary signal, which can be presented to a decoder module  134 . The decoder module  134  is configured to decode the data from the recovered primary signal. It will be appreciated that displays, control systems or other peripherals can be connected to the signal processor  126  for the purpose of displaying, storing or utilizing the processed signals. 
     Turning to  FIG. 3 , shown therein is a process flow diagram for a method  200  of reducing noise from a signal generated by the MWD tool  108 . The process begins at steps  202  and  204 , which may take place simultaneously or in sequence. At step  202 , a reference electric signal is obtained by the signal processor  126 . In exemplary embodiments, the step of obtaining the reference electric signal includes the steps of positioning the reference transducer  124  in close proximity to the mud pump  116  and generating the reference electric signal that is representative of the pressure pulses produced by, and reflected from, the mud pump  116 . 
     At step  204 , a primary electric signal is obtained by the signal processor  126 . The step  204  of obtaining the primary electric signal includes positioning the primary transducer  122  at a spaced-apart distance from the reference transducer  124  and generating the primary electric signal that is representative of the pressure pulses measured by the primary transducer  122 . The primary transducer  122  is placed at a location within the wellbore  102  or standpipe  118  that minimizes the ratio of noise to the primary signal produced by the MWD tool  108 . 
     The process continues at step  206 , during which the adaptive filter  130  is applied by the signal processor  126  to the output of the primary transducer  122  and reference transducer  124  to produce a first-filtered electric signal. The adaptive filter  130  can be a least means squared (LMS) adaptive filter. The step  206  of applying the adaptive filter  130  may include applying an LMS adaptive filter with a step size of about 0.00003 for a filter length of about 5000. The step  206  of applying the adaptive filter  130  generally uses the reference signal as a basis for removing noise associated with the mud pump  116  from the signal produced by the primary transducer  122 . 
     Next, at step  208 , the output from the adaptive filter  130  is routed through a low pass filter  132  to produce a second-filtered electric signal. The low pass filter  132  is configured to remove higher frequency signals that are not associated with the primary signal produced by the MWD tool  108 . The low pass filter  132  can be a finite impulse response (FIR) low pass filter. Finally, at step  210 , the second-filtered electric signal is sent from the two-stage filter  128  to downstream processing where the extracted primary signal is decoded, displayed and used as a basis for reviewing the measurements made by the MWD tool  108 . 
     Thus, in exemplary embodiments, the present invention provides a system and method for extracting a primary encoded signal produced by the MWD tool  108  from noise present in the wellbore  102  and standpipe  118 . The use of the two-stage filter  128  in combination with the strategically located primary transducer  122  and reference transducer  124  presents a significant advancement over prior art signal processing systems. It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention.