Abstract:
The present invention is directed to overcoming analog transmission difficulties by digitizing transducer signals at or near the transducer of an acoustic pulse gun and then transmitting the transducer signals in a digital form so that the signals can be recovered with greater fidelity by a remote computer or recorder. System, apparatus and method aspects of the invention are provided. Advantages of the present invention include better transmission of the acoustic signal from the pulse gun assembly to the computer or recorder, reduced noise and electronic interference, and better data capture.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to the telemetry of signals generated by an acoustic sensor to a remote device and to an apparatus for the implementation thereof. More particularly, the invention relates to digitizing electrical signals produced by an acoustic transducer inside an acoustic pulse gun and subsequently transmitting the digitized signals to a remote receiver or recorder.  
       BACKGROUND OF THE INVENTION  
       [0002]     The level of fluid in the borehole of a well is an important element in the field of oil well testing and operation. Determination of the liquid level in a well by an acoustic pulse has been successfully performed for many years. For example, U.S. Pat. No. 2,232,476 issued to Ritzmann in 1941, discloses the basic methodology wherein a high frequency acoustic pulse, generated by an acoustic pulse gun, is projected down the annulus between the tubing string and the well casing string. Acoustic pulse generating means typically include employing a blank shotgun shell to generate the sonic event, discharging a compressed gas into the annulus to generate the sonic event, or in a wellbore which has a substantial gas pressure it is possible to use the gas pressure itself to create the sonic event. Reflections of the sonic event or acoustic pulse are generated by cross-sectional variations along the length of the tubing string, such as are created by tubing collars or the surface of the liquid column in the annulus. A microphone or acoustic transducer is then used to sense the reflections and provide a signal indicative of those reflections.  
         [0003]     The depth to the liquid surface is then determined by counting the number of tubing collars above the liquid interface and multiplying by the average distance between the collars, as indicated by the reflections. Interpretation of the reflection results is typically assisted by passing the electrical output signal of the acoustic transducer of the pulse gun through: 1) a high-pass or band pass filter so as to emphasize the short, high-frequency reflections from tubing collars; and/or 2) a low-pass filter to emphasize the low-frequency pulse from the gas-liquid interface.  
         [0004]     As shown in  FIG. 1 , modern day pulse gun systems often comprise a pulse gun and microphone assembly connected to a computer or recorder device by means of a lead, cable or similar conductor. Analog signals produced by the microphone or acoustic transducer inside the gun assembly are transmitted along the length of cable and fed to the computer or recording device. Typically the recording device contains electronics to subsequently amplify, filter and then digitize the analog signals received from a cable or conductor. For example, see U.S. Pat. No. 5,117,399 to McCoy et. al where an electronics module contains the electronics to amplify, filter and digitize the analog signals from a microphone cable.  
         [0005]     The digitization of the transducer&#39;s signal allows for additional analysis of the signal and also for digital storage of the signal. Additionally, various schemes for computer aided interpretation of the reflections are taught by the prior art, see for example U.S. Pat. No. 4,318,298, issued to Godbey, U.S. Pat. No. 4,793,178, issued to Ahern, U.S. Pat. No. 5,200,894, issued to McCoy and Canada Pat. No. 2,201,215 to Grande.  
         [0006]     Accordingly, a necessary component of the acoustic pulse gun system is the means for reliably transmitting the signals produced by the transducer inside the pulse gun, which are indicative of the acoustic reflections, to the computer or recording device. However, state-of-the-art cables have relatively poor transmission qualities and the traditional cable system is sensitive to static and electronic noise which may be picked up along the length of a cable. The cable often acts as an antennae picking up electronic noise from a variety of sources. Typical sources of such noise in a well operation environment include electric motors operating nearby, the cathotic protection system installed to protect the metal elements of a well from deteriorating, and cell phones used by personnel. Noise and other extraneous signals can also be produced if the cable is moved during operations; such as due to wind or by an operator accidentally bumping it.  
         [0007]     What is desired therefore is a system or method which overcomes the analog transmission difficulties and provides reliable transmission of the signals from a pulse gun assembly to a computer or recorder.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed to overcoming analog transmission difficulties by digitizing transducer signals at or near the transducer of an acoustic pulse gun and then transmitting the transducer signals in a digital form so that the signals can be recovered with greater fidelity by a remote computer or recorder.  
         [0009]     In one aspect the invention provides a system for converting and transmitting analog signals produced by a transducer of a pulse gun assembly to a remote recorder device, the system comprising an analog-to-digital converter located proximate the transducer and digital signal transmission means, wherein the signals produced by the transducer are converted to digital form by the analog-to-digital converter and are transmitted to the remote recorder device by the digital signal transmission means.  
         [0010]     In another aspect of the invention there is provided a pulse gun assembly for delivering an acoustic pulse and monitoring resultant reflections from an annulus of a well, the well having a wellhead enabling access to the annulus, comprising a housing having a sidewall forming a chamber and an open end for connecting to the wellhead, an acoustic pulse generating means for creating an acoustic pulse in the chamber, a transducer positioned in the housing and in communication with the chamber for converting said resultant reflections into analog signals, an analog-to-digital converter located proximate the transducer and digital signal transmission means, wherein said analog signals produced by the transducer are converted to digital form by the analog-to-digital converter and are transmitted to a remote recorder device by said digital signal transmission means.  
         [0011]     In a third aspect of the invention there is provided a transducer assembly for connection to a pulse gun, comprising a housing, a transducer projecting from the housing and for insertion into the pulse gun assembly, an analog-to-digital converter, positioned inside the housing proximate the transducer, and digital signal transmission means.  
         [0012]     In a fourth aspect of the invention there is provided a method for transmitting signals from a transducer inside an acoustic pulse gun assembly to a remote device, said signals indicative of reflections resulting from a high frequency acoustic pulse generated by an acoustic pulse projected down an annulus between a tubing string and a well casing string of a well, the acoustic pulse gun assembly having an analog-to-digital converter proximate the transducer and digital signal transmission means, the method comprising digitizing said signals from said transducer into digital signals using the analog-to-digital converter and transmitting said digital signals to the remote device using the digital signal transmission means.  
         [0013]     Advantages of the present invention include better transmission of the acoustic signal from the pulse gun assembly to the computer or recorder, reduced noise and electronic interference, and better data capture. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  diagrammatically shows a prior art system for transmitting transducer output signals from a pulse gun assembly to a remote recorder device;  
         [0015]      FIG. 2  diagrammatically shows a preferred embodiment of a system for transmitting transducer output signals from a pulse gun assembly to a remote recorder device;  
         [0016]      FIGS. 3   a  and  3   b  are electrical schematics of the major electronic components of the embodiment of system of  FIG. 2 ;  
         [0017]      FIG. 4  is an electrical schematic of a preferred embodiment of an analog-to-digital converter and a communications microprocessor;  
         [0018]      FIG. 5  is perspective view on one embodiment of an apparatus housing the electronic components of the present invention and suitable for connection to a pulse gun;  
         [0019]      FIG. 6  is a partial exploded perspective view of the apparatus of  FIG. 5 ;  
         [0020]      FIG. 7  is an electrical schematic of the major electronic components of another embodiment of the system of the present invention;  
         [0021]      FIG. 8  is an electrical schematic of another embodiment of an analog-to-digital converter and a communications microprocessor; and  
         [0022]      FIG. 9  is an electrical schematic of yet another embodiment of an analog-to-digital converter and a communications microprocessor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Reference is to be had to  FIGS. 2-9  in which identical reference numbers identify similar components.  
         [0024]      FIGS. 2-4  show a preferred embodiment of a system  1  for transmitting acoustic pulse gun signals  5  from a pulse gun assembly  10  to a computer or other similar recorder device  12 . The system  1  comprises a microphone or acoustic transducer  7  inside the pulse gun  10  assembly, for producing an analog signal  5   a  indicative of acoustic reflections generated by an acoustic pulse projected down a wellbore, an analog-to digital-converter  20 , for converting the analog signal  5   a  to a digital signal  5   b , and digital signal transmission means  16  for transmitting the digital signal  5   b  to the recording device  12 . In this embodiment the digital signal transmission means  16  is a length of cable or conductor  16   a . Preferably the analog signal  5   a  is amplified by a preamplifier  14  and filtered by a filter  18  prior to entering the analog digital converter  20 . More preferably, the filter  18  further comprises a 0-5 Hz low pass filter  18   a  and a 5-10 Hz band pass filter  18   b  as more clearly shown in  FIG. 3   a . Even more preferably, the system  1  further comprises communications microprocessor  22  for encoding the digital signal  5   b  for transmission over the cable  16   a  via the RS485 serial method in packets using a transmission protocol with error-checking. A suitable transmission protocol with error-checking is the Modbus protocol.  
         [0025]     By positioning at least the analog-to-digital converter circuitry  20  physically proximate to the transducer  7 , the amount of interference or electronic noise that is picked up by the system of the present invention is drastically minimized when compared to the prior art systems. The analog-to-digital converter  20  may be placed inside the pulse gun assembly  10  proximate to the transducer  7 , as in the present embodiment of the system  1 .  
         [0026]     In this embodiment, the converter  20  is approximately two inches from the transducer  7 . However, in other embodiments (not shown), good results have been obtained by positioning the analog-to-digital converter so that it was physically touching the transducer or as far away as nine inches from the transducer. Preferably, the housing of the pulse gun assembly is made from metal so as to provide additional shielding, from outside electronic noise and interference, to the analog components of the electronics inside the pulse gun assembly.  
         [0027]     Alternatively, a retro-fit transducer assembly, comprising both a transducer  7  and analog-to-digital converter  20 , may be provided to replace analog acoustic transducers in existing art pulse gun assemblies; as is further described below.  
         [0028]     By transmitting the signal  5  in digital form  5   b  over a cable  16   a , rather than in analog form, the signal  5  can be recovered with much greater fidelity by the recorder device  12  than was possible with the prior art systems. It will therefore be obvious to those skilled in the art that, although desirable, a preamplifier, a filter and a communications microprocessor are not essential elements to the system  1  of the present invention. For example, the filtering of the signal  5  may be done digitally by circuitry or software of the recorder  12 .  
         [0029]     It is to be understood that the foregoing described circuit elements are merely representations of certain embodiments of the present invention. Various other types and values of circuit components may be utilized. For example,  FIGS. 7-8  illustrate other embodiments of the system and of the analog-to-digital converter and a communications microprocessor respectively. Advantageously, the embodiment of the  FIG. 8  further comprises a memory storage component  28 .  
         [0030]     Often, in a pulse gun system it is also desirable to energize solenoids (which in turn actuate valves to trigger acoustic pulses) and to transmit data from pressure and temperature sensors or transducers located near the wellbore to the remote recording device  12 . Accordingly, and referring now to  FIG. 9 , yet another embodiment of an analog-to-digital converter  20  and a communications microprocessor  22  is shown. In this embodiment of the converter  20  and microprocessor  22  two solenoids  24   a ,  24   b  can be actuated by the microprocessor  22  and the microprocessor  22  can also receive data from pressure sensors (not shown) via auxiliary port  26 . The data received by auxiliary port  26  is subsequently transmitted along the same signal transmission means  16  as the digitized signal from the acoustic transducer.  
         [0031]     As will be obvious to those skilled in the art, the signal  5 , once digitized into a digital signal  5   b , can also be transmitted wirelessly to the recorder  12 . Therefore, in another embodiment (not shown) the signal transmission means  16  comprises a wireless means, such as that of a wireless network. A suitable protocol for use with the wireless network is the Bluetooth™ protocol.  
         [0032]     Now referring to  FIGS. 5 and 6 , one embodiment of a transducer assembly  30 , suitable for housing the analog-to-digital converter circuitry  20  physically proximate a transducer  7  and for connecting to a pulse gun, is shown. The transducer assembly  30  comprises a metal cylindrical housing  32  of approximately three inch diameter and eight inches in length, a circular metal end cap  34 , a circular metal end plate  36  with externally threaded section  37 , a first circular circuit board  39  with the preamplifier (not shown) and filter (not shown) and a second circular circuit board  40  with the digital-to-analog converter  20  and the communications microprocessor  22 . Preferably the end plate  36  is ¾″ thick stainless steel and able to withstand pressures of up to 3000 psi, so as to isolate the circuit boards  39 ,  40  inside the housing  32  from the pressures that may be present in the pulse gun. More preferably, the housing  32  of the transducer assembly  30  is made from metal so as to provide additional shielding from outside noise and interference to the analog components of the electronics inside assembly  30 .  
         [0033]     The transducer assembly  30  further comprises cable connecting means  16   c  on end cap  34 , for connecting the transducer assembly  30  to a cable  16   a ; and thus the cable connect means  16   c  and cable  16   a  are yet another embodiment of the digital signal transmission means  16 . Advantageously, the end cap  34  protects the circuit boards  39 ,  40  from the weather and elements to which the assembly  30  may be exposed.  
         [0034]     In this embodiment, the transducer  7  is mounted on end plate  36  and projects axially from the transducer assembly  30  as shown in  FIG. 8 . Advantageously, the transducer  7  can be inserted into a pulse gun (not shown) and, by threading the threaded section  37  of the microphone assembly  30  into a matching threaded section on the pulse gun, the transducer assembly  30  is held in place. More advantageously, the transducer assembly  30  may be retrofit onto existing pulse guns, by removing the existing transducer from the pulse gun, ensuring that the treaded section  37  matches the treaded section of the removed transducer, inserting transducer  7  of assembly  30  into the pulse gun and treading the transducer assembly  30  into place.  
         [0035]     The first circular board  39  and the second circular board  40  are positioned inside the cylindrical housing  32 , the outside diameter of the circular boards being slightly smaller than the inside diameter of the housing  32 . Connectors or wires (not show) operationally connect the transducer  7  to the first circuit board  39 , the first circuit board  39  to the second circuit board  40 , and the second circuit board  40  to the cable connecting means  16   c . The end cap  34  and end plate  36  connect to either end of the housing  32  (as shown), sealing the boards  39 ,  40  and other electronic components inside and protecting them from the elements. Since the transducer  7  projects axially from end cover  36 , it can be inserted into a pulse gun.  
         [0036]     It is to be understood that the foregoing described transducer assembly components are merely representations of certain embodiments of the present invention. Various other types and dimensions of transducer assembly components may be utilized. For example, the housing could be a square box, rather than a cylinder and the two circular circuit boards could be combined into one square circuit board.