Abstract:
A downhole acoustic sensing system includes a pulsator device configured and disposed to be arranged in a downhole environment, and a control system operatively connected to the pulsator device. The control system delivers at least one control input to the pulsator device to generate a sinusoidal acoustic signal.

Description:
BACKGROUND 
       [0001]    The present invention relates to the art of production fluid monitoring systems and, more particularly, to a production fluid monitoring system including a downhole acoustic sensing system having a downhole pulsator. 
         [0002]    Acoustic devices are used to measure various parameters in a downhole environment. Often times, an acoustic device may be used to determine parameters of a downhole acoustic medium including solids and/or fluids proximate to a drill head. In such cases, the acoustic device may be mounted to the drill string. In many cases, the acoustic device takes the form of a piezo-electric transducer. Piezo-electric transducers may also be mounted to production tubing and operated to transmit and/or receive acoustic signals through the acoustic medium. 
       SUMMARY 
       [0003]    A downhole acoustic sensing system includes a pulsator device configured and disposed to be arranged in a downhole environment, and a control system operatively connected to the pulsator device. The control system delivers at least one control input to the pulsator device to generate a sinusoidal acoustic signal. 
         [0004]    A production fluid monitoring system includes a pulsator device configured and disposed to be arranged in a downhole environment and a control system operatively connected to the pulsator device. The control system delivers at least one control input to the pulsator device to deliver a sinusoidal acoustic signal through downhole fluids. A data acquisition system is configured and disposed to detect the sinusoidal acoustic signal passing through the downhole production fluids. 
         [0005]    A method of monitoring downhole production fluids includes delivering a positive pressure pulse from a downhole pulsator to form a first portion of a downhole acoustic signal, delivering a negative pressure pulse downhole to form a second portion of the downhole acoustic signal, passing the acoustic signal through a production fluid, and sensing the acoustic signal to determine a quality of the production fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0007]      FIG. 1  is a partial cross-sectional view of a downhole production tubing passing alongside a downhole acoustic device, in accordance with an exemplary embodiment; 
           [0008]      FIG. 2  is a schematic view of a downhole production fluid acoustic sensing system including the downhole acoustic device of  FIG. 1 ; 
           [0009]      FIG. 3  is a view of the downhole acoustic device of  FIG. 1  delivering a negative pressure pulse; 
           [0010]      FIG. 4  is a view of the downhole acoustic device of  FIG. 1  delivering a positive pressure pulse; and 
           [0011]      FIG. 5  is a graphical representation of an acoustic signal produced by the downhole acoustic device, in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Exploration companies routinely drill wells in a medium, indicated at  2  in  FIG. 1 , in search of natural resources such as natural gas and/or oil. The wells are formed by drilling a bore, indicted generally at  4 , into medium  2 . Bore  4  extends to a zone or region (not shown) in which a natural resource resides. After forming bore  4 , production tubing  6  is inserted downhole into the bore  4 . At this point it should be understood that the term “downhole” refers to a zone within medium  2  in which bore  4  is formed. Bore  4  may begin at an exposed earthen or sand surface, or under water. The term “uphole” as used herein refers to a zone or region outside of medium  2 . 
         [0013]    In accordance with an exemplary embodiment, a production fluid monitoring system, indicated generally at  14  in  FIG. 2 , is employed to monitor production fluids passing through production tubing  6 . Production fluid monitoring system  14  includes a downhole acoustic sensing system  20  and a data acquisition system  24 . Downhole acoustic sensing system  20  includes a pulsator device  30  which, as will be discussed more fully below, delivers an acoustic signal into production fluids passing through production tubing  6 . 
         [0014]    Pulsator device  30  may include a piston  32  shiftably mounted in a cylinder  34 . Of course, it should be understood that pulsator device  30  may take on a variety of forms including diaphragms, pumps and the like, capable of delivering a pressure pulse into production fluids passing through production tubing  6 . In the exemplary embodiment shown, cylinder  34  extends from a first end  36  exposed to the production fluids to a second, closed end  38  defining a volume  40 . Piston  30  includes a first piston element  43  exposed at first end  36  and a second piston element  45  spaced from first piston element  43  by a support rod  47 . Second piston element  45  separates volume  40  into a first portion  54  and a second portion  56 . 
         [0015]    In accordance with an exemplary embodiment, pulsator device  30  is operatively connected to a control system  70 . Control system  70  is connected to a valve  74  which, in turn, may be fluidically coupled to a source of fluid  78  and pulsator device  30 . Valve  74  may take the form of a ball valve or other form of fast switching valve. In the exemplary embodiment, shown, valve  74  is fluidically connected to cylinder  34  through a first control input  84  and a second control input  86 . First control input  84  takes the form of a first hydraulic line  90  and second control input  86  takes the form of a second hydraulic line  92 . Control system  70  operates valve  74  to alternatingly deliver control signals to pulsator device  30  causing an acoustic signal to pass into the production fluids. The control signals may take the form of pulses of a fluid passing through first and second hydraulic lines  90  and  92 . The fluid may be a non-compressible fluid or a compressible fluid. 
         [0016]    In accordance with an aspect of an exemplary embodiment, control system  70  operates valve  74  to delver a pulse of fluid through first hydraulic line  90  causing piston  32  to move in a first direction towards second end  38  of cylinder  34  creating a negative pressure pulse  96  ( FIG. 5 ) into the production fluid, as shown in  FIG. 3 . Control system  70  then operates valve  74  to deliver another pulse of fluid into second hydraulic line  92  causing piston  32  to move in a second direction away from second end  38  of cylinder  34  creating a positive pressure pulse  98  ( FIG. 5 ) into the production fluid, as shown in  FIG. 4 . Control system  70  alternates between sending pulses of fluid to first and second hydraulic lines  90  and  92  creating a sinusoidal acoustic signal  100 , as shown in  FIG. 5 , that is delivered into the production fluid. Of course it should be understood that the sinusoidal signal may represent a summation of sinusoids. 
         [0017]    In accordance with an aspect of an exemplary embodiment, data acquisition system  24  includes a data collection and analysis device  104  operatively connected to a plurality of downhole sensors  108 . Downhole sensors  108  may take the form of fiber optic sensors  110  that are arranged at various points along production tubing  6 . Acoustic signal(s)  100  passes in an uphole direction and a downhole direction through the production fluids. Data acquisition system  24  collects and analyzes acoustic signal(s)  100  at various points along production tubing  6  to monitor the production fluids. 
         [0018]    At this point it should be understood that the exemplary embodiments describe a system for delivering pressure pulses into production fluids passing through production tubing in a resource collection system. The pressure pulses form an acoustic source that may be monitored to determine various attributes of the production fluid. The timing, duration, period and frequency of the pressure pulses may be varied depending upon desired sensing parameters. For example, a low frequency acoustic signal may be desirable when sensing deep downhole. It should also be understood that while described as a hydraulically actuated piston responding to two control signals, the present invention may employ a single control signal. A second control may be provided by a spring that is compressed by the piston in response to the single control signal. Further, other systems including electric and magnetic may be used to drive the piston. 
         [0019]    It should be further understood that the control system may be provided uphole to provide technicians with greater control of the acoustic signal. For example, in contrast to current acoustic sources used during drilling which operate continuously, the pulsator device of the present invention may be operated only during select periods. Periodic, as opposed to continuous operation, may extend an overall service life of the downhole acoustic sensing system. Moreover, by mounting the control system and the valve uphole, maintenance may be performed to further extend service life. However, it should be understood that both the valve and the control system may be arranged downhole. 
         [0020]    While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.