Abstract:
A valving system is disclosed which generally comprises a body including an inlet and an outlet where the inlet is disposed in fluid communication with a fluid flow passage and the outlet is disposed in fluid communication with a pressurized fluid member, the body further defining an internal bore in which is slidably disposed a piston moveable between a first and a second position such that fluid communication between the fluid flow passage and the fluid flow member is established when the piston is disposed in the first position but not in the second position, an apparatus and to move the piston from the first position to the second position so as to interrupt fluid flow from the fluid flow passage to the fluid member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to marine acoustic generators and methods for their operation and use. More specifically, the present invention relates to a method and apparatus to selectively cut off fluid flow to any one of an array of marine acoustic generators. 
     2. Description of the Prior Art 
     Seismic exploration of subsea formations has involved the use of a variety of differing tools and techniques. One of the most successful tools for a marine seismic exploration is the marine acoustic generator which are commonly referred to as “airguns.” 
     In a general embodiment, the airgun comprises a body in which a shuttle reciprocates between an open and a closed position so as to define an internal cavity. Air is supplied to and pressurized within the cavity until a selected pressure is achieved. The shuttle is then released to exhaust this pressurized air into the surrounding water to create a primary pressure pulse and a series of secondary pulses. It is these pulses which are useful in seismic evaluation. 
     Disadvantages associated with contemporary marine acoustic generators arise when one in an array of such generators demonstrates a leakage of fluid. Such leakage distorts the signal produced by the operation of the leaking generator and other generators in the array. Accordingly, prior procedure has required that the entire array be shut down and then retrieved on the streaming vessel. It is then necessary to locate the malfunctioning device, replace or repair the generator, restream the array and then repeat the prior seismic track. For obvious reasons, such retrieval of efforts are very costly terms of lost hours and equipment charges. 
     Disadvantages associated with prior marine acoustic generators also included the danger associated with their disassembly and repair. In this connection, it is not always obvious that a given device still contains a quantity of pressurized fluid (water or air). As a result, attempts to disassemble the device has often resulted in injury and death as a result of accidental explosions of these devices. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above and other disadvantages of prior marine acoustic systems by providing a method and apparatus to selectively shut off pressurized fluid flow to one or more generators. 
     In a general embodiment, the present invention comprises a valving system which is adapted to be used with existing marine acoustic generators to provide a mechanism to selectively disable one or more generators comprising an array of such generators. The instant system also enables visual detection of the disabled generators and further provides means to vent such generators to prevent accidental explosion during inspection and/or disassembly. 
     In a preferred embodiment, the present invention comprises a housing defining an inlet, an outlet and an internal cavity where a shuttle is reciprocally disposed in said cavity between a first and a second position. The housing further defines a series of fluid flow portals disposed about the shuttle in said housing where some of said portals may be closed, and thus air redirected, upon the actuation of a second piston which is also reciprocally disposed in said housing. In one preferred embodiment, the second piston defines a solenoid. 
     The inlet is coupled via a pressurized fluid line to a supply of pressurized air. The outlet is coupled via a second pressurized line to the marine acoustic generator. 
     During operation of the marine acoustic generator, air passes unobstructed through the subject valve to be released by the acoustic generator in the generation of acoustic pulses. Upon receipt of a discrete electrical signal, however, the solenoid in the valve moves to a “closed” orientation, thereby selectively disabling the generator by preventing the continuing flow of air to said generator. 
     The present invention presents a number of advantages over the prior art. One such advantage is the ability to selectively disable a malfunctioning acoustic generator without the need for the wholesale shutdown and retrieval of the seismic array. In such a fashion, significant savings in terms of cost and time may be observed. 
     Another advantage of the invention is the ability to safely vent a pressurized generator prior to inspection and disassembling. In such a fashion, serious injuries may be avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B illustrate a diagrammatic view of a towed acoustic array. 
     FIG. 2 illustrates a diagrammatic view of one preferred embodiment of the invention as it may be used in a towed array. 
     FIG. 3 illustrates an electrical, diagrammatic view of the valve embodiment illustrated in FIG.  2 . 
     FIG. 4 illustrates a pneumatic, diagrammatic view of the valve embodiment illustrated in FIG.  2 . 
     FIG. 5 illustrates a detail, cut-away view of the valve embodiment-illustration in FIG.  2 . 
     FIG. 6 illustrates a detail, cut-away view of the invention as it appears when the seismic generator is being pressurized. 
     FIG. 7 illustrates a detail, cut-away view of the invention as it appears when the seismic generator is isolated from a source of pressurized fluid. 
     FIG. 8 illustrates a detail, cut-away view of the invention as it appears when the system is being vented. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The valving system of the present invention has specific application to seismic arrays such as the array illustrated in FIGS. 1A-1B. By reference to these figures, one or more acoustic generators  2  are suspended via a chain  7  or other support beneath a towing bar  3  which is in turn suspended beneath a float or a buoy  6  secured behind a towing platform, e.g. a ship  10 , via a tether  9  at a selected distance and orientation to achieve a desired seismic profile. Tether  9  includes a structural member, e.g. a steel cable, and also includes an electrical  13  and pneumatic  16  lines for pressurizing and actuating generators  2  in a manner familiar to those skilled in the art. 
     In a conventional deployment, each generator  2  is provided with an individual fluid flow member  11  which in turn could be monitored on the towing platform  10 . Hence, it is conventionally possible to determine if and when a given generator begins to malfunction and the extent of the malfunction. While such determination has heretofore been possible, it has not been possible to selectively disable the malfunctioning generator  2  so as to avoid the necessity of interrupting the collection of data from the remaining, fully functioning generators  2 . 
     One embodiment of the present invention may be seen by reference to FIGS. 2-5 in which is illustrated a marine acoustic generator  20  which is secured to a frame  24  via a chain  25  or other support means. As illustrated, generator  20  is coupled to an air pressure line or jumper  21  and electrical lines  23  and  26  in a conventional fashion. 
     Instead of the arrangement of prior art seismic arrays as illustrated in FIGS. 1A-1B, a shut-off valve  60  of the invention is interposed between the pressurized air source (not shown) and a generator  20  in a manner described in greater detail below. By reference to FIGS. 2-4, valve  60  is also electrically connected between the towing platform (not shown) and generator  20 . As illustrated in FIG. 2, in one embodiment valve  60  may be secured to a floatable member  24 . 
     A detailed view of a preferred embodiment the shuttle valve of the invention may be seen by reference to FIG. 5, in which is illustrated a housing  80  which defines an inlet  82 , an outlet  84  and an internal cavity or bore  85 . A piston or shuttle  89  is reciprocally disposed in said cavity  85  between a first or “closed” orientation and a second or “open” orientation, the “closed” or “open” nomenclature referring to whether pressurized air passes through said valve  60  to the generator  20 . 
     In the embodiment illustrated in FIG. 5, piston  89  defines an elongate body where the mid portion  94  of said body defines a greater diameter than the lower portion  93  or the upper portion  91 . In a complimentary fashion, cavity  85  defines upper and lower sub-bores  101  and  102 , respectively, where the mid portion  104  of cavity  85  defines a sufficiently large diameter to accommodate mid portion  94  so as to allow it a limited range of reciprocation, as will be discussed further herein. 
     As illustrated in FIGS. 5 and 6, upper portion  91  of shuttle  89  defines an arcuate shoulder  112  where such shoulder is adapted to seat against a retaining flange  117  when said valve is disposed in an “open” position. Conversely, mid portion  94  of piston  89  defines a flange  180  which is adapted to seat against shoulder  184  when the valve is disposed in a “closed” position (See FIG.  7 ). Upper  91  and lower  93  portions of shuttle  89  are adapted to fit in close tolerance to bores  101  and  102  so as to prevent the leakage of pressurized air therethrough. Leakage is further prevented through the use of sealing members, e.g. O-rings  123 , as illustrated. 
     Housing  80  defines a first connecting port  121  which allows fluid communication between inlet  82  and outlet  84  when shuttle  91  is disposed in an “Open” position, as illustrated in FIGS. 5 and 6. In such a fashion, pressurized air supplied to valve  60  when in an “open” position passes from inlet  82  to outlet  84  and to generator  20 . Such pressurized fluid flow acts on the under surface  146  of mid portion  94  so as to maintain piston  89  in a first or “open” position. 
     Housing  80  also defines a second connecting port  132  which is disposed in fluid communication with solenoid  140  and a third portal  145 . Third portal  145  is disposed in fluid communication with a sub-chamber  109  and thus the top surface  163  of the upper portion  91  of piston  89 . Thus, when fluid flow to third portal  145  is uninterrupted, pressurized air from inlet  82  acts against surface  163  to move piston  89  into a second or “closed” orientation (See FIG.  7 ). 
     During the ordinary operation of generators  20 , air flow to portal  145  is interrupted by solenoid  140  which itself reciprocates between an “open” and “closed” orientation depending on the receipt of electrical impulses through lines  23  and  26 . (See FIGS. 2,  3 ,  6  and  7 ). The default or initiating position for solenoid  140  is in a second or “closed” orientation. (See FIG.  6 ). In this position, fluid flow to portal  145  is interrupted and fluid flow to generator  20  is uninterrupted. 
     In the preferred embodiment illustrated in FIG. 5, the posture of valve  60  may be visually determined by the position of the lower portion  93  of piston  89 . If piston  89  is positioned in an “open” or starting position, the lower portion  93  of piston  89  does not extend from housing  80 , as illustrated in FIGS. 5-6 and  8 . However, when piston  89  is positioned in a “closed” position, lower portion  93  extends from housing  80 , as illustrated in FIG. 7, thereby providing a ready visual reference to those generators  20  which have been disabled. 
     In the embodiment illustrated in FIGS. 6-8, solenoid  140  includes a plunger  147  and a poppet  211  which is biased in a down or closed position by a spring  210 . The biasing effect of spring  210  may be overcome when coil  164  is energized. 
     Solenoid  140  is electrically coupled to electrical lines  23  and  24  which in turn are coupled to generators  20 . Generators  20  are actuated by electrical pulses  4  which are transmitted along said lines  23  and  24  in a conventional fashion as will be recognized by those skilled in the art. A diode  63  is electrically integrated between solenoid  140  and lines  23  and  24  to prevent solenoid  140  from also being actuated upon the transmission of each of the i 1  pulses, as shown in FIG.  3 . When, however, it is ascertained that a given generator  20  is malfunctioning, a second pulse i 2  of a different polarity is transmitted through lines  23  and  24 , which pulse also actuates solenoid  140 . No extra firing time is required. This is significant in operation since there is a physical limitation due to drag on the number of electrical lines which may be deployed on the towing vessel. For example, a typical string of acoustic generators comprises 6-12 units which would conventionally require 6-12 extra electrical lines. 
     The operation of valve  60  may be described as follows by reference to FIGS. 6-8. Pressurized air flows through inlet  82  into cavity  85 , moving pistons  89  to an “open” position thereupon allowing air flow through outlet  84  to generators  20 . (See FIG.  6 ). 
     Shuttle  89  is initially positioned in an “open” orientation by and is maintained in an “open” orientation when pressurized air passing through inlet  82  and portal  121  acts on the surface area of the underside shoulder  146  of the shuttle  94 . Generators  20  are now operated in a manner consistent with conventional practice. When valve  60  is unpressurized and lower portion  93  of piston  89  extends from housing  80 , it is possible to manually replace piston  89  to an “open” position. In this orientation, the lower part  93  of piston  89  does not extend from housing  80 . However, when valve  60  is pressurized (even with low pressure) it is impossible to manually move piston  89  to an “open” position. As a consequence, it is possible to manually test valve  60  for any pressurized air inadvertently remaining in housing  80  or in any connecting lines. 
     When a given generator  20  is identified as malfunctioning, valve  60  is actuated to disable said generator  20 . When solenoid  140  is actuated, coil  164  is energized thereby causing plunger  147  to move upward against the biasing force of spring  210 . Poppet  211  likewise moves upwardly, thereby removing the obstruction to portal  145 . Pressurized air then flows through ports  132  and  145  and acts on the top surface area  163  of shuttle  94 . Since the surface area of top  163  is greater than the surface area of shoulder  146 , shuttle then moves to a “closed” orientation, thereby preventing further flow of pressurized air to generator  20 . 
     The pressure on top surface  163  of shuttle  89  is slowly vented out through orifice  143  (see FIG.  5 ), but shuttle  89  remains and is maintained in a “closed” position by the pressure applied when air line  21  is depressurized and if, for any reason, air pressure remains in generator  20 , shuttle  89  will be moved to an “open” position. The movement of shuttle  89  in this fashion occurs when the pressure acting on the mid portion of piston  89  becomes less than about 0.7 times the pressure acting on shoulder  146  of piston  89 . The movement of shuttle  89  automatically allows air pressure that could be trapped in generator  20  to be vented out through outlet  84  into cavity  85  and then into main line  21  through inlet  82  (See FIG.  8 ). This pressure relief system provides an important safety feature for proper handling of generator  20 , on the mid portion  94  of piston  89 . As a consequence, no permanent current is needed to maintain valve  60  is a “closed” orientation. Generator  20  is now effectively disabled. 
     Any pressurized air in generator  20  passes back through inlet  84  and moves piston  89  off of seat  184  to vent through inlet  82 . In such a fashion, each disabled generator  20  is also automatically depressurized for purposes of inspection and disassembly. 
     Although particular detailed embodiments of the apparatus and method have been described herein, it should be understood that the invention is not restricted to the details of the preferred embodiment. Many changes in design, composition, configuration and dimensions are possible without departing from the spirit and scope of the instant invention.