Abstract:
A method for conducting seismic operations includes the steps of deploying a seismic streamer carrying an electrically powered device from a vessel into water having waves, providing an in-sea generator in electrical connection with the device, producing electricity from the in-sea generator by harvesting mechanical energy from the waves, and providing the produced electricity to the device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates in general to conducting marine seismic surveys, and more particularly to methods and apparatus for providing backup and/or primary electrical power to the in-sea electrical equipment. 
       BACKGROUND 
       [0002]    In the field of marine seismic exploration, it is important to determine the configuration of the rock strata underlying the subsea earth&#39;s surface to locate subsurface structures favorable to the accumulation of oil and gas. In marine seismic surveying, this is accomplished by generating acoustic pulses or shock waves with sound sources, such as air guns, and by monitoring the resultant acoustic waves which reflect off the subsea interfaces with acoustic sensors. In a typical marine surveying operation, the seismic sound sources and the acoustic sensors are towed in designated patterns behind a seismic vessel. The basic principles of these surveying operations are well known to those skilled in the art. 
         [0003]    Commonly, an array of seismic acoustic sensors, such as hydrophones, are configured in a seismic cable where the hydrophones are spaced along the length of the seismic cable. This seismic cable typically is called a streamer or streamer cable. The streamers are connected to apparatus on the vessel which includes the power source and the data control system. 
         [0004]    To optimally develop 3-D marine surveys, to reduce the number of passes required of the seismic vessel in surveying a specific area and to improve the quality of the resulting geophysical information, multiple streamer cables typically are deployed in a pattern parallel to the centerline of the vessel. The streamer cables are separated from each other by calculated offset distances to provide the desired, spaced parallel pathways which minimize duplicate coverage but are adequate to cover the area to be surveyed. To obtain and maintain the desired lateral distances between adjacent streamer cables throughout the time period during which the seismic vessel is traversing the survey area, the streamer cables are attached at predetermined tow points on the cable to devices referred in the art of seismic exploration as pullavanes or para-vanes. The para-vanes are towed to the side of the vessel and provide the means to tow the streamer cables along pathways parallel to but laterally spaced from the pathway of the towing vessel. 
         [0005]    The streamer cable typically is filled with a fluid which acts as a buoyancy material to keep the streamer cable at the desired depth beneath the surface of the water during the surveying operation. Because of the length of the streamers (sometimes several miles/kms in length), the streamers are in danger of colliding with other vessels. Therefore, a floatation device, such as a tail buoy, is attached to the submerged, tail end of the streamer to provide means to visibly approximate the location of the end of the streamer cable. The tail buoy is also quite useful for retrieval operations. If the vessel-end of the marine cable becomes detached from the vessel, the marine cable can be retrieved from the tail buoy end of the cable by using the tow line attached to the tail buoy and the streamer. 
         [0006]    Additionally, the tail buoy commonly contains equipment for receiving data from a positioning system, such as the satellite navigation system known as the Global Positioning System (GPS), processing the data and transmitting the tail buoy&#39;s position information to a tracking system on the vessel. The tail buoy&#39;s positioning data not only provides a means to physically locate the tail buoy but can also be used to assist in determining the actual position of the end of the streamer cable. Increased accuracy in the calculated position of end of the streamer cable, and thereby increased accuracy for the positions of the acoustic sensors in the streamer cable, provides for increased precision in correlating the seismic signals received by the acoustic sensors to actual earth formations. 
         [0007]    Various devices through the streamer require electricity to operate. This electricity is primarily provided from the vessel through the streamer and/or through batteries. Typically the equipment utilized for positioning the streamers and other spread elements such as the seismic source and tail buoys equipped with GPS has been batteries. 
         [0008]    It is therefore a desire to provide an in-sea power generator for providing a source of electricity to the in-sea equipment. It is a still further desire to provide an in-sea power generation that is not propeller driven or provided by solar energy. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the foregoing and other considerations, the present invention relates to a system and method for providing power to seismic equipment from energy harvested from ocean waves. Accordingly, in-sea power generators that do not use a propeller or solar panels and geological survey systems are provided. It is noted that “seismic” is used herein to include traditional seismographic surveys and the like, as well as electromagnetic studies, and the associated equipment. 
         [0010]    A seismic survey system for use in a marine environment having sea waves includes at least one streamer carrying an electrically powered device that is electrically connected to a mechanism for generating electricity from movement of the sea waves. 
         [0011]    A method for conducting seismic operations includes the steps of deploying a seismic streamer carrying an electrically powered device from a vessel into water having waves, providing an in-sea generator in electrical connection with the device, producing electricity from the in-sea generator by harvesting mechanical energy from the waves, and providing the produced electricity to the device. The produced electricity may be provided directly to the devices or stored in a battery, capacitor or other like device. 
         [0012]    The foregoing has outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The foregoing and other features and aspects of the present invention will be best understood with reference to the following detailed description of a specific embodiment of the invention, when read in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a schematic side view illustration of a marine seismic system utilizing elements of the in-sea power generation of the present invention; 
           [0015]      FIG. 2  is a partial sectional view of an example of an in-sea generator of the present invention; 
           [0016]      FIG. 3  is a partial sectional view of another example of an in-sea generator of the present invention; 
           [0017]      FIG. 4  is a partial sectional view of another example of an in-sea generator of the present invention; and 
           [0018]      FIG. 5  is a partial sectional view of another example of an in-sea generator of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0020]      FIG. 1  is a schematic side view illustration of a seismic survey system, generally denoted by the numeral  10 , utilizing in-sea power generation of the present invention. System  10  includes a marine vessel or ship  12 , towing a streamer  14 . Although  FIG. 1  illustrates only one streamer  14 , typically multiple streamers  14  will be deployed to form an array. Streamer  14  may include various elements such as a para-vane  16 , a tail buoy  18 , electrically powered devices  20  (compass, GPS, etc.), and air guns  22 , and one or more in-sea generators  24 . 
         [0021]    Electrically powered devices  20  may include many devices which may be utilized in system  10 , such as, without limitation, acoustic sources  20   c  such as pingers, acoustic receivers  20   d  and hydrophones, navigation systems  20   a , positioning systems  20   b , and various signal transmitters and receivers. The various electrical devices are utilized in various aspects of the marine seismic operations such as deployment of streamers  14  in an array, positioning of the array, ranging, and conducting seismic surveys. In-sea generators  24  are electrically connected with one or more of electrically powered devices  20  to provide primary, supplemental or auxiliary electrical power. Generators  24  may be connected to devices  20  through an electrical storage device such as a battery, or rechargeable battery. 
         [0022]    Vessel  20  deploys streamer  14  via a cable  26  into a body of water  28  having movement designated as sea waves  30 . As is known, sea waves represent movement to some degree throughout the water column. Cable  26  typically provides electrical power from a primary electrical power source  32  located on vessel  20  to at least some of the electrical devices  20  and also provides electrical and/or optical communication between the operations controls  34  on the ship seismic devices. 
         [0023]    Electrical power is not provided to all of the electrical devices  20  via cable  26  at all times. For example, some devices are powered by batteries and some devices  20  require electrical power when power through streamer  14  (cable  26 ) is not available. For example, electrical power is needed for navigation and positioning devices that give headings or distance measures (acoustic ranging) when vessel power is not available. The present invention provides in-sea generator  24  to harvest mechanical energy from the water movement referred to as sea wave movement and convert it to electricity to one or more of devices  20 . 
         [0024]    Para-vane  16  is often deployed on streamer  14  to positioned and maintain streamer  14  is a desired position relative to vessel  20  and other streamers  14 . Para-vane  16  may include electrical powered navigation and/or positioning equipment  20   a . Often devices  20   a  are not powered by vessel  20  or they require electrical power when streamer power is not available. An in-sea generator  24  of the present invention may be deployed in para-vane  16  to provide the auxiliary power required for device  20   a  or other devices  20  positioned along streamer  14 . 
         [0025]    Another example of positioning of in-sea generator  24  is in tail buoy  18 . Tail buoy  18  is commonly provided as a part of a streamer  14  to serve various purposes. Of relevance to the present invention, tail buoy  18  often carries positioning devices  20   b  such as a GPS and communication link, and a large platform for equipment. An in-sea generator  24  may be positioned in buoy  18  and electrically connected to devices  20   b  or other devices positioned along streamer  14 . 
         [0026]    Another example of positioning of in-sea generator  24  is along streamer  14 . An in-sea generator  24  that may be integrated into or as a portion of cable  26  is described in more detail in reference to  FIG. 4 . 
         [0027]    In-sea generator  24  converts the mechanical energy of movement of water body  28 , or more particularly the movement of in-sea generator  24 , into electricity. In-sea generator  24  does not utilize propellers and therefore avoids the disadvantages of propeller operated systems. As is noted, in-sea generator  24  may provide electricity directly to devices  20  or to recharge batteries. 
         [0028]    Refer now to  FIG. 2 , wherein an example of a mechanical differential in-sea generator  24   a  is illustrated. In-sea generator  24   a  includes a rotary generator  36  that is positioned in a housing  38  and a mass or load  40  that is moveably and functionally connected to rotary generator  36 . It should be recognized that housing  38  may be a portion of a device such as buoy  18  or para-vane  16 . Mass  40  is connected to generator  36  via shaft  41  and gear  42 , or other suitable connecting mechanisms. In operation, load  40  moves relative to generator  36  in response to the sea wave motion actuating generator  36  to produce electricity. In-sea generator  24   a  is then electrically connected to at least one electrical device  20 . In-sea generator  24   a  may be connected directly to electrical device  20  or may be connected to a battery or other electrical storage device  44 . In-sea generator  24   a  may further include an interface circuit  46  to selectively supply the generated power when and where needed. 
         [0029]    Refer now to  FIG. 3  wherein a magnetic field in-sea generator  24   b  is illustrated. In-sea generator  24   b  includes a permanent magnet  48  that generates a magnetic field  50 , and a magnetic field sensor or sensing element  52 . Magnetic field sensor  52  includes a first magnetostrictive material layer  54  bonded to a second electroactive layer  56 . First layer  54  responds to variations in magnetic field  50  by generating stress and second layer  56  responds to stress by producing electricity. Magnet  48  is positioned so as to be moveable relative to magnetic field sensor  52  in response to the motion of the sea waves  30 . 
         [0030]    Refer now to  FIG. 4  wherein an example of an elongated in-sea generator  24   c  is provided. In-sea generator includes an elongated, flexible piezoelectric member  58  having a first end  60  and a second end  62 . Member  58  may be formed of a material such as polyvinylidene fluoride (“PVDF”). As illustrated, member  58  may be formed as a portion of cable  26  of streamer  14 . Piezoelectric member  58  produces electricity from stress induced in the member. Wave motion  30  creates a deformation “D” in piezoelectric member  58  which induces stress which is converted into electricity. 
         [0031]    Refer now to  FIG. 5  wherein a micro-electro-mechanical system (MEMS) resonator type in-sea generator  24   d  is illustrated. In-sea generator  24   d  includes a magnetic mass  64  connected to housing  38  by a spring  66  to move in response to wave motion  30 . Magnetic mass  64  is positioned proximate to coil  68  such that the movement of mass  64  induces a voltage in coil  68 . 
         [0032]    From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system and method for generating power for marine seismic equipment based on displacement by ocean waves has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.