Abstract:
A self-righting buoy having an oil/water sensor is provided which includes a radio transmitter or signaling beacon to trail a loading hose or a potential source of leaking oil, such as a FPSO, down current for remote detection of oil sheens.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
     The priority of U.S. Provisional Application No. 60/079,284 filed on Mar. 25, 1998 is claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of offshore transfer of hydrocarbons from a subsea well to a Floating Oil Storage or Production (FPSO) Vessel or between a pipeline and a CALM buoy and swivel and a tanker. In particular, the invention concerns detection of floating oil on the sea surface where the oil leaks from the connection of an oil conduit connected between an oil storage vessel for subsea wells or between a tanker and a subsea pipeline. 
     2. Description of the Prior Art 
     Environmental concerns make it increasingly important that any oil that might be leaking from a connection of an oil transfer riser to a storage or production vessel or between a tanker and a subsea pipeline be quickly detected in order that corrective action may be taken immediately. 
     Oil-in-water detection apparatus exists for determining the presence of hydrocarbons floating on water. For example AGAR Technologies, Ltd. of Houston, Tex., commercially offers an oil-in-water sensor based on the principle of electromagnetic absorption. Such sensor comprises a very high frequency transmitter connected to a mismatched antenna. The antenna is immersed in water with oil floating on it. The higher the energy absorption of the fluid, the more the loading of the antenna, and therefore, the more energy which must be applied to the transmitter. Water absorbs much more energy than does oil (or other insulating materials such as air, glass, plastic, etc.). If the antenna is surrounded by an oil/water mixture, the loading is proportional to the water content. Thus, an instrument based upon antenna loading is capable of detecting very small thickness oil sheens floating on water. It is also capable of monitoring the thickness of a layer of oil on water. 
     The AGAR Company mentioned above commercially provides a flotation device or buoy on which a sensor as described above is mounted. Such flotation device is designed for offshore waters near oil tanker terminals to detect floating oil sheens resulting from spills or leaks which may occur during the loading/unloading process of tankers. Nevertheless, several deficiencies have been identified with AGAR arrangement when used in certain mooring applications. 
     The AGAR buoy is connected to a vessel by a tether which includes an electrical cable, typically 10 min length. Such cable provides electrical power to the oil/water sensor mounted on the buoy and provides a signal path between the sensor and the tanker. But, an electrical cable running between the vessel and the AGAR buoy has safety deficiencies where oil spills are involved. Furthermore, the AGAR buoy on which its sensor is mounted is not self-righting which is a disadvantage where extremely rough seas are encountered. 
     In view of the disadvantages identified above, the AGAR buoy and sensor is not ideally suitable for the detection of oil leaking into the sea for a tanker vessel moored to a CALM buoy or to a single point mooring loading system for a floating oil storage or production vessel, because it is dependent on an electrical cable for power and communication and its buoy configuration is not self-righting. 
     3. Identification of Objects of the Invention 
     A primary objective of this invention is to provide an improved oil-in-water detector buoy for detecting oil on the surface of the sea where offshore single point mooring terminals are being utilized. Due to the natural orientation behavior of a ship at a single point mooring, all oil leakage or spills will eventually be carried by the ocean current and/or winds which is orienting the ship, past a buoy tethered to the ship and held down-current by the same ocean currents. Leakage from the subsea risers and both subsea and floating hoses and the mechanical components of the terminals will be carried to the buoy by the ocean currents. 
     A further object of the invention is to provide an oil-in-water detector that is self powered, transmits its oil/water information via radio to a ship board antenna, and is mounted on a self-righting buoy capable of withstanding high seas. 
     SUMMARY OF THE INVENTION 
     An oil-in-water detector is mounted on a self-righting buoy which is battery powered and includes an electromagnetic antenna for transmitting radio signals representative of the oil/water ratio sensed by the detector. In one embodiment the heavy batteries are mounted in a bottom pod of the buoy thereby contributing to the self-righting characteristics of the buoy. In another embodiment, concrete or other heavy ballast material is provided in the bottom pod, and the batteries are placed at other locations of the buoy. The oil/water detector may be tethered behind a FPSO vessel or behind the “U” of floating hoses of a tanker moored and loaded via a CALM system. The oil/water detector buoy may be tethered to any offshore or water location requiring oil detection where the combined features of self-contained powering, self righting and radio transmitted signals are desired over existing units which do not offer these features. Such locations include use with a spread moored vessel, a marine loading arm terminal, a pier or jetty or an offshore floating or fixed structure for a hydrocarbon well. Alternatively, a beacon signal such as a strobe light or horn may be used in place of a radio transmitted signal on the oil/water detector buoy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, advantages, and features of the invention will become more apparent by reference to the drawings which are appended hereto and wherein like numerals indicate like parts and wherein an illustrative embodiment of the invention is shown, of which: 
     FIG. 1 is a diagrammatic illustration of a buoy-mounted oil/water detector trailing a storage vessel which is moored at sea and is configured to load oil via a subsea riser system from a subsea well; 
     FIG. 2 is an enlarged illustration of the oil/water detection buoy; 
     FIG. 3 is an illustration of the invention where an oil/water detection buoy is tethered down current of the “U” position where floating hoses enter a tanker moored by a CALM buoy at an offshore loading/unloading terminal; and 
     FIG. 4 is an illustration of the invention where the oil/water detection buoy is tethered to the end of floating hoses of a CALM buoy and further illustrating an alternative beacon on the buoy. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 illustrate an oil/water detector system  30  mounted on a buoyant buoy  50  which is connected to a Floating Production and Storage (FPSO) Vessel  5 . Such vessel may be moored as in FIG. 1 where the vessel  5  floats on the sea surface  7  and is rotatably secured to a turret system  10  which is anchored by anchor legs  22  to anchors  28  on the sea bead  90 . A riser  24  is connected between a subsea well  17  and the turret system  10 . The mooring system of FIG. 1 may be of the disconnectable type or the storage vessel  5  may be permanently moored via a turret or other single point mooring device. Oil that spills from the connection of riser  24  to the vessel may be detected with oil/water detector buoy  30 . 
     The oil/water detector buoy  30  of the invention is tethered by means of a line or tether  34  behind a vessel  5 . If hydrocarbons leak from the riser  24  or turret  10 , such hydrocarbons will flow past the stem of the vessel  5  due to the sea currents and/or wind into which the vessel is heading. The oil/water detector buoy will be in the path of such hydrocarbons, because as the vessel  5  weathervanes about turret  10 , the oil/water detector trails the vessel and remains in the path of the floating hydrocarbons. 
     FIGS. 1 and 2 illustrate the salient features of the oil/water detector according to the invention. The buoy  30  is configured to be a self-righting buoy in order to survive heavy seas. Buoyancy of the buoy is provided with flotation material or by water-tight, air-filled spaces. The sensor  60  is electrically powered by on-board batteries  52 , which as illustrated in FIG. 2, are mounted in a bottom pod  36  of the buoy  50 . Alternatively, bottom pod  36  may be filled with a heavy material such as concrete for ballasting the buoy  50  with the batteries placed elsewhere on the buoy. 
     An oil/water sensor  60 , is placed in a channel  54  through which sea water (possibly contaminated by leaking hydrocarbon crude oil) passes through. The channel  54  is designed in coordination with the buoyancy of the buoy  50  to be at the same height as the sea surface  7 . The sensor  60  preferably includes a very high frequency transmitter connected to a mismatched antenna submerged in the sea water  7 . The principle of operation of the sensor is the same as that of an AGAR LEAKWISE® ID-227 Oil Sheen Monitoring System sold by AGAR Technologies, Ltd. of Houston, Tex. 
     The sensor  60  is powered by batteries  52  which are mounted and self contained on the buoy  50  as explained above. Dashed line  82  schematically indicates the power communication path between batteries  52 , sensor  60  and an electronics module  80  which is coupled to sensor  60  and to batteries  52  for measuring the oil/water ratio of sea water in channel  54 . Electronic module  80  is arranged and designed to apply a signal representative of that ratio to an electromagnetic antenna  32 , whereby radio waves  40  are broadcast for being received by antenna  38  and receiving electronics  36  on board vessel  5 . 
     FIG. 3 illustrates a CALM buoy  50  to which a tanker  100  is tethered by mooring lines  51 . Such lines  51  may be rigid or flexible. Loading hoses  70  run from a conduit  56  to swivel  54  of buoy  50 . The tanker may be arranged for unloading hydrocarbons to a pipeline  56  or conduit  56  may be a riser from a subsea well for transferring hydrocarbons to a storage vessel. Floating hoses  60  run from swivel  54  to the side of the vessel  100  to storage holds in the vessel. A portion of the loading hoses  60  form a “U”-shape  62 , as they enter the vessel  100 . For the arrangement of FIG. 3, it is preferred to tether the oil/water detector buoy  30  at the “U”-shape  62  of floating hoses  60 . This arrangement advantageously places the buoy  30  in the path of any oil leaking from loading hoses  70 , swivel  54  or floating hoses  60 . A control module  36 ′ and antenna  38 ′ on vessel  100  provide communication between oil/water buoy  30  and vessel  100  via antennas  32  and  38 ′. Alternatively, oil/water detector buoy  30  may be tethered from the side of the vessel  100  as a rail tethered buoy  30 ′, where the tether is connected on the down current end (that is stem end) of the vessel as compared to the position where the floating hoses  60  enter the vessel. 
     The oil/water detector buoy  30  may be used at other locations and in alternative arrangements. For example, the detector buoy may detect oil from an oil source down current from a spread moored vessel, a marine loading arm terminal, a pier or jetty, or an offshore floating or fixed structure for a hydrocarbon well. FIG. 4 illustrates one example of such alternative arrangements. A CALM buoy  500  is anchored to the sea floor by anchor legs  530 . A riser  560  extends from a subsea well  580  to a swivel  540  of the buoy  500 . A loading hose  600  floats on the sea surface down current, until it is needed for coupling with a storage vessel. While in the condition of FIG. 4, an oil/water sensor buoy  30 ″ is tethered to the end of loading hose  600  which places it in the path of any oil leaking from the swivel  540  or the hose  600 . Alternative to the electromagnetic antenna of the buoy  30  in FIG. 2, other signal producing devices can be connected to the sensor  60  and electronics module  80  of the buoy  30 ″. For example, a strobe light  700  may be provided, or a horn could be provided, to alert personnel from passing ships or planes or the like that oil is leaking from the buoy  500 , swivel  540  or hose  600 . 
     While preferred embodiments of the present invention have been illustrated and/or described in some detail, modifications and adaptions of the preferred embodiments will occur to those skilled in the art. Such modifications and adaptations are within the spirit and scope of the present invention.