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.
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.
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 xe2x80x9cUxe2x80x9d 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.