Subsea hydrocarbon sensor system

DETAILED DESCRIPTION What is claimed is: 1.
In a subsea hydrocarbon production installation which includes at least first and second production tree assemblies spaced apart on the sea floor, at least one electro-hydraulic control module located at the sea floor at a substantial distance from at least said first tree assembly, and a plurality of elongated cables extending from said module to at least said first tree assembly for conducting tree-assembly condition indicative signals from said first tree assembly to said control module and other signals from said module to said first tree assembly and in which said cables are coupled to said control module by means of magnetic coupling devices which permit physical removal of said module from the sea floor without exposing current carrying conductors to the sea-water environment, a hydrocarbon-leak detecting and reporting subsystem comprising: means contained within said control module for providing a frequency-modulated interrogation signal with the frequency of said signal varying as a function of time over a preselected frequency range; means comprising at least one of said cables and at least one of said magnetic coupling devices for conducting said signal to said first tree assembly; hydrocarbon-presence-responsive sensor means, located adjacent a portion of the hydrocarbon-containing equipment of said first tree assembly, for transmitting and attenuating said signal as a predetermined function of the amount of hydrocarbon compounds in an environmental medium adjacent said sensor means; means comprising at least one of said cables and one of said magnetic coupling devices for conducting said attenuated signal to the interior of said control module; a peak detector in said module responsive to said attenuated signal for producing a hydrocarbon-presence-indicative electrical signal whose amplitude is substantially independent of resonant frequency variations of said sensor means; and means responsive to the signal produced by said peak detector for communicating hydrocarbon-presence-indicative intelligence signals to a sea-surface or land-based facility