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Abstract

The magnetotelluric system for seafloor petroleum exploration comprises a first waterproof pressure case containing a processor, AC-coupled magnetic field post-amplifiers and electric field amplifiers (the 'logger unit'), a second waterproof pressure case containing an acoustic navigation/release system, four silver-silver chloride (Ag-AgCl) electrodes mounted on booms and at least two magnetic induction coil sensors. These elements are mounted together on a plastic and aluminum frame along with flotation devices and an anchor for deployment to the seafloor. The acoustic navigation/release system serves to locate the system by responding to acoustic pings generated by a ship-board unit and receives a release command which initiates detachment from the anchor so that the buoyant package floats to the surface for recovery. The electrodes used to detect the electric field are configured as grounded dipole antennas. Booms by which the electrodes are mounted onto frame are positioned in an 'X' configuration to create two orthogonal dipoles, which are used to measure the complete vector electric field. The magnetic field sensors are multi-turn Mu-metal core coils which detect within the frequency range typically used for land-based MT surveys. The magnetic field coils are encased in waterproof pressure cases and are connected to the logger package by high pressure waterproof cables. The logger unit includes the amplifiers for amplifying the signals received from the various sensors, which signals are then provided to the processor which controls timing, logging, storing and power switching operations. Temporary and mass storage is provided within and/or peripheral to the processor.

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First Claim