Abstract: An EM receiver instrument suitable for making underwater electric field measurements. The EM receiver comprises a dipole antenna; an AM modulator for applying modulation to a signal detected by the antenna; a fiber-optic voltage sensor and an application of AM demodulator for applying demodulation to the signal. The fiber-optic sensor may be an interferometric voltage sensor or a phase sensitive voltage sensor.

Abstract: A passive listening acoustic system and method of use may include source means for providing continuous, pulsed, or pulse coded acoustic signals at two or more frequencies and at least two acoustic sensors or hydrophones which detect and record a signal for use within a Seabed Logging system to determine the position and/or orientation of instruments in the system.

Abstract: A method for measuring an enhanced electromagnetic field response, especially in a submarine environment, for the purposes of subsurface data acquisition and processing. An electromagnetic field is applied to subterranean strata at two or more different frequencies, a response at each frequency is detected, and the responses at different frequencies are resolved. The differences in the phase and/or amplitude of the responses are analyzed and the nature of the strata is determined. The same method can be used to determine the hydrocarbon content of a reservoir via the use of a borehole.

Abstract: A submersible high current PWM-based source system for marine electromagnetic surveying for hydrocarbon exploration. The system converts a periodic, arbitrary digital signal to a high output current in a HED optimized for maximum dipole moment, using PWM modulation and real-time current regulation for precise output amplitude. The design and choice of components allows a wideband EM signal to be generated with sharp transition characteristics and substantially independent of the AC input power characteristics. This in turn enables for improved tailoring of an EM source signal for a specific subterranean prospect, and thus increased accuracy of the EM data.

Abstract: An EM receiver instrument suitable for making underwater electric field measurements. The EM receiver comprises a dipole antenna; an AM modulator for applying modulation to a signal detected by the antenna; a fiber-optic voltage sensor and an application of AM demodulator for applying demodulation to the signal. The fiber-optic sensor may be an interferometric voltage sensor or a phase sensitive voltage sensor.

Abstract: A method for measuring an enhanced electromagnetic field response, especially in a submarine environment, for the purposes of subsurface data acquisition and processing. An electromagnetic field is applied to subterranean strata at two or more different frequencies, a response at each frequency is detected, and the responses at different frequencies are resolved. The differences in the phase and/or amplitude of the responses are analyzed and the nature of the strata is determined. The same method can be used to determine the hydrocarbon content of a reservoir via the use of a borehole.

Abstract: A device and method for measuring electromagnetic signals that can be used to take measurements at or near the sea floor. The device comprises a central housing, a data management system located within the housing and at least two arms extending outwards from the housing. Each arm comprises a flexible elongate sheath attached to the housing, a sensor head, a flexible electrical cable attached to the sheath and connecting the sensor head to the data management system and a rod which is removeably locatable within the sheath. The rod is connectable relative to the housing at one end and connectable relative to the sensor head at the end remote from the housing.

Abstract: A system for determining the position and/or orientation of electromagnetic receivers in a network of receiver instruments at a remote location, a first receiver instrument including one or more electromagnetic sensors, the system comprising transmitting means to send a characteristic signal, detecting means to detect transmitted signals from a plurality of receiver instruments, depth measurement means to measure the depth of the first instrument, recording means to store data from the transmitting means, the detecting means and the depth measurement means, and processing means for processing data from the receiver instruments.

Abstract: A passive listening acoustic system and method of use may include source means for providing continuous, pulsed, or pulse coded acoustic signals at two or more frequencies and at least two acoustic sensors or hydrophones which detect and record a signal for use within a Seabed Logging system to determine the position and/or orientation of instruments in the system.

Abstract: A method of producing a survey report on the presence and nature of a subterranean strata: includes simultaneously towing an EM field transmitter and a seismic source behind a vessel, towing at least one streamer behind the vessel, said streamer or streamers having EM field receivers for measuring an electric field and seismic receivers for measuring a seismic response, applying an EM field to the strata using the EM field transmitter and detecting an EM field response using the EM field receivers, applying a seismic event to the strata using the seismic source and detecting the seismic response using the seismic receivers, analysing the EM field response, analysing the seismic responses and reconciling the EM field response and the seismic response to produce the survey report.