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 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 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 concrete formulation, which undergoes controlled deterioration in water, that can be used for making anchors for releasably tethering submarine devices at the seabed. The anchor may have handles for a device release mechanism or a central hole for a central device release mechanism. The formulation includes additives, which cause the cement to transform into non-binding Thaumasite over a pre-set period of time, leaving only natural material on the seafloor.

Abstract: A source arrangement for generating electrogmagnetic (EM) wavefields, comprising an EM signal generator, at least three electrodes (141-144) connected to the generator, and a control system. The electrodes are spaced apart but not all in line. The control system is arranged to apply non-coincident time-varying signals or transmissions from the generator between different pairs of the electrodes. The non-coincidence can be by applying the signals sequentially or by applying the signals out of phase.

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 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.

Abstract: A system for investigating subterranean strata. An electromagnetic field and a seismic event are applied from the same location and the responses are detected using respective receivers both located at a second location spaced from the first. The responses are combined to identify the presence and/or nature of subterranean reservoir. The refracted wave components are used.

Abstract: A concrete formulation, which undergoes controlled deterioration in water, that can be used for making anchors for releasably tethering submarine devices at the seabed. The anchor may have handles for a device release mechanism or a central hole for a central device release mechanism. The formulation includes additives, which cause the cement to transform into non-binding Thaumasite over a pre-set period of time, leaving only natural material on the seafloor.

Abstract: An electromagnetic survey method for surveying an area previously identified as potentially containing a subsea hydrocarbon reservoir, comprising obtaining first and second survey data sets with an electromagnetic source aligned end-on and broadside relative to the same or different receivers. The invention also relates to planning a survey using this method, and to analysis of survey data taken in combination allow the galvanic contribution to the signals collected at the receiver to be contrasted with the inductive effects, and the effects of signal attenuation, which are highly dependent on local properties of the rock formation, overlying water and air at the survey area. This is very important to the success of using electromagnetic surveying for identifying hydrocarbon reserves and distinguishing them from other classes of structure.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: The present invention relates to a system and apparatus for detecting and recovering hydrocarbons located in a subterranean reservoir In some embodiments, an electromagnetic field is applied by a transmitter positioned on a seabed and detected by antenna also positioned on the seabed.

Abstract: A system for investigating subterranean strata. An electromagnetic field and a seismic event are applied from the same location and the responses are detected using respective receivers both located at a second location spaced from the first. The responses are combined to identify the presence and/or nature of subterranean reservoir. The refracted wave components are used.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: A method for mapping a submarine or subterranean reservoir by conducting an electromagnetic survey using an electromagnetic field in the form of a wave. An electromagnetic field is applied by a transmitter on the seabed and detected by antennae. The nature of the detected reflected waves is used to determine whether the reservoir contains water or hydrocarbons, which may then be produced from a well that penetrates the reservoir.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. Phase information is extracted from a refracted wave response and used to identify the presence and/or nature of a subterranean reservoir.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a fixed dipole antenna transmitter and this is detected using a dipole antenna receiver. The receiver is moved from one location to another in dependence upon the strength of the detected signal.

Abstract: Methods and devices are disclosed for determining if hydrocarbons or water is present in a subterranean reservoir are described. Certain embodiments involve an electromagnetic field applied by a transmitter on the seabed and detected by at least one antenna also on the seabed, wherein a refracted wave component is sought in the wave field response, and is analyzed to determine the nature and contents of the resevoir.