Abstract: A marine survey node can include a body to be deployed to a seabed, a marine survey receiver coupled to the body and to acquire marine survey data, and a soil sample module associated with the body to collect a soil sample from the seabed. A soil sample module can include a vessel, a first valve coupled to the vessel, and a spike coupled to the vessel. The spike can penetrate an earth surface. The first valve can maintain a pressure difference between the vessel and the spike when closed and equalize a pressure between the vessel and the spike when open. An inlet in the spike can equalize pressure between an inside of the spike and an outside of the spike and to collect a soil sample from the earth surface.

Abstract: A marine survey node can include a body to be deployed to a seabed, a marine survey receiver coupled to the body and to acquire marine survey data, and a soil sample module associated with the body to collect a soil sample from the seabed. A soil sample module can include a vessel, a first valve coupled to the vessel, and a spike coupled to the vessel. The spike can penetrate an earth surface. The first valve can maintain a pressure difference between the vessel and the spike when closed and equalize a pressure between the vessel and the spike when open. An inlet in the spike can equalize pressure between an inside of the spike and an outside of the spike and to collect a soil sample from the earth surface.

Abstract: A marine survey system can include a first cable including a first end configured to be coupled to a direct current (DC) power supply on a marine survey vessel and a support module coupled to a second end of the first cable and configured to receive power therefrom. A first electrode of towable electromagnetic (EM) source equipment can be coupled to the support module and configured to receive power therefrom. A depth control device can be coupled to the first electrode and configured to control a depth of the first electrode. A first end of a second cable can be coupled to the support module and configured to receive power therefrom. A second electrode of the towable EM source equipment can be coupled to a second end of the second cable and configured to receive power therefrom.

Abstract: Techniques are disclosed relating to electrical safety systems that may be useful, for example, in electromagnetic geophysical prospecting. Electromagnetic streamer systems often include a number of electrical loads in series that are powered by a constant-current power supply unit. Known techniques for detecting electrical faults have various drawbacks in such an arrangement. Embodiments of this disclosure may be used to mitigate some or all of such drawbacks.

Abstract: A marine survey system can include a first cable including a first end configured to be coupled to a direct current (DC) power supply on a marine survey vessel and a support module coupled to a second end of the first cable and configured to receive power therefrom. A first electrode of towable electromagnetic (EM) source equipment can be coupled to the support module and configured to receive power therefrom. A depth control device can be coupled to the first electrode and configured to control a depth of the first electrode. A first end of a second cable can be coupled to the support module and configured to receive power therefrom. A second electrode of the towable EM source equipment can be coupled to a second end of the second cable and configured to receive power therefrom.

Abstract: Embodiments described herein provide an EM source cable assembly with a buoyant member having first and second ends, and a longitudinal axis connecting the first end to the second end, and a plurality of indentations disposed along a surface of the buoyant member between the first end and the second end, wherein the indentations are operable to receive corresponding cables. The indentations extend along the longitudinal axis, and may be arranged helically about the longitudinal axis. The buoyant member may have a low density core material and a dense outer material, each of which may be a polymeric material. The low density material may be a foam, and the buoyant member may be formed by coextruding the low density material and the dense outer material.

Abstract: Techniques are disclosed relating to electrical safety systems that may be useful, for example, in electromagnetic geophysical prospecting. Electromagnetic streamer systems often include a number of electrical loads in series that are powered by a constant-current power supply unit. Known techniques for detecting electrical faults have various drawbacks in such an arrangement. Embodiments of this disclosure may be used to mitigate some or all of such drawbacks.

Abstract: A method and apparatus for generating an electromagnetic (EM) field from a sub-sea source is disclosed. In one embodiment, a sub-sea source includes a step-down transformer coupled to receive a sinusoidal source wave via a tow cable, and is further coupled to output a sinusoidal wave to a silicon-controlled rectifier (SCR) circuit. A control circuit coupled to the SCR circuit is configured to selectively activate various ones of the SCRs therein in order to control a portion of the sinusoidal wave that is rectified. The output current provided by the SCR is determined by the portion of the sinusoidal wave that is rectified thereby. The output current is provided to electrodes coupled to the sub-sea source, and the output current is passed therebetween. The strength of the EM field is based on the output current.

Abstract: Embodiments described herein provide an EM source cable assembly with a buoyant member having first and second ends, and a longitudinal axis connecting the first end to the second end, and a plurality of indentations disposed along a surface of the buoyant member between the first end and the second end, wherein the indentations are operable to receive corresponding cables. The indentations extend along the longitudinal axis, and may be arranged helically about the longitudinal axis. The buoyant member may have a low density core material and a dense outer material, each of which may be a polymeric material. The low density material may be a foam, and the buoyant member may be formed by coextruding the low density material and the dense outer material.

Abstract: A method and apparatus for generating an electromagnetic (EM) field from a sub-sea source is disclosed. In one embodiment, a sub-sea source includes a step-down transformer coupled to receive a sinusoidal source wave via a tow cable, and is further coupled to output a sinusoidal wave to a silicon-controlled rectifier (SCR) circuit. A control circuit coupled to the SCR circuit is configured to selectively activate various ones of the SCRs therein in order to control a portion of the sinusoidal wave that is rectified. The output current provided by the SCR is determined by the portion of the sinusoidal wave that is rectified thereby. The output current is provided to electrodes coupled to the sub-sea source, and the output current is passed therebetween. The strength of the EM field is based on the output current.

Abstract: A method for communicating with a receiver during an electromagnetic survey. In one implementation, the method may include sending a survey signal to a subsurface region, wherein the survey signals is a first electromagnetic signal and sending a diagnostic signal to the receiver. The diagnostic signal is a second electromagnetic signal having a diagnostic message.

Abstract: A method for determining a formation electrical property under a sea floor includes obtaining measurement data using a receiver having an impedance lower than an impedance of seawater at a measurement site; correcting the measurement data to obtain corrected data corresponding to data that would have been acquired using a receiver having an impedance matched with the impedance of the seawater; and deriving the formation property from the corrected data.

Abstract: A method for communicating with a receiver during an electromagnetic survey. In one implementation, the method may include sending a survey signal to a subsurface region, wherein the survey signals is a first electromagnetic signal and sending a diagnostic signal to the receiver. The diagnostic signal is a second electromagnetic signal having a diagnostic message.

Abstract: Multiple sources are provided for a transmitter cable for use in electromagnetic surveying. The transmitter cable includes a dipole antenna comprising a pair of spaced apart electrodes mounted on their respective cables. Two antennas may be powered from each source. Alternatively, the outputs of each source are connected to a common antenna pair. A single large power supply may be mounted on a vessel to supply power through the tow cable. Alternatively, a number of power supplies may be provided aboard the vessel, with each power supply having dedicated conductors through the tow cable to power the plurality of current sources.

Abstract: A receiver for electromagnetic measurements includes a polyhedron structure having m faces, where m?4 and m?6: n electrodes each disposed on one face of the polyhedron structure, wherein 3?n?m; and at least one circuitry connected to the n electrodes for signal measurement. A method for electromagnetic measurements includes obtaining a plurality of electric current measurements using a plurality of electrodes each disposed on a surface of a polyhedron receiver, wherein the plurality of electric current measurements comprise at least three different measurements; and determining electric field components in a three dimensional space from the plurality of electric current measurements by using a number of matrices that correlate orientations of surfaces of the polyhedron receiver to a coordinate system in the three dimensional space.

Abstract: A receiver for electromagnetic measurements includes a polyhedron structure having m faces, where m?4 and m?6: n electrodes each disposed on one face of the polyhedron structure, wherein 3?n?m; and at least one circuitry connected to the n electrodes for signal measurement. A method for electromagnetic measurements includes obtaining a plurality of electric current measurements using a plurality of electrodes each disposed on a surface of a polyhedron receiver, wherein the plurality of electric current measurements comprise at least three different measurements; and determining electric field components in a three dimensional space from the plurality of electric current measurements by using a number of matrices that correlate orientations of surfaces of the polyhedron receiver to a coordinate system in the three dimensional space.

Abstract: A method for determining a formation electrical property under a sea floor includes obtaining measurement data using a receiver having an impedance lower than an impedance of seawater at a measurement site; correcting the measurement data to obtain corrected data corresponding to data that would have been acquired using a receiver having an impedance matched with the impedance of the seawater; and deriving the formation property from the corrected data.

Abstract: Multiple sources are provided for a transmitter cable for use in electromagnetic surveying. The transmitter cable includes a dipole antenna comprising a pair of spaced apart electrodes mounted on their respective cables. Two antennas may be powered from each source. Alternatively, the outputs of each source are connected to a common antenna pair. A single large power supply may be mounted on a vessel to supply power through the tow cable. Alternatively, a number of power supplies may be provided aboard the vessel, with each power supply having dedicated conductors through the tow cable to power the plurality of current sources.

Abstract: Multiple sources are provided for a transmitter cable for use in electromagnetic surveying. The transmitter cable includes a dipole antenna comprising a pair of spaced apart electrodes mounted on their respective cables. Two antennas may be powered from each source. Alternatively, the outputs of each source are connected to a common antenna pair. A single large power supply may be mounted on a vessel to supply power through the tow cable. Alternatively, a number of power supplies may be provided aboard the vessel, with each power supply having dedicated conductors through the tow cable to power the plurality of current sources.

Abstract: Multiple sources are provided for a transmitter cable for use in electromagnetic surveying. The transmitter cable includes a dipole antenna comprising a pair of spaced apart electrodes mounted on their respective cables. Two antennas may be powered from each source. Alternatively, the outputs of each source are connected to a common antenna pair. A single large power supply may be mounted on a vessel to supply power through the tow cable. Alternatively, a number of power supplies may be provided aboard the vessel, with each power supply having dedicated conductors through the tow cable to power the plurality of current sources.