A system for determining the nature of a subterranean reservoir 12 whose position and geometry is known from previous seismic surveys. An electromagnetic field 24, 25, 26, 27 is applied by a transmitter 18 on the seabed 14 and detected by antenna 21, 22,23 also on the seabed 14. The nature of the detected reflected ...

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 signa...

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 subte...

Multifrequency electromagnetic signals which may be used in the field of sea bed logging, the signal being optimised for use at a particular site, in order to greatly improve data inversion, and a method for producing the optimum multifrequency signal.

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 additi...

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 m...

A system for detecting a subterranean reservoir or determining the nature of a subterranean reservoir (35) whose position and geometry is known from previous seismic surveys. An electromagnetic field (42,43) is applied by a transmitter (37) on the seabed (33) and detected by antenna (38) also on the seabed (33). A ...

A method of determining the nature of subterranean strata. The transmitter antenna (11) is towed by vessel (12) at a distance h above the sea floor (13). The antenna (11) in its wave field whose strength is proportional to the current delivered to the antenna (11) and this is monitored. The input voltage to the ante...