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US 7,683,625 B2Granted
Electromagnetic surveying
AssigneeOHM Limited
InventorsJames Milne, Jennifer Rust, Chris Sykes, Mark Bennett
Life of this patent
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Abstract
A submersible electromagnetic (EM) field generator for seafloor electromagnetic surveying comprising an AC to DC converter operable to generate a DC output from an AC input and a switching module operable to generate a waveform driving signal by selectively switching the DC output. The EM field generator also comprises an antenna that is operable to generate an EM field in response to the waveform driving signal. This design approach of using a switched DC source allows square or rectangular wave EM signals to be generated which have sharp transition characteristics and which are substantially independent of the AC input characteristics.
Claims36
A submersible electromagnetic (EM) field generator for seafloor electromagnetic surveying, comprising:
- an AC to DC converter operable to generate first and second DC outputs from an AC input as positive and negative DC signals on the first and second DC outputs;
- a switching module operable to generate a tristate waveform driving signal of a desired functional form by selective switching of the first and second DC outputs, the switching module comprising a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair;
- an antenna formed by first and second antenna electrodes connected to the first and second waveform output electrodes respectively, wherein the antenna electrodes are spaced apart along the length of the antenna and separated from each other by seawater when submerged, wherein said selective switching of the first and second DC outputs switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate an EM field in response to the waveform driving signal that follows the desired functional form defined by said selective switching;
- and
- a controller that is operable to control selective switching of the switching module so as to generate the tristate waveform driving signal.
2 more elements
A method of generating an electromagnetic (EM) field for seafloor electromagnetic surveying, comprising:
- providing an AC signal;
- generating first and second DC outputs from the AC signal as positive and negative DC signals on the first and second DC outputs;
- generating a waveform driving signal of a desired functional form by selective switching of the positive and negative DC signals using a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair, wherein the waveform driving signal is a tristate waveform driving signal produced by generating a sequence of forward currents, reverse currents and zero currents between the first and second waveform output electrodes;
- and
- driving an electric dipole antenna formed by a pair of antenna electrodes connected to respective ones of the waveform output electrodes with the waveform driving signal to generate the EM field, wherein the antenna electrodes are spaced apart along the length of the antenna and submerged in seawater, wherein said selective switching of the first and second DC signals switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate the EM field following the desired functional form defined by said selective switching.
2 more elements
A method for obtaining hydrocarbon from an area that contains a subterranean hydrocarbon reservoir, comprising:
- providing survey data from an electromagnetic survey of the area performed using a submersible electromagnetic (EM) field generator comprising:
- an AC to DC converter operable to generate first and second DC outputs from an AC input as positive and negative DC signals on the first and second DC outputs;
- a switching module operable to generate a tristate waveform driving signal of a desired functional form by selective switching of the first and second DC outputs, the switching module comprising a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair;
- an antenna formed by first and second antenna electrodes connected to the first and second waveform output electrodes respectively, wherein the antenna electrodes are spaced apart along the length of the antenna and separated from each other by seawater when submerged, wherein said selective switching of the first and second DC outputs switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate an EM field in response to the waveform driving signal that follows the desired functional form defined by said selective switching;
- and
- a controller that is operable to control selective switching of the switching module so as to generate the tristate waveform driving signal;
- the method further comprising:
- analyzing the survey data to identify the subterranean hydrocarbon reservoir;
- penetrating the subterranean hydrocarbon reservoir with a hydrocarbon-producing well;
- and
- extracting hydrocarbon from the subterranean hydrocarbon reservoir using the hydrocarbon-producing well.
8 more elements
A method of obtaining a results data set representing an area that is thought or is known to contain a subterranean hydrocarbon reservoir, the method comprising:
- performing an electromagnetic survey of the area using a submersible electromagnetic (EM) field generator comprising:
- an AC to DC converter operable to generate first and second DC outputs from an AC input as positive and negative DC signals on the first and second DC outputs;
- a switching module operable to generate a tristate waveform driving signal of a desired functional form by selective switching of the first and second DC outputs, the switching module comprising a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair;
- an antenna formed by first and second antenna electrodes connected to the first and second waveform output electrodes respectively, wherein the antenna electrodes are spaced apart along the length of the antenna and separated from each other by seawater when submerged, wherein said selective switching of the first and second DC outputs switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate an EM field in response to the waveform driving signal that follows the desired functional form defined by said selective switching;
- and
- a controller that is operable to control selective switching of the switching module so as to generate the tristate waveform driving signal;
- and
- generating the results data set based on data obtained during the survey.
5 more elements
An electromagnetic (EM) field generation system for seafloor electromagnetic surveying, comprising:
- a submersible electromagnetic (EM) field generator for seafloor electromagnetic surveying, comprising:
- an AC to DC converter operable to generate first and second DC outputs from an AC input as positive and negative DC signals on the first and second DC outputs;
- a switching module operable to generate a tristate waveform driving signal of a desired functional form by selective switching of the first and second DC outputs, the switching module comprising a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair;
- an antenna formed by first and second antenna electrodes connected to the first and second waveform output electrodes respectively, wherein the antenna electrodes are spaced apart along the length of the antenna and separated from each other by seawater when submerged, wherein said selective switching of the first and second DC outputs switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate an EM field in response to the waveform driving signal that follows the desired functional form defined by said selective switching;
- and
- a controller that is operable to control selective switching of the switching module so as to generate the waveform driving signal;
- a power source operably coupled to the AC to DC converter of the electromagnetic field generator;
- and
- a control module operably coupled to the controller of the submersible electromagnetic field generator;
- wherein the control module is operable to control the waveform driving signal that drives the antenna, wherein the control module is operably coupled to a global positioning satellite (GPS) receiver, and is further operable to generate a clock signal in synchronization with a GPS transmitter signal, and wherein the control module is operable to supply a data gathering module with the clock signal.
7 more elements
Dependencies are inferred from the claim text.