Measuring seawater capacitance in three dimensions as well as time
First Claim
1. A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plumes in seawater, the method comprising:
- towing a streamer array having three or more vertically stacked streamer cables at three or more depths, respectively, through a seawater column containing a hydrocarbon plume;
energizing two or more transmitter electrodes on each streamer cable with an electrical current signal, the transmitter electrodes injecting electrical current into the seawater column;
episodically turning off transmission of the electrical current signal;
arranging a plurality of receiver electrodes on each streamer cable into one or more receiver sets, each receiver set sampling a volume of seawater surrounding it and detecting any returned secondary signals produced by a capacitive effect resulting from injecting the electrical current into the seawater column and turning off the transmission of the electrical current signal, and each receiver set successively sampling a larger volume of water as the receiver sets are positioned further away from the transmitter electrodes;
processing the returned secondary signals, for each adjacent pair of receiver sets, by subtracting the smallest volume of seawater from the next smallest volume of seawater to yield a capacitance value of a donut-shaped sampling volume of seawater outside the smallest volume, the receiver sets positioned further away from the transmitter electrodes providing increasingly larger donut-shaped sampling volumes of sampling data of the capacitance of the seawater column through which the streamer cables are towed;
processing and geometrically correcting the capacitance values of the donut-shaped sampling volumes of seawater to yield a frequency-varying final seawater capacitance value for the volume of seawater sampled by each receiver set; and
mapping and characterizing the hydrocarbon plume using the final seawater capacitance values of the receiver sets.
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Accused Products
Abstract
A system for mapping and characterizing a hydrocarbon plume in seawater by measuring seawater capacitance. Multiple streamer cables are towed in the sea behind a ship, each at a different depth, simultaneously. Each streamer cable includes transmitters and receivers at the free end thereof. The free ends of the streamer cables pass through the plume and the transmitters transmit an electrical current into the plume. The receivers detect any secondary signals produced by capacitive effects of the hydrocarbon or hydrocarbon and dispersant surrounded by conductive seawater in response to the inducing electrical current. Pre-amplifiers connected to the receivers and a two-step calibration procedure and various grounding and shielding steps provide noise rejection. An electronics system on board the ship processes the secondary signals to provide immediate development of detailed maps of plume location, and to provide tracking and characterization of how the plume changes shape and character over time.
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Citations
22 Claims
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1. A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plumes in seawater, the method comprising:
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towing a streamer array having three or more vertically stacked streamer cables at three or more depths, respectively, through a seawater column containing a hydrocarbon plume; energizing two or more transmitter electrodes on each streamer cable with an electrical current signal, the transmitter electrodes injecting electrical current into the seawater column; episodically turning off transmission of the electrical current signal; arranging a plurality of receiver electrodes on each streamer cable into one or more receiver sets, each receiver set sampling a volume of seawater surrounding it and detecting any returned secondary signals produced by a capacitive effect resulting from injecting the electrical current into the seawater column and turning off the transmission of the electrical current signal, and each receiver set successively sampling a larger volume of water as the receiver sets are positioned further away from the transmitter electrodes; processing the returned secondary signals, for each adjacent pair of receiver sets, by subtracting the smallest volume of seawater from the next smallest volume of seawater to yield a capacitance value of a donut-shaped sampling volume of seawater outside the smallest volume, the receiver sets positioned further away from the transmitter electrodes providing increasingly larger donut-shaped sampling volumes of sampling data of the capacitance of the seawater column through which the streamer cables are towed; processing and geometrically correcting the capacitance values of the donut-shaped sampling volumes of seawater to yield a frequency-varying final seawater capacitance value for the volume of seawater sampled by each receiver set; and mapping and characterizing the hydrocarbon plume using the final seawater capacitance values of the receiver sets. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plumes in seawater, the method comprising:
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towing a streamer array having three or more vertically stacked streamer cables at three or more depths, respectively, through a seawater column; placing two or more transmitter electrodes and a plurality of receiver electrodes on each streamer cable; transmitting, by the transmitter electrodes, an electrical current into the seawater; episodically terminating transmission of the electrical current signal; measuring, by the receiver electrodes, returned secondary signals produced in response to terminating transmission of the electrical current signal, a non-zero capacitance value of the returned secondary signals indicating the presence of a hydrocarbon plume in the seawater; calculating, based on the returned secondary signals, a capacitance value for discrete volume points within the hydrocarbon plume and seawater mixture sampled by the receiver electrodes; and mapping and characterizing the hydrocarbon plume using the capacitance values. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A seawater capacitance detection method for rapidly mapping and characterizing hydrocarbon plumes in seawater, the method comprising:
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towing a master streamer cable through a seawater column; attaching a sled to an end of the master streamer cable to maintain it substantially vertical in the seawater column; attaching a plurality of parasitic streamer cables to the master streamer cable, each parasitic streamer cable extending from the master streamer cable and sampling different depths simultaneously; placing two or more transmitter electrodes and a plurality of receiver electrodes on each parasitic streamer cable; transmitting, by the transmitter electrodes, an electrical current into the seawater; episodically terminating transmission of the electrical current signal; measuring, by the receiver electrodes, returned secondary signals produced in response to terminating transmission of the electrical current signal, a non-zero capacitance value of the returned secondary signals indicating the presence of a hydrocarbon plume in the seawater; calculating, based on the returned secondary signals, a capacitance value for discrete volume points within the hydrocarbon plume and seawater mixture sampled by the receiver electrodes; and mapping and characterizing the hydrocarbon plume using the capacitance values.
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Specification