Methods and apparatus for electromagnetic surveying using dynamically-selected source waveforms

Patent metadata

Field	Value
Publication number	US-2016103239-A1
Application number	US-201414511625-A
Country	US
Kind code	A1
Filing date	Oct 10, 2014
Priority date	Oct 10, 2014
Publication date	Apr 14, 2016
Grant date	—

Abstract

Disclosed are methods and apparatus for electromagnetic surveying using dynamically-selected source waveforms. In accordance with an embodiment of the invention, a source waveform is adapted by dynamically selecting a source waveform from the set of pre-calculated waveform sequences. The dynamic selection of the source waveform may depend on a measured background noise level. Other embodiments, aspects, and features are also disclosed.

First claim

What is claimed is:

1 . A method for electromagnetic surveying of a subsurface formation, the method comprising:
transmitting an outgoing electromagnetic signal which is based on a source waveform; detecting, using at least one electromagnetic sensor, a responsive electromagnetic signal; obtaining a receiver signal which is based on the responsive electromagnetic signal; and adapting the source waveform by dynamic selection of the source waveform from a set of pre-calculated waveform sequences.

2 . The method of claim 1 , further comprising generating the set of pre-calculated waveform sequences.

3 . The method of claim 1 , wherein the dynamic selection of the source waveform uses at least the receiver signal.

4 . The method of claim 3 , wherein the dynamic selection of the source waveform further uses an auxiliary signal obtained from an auxiliary sensor.

5 . The method of claim 1 , further comprising:
amplifying the source waveform to provide an amplified source waveform; and using the amplified source waveform to drive the outgoing electromagnetic signal.

6 . The method of claim 1 , further comprising:
obtaining a pre-amplified receiver signal from the at least one electromagnetic sensor; and amplifying the pre-amplified receiver signal to obtain the receiver signal.

7 . The method of claim 1 , further comprising:
repeating the transmitting, detecting, obtaining, and adapting steps during an electromagnetic survey of the subsurface formation.

8 . The method of claim 1 , wherein the subsurface formation is below a body of water, the outgoing electromagnetic signal is transmitted with an antenna, and wherein the antenna are towed in the body of water during the electromagnetic survey of the subsurface formation.

9 . The method of claim 8 , wherein the at least one electromagnetic sensor is towed in the body of water during the electromagnetic survey of the subsurface formation.

10 . The method of claim 1 , wherein the set of pre-calculated waveform sequences include waveform signals with a plurality of frequency peaks in a frequency band.

11 . The method of claim 10 , wherein the plurality of frequency peaks in the frequency band have amplitudes that are inversely proportional to their frequencies.

12 . The method of claim 10 , wherein a source waveform with peaks in a higher-frequency band is selected if a frequency shift of the Earth's frequency response signal is positive, and wherein a source waveform with peaks in a lower-frequency band is selected if the frequency shift of the Earth's frequency response signal is negative.

13 . The method of claim 1 further comprising:
measuring a background noise level,
wherein the dynamic selection of the source waveform depends on the background noise level in a frequency band.

14 . The method of claim 13 , wherein the dynamic selection selects a source waveform with a smaller number of frequency peaks in the frequency band when the background noise level is high, and the dynamic selection selects a different source waveform with a larger number of frequency peaks in the frequency band when the background noise level is low.

15 . An apparatus for electromagnetic surveying of a subsurface formation, the apparatus comprising:
a receiver for detecting a responsive electromagnetic signal so as to obtain a receiver signal; a source adaptor for adapting a source waveform using at least the receiver signal; an antenna for transmitting an outgoing electromagnetic signal which is an amplified version of the source waveform; and a set of pre-calculated waveform sequences stored in data storage, wherein the source adaptor comprises a source selector for dynamically selecting a source waveform from the set of pre-calculated waveform sequences.

16 . The apparatus of claim 15 , wherein the source waveform comprises a plurality of frequency peaks in a frequency band.

17 . The apparatus of claim 16 , wherein the plurality of frequency peaks in the frequency band have amplitudes that are inversely proportional to their frequencies.

18 . The apparatus of claim 15 , wherein dynamically selecting the source waveform depends on a background noise level in a frequency band.

19 . The apparatus of claim 18 , wherein a source waveform with larger peak amplitudes in the frequency band is dynamically selected when the background noise level is high, and a different source waveform with smaller peak amplitudes in the frequency band is dynamically selected when the background noise level is low.

Assignees

• Pgs Geophysical As

Inventors

• Juhasz Robert
• Lindqvist Peter

Classifications

• G01V2003/084

  Sources · CPC title

• G01V3/165 Primary

  operating with magnetic or electric fields produced or modified by the object or by the detecting device (with electromagnetic waves G01V3/17) · CPC title

• G01V2003/085

  Receivers · CPC title

• G01V3/083 Primary

  Controlled source electromagnetic [CSEM] surveying · CPC title