METHOD AND APPARATUS FOR SUPPRESSION OF THE AIRWAVE IN SUBSEA EXPLORATION

• US 20140191760A1
• Filed: 01/17/2014
• Published: 07/10/2014
• Est. Priority Date: 01/17/2014
• Status: Abandoned Application

• Current Assignee: Bentsion Zinger
• Original Assignee: Bentsion Zinger
• Inventors: Zinger, Bentsion
• Application Number:
  US14/157,542
• Publication Number:
  US 20140191760A1
• Time in Patent Office: Days
• US Class Current: 324/334
• CPC Class Codes: G01V 2003/084 Sources
• CPC Class Codes: G01V 3/083 Controlled source electromagnetic [CSEM] surveying

Abstract

The far zone “airwave” that arises when surveying subsea formations is greatly diminished by deployment of the transmitter combining mutually orthogonal horizontal electric and magnetic dipoles with the electric and magnetic dipole moments being locked in a special relationship. At each of the operating frequencies, the amplitude and phase characteristics of the transmitter electric and magnetic dipole moments are determined either from a supplementary measurement earned out using natural and/or controlled field sources, or by minimization of the vertical magnetic field at a remote receiver. Similar results can be obtained when data acquired in two independent surveys—one with the horizontal electric dipole transmitter pointing in one direction and another with a horizontal magnetic dipole transmitter pointing in the orthogonal direction and towed over the same or close positions—are linearly combined to minimize the vertical component of the combined magnetic field at remote receivers.

Claims

1. A “

Low-B_z”

transmitter for marine electromagnetic, surveying or monitoring comprising;

an electric dipole combined with a magnetic dipole, which has the horizontal component of its magnetic dipole moment orthogonal to the direction of the horizontal component of the current dipole moment of the electric dipole, and which varies in time in accordance with the law assuring suppression of the vertical magnetic field at large horizontal separations from the transmitter either within the operational time window or at each operating frequency chosen for surveying.

2. A method of marine electromagnetic surveying or monitoring using receivers of the electric and/or magnetic fields acquiring components of the electromagnetic field induced by a “

low-B_z”

transmitter of claim 1.

4. A method of marine electromagnetic surveying or monitoring in which tuning up the “

Low-B_z”

transmitter of claims 1 and 2 is achieved within the operational time window or at each operating frequency by measurement of the vertical component of the magnetic field at a receiver or receivers located in a reasonable proximity to the area of interest but at a large horizontal separation from the transmitter and by subsequent adjustment of the current dipole moment of the electric dipole and the magnetic dipole moment of the magnetic dipole of the “

Low-B_z”

transmitter of claim 1 in a manner allowing for suppression of the vertical magnetic field at these receivers.

5. A method of marine electromagnetic surveying or monitoring in which the tuning up the “

Low-B_z”

transmitter of claims 1 and 2 is carried out using the plain wave impedance or a related transfer function evaluated for one or several locations;

the evaluation of the plain wave impedance or the related transfer function is carried out from measurements of the electromagnetic fields induced by natural and/or controlled sources and/or from the borehole resistivity logs acquired in a reasonable proximity to the area of interest.

6. A method of marine electromagnetic surveying or monitoring in which the transmitter or transmitters of claim 1, 2, 3, 4, or 5 are either stationary or towed behind a vessel or vessels.

7. A method of marine electromagnetic surveying or monitoring in which the receiver or receivers of claim 2, 3, 4, or 5, are either stationary or towed behind a vessel.

8. An apparatus to survey the subterranean formations, comprising:

a “

Low-B_z”

transmitter of claim 1, cables connecting this transmitter to the power source located on the vessel or otherwise, a set of receivers registering components of the electromagnetic field, the transmission, acquisition, and positioning controlling hardware and software, and a system to process the acquired signals and generate a representation of the subterranean formation.

9. A method of marine electromagnetic surveying or monitoring in which information on the subsea formation or its part is implicitly or explicitly using data acquired in a survey with a “

Low-B_z”

transmitter of claim 1 or the combined data of claim 3.

3. A method of marine surveying or monitoring, and processing of the electric and/or magnetic fields comprising:

acquisition of at least two sets of electromagnetic data such that positions of the transmitter and receivers when acquiring the second set of data are the same or close to the corresponding transmitter and receiver positions when acquiring the first set of data;

during acquisition of the first set of data the transmitter may represent an electric dipole, then during acquisition of the second set of the data the transmitter represents a magnetic dipole with the direction of the horizontal component of its magnetic dipole moment being orthogonal to the direction of the horizontal component of the current dipole moment of the transmitter when acquiring the first set of data;

after full or partial completion of the measurements the sets of the electromagnetic field data acquired for the same or close transmitter and receiver positions are linearly combined, in a way permitting suppression of the combined vertical magnetic field at large offsets.