Method and apparatus for transmitting electromagnetic signals into the earth at frequencies below 500 KHz from a capacitor emplaced on the surface of the earth or raised aloft in an aircraft
First Claim
1. A method for transmitting an electromagnetic signal or pulse to and through an earth formation and recovering from the return signal or pulse, select frequencies that are strongly coupled to the earth at aircraft heights or on the surface of the earth and at the same time penetrate to great depths of the order of tens of thousands of feet or more including the steps of:
- (a) disposing capacitor plates having a largest dimension L either in direct contact with the earth formation or elevated a height Z above the earth formation to form an earth capacitor comprising the plate assembly, the air or space between the plates and the earth if Z>
0 and the region in the earth formation either in direct contact with the plates or separated from the plates by the height, Z>
0, whereupon returning frequencies are selected that in the earth formation are electrically coupled or for each frequency up to the highest selected frequency, where KoZ<
1 and Ko is the wave number in air,(b) applying a short voltage or current pulse via a transformer with core magnetic flux adjusted for enhanced radiation at lower frequencies <
500 KHZ, across the capacitor plates from a pulse generator to transmit electromagnetic radiation into the earth formation, where for each returning lower frequency component of the electromagnetic radiation, the largest dimension L is small such that Re(KL)<
1 and KoZ<
1, where Re(K) is the positive wave number in the earth formation of said lower frequency component and Ko is the positive wave number in air of each returning lower frequency component at all frequencies present <
1 MHZ and indeed very much less than 1 MHZ,(c) detecting electromagnetic radiation that has propagated through the earth formation in response to application of the short voltage or current pulse, and(d) processing only frequency components of the desired electromagnetic radiation, in a select lower frequency window, in the broad frequency continuum <
1 MHZ which lower frequencies have propagated into the earth formation to penetration depth very much greater than of the order of several tens of thousands of feet to detect the electrical properties,that is, the reconstituted pulse amplitude as a function of time is transformed into the magnitude of the relative dielectric and the conductivity as a function of depth using a model for a system of vertically traveling up-going and down-going waves and Maxwell'"'"'s Equations to deduce said electrical properties with an iterative process.
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Abstract
A method and apparatus comprising four co-planar metallic plates, two for transmission and two for reception, in which each pair of co-planer metallic plates of overall length L are disposed either in direct contact with the earth or are elevated a distance Z above the earth to form a capacitor comprising the metallic plates and the earth if Z=0 or if Z>0, the metallic plates, the air space and the earth. A short voltage or current pulse is applied to this capacitor via a transformer in which the magnetic flux current is adjusted to provide a pulse of the desired frequency composition in the air-earth propagation medium. This results in a frequency controlled pulse of electromagnetic radiation into the targeted subterranean geology at frequencies <500 KHZ. In the preferred embodiment, the electromagnetic radiation that has propagated through the subsurface is iterated against a theoretical model for earth propagation of vertically traveling up-going and down-going waves to get a solution for the magnitude of the electrical properties as a function of the depth in the medium through which these waves have traveled. Electrical property vs depth profiles of the relative dielectric and the conductivity in addition to wave velocity and attenuation rate at depth in the subsurface are recovered by the iteration. For operation at capacitor altitude Z above the surface of the earth, the overall size of the capacitor, L, can be specified for use in the pulse spectrum below 500 khz.
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Citations
17 Claims
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1. A method for transmitting an electromagnetic signal or pulse to and through an earth formation and recovering from the return signal or pulse, select frequencies that are strongly coupled to the earth at aircraft heights or on the surface of the earth and at the same time penetrate to great depths of the order of tens of thousands of feet or more including the steps of:
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(a) disposing capacitor plates having a largest dimension L either in direct contact with the earth formation or elevated a height Z above the earth formation to form an earth capacitor comprising the plate assembly, the air or space between the plates and the earth if Z>
0 and the region in the earth formation either in direct contact with the plates or separated from the plates by the height, Z>
0, whereupon returning frequencies are selected that in the earth formation are electrically coupled or for each frequency up to the highest selected frequency, where KoZ<
1 and Ko is the wave number in air,(b) applying a short voltage or current pulse via a transformer with core magnetic flux adjusted for enhanced radiation at lower frequencies <
500 KHZ, across the capacitor plates from a pulse generator to transmit electromagnetic radiation into the earth formation, where for each returning lower frequency component of the electromagnetic radiation, the largest dimension L is small such that Re(KL)<
1 and KoZ<
1, where Re(K) is the positive wave number in the earth formation of said lower frequency component and Ko is the positive wave number in air of each returning lower frequency component at all frequencies present <
1 MHZ and indeed very much less than 1 MHZ,(c) detecting electromagnetic radiation that has propagated through the earth formation in response to application of the short voltage or current pulse, and (d) processing only frequency components of the desired electromagnetic radiation, in a select lower frequency window, in the broad frequency continuum <
1 MHZ which lower frequencies have propagated into the earth formation to penetration depth very much greater than of the order of several tens of thousands of feet to detect the electrical properties,that is, the reconstituted pulse amplitude as a function of time is transformed into the magnitude of the relative dielectric and the conductivity as a function of depth using a model for a system of vertically traveling up-going and down-going waves and Maxwell'"'"'s Equations to deduce said electrical properties with an iterative process. - View Dependent Claims (2, 3, 4, 5)
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6. An apparatus for transmitting an electromagnetic signal or pulse through an earth formation and recovering the returning signal or pulse for processing to determine electrical properties at depth including,
a capacitor assembly comprising a co-planar pair of highly conductive metallic plates with electrical input or output terminals between the plates wherein each pair of terminals connect to an input or output transformer with magnetic flux cores and wherein each pair of plates has a largest dimension L disposed either in direct contact with the earth formation to form an earth capacitor comprising the capacitor assembly and the region of the earth formation near said capacitor assembly; - or elevated above the earth formation to form a capacitor comprising the capacitor assembly, and the earth formation separated from the capacitor assembly by the air of thickness Z,
a means for applying a short voltage or current pulse to the capacitor assembly via the transformer with magnetic flux core adjusted for radiation <
0.5 MHZ, to transmit electromagnetic radiation into the earth formation either directly or via the air of thickness Z, wherein for each frequency component of the electromagnetic radiation, the largest dimension L satisfies the relation Re(KL)<
1, where K is the wave number in the earth formation of said frequency component, wherein the short voltage or current pulse as applied to earth capacitor plates via and in convolution with the transformer with magnetic flux core has frequency components in the broadband <
1 MHZ and,a means for detecting electromagnetic radiation that has propagated through the earth formation in response to application of the short voltage or current pulse, including means for processing only frequency components of the detected electromagnetic radiation having an upper frequency less than 1 MHZ and a lower frequency very much less than 1 MHZ depending upon the depth of interest for wave penetration. - View Dependent Claims (7, 8, 9, 10, 11, 12)
- or elevated above the earth formation to form a capacitor comprising the capacitor assembly, and the earth formation separated from the capacitor assembly by the air of thickness Z,
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13. A method for transmitting electromagnetic signals through the earth formation, including the steps of:
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(a) disposing capacitor plates having a largest dimension L in direct contact with the earth formation or elevated a distance Z above the earth formation forming an earth capacitor comprising the plates and a region of the earth formation near the plates or the region of air between the plates and the earth formation whereupon the frequencies employed make the air thickness electrically small so that the plates are electrically close to the earth formation, (b) applying a short voltage or current pulse to transmit electromagnetic radiation into the earth formation, wherein for each frequency component of the electromagnetic radiation, the largest dimension L satisfies the relation Re(KL)<
1, where K is the wave number in the earth formation of said frequency component, wherein the short voltage or current pulse applied through the transformer has radiation field components in a broad band below 1 MHZ with the additional requirement that KoZ<
1 thus enforcing the further desirable restriction of using much lower frequencies below 500 KHZ,(c) detecting electromagnetic radiation that has propagated through the earth formation in response to application of the short voltage or current pulse; and (d) processing only frequency components of the detected electromagnetic radiation in a frequency window having an upper frequency less than 0.5 MHZ which have propagated into the formation to a penetration depth very much greater than the largest dimension L. - View Dependent Claims (14)
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15. An apparatus for transmitting an electromagnetic signal through the earth formation to very great depths relative to a restrictive size, R, of the capacitor plates, including:
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a capacitor assembly having a largest dimension L<
R disposed in direct contact with the earth formation or elevated above the earth formation a distance Z to form an earth capacitor comprising the capacitor assembly, the space between the capacitor assembly and the earth formation if Z>
0, and a region of the earth formation coupled to the capacitor assembly or if Z=0, comprising the capacitor assembly and the adjacent earth formation, also includinga means for applying a short voltage or current pulse to capacitor assembly to transmit electromagnetic radiation into the earth formation, wherein for each frequency component of the electromagnetic radiation, the largest dimension L satisfies the relation Re(KL)<
1, where K is the wave number in the earth of said frequency component, provided if Z>
0, KoZ<
1 and a means for detecting electromagnetic radiation that has propagated through the earth formation and the space Z>
0, in response to the application of a short voltage or current pulse, including means for identifying frequency components of the detected electromagnetic radiation in a frequency window which have propagated into the earth formation to a penetration depth much greater than several tens of thousand feet, wherein the means for applying the short voltage or current pulse to the capacitor assembly includes;a pulse generator a transmission line transformer or a conventional transformer both with core magnetic flux current adjusted for frequencies <
0.5 MHZ, between the pulse generator and the capacitor assembly. - View Dependent Claims (16, 17)
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Specification