Antenna of an electromagnetic probe for investigating geological formations
First Claim
1. An antenna of an electromagnetic probe used in investigation of geological formations surrounding a borehole comprising a conductive base and an antenna element, the conductive base comprising an opened non-resonant cavity, the antenna element being embedded in the cavity and going right through the cavity, the antenna configured to radiate a substantially symmetrical electromagnetic field, wherein the antenna is configured to define either a substantially pure magnetic dipole when an electronic module applies a current to the antenna element such that the current increases from one extremity to the middle of the antenna element and decreases from the middle of the antenna element to the other extremity, or a substantially pure electric dipole when the electronic module applies a current to the antenna element such that the current increases from one extremity to the middle of the antenna element and continues to increase from the middle of the antenna element to the other extremity.
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Accused Products
Abstract
An antenna 3 of an electromagnetic probe used in investigation of geological formations GF surrounding a borehole WBH comprises a conductive base 31 and an antenna element 32. The conductive base 31 comprises an opened non-resonant cavity 33. The antenna element 32 is embedded in the cavity 33 and goes right through the cavity. The antenna element 32 is isolated from the conductive base 31. The antenna element 32 is coupled to at least one electronic module via a first 34A and a second 34B port, respectively. The electronic module operates the antenna so as to define either a substantially pure magnetic dipole, or a substantially pure electric dipole.
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Citations
17 Claims
- 1. An antenna of an electromagnetic probe used in investigation of geological formations surrounding a borehole comprising a conductive base and an antenna element, the conductive base comprising an opened non-resonant cavity, the antenna element being embedded in the cavity and going right through the cavity, the antenna configured to radiate a substantially symmetrical electromagnetic field, wherein the antenna is configured to define either a substantially pure magnetic dipole when an electronic module applies a current to the antenna element such that the current increases from one extremity to the middle of the antenna element and decreases from the middle of the antenna element to the other extremity, or a substantially pure electric dipole when the electronic module applies a current to the antenna element such that the current increases from one extremity to the middle of the antenna element and continues to increase from the middle of the antenna element to the other extremity.
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13. A method of investigation of geological formations surrounding a borehole using an electromagnetic logging apparatus comprising at least one transmitting antenna and at least one receiving antenna, the method comprising:
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a) running the logging apparatus through the borehole and engaging a pad with a borehole wall so as to define a selected zone made of a medium to be investigated, b) performing a first set of measurements at a deep radial depth of investigation in the selected zone by; b1) operating the antennas so that each antenna defines a substantially pure magnetic dipole by applying a current to an antenna element such that the current increases from a first extremity to a middle of the antenna element and decreases from the middle of the antenna element to a second extremity, and radiating electromagnetic signals in the medium, b2) measuring a first set of attenuation and phase shift of the electromagnetic signals having traveled in the medium between the transmitting and receiving antennas, c) performing a second set of measurements at a shallow radial depth of investigation in the selected zone by; c1) operating the antennas so as each antenna defines a substantially pure electric dipole by applying a current to the antenna element such that the current increases from the first extremity to the middle of the antenna element and continues to increase from the middle of the antenna element to the second extremity, c2) radiating electromagnetic signals into the formation surrounding the borehole and measuring a first sub-set of attenuation and phase shift of the electromagnetic signals having traveled in the formation between the transmitting and receiving antennas, c3) radiating electromagnetic signals into the formation surrounding the borehole and measuring a second sub-set of magnitude and phase of the electromagnetic signals reflected by the formation at a transmitting antenna input, and d) performing an inversion calculation based on the first and second set of measurements and determining the permittivity ε and
the conductivity σ
of the in the selected zone. - View Dependent Claims (14, 15, 16, 17)
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Specification