Multi-frequency cancellation of dielectric effect
First Claim
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1. A method of determining a resistivity of an earth formation, the method comprising:
- (a) conveying into a borehole in the earth formation a resistivity measuring instrument having at least one transmitter and at least one receiver spaced apart from the at least one transmitter;
(b) activating the at least one transmitter at a plurality of frequencies and inducing signals in the at least one receiver, the induced signals indicative of the resistivity and a permittivity of the earth formation; and
(c) applying a multifrequency focusing (MFF) to the induced signals by forming a weighted summation thereof to give a focused signal from which the resistivity is determined;
wherein coefficients of the MFF are selected to substantially eliminate an effect of the permittivity on the focused signal.
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Abstract
Measurements made with an induction logging tool are responsive to formation conductivity and permittivity. The effect of permittivity can be substantially removed by multifrequency focusing.
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Citations
16 Claims
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1. A method of determining a resistivity of an earth formation, the method comprising:
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(a) conveying into a borehole in the earth formation a resistivity measuring instrument having at least one transmitter and at least one receiver spaced apart from the at least one transmitter; (b) activating the at least one transmitter at a plurality of frequencies and inducing signals in the at least one receiver, the induced signals indicative of the resistivity and a permittivity of the earth formation; and (c) applying a multifrequency focusing (MFF) to the induced signals by forming a weighted summation thereof to give a focused signal from which the resistivity is determined; wherein coefficients of the MFF are selected to substantially eliminate an effect of the permittivity on the focused signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus configured for determining a resistivity of an earth formation, the apparatus comprising:
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a resistivity measuring instrument configured to be conveyed into a borehole in the earth formation, the resistivity instrument having at least one transmitter and at least one receiver spaced apart from the at least one transmitter, the at least one transmitter configured to operate at a plurality of frequencies, the at least one receiver configured to produce induced signals indicative of the resistivity and a permittivity of the earth formation; and a processor configured to apply a multifrequency focusing (MFF) to the induced signals by forming a weighted summation thereof to give a focused signal from which the resistivity is determined using coefficients of the MFF selected to substantially eliminate an effect of the permittivity on the focused signal. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A computer readable medium product having stored thereon instructions that when read by a processor cause the processor to execute a method, the method comprising:
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applying a multifrequency focusing (MFF) to signals induced in a receiver in a borehole in an earth formation at a plurality of frequencies by forming a weighted summation thereof to give a focused signal, the induced signals being indicative of a resistivity and a permittivity of the formation; selecting coefficients of the MFF to substantially eliminate an effect of the permittivity on the focused signal; and determining from the focused signal the formation resistivity. - View Dependent Claims (16)
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Specification