Phase and amplitude calibration system for electromagnetic propagation based earth formation evaluation instruments
First Claim
1. A method of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
- tightly coupling calibration antenna means to each receiving antenna to define at least one pair of coupled calibration/receiving antennas;
transmitting in-phase, equal-amplitude reference signals to each calibration receiving antenna;
sensing the reference signals transmitted to said calibration/receiving antennas;
delivering said sensed reference signals to microprocessor means; and
calculating an error output from a comparison of the sensed reference signals using said microprocessor means.
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Accused Products
Abstract
A phase and amplitude calibration system for an electromagnetic propagation based earth formation evaluation tool is presented. In accordance with the present invention, improved phase and amplitude logs of a borehole section are provided by an automatic calibration system which compensates for errors caused by temperature and pressure variations in the borehole. This improvement is accomplished by applying in-phase, equal-amplitude reference signals to both measurement channels of a two channel system to thereby characterize system errors for correction of data used for logging. The reference signals are applied by tightly coupling a calibration signal to each receiving antenna. In a first embodiment, this is accomplished by adding a second antenna (a calibration antenna) to each of the two spaced receiving antennas. Each of the calibration antennas communicates with an attenuator which acts to make the calibration antenna transparent or invisible to the receiving antenna when the receiving antenna is in the measurement mode. The attenuator also sets the signal level delivered to the calibration antenna to a value that the receiving antenna would normally see in a measurement mode. In a second and preferred embodiment, the electrostatic shield surrounding each receiving antenna is used as a calibration antenna. The attenuator is then connected across the gap of the shield.
76 Citations
35 Claims
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1. A method of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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tightly coupling calibration antenna means to each receiving antenna to define at least one pair of coupled calibration/receiving antennas; transmitting in-phase, equal-amplitude reference signals to each calibration receiving antenna; sensing the reference signals transmitted to said calibration/receiving antennas; delivering said sensed reference signals to microprocessor means; and calculating an error output from a comparison of the sensed reference signals using said microprocessor means. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A calibration system for an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having a transmitter normally connected to at least one transmitting antenna and at least one pair of spaced receiving antennas, comprising:
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calibration antenna means tightly coupled to each receiving antenna to define at least one pair of coupled calibration/receiving antennas; transmitting means for transmitting in-phase, equal-amplitude reference signals from the transmitter to each calibration/receiving antenna; sensing means for sensing the reference signals transmitted to the calibration/receiving antennas; and microprocessor means for calculating an error output from a comparison of the sensed reference signals. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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tightly coupling a calibration signal to each receiving antenna to define in-phase, equal-amplitude reference signals; sensing the reference signals; delivering said sensed reference signals to microprocessor means; and calculating an error output from a comparison of the sensed reference signals using said microprocessor means. - View Dependent Claims (23, 24)
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25. A system of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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means for tightly coupling a reference signal to each receiving antenna to define in-phase, equal-amplitude reference signals; sensing means for sensing the reference signals; and microprocessor means for calculating an error output from a comparison of the sensed reference signals. - View Dependent Claims (26, 27)
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28. A method of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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tightly coupling calibration antenna means to each receiving antenna to define at least one pair of coupled calibration/receiving antennas; transmitting reference signals to each calibration/receiving antennas, said reference signals having known pre-selected phase and amplitude relationships; sensing the reference signals transmitted to said calibration/receiving antennas; delivering said sensed reference signals to microprocessor means; and calculating an error output from a comparison of the sensed reference signals using said microprocessor means. - View Dependent Claims (29)
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30. A calibration system for an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having a transmitter normally connected to at least one transmitting antenna and at least one pair of spaced receiving antennas, comprising:
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calibration antenna means tightly coupled to each receiving antenna to define at least one pair of coupled calibration/receiving antennas; transmitting means for transmitting reference signals from the transmitter to each calibration receiving antenna, said reference signals having known pre-selected phase and amplitude relationships; and sensing means for sensing the reference signals transmitted to the calibration/receiving antennas; and microprocessor means for calculating an error output from a comparison of the sensed reference signals. - View Dependent Claims (31)
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32. A method of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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tightly coupling a reference signal to each receiving antenna to define reference signals having known pre-selected phase and amplitude relationships; sensing the reference signals; and delivering said sensed reference signals to microprocessor means; and calculating an error output from the sensed reference signals using said microprocessor means. - View Dependent Claims (33)
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34. A system of calibrating an electromagnetic propagation based earth formation evaluation instrument, the instrument including a drillstring segment having at least one transmitting antenna and at least one pair of spaced receiving antennas, including the steps of:
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means for tightly coupling a reference signal to each receiving antenna to define reference signals having known pre-selected phase and amplitude relationships; sensing means for sensing the reference signals; and microprocessor means for calculating an error output from a comparison of the sensed reference signal. - View Dependent Claims (35)
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Specification