Method for making cement impedance measurements with characterized transducer
First Claim
1. A method of characterizing an acoustic transducer, comprising:
- a) arranging said acoustic transducer a predetermined distance from a calibration target, wherein said calibration target is of known thickness, and said calibration target is in contact with matter of known impedance along its inner surface and outer surface;
b) transmitting a pulse from said acoustic transducer toward said calibration target and measuring a return signal received therefrom; and
c) fitting a return signal calculation generated by a model of said return signal to said return signal, said model having a limited number of parameters, to determine a value for at least one of said parameters and thereby characterizing said transducer, by substantially minimizing the difference between said return signal calculation and said measured return signal.
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Accused Products
Abstract
Methods for characterizing acoustic transducers and using a characterized acoustic transducer for measuring cement impedance of a cased well are disclosed. The method for characterizing the acoustic transducer generally comprises: arranging the acoustic transducer a predetermined distance from a calibration target of known thickness; transmitting a pulse from the acoustic transducer through a known medium and toward the calibration target and measuring a return signal received therefrom; and fitting, via minimization, a return signal calculation generated by a model of the return signal which has a limited number of parameters, to the received return signal to determine a value for at least one of the parameters and thereby characterize the transducer. The preferred parameters for characterization are the transducer radius and stand-off, such that the transducer may be characterized as having an effective stand-off and an effective radius. The method for measuring cement impedance behind the casing in a well utilizes the method for characterizing the transducer, where the calibration target is preferbly of the same radius and thickness as the casing of the well. Then, downhole, a pulse is transmitted toward the casing in the well and the return signal is measured. Using the effective stand-off and effective radius previously determined as fixed values, the model of the return signal, which utilizes reflective coefficients which, inter alia, are a function of the cement impedance, is fit to the actual return signal to determine an indication of the cement impedance.
37 Citations
57 Claims
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1. A method of characterizing an acoustic transducer, comprising:
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a) arranging said acoustic transducer a predetermined distance from a calibration target, wherein said calibration target is of known thickness, and said calibration target is in contact with matter of known impedance along its inner surface and outer surface; b) transmitting a pulse from said acoustic transducer toward said calibration target and measuring a return signal received therefrom; and c) fitting a return signal calculation generated by a model of said return signal to said return signal, said model having a limited number of parameters, to determine a value for at least one of said parameters and thereby characterizing said transducer, by substantially minimizing the difference between said return signal calculation and said measured return signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 45, 46, 47, 48)
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21. A method of measuring cement impedance of a cased well with a tool having an acoustic transducer, the casing of the well being of substantially known diameter, said method comprising:
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a) characterizing said acoustic transducer by testing said acoustic transducer relative to a calibration target having a diameter substantially equal to the diameter of said casing of said well, and characterizing said acoustic transducer as having at least one of an effective radius (ae), and an effective stand-off (Se); b) transmitting a pulse from said acoustic transducer toward said casing in said well and measuring a return signal received therefrom; and c) fitting a return signal calculation generated by a model of said return signal to said return signal to determine an indication of said cement impedance, by substantially minimizing the difference between said return signal calculation and said return signal, wherein said model of said return signal utilizes at least one of said effective radius and said effective stand-off of said acoustic transducer as determined during said characterizing step, and wherein said model of said return signal includes reflection coefficients which are a function of said cement impedance. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 50, 51, 52, 53, 54, 55, 56, 57)
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44. A method of measuring the mud impedance of mud in a cased well with a tool having an acoustic transducer, the casing of the well being of substantially known diameter, said method comprising:
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a) arranging said acoustic transducer a predetermined distance from a calibration target, wherein said calibration target is of known thickness, and said calibration target is in contact with matter of known impedance along its inner surface and outer surface; b) transmitting a pulse from said acoustic transducer toward said calibration target and measuring a return signal received therefrom; c) fitting return signal calculations generated by a return signal model to said first signal, said model having a limited number of parameters, to determine a value for at least one of said parameters, and thereby characterizing said transducer, by substantially minimizing the difference between said return signal calculation and said measured first return signal; d) placing said tool in said mud in said well; e) transmitting a pulse from said acoustic transducer through said mud toward a target in said well, said target in said well being of substantially the same thickness as said calibration target, and having said mud along at least one surface of said target, and measuring a second return signal received therefrom; and f) determining an indication of said mud impedance by minimizing the difference between said second return signal and additional return signal calculations generated by said model, wherein said additional return signals are a function of different mud impedances. - View Dependent Claims (49)
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Specification