Apparatus and method for determining the quality of clamping of a borehole seismic sensor system to the wall of a wellbore
First Claim
1. A method of evaluating the acoustic coupling between a borehole seismic sensor system and the wall of a wellbore, the system comprising at least one seismic sensor and a locking arm powered by a motor, the method comprising the steps of:
- lowering the borehole seismic sensor system into the wellbore to a depth of interest in the wellbore, the system electrically connected to equipment at the earth'"'"'s surface by an electrical cable;
extending the locking arm until the arm contacts the wall of the wellbore, by applying a direct current to the motor;
applying a broadband alternating current to the motor, the alternating current having a substantially constant amplitude at a plurality of frequencies within a predetermined frequency range;
detecting signals generated by the at least one seismic sensor;
transmitting the signals to the earth'"'"'s surface by the electrical cable; and
processing the signals in a spectrum analyzer and generating an output representing amplitude of the signals as a function of frequency.
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Accused Products
Abstract
The invention is a method and apparatus for measuring the quality of acoustic coupling between a wellbore wall and a borehole seismic sensor system. The system includes the steps of positioning the system at a desired depth in the wellbore and activating a locking mechanism powered by a DC motor. The motor then has broadband AC applied to it to cause vibration of the system. The output of at least one seismic sensor in the system is processed in a spectrum analyzer, and the result is checked for the presence or absence of natural resonance of the system. In a particular embodiment, the system response to the broadband AC is used to generate an inverse filter operator to compensate the system response to a geophysical survey for partial acoustic coupling.
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Citations
18 Claims
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1. A method of evaluating the acoustic coupling between a borehole seismic sensor system and the wall of a wellbore, the system comprising at least one seismic sensor and a locking arm powered by a motor, the method comprising the steps of:
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lowering the borehole seismic sensor system into the wellbore to a depth of interest in the wellbore, the system electrically connected to equipment at the earth'"'"'s surface by an electrical cable; extending the locking arm until the arm contacts the wall of the wellbore, by applying a direct current to the motor; applying a broadband alternating current to the motor, the alternating current having a substantially constant amplitude at a plurality of frequencies within a predetermined frequency range; detecting signals generated by the at least one seismic sensor; transmitting the signals to the earth'"'"'s surface by the electrical cable; and processing the signals in a spectrum analyzer and generating an output representing amplitude of the signals as a function of frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for measuring the acoustic coupling between a borehole seismic sensor system and the wall of a wellbore, the apparatus comprising:
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a housing adapted to traverse the wellbore; at least one seismic sensor, disposed within the housing, the at least one sensor adapted to detect motion of the housing and generate signals as a result of detecting motion of the housing; a signal processing unit, disposed within the housing and electrically connected to the at least one sensor, the signal processing unit adapted to transmit of the signals to the earth'"'"'s surface; a locking mechanism, disposed within the housing, the mechanism comprising a locking arm and a bi-directional direct current powered motor cooperatively attached to the arm, the locking mechanism adapted to force the housing into contact with the wall of the wellbore upon application of a direct current to the motor; a source of broadband alternating current, selectively operating within a predetermined frequency range, the source electrically connected to the motor; and a spectrum analyzer, electrically connected to the output of the signal processing unit, the analyzer capable of providing at least one output representing signal amplitude as a function of frequency component, so that when the locking mechanism is set to force the housing into contact with the borehole wall, application of the broadband alternating current to the motor causes motion of the housing, the at least one sensor detecting the motion generates signals which are filtered and amplified by the signal processing unit, and transmitted to the spectrum analyzer, to characterize the frequency response of the motion of the housing. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of adjusting a response of a borehole seismic sensor system comprising a DC powered locking mechanism, to compensate for partial acoustic coupling with the wall of a wellbore, the method comprising the steps of:
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lowering the system to a depth of interest in the wellbore; actuating the locking mechanism by applying direct current to the mechanism; applying a broadband alternating current to the mechanism; processing signals, generated by the system as a result of applying the broadband alternating current, in a spectrum analyzer; applying an output of the spectrum analyzer, representing frequency content of the signals generated by the system in response to the broadband alternating current, to an inverse filter generator and generating an inverse filter operator; conducting a geophysical survey at the depth of interest; and convolving a result of the geophysical survey with the inverse filter operator, whereby the result of the geophysical survey is adjusted to reduce an effect of the response of the system to partial acoustic coupling.
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Specification