Abstract: A system and method for performing seismic prospecting and monitoring during drilling of a well are disclosed. The system generates energy, such as acoustic vibrations and electromagnetic energy, at a downhole location and imparts the same into the surrounding earth. The energy may be imparted by the drilling operation itself, or may be generated by a downhole apparatus. Downhole sensors are provided which sense the energy after it has passed through the earth surrounding the wellbore. The sensed energy is either communicated to the surface, or is communicated to a downhole computer for analysis, with the results of the analysis communicated to the surface. Due to the use of both downhole generation and sensing of the energy, high frequency energy may be used. As a result, the resolution of the resulting survey is improved over techniques which utilize surface detectors for energy traveling through the earth.

Abstract: A method of analyzing vibrations transmitted along a structure such as a drill string is disclosed. The detected vibrations include both axial and torsional vibrations generated from the same location, so that the time delay between the two, due to the difference in axial and torsional velocities, can be determined. After deconvolution to take into account the non-ideal frequency response of the structure, such deconvolution preferably retaining the values of the transmission time for each component, one of the time series is shifted by the amount of the time delay, so that the vibrations generated from the same location coincide. A weighted sum of the two representations will provide reinforcement of the desired signal. The method may be used in determining a seismic source signature in prospecting where a drill bit is the source, in analyzing drilling parameters from drill string vibrations, and in stress wave telemetry.

Abstract: A method of deconcolving the non-ideal frequency response from acoustic vibrations transmitted along a structure such as a drill string is disclosed. The deconvolution retains the values of the transmission time between the signal source and the receiver, in the form of an exponential phase term, and is multiplied by the amplitude frequency response of the structure. The input data time series, after transformation into the frequency domain, is then divided by the deconvolution operator. The deconvolution method may be used in a noise reduction method where both axial and torsional vibrations are generated from the same location, where one of the time series is shifted by the amount of the time delay, so that the vibrations generated from the same location coincide, providing reinforcement of the desired signal.

Abstract: A method of analyzing vibrations transmitted along a structure such as a drill string is disclosed. The detected vibrations include both axial and torsional vibrations generated from the same location, so that the time delay between the two, due to the difference in axial and torsional velocities, can be determined. After deconvolution to take into account the non-ideal frequency response of the structure, such deconvolution preferably retaining the values of the transmission time for each component, one of the time series is shifted by the amount of the time delay, so that the vibrations generated from the same location coincide. A weighted sum of the two representations will provide reinforcement of the desired signal. The method may be used in determining a seismic source signature in prospecting where a drill bit is the source, in analyzing drilling parameters from drill string vibrations, and in stress wave telemetry.

Abstract: Fluid leakage from a crack or other leakage point and other vibration-generating events in pipes and conduits may be located and analyzed by sensing axial and torsional vibrations and pressure fluctuations created by such events by placing accelerometers and/or strain gauges and pressure sensors on the conduit at selected points. The location of the event may be determined by comparing the travel time of selected pairs of signals such as axial propagated signals as compared with torsional propagated signals as a result in the difference of the acoustic wave speed of axial versus torsional waves. Cross correlation and deconvolution processes are carried out on the measured signals to determine differential signal arrival times at the sensors and to eliminate pipe response signals.

Abstract: The resistivity of a geologic formation is measure through drillpipe or casing by applying a low frequency bipolar voltage to the casing and to a ground electrode and traversing the casing with a tool having contractors which are connected to a differential amplifier to detect a differential voltage within the casing caused by current leaving the casing into the formation. The differential amplifier is connected to a unity gain inverter and a switching arrangement for alternately reversing the polarity of the connection of input voltages to the differential amplifier. A switching network alternately connects the outputs of the differential amplifier and the output of the inverter to the input of a low pass filter, and a clock is provided for driving the network in synchronization.