Abstract: A seismic acquisition system comprising a remote-controlled buoy for conducting seismic acquisition operations. The buoy comprises an operating system for operating a seismic wave production device on the buoy, a placement system, a communications system, and dynamic position locating system. The seismic acquisition system also comprises a remote control system for controlling the buoy systems. The seismic acquisition system also comprises receivers for receiving the seismic wave and generating a data signal indicative of the received seismic wave. The seismic acquisition system operates by controlling the placement system with the remote control system to position the buoy and then controlling the operating system with the remote control system to produce a seismic wave from the seismic wave production device. The receivers then receive the seismic wave and generate a data signal indicative of the seismic wave.

Abstract: A downhole crystal-based clock that is substantially insensitive to the factors that may cause frequency deviation as a result of downhole temperature. The clock may include a plurality of crystals, where a first crystal may be more stable, with respect to temperature, than a second crystal. The crystals may be thermally coupled together so that they may have substantially the same temperature. An error detector may monitor the differences between the frequencies associated with each crystal and provide this information to a storage device. This information may be determined prior to deploying the clock downhole. When deployed downhole, the signal from the error detector may be interpreted in light of the information in the storage device to provide a temperature measurement of the two crystals. The downhole temperature measurement then may be used to reduce frequency deviations in the downhole clock that may result from downhole temperatures.

Abstract: An axially extended downhole seismic source is disclosed. In one embodiment, the seismic source includes multiple pressure storage chambers, each having an inlet valve and an outlet valve. The inlet valve is coupled between the pressure storage chamber and the interior of the drill string, and the outlet valve is similarly coupled between the pressure storage chamber and the annular space around the drill string. A compressible fluid may be provided in the pressure storage chambers, and pistons may be positioned to contact the compressible fluid. For each pressure storage chamber, an inlet piston contacts the compressible fluid and fluid inside the drill string, while an outlet piston contacts the compressible fluid and fluid in the annular space around the drill string. When the outlet valve is closed, the inlet valve can be opened to allow pressure inside the drill string to compress the compressible fluid inside the pressure storage chamber.

Abstract: A system is disclosed for synchronizing a clock in a well containing a drill string with a clock located near the surface of the well. The system includes devices for transmitting and receiving a pair of acoustic signals between locations associated with each clock and processing those signals. The system determines the time of arrival of each acoustic signal by analyzing the shape of a function of the acoustic signal chosen from a group of functions suitable to determine a clock offset with millisecond accuracy.

Abstract: A system based on a series of data accumulation hubs, connected together by high speed communication backbone for routing a limited number of data and power cables is suggested. Each hub is connected to arrays of sensor pods which contain the actual sensor elements and minimal, if any, interface electronics. Preferably, as many as 20 sensor pods can be connected to each single hub element wherein a system including five hub elements with 20 sensor pods each would comprise a 100 element array. The data from the individual sensors are accumulated in the hubs, buffered, and conditioned for transmission to the surface data acquisition system through the high speed metal backbone comprising multiple paths of transmission for redundancy in the event of failure. Provisions are made within each of the hubs so that if a hydrostatic leak were to occur, the fault can be isolated and the remainder of the system will function as designed.

Abstract: A vertical seismic profiling system includes seismic receivers for placement on a drillstring and surface seismic sources. One-way checkshot data may thus be measured without tripping the drillstring. A downhole acoustic tool measures the local interval transit time of the formation, and improves the detection of targets ahead of the drill bit. The local interval transit time may be applied to the time of travel from reflections in front of the bit to establish distance to the bit. The down-going wavetrain may be deconvolved with the total up-going wavetrain to extract the nearest reflector and the relative acoustic impedance at the reflector. A synthetic seismogram may also be created based on reflection depth data and corrected with checkshot data.

Abstract: A system for eliminating the tool mode signal from a received combined signal comprising both tool mode and formation mode components, comprising: a formation receiver for receiving said combined signal, a reference receiver for receiving a tool mode reference signal, a filter for processing said tool mode reference signal and generating a predicted tool mode component of the combined signal, and a summation element for subtracting said predicted tool mode component from said combined signal and generating a predicted formation mode component. The filter preferably incorporates a portion of the output of the summation element as an error signal, enabling the filter to adapt to changing conditions and update the algorithm on which it makes its predictions. According to an alternative system, an average value for the tool mode signal is updated according to a moving average to which new data points are added as they become available.

Abstract: For use with a photomultiplier tube responding to gamma ray induced scintillation pulses in a well logging sonde, a system having the preferred and illustrated embodiment of an input amplifier DC connected with a differential amplifier output to an integrating amplifier. The integrating amplifier is output to another differential amplifier then output to a sample and hold amplifier. This provides the input for a successive approximation digitizer. A feedback loop is incorporated in the system connected from the output of the integrating amplifier. It detects an error component due to noise, offset voltage, and drift accumulated at the integrator. It comprises a track and hold amplifier which is output to a pair of voltage comparators, one determining an excessive negative value and the other determining an excessive positive value. The two comparators are input to appropriate up and down terminals of a bidirectional counter.

Abstract: A method of well logging utilizing naturally occurring gamma radiation is disclosed. In the preferred and illustrated embodiment, the thickness of the casing in a well borehole is measured. The photoelectric absorption of gamma rays from the formation by the iron in the casing varies as a function of the energy of the gamma radiation. The detected gamma spectrum below about 350 KeV from the surrounding earth formation is preferably divided into two energy ranges or windows, and a ratio between the two to indicate the thickness of any intervening steel casing material. With suitable scale factors in calibration of the system, casing thickness can be determined from the ratio of the summed naturally occurring gamma count rate in the range of about 35 to about 120 KeV divided by the count rate in a higher energy range from about 180-325 KeV.

Abstract: A gain stabilized natural gamma ray spectroscopy system is used to measure casing thickness in a cased well borehole. A ratio of gamma ray intensity in two selected energy ranges forms a measurement signal representative of casing thickness based on the photoelectric absorption of natural gamma rays by iron. A coincidence technique employing dual scintillation crystals and a stabilization source of charged particles and known energy gamma rays is used for gain stabilization.

Abstract: An oil well logging apparatus is disclosed for detecting radiation emanating or returning from an oil well formation. The apparatus has a scintillation crystal adjacent a photomultiplier tube for detecting light flashes generated in the crystal by radiation. A low energy gamma source is included in the crystal for generating a known peak of pulse counts in the energy spectrum. A cadmium shield is placed over the crystal to block low energy radiation which would tend to mask the peak of gamma source pulses. This known peak is divided electrically downhole by window discriminators such that the peak is equally divided into two windows at a standard condition. If the frequency of pulses in one window varies from the frequency of pulses in the second window, a correction factor is generated downhole for varying the pulse height of the entire spectrum until the frequency of pulses in each window is again equal. Salinity compensation is also accomplished by samarium sleeves in the logging sonde.