Abstract: The acoustic impedance of a fluid in a borehole is determined by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer. The sonic velocity of the fluid is also measured and, when combined with the acoustic impedance, is used to determine fluid density.

Abstract: A method of determining the acoustic impedance of a fluid in a borehole, by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The comparison is performed by comparing a ratio of an integration of a first ring down time slot and a second ring down time slot, to an integration of an internal reflection time slot. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer.

Abstract: A method for inferring the photoelectric absorption of a formation by directly mapping spectroscopic measurements of gamma rays induced in the formation using a fast neutron source. The mapping is accomplished by creating a polynomial function based on counts of gamma-ray events in the gamma-ray energy spectrum; the coefficients of the polynomial function are determined in known calibration environments, and the value of the polynomial is the inferred photoelectric absorption parameter. The spectroscopic measurements are preferably generated by sorting gamma-ray counts of the gamma-ray spectrum into a plurality of energy-dependent channels, and measuring these gamma-ray energy distributions during different portions of the firing cycle where different types of dominant gamma-ray production reactions occur.

Abstract: A method of determining the acoustic impedance of a fluid in a borehole, by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The comparison is performed by comparing a ratio of an integration of a first ring down time slot and a second ring down time slot, to an integration of an internal reflection time slot. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer.

Abstract: A device for measuring the density of a formation uses a high-energy pulsed neutron source which induces gamma rays in the formation, and determines a gamma diffusion length of the formation based on the attenuation of gamma rays produced by inelastic scattering of fast neutrons. The borehole tool houses the neutron source along with a near gamma ray detector and a far gamma ray detector. The gamma ray detectors are located at different distances from the fast neutron source and spaced sufficiently from the fast neutron source such that dependence of inelastic gamma counts on fast neutron transport and gamma production of the formation is substantially reduced. Gamma ray events can be sorted and counted in time- and energy-dependent bins. The present invention has several advantages over gamma-gamma logging, including deeper penetration of gamma, and is also superior over systems which measure, e.g., hydrogen-based porosity.

Abstract: An induction logging tool is disclosed for utilization in conjunction with surface electronic equipment for measuring a characteristic of subsurface formations. A transmit signal which is comprised of a repetitive sequential series of at least three transmit frequencies is generated by coupling an oscillator to a transmitter coil and a plurality of selectable tuning capacitors. A signal characteristic of the response of the formation to this transmit signal is detected at a receiver coil array and two phase sensitive detectors are then utilized to generate output signals indicative of the magnitude of the X and R components of the formation signal which is in phase with a reference phase signal. The output signal of each phase sensitive detector is then utilized to accurately determine the X and R component of the receiver coil signal for each frequency by nulling the output of the phase sensitive detector utilizing a closed loop conversion circuit which eliminates errors due to phase and gain variations.

Abstract: An induction logging tool is disclosed for utilization in conjunction with surface electronic equipment for measuring a characteristic of subsurface formations. A transmit signal which is comprised of a repetitive sequential series of at least three transmit frequencies is generated by coupling an oscillator to a transmitter coil and a plurality of selectable tuning capacitors. A signal characteristic of the response of the formation to this transmit signal is detected at a receiver coil array and two phase sensitive detectors are then utilized to generate output signals indicative of the magnitude of the X and R components of the formation signal which is in phase with a reference phase signal. The output signal of each phase sensitive detector is then utilized to accurately determine the X and R component of the receiver coil signal for each frequency by nulling the output of the phase sensitive detector utilizing a closed loop conversion circuit which eliminates errors due to phase and gain variations.

Abstract: A sonic well logging tool radially measures circumferential cement conditions longitudinally along a well casing. Sonic signals are transmitted from a plurality of angularly displaced transmitter-transducers, through a borehole fluid, down a longitudinally extending sector of the well casing, and then through the borehole fluid to a plurality of angularly displaced receiver-transducers, which are distally disposed from the transmitter-transducers.

Abstract: A caliper logging sonde is provided having a plurality of sensing fingers each of which is pivotally mounted to the sonde and movable with respect to the sonde in response to variations in the internal dimensions of a wellbore tube through which the sonde passes. An electrical signal which is proportional to variations in the internal dimensions of a wellbore tube is determined at regular time intervals at a series of points around the circumference of the wellbore tube. A maximum and minimum dimension for each point around the circumference of the wellbore tube during a selected time interval is temporarily stored and thereafter transmitted to the surface at regular intervals. A high density array of sensors is provided by utilizing a transducer plate having a large number of cylindrical apertures disposed around the circumference thereof.

Abstract: A radioactive energy detector for well logging utilizes a Dewar flask. The Dewar flask has an inner housing containing a gamma ray detector. An outer housing surrounds the inner housing, with the annular clearance being evacuated. A window section is integrally formed in the side wall of the outer housing. The window section has a wall thickness that is less than the wall thickness of the side wall of the outer housing. The outer housing is constructed of a material of relatively low atomic number.