Dresser Industries, Inc.

Baker Hughes Corporation

Western Atlas International, Inc.

Russel R Randall

Mathew G Schmidt

David M Schneider

Mark W Hutchinson

Steven L Hobart

Timothy P Gray

The present invention relates to the transformation of measurement while drilling (MWD) data acquired during various time intervals into corresponding equal depth intervals. Once the data are transformed into the depth domain, depth based statistical, filtering sensor resolution matching and depth shifting techniques are utilized. The transformation process maximizes sensor vertical resolution while minimizing observed and statistical errors associated with sensor response.

Comprehensive method of processing measurement while drilling data from

A generalized computer-based system and method for acquisition of nuclear well logging data. A feature of the present invention is the ability to provide time distribution spectra over the entire interval between source firings, such spectra including the gamma radiation produced from both the inelastic scattering and capture of neutrons from said neutron source. The spectra so generated may be analyzed and processed to derive parameters indicative of formation and borehole conditions, for example, a parameter sensitive to borehole geometry and a parameter sensitive to porosity. Certain parameters may be compared as an indication of the presence of gas in a fluid filled formation. Still further, a quantitative measure of the repeatability of the macroscopic thermal neutron absorption capture cross-section may be derived and used to control the weight of the capture cross-section filter.

Method for quality control of counting logs

A generalized computer-based system and method for acquisition of nuclear well logging data, including downhole generation of spectral information. A downhole instrument traverses a borehole introducing high energy neutrons into the formation at prescribed depths. Resultant gamma rays are detected and converted into pulses which are amplified and conditioned. For acquiring temporal spectral data, a multi-channel scale section is provided which includes a channel number generator which produces a numerical sequence of memory address codes corresponding to a sequence of adjacent time windows. Each code uniquely defines a start time, whereby the windows collectively comprise the time interval of the desired spectrum. Each time a gamma ray pulse is detected, the memory address generated at that time addresses a corresponding memory location and increments the count value resident therein. At the conclusion of the time spectrum interval of interest, the memory locations may be interrogated by the CPU and the resultant spectral data analyzed, transmitted to the surface, or presented visually as a gamma ray emission count versus time plot.

Neutron logging time spectral data acquisition system and method

Method for induced gamma ray logging

A neutron source in a well logging instrument is periodically pulsed and secondary radiations emanating from the irradiated formations are measured by a detector system. Circuitry is provided for establishing the points in time at which radiation is detected within a signal measurement time interval and generating a timing function relating to the time distribution of the detected pulses. Additionally, the total count rate for the detected pulses within the signal measurement interval and count rate of detected pulses within a background measurement time interval are processed to obtain a measurement of relative background intensity. The relative background intensity and a timing function for background only within the signal measurement interval are used to correct the timing function for total detected pulses to provide a timing function for only the exponential signal. Each value of corrected timing function will define a single value of the macroscopic absorption cross-section of the irradiated earth formations.

Background correction method and apparatus for pulsed neutron logging of

A pulsed source of fast neutrons and a radiation detector system are utilized in a well logging instrument, the detector being responsive to the thermal neutron population decay rate. The inverse of the decay rate is proportional to the measured macroscopic neutron absorption cross-section (Sigma). A Sigma is calculated by taking the natural logarithm of the ratio of the detected radiation counts occurring within two measurement intervals of fixed duration and starting at a fixed time after the neutron burst. This Sigma measurement provides a feedback voltage which is used in altering the starting time of a single measurement interval in a subsequent source pulsing cycle to provide a measured Sigma value.

Method and apparatus for measuring neutron characteristics of material

A pulsed source of fast neutrons and a radiation detector system are utilized in a well logging instrument, the detector being responsive to the thermal neutron population decay rate. The inverse of the decay rate is proportional to the measured macroscopic neutron absorption cross-section (Sigma). A Sigma is calculated by taking the natural logarithm of the ratio of the detected radiation counts occurring within two measurement intervals of fixed duration and starting at a fixed time after the neutron burst. This Sigma measurement provides a feedback voltage which is used in altering the starting time of two measurement intervals in a subsequent source pulsing cycle to provide a measured sigma value.

A source of fast neutrons and a detector responsive to the thermal neutron population decay rate are utilized in a well logging instrument. The instrument is placed within a sample retention chamber. The neutron generator is periodically pulsed and the neutron detector is gated on at intervals of 100-150, 150-200, and 800-850 microseconds, respectively, following the termination of each burst of fast neutrons. The detected radiations within these intervals are used to indicate the apparent absorption cross section of the small fluid sample within the chamber. The absorption cross section is measured for a number of small samples of known salinity and calculatable true absorption cross section. A relationship is constructed of the true absorption cross section of the samples versus the measured absorption cross sections of the samples. When the chamber is filled with an unknown fluid sample the measured absorption cross section is correlated with the reference curve which will yield single unique true absorption cross section substantially free of diffusion effects for the measured absorption cross section value of the unknown small quantity sample.

Method for determining the absorption cross section of small fluid

A source of fast neutrons and two differently spaced detectors are utilized in a well logging instrument, each of such detectors being responsive to the thermal neutron population decay rate. The inverse of this decay rate is proportional to the measured macroscopic absorption cross section (Sigma). The measured Sigma is obtained simultaneously as a function of the radiation detected by each of two detectors. The signal generated which is indicative of the Sigma observed from one detector is subtracted from the Sigma observed by the second detector. The difference between the measured Sigma from two differently spaced detectors provides a unique function of the fluid-filled porosity of the formations giving rise to the measured Sigma values.

Pulsed neutron porosity logging method and apparatus using dual detectors

A neutron generator in a well logging instrument is periodically pulsed and has an off period between pulses of 1000 microseconds. A neutron detector is gated on at intervals of 400-500, 550-650, and 700-800 microseconds, respectively, following the termination of each burst of fast neutrons. Circuitry is provided for determining the background radiation by the equation: ##EQU1## where B is the background, and N.sub.1, N.sub.2 and N.sub.3 are the counts observed during the three gates, respectively. Circuitry is also provided for determining the macroscopic absorption (.SIGMA.) from the equation: ##EQU2## where V is the velocity of thermal neutrons, being a constant and .DELTA.t represents an increment of time.

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Houston, TX, United States of America

Russel R Randall