Computer-based system for acquisition of nuclear well log data

Apparatus for acquisition of induced gamma ray well logging data indicative of the macroscopic neutron absorption capture cross-section of a subsurface formation and based upon electrical pulse signals produced by detection of gamma ray emission from the formation following release of a burst of neutrons directed into the formation, comprising:

• a multichannel scaling unit for receiving electrical pulse signals, for producing digital data representative of neutron population decay rate;
• a display unit coupled to the multichannel scaling unit, for presentation of neutron population decay rate data as a plot of gamma ray counts versus time;
• and
• a central processing unit (CPU), for issuing control commands to the multichannel scaling unit and display unit to sequence the acquisition and presentation of neutron population decay rate data.

Apparatus for acquisition of spectral gamma ray well logging data from electrical pulse signals produced by detection of induced gamma ray emission from a subsurface formation and synchronizing signal pulses indicative of neutron source triggering producing a burst of neutrons to induce gamma ray emission, comprising:

• a pulse height analyzer for receiving electrical signal pulses indicative of the energy of detected gamma rays and producing a multiple bit digital code representative of the peak amplitude of each pulse signal;
• a sync generator responsive to synchronizing signal pulses for producing a single bit digital code to distinguish between electrical signal pulses attributable to inelastic gamma rays and electrical signal pulses attributable to capture gamma rays;
• a random access memory for accumulating counts to detected gamma rays according to the energy level in addressable locations therein, said accumulated counts providing digital data representative of the spectrum of detected gamma ray energies;
• said memory being coupled to the pulse height analyzer and the sync generator so as to be addressed by a digital code word comprising the multiple bit code from the pulse height analyzer and the single bit code of the sync generator;
• means for incrementing the count in an addressed memory location;
• control logic coupled to the pulse height analyzer, the random access memory, and the count incrementing means, for controlling the incrementing of a count in an addressed memory location;
• a spectrum display unit coupled to said memory, for real-time presentation of spectral gamma ray well logging data as a plot of accumulated counts per incremental energy level;
• and
• means for issuing control commands to the control logic and the spectrum display to sequence the acquisition and presentation of well logging data.

Apparatus for acquisition of spectral gamma ray well logging data from electrical pulse signals produced by detection of gamma ray emission from a subsurface formation and transmitted over a logging cable, comprising:

• signal conditioning means for receiving electrical pulse signals having amplitudes indicative of the energy of detected gamma rays and providing signal gain to compensate for logging cable attenuation losses;
• said signal conditioning means being adjustable to provide variable signal gain in response to a control signal applied thereto;
• a digital-to-analog converter, for producing an analog output signal representative of a gain control input digital value applied thereto;
• circuit means interconnecting the digital-to-analog converter and said signal conditioning means, for applying the control signal to said signal conditioning means;
• a signal recovery unit coupled to said signal conditioning means, for producing digital data representative of the spectrum of detected gamma ray energies;
• and
• a central processing unit (CPU), for accessing the signal recovery unit to acquire digital gamma ray energy spectrum data therefrom, for evaluating the acquired data to determine the location in the energy spectrum of a particular energy peak and comparing the actual location to a desired location, for computing a gain control input digital value based on the difference between the actual and desired energy peak locations, so as to automatically compensate for gain drifting.

Apparatus for acquisition of spectral gamma ray well logging data, comprising:

• a sample and hold circuit coupled to said logging cable, for producing a voltage level equivalent to the peak amplitude of a gamma spectrometer electrical pulse signal;
• a successive approximation analog-to-digital converter for converting the voltage level to an equivalent digital code;
• a random access memory for accumulating counts of detected gamma rays according to energy levels in addressable locations therein;
• said memory being coupled to the analog-to-digital converter so as to be addressed by said digital code;
• means for incrementing the count in a memory location addressed by said digital code;
• a spectrum display unit coupled to the random access memory, for real-time presentation of accomulated counts as a plot of counts versus gamma ray energy level;
• and
• means for issuing control commands to sequence the acquisition and presentation of the detected gamma ray counts.

Apparatus for acquisition of nuclear well logging data from electrical pulse signals produced by a nuclear particle detector in a subsurface well logging instrument as it traverses a well borehole, and transmitted to the surface over a logging cable coupled to the logging instrument, comprising:

• a pulse height analyzer (PHA) responsive to detector electrical pulse signals, for producing a digital code representative of the peak amplitude of a pulse signal;
• an address generator, for producing a sequence of address codes, the address codes defining incremental units of time;
• a multiplexer connected to said pulse height detector and said address generator, for selecting an output code from between the PHA and the address generator depending upon a selected data acquisition mode;
• a random access memory connected to said multiplexer so as to be addressed by the selected output code, said memory accumulating counts of detected gamma rays according to energy level when operation is in a spectral gamma ray well logging data acquisition mode, and memory accumulating counts of detected gamma rays according to their time of occurrence when operation is in an induced gamma ray well logging data acquisition mode;
• means for incrementing the value in an addressed memory location;
• control logic, for producing a mode select signal for actuating said multiplexer to select between the PHA and the address generator, for producing memory control commands to output the value in an addressed memory location and write an incremented value into the addressed memory location, and for producing a series of clock pulses to step said address generator through the sequence of address codes upon command and provide for reading count values out of memory when operation is in a data output mode;
• means for placing a count value read out of memory onto a buss line;
• a display unit coupled to the buss line, for receiving count values read out of memory and providing a presentation of the count values as well logging data;
• and
• a central processing unit (CPU), for issuing commands to said control logic and said display to sequence the acquisition and presentation of nuclear well logging data.

Apparatus for acquisition of spectral gamma ray well logging data, comprising:

• subsurface well logging instrument to traverse a well borehole, the instrument including a gamma spectrometer, for detecting gamma ray emission from subsurface formations and producing electrical pulse signals indicative of the energies of detected gamma rays;
• a logging cable coupled to the subsurface well logging instrument, for providing a transmission medium to the surface for gamma spectrometer electrical pulse signals;
• a signal recovery unit coupled to the logging cable for receiving gamma spectrometer electrical pulse signals and producing digital data representative of the spectrum of detected gamma ray energies;
• a spectrum display unit coupled to the signal recovery unit, for presentation of spectral gamma ray well logging data as a plot of relative gamma ray emissions activity versus energy level;
• and
• a computer, for issuing control commands to the signal recovery unit and the spectrum display to sequence the acquisition and presentation of spectral gamma ray well logging data.

Apparatus for acquisition of gamma ray well logging data including data indicative of the macroscopic neutron absorption capture cross-section of a subsurface formation and data indicative of the energy spectrum of gamma ray emission from a subsurface formation from electrical pulse signals produced by detection of gamma ray emission from a subsurface formation, comprising:

• a pulse height analyzer for receiving an electrical pulse signal having an amplitude indicative of the energy of a detected gamma ray producing the pulse and producing a digital code representative of the peak amplitude of the pulse signal;
• an address generator, for producing a sequence of address codes following a neutron burst into a subsurface formation, the address codes serving to address successive memory locations and define incremental time units;
• means for selecting between the codes available from said pulse height analyzer and said address generator;
• a random access memory coupled to said selecting means to receive the selected code,
• said random access memory for accumulating counts of detected gamma rays according to energy levels in addressable locations therein when addressed by the pulse height analyzer code, so as to produce digital data representative of the spectrum of detected gamma ray energies;
• said random access memory for accumulating counts of detected gamma rays according to their time of occurrence following a neutron burst, said memory accumulating counts in addressable memory locations therein corresponding to specific incremental units of time following a neutron burst, when addressable by the address generator address codes, so as to produce digital data representative of neutron population decay rate in the formation;
• a display coupled to said memory for presentation of the digital data in said memory;
• and
• a central processing unit (CPU), for issuing control commands to sequence the production and presentation of digital data in said memory.