Time-derived sigma for pulsed neutron capture logging

Journal Article · Wed Jun 01 04:00:00 EDT 1983 · J. Pet. Technol.; (United States)

DOI:https://doi.org/10.2118/9614-PA· OSTI ID:5406625

Randall, R R; Fertl, W F; Hopkinson, E C

This paper reviews field applications of the Dresser Atlas Neutron Lifetime Log /SUP TM/ (NLL) service and examines recent technical advances in the instrumentation and data-analysis system. The major improvement discussed is a new method for computing ..sigma.., the thermal neutron capture cross section of an earth formation. In the new method, the time after the neutron burst is measured for each gamma ray pulse detected by the instrumentation system within a gate of fixed width. This ''average pulse time'' is uniquely related to the thermal neutron decay rate observed in a borehole environment. The technique discussed is applicable for any condition where the neutron or gamma ray flux is timedependent. The advantages of this signal-processing method, however, are most apparent for cases of rapid flux change with time, as in an exponential decay. A simple two-gate method of measurement suffers, statistically, from the lower count rate of the second gate. An average-pulse-time measurement over the same range covered by both gates of a two-gate system is less affected by statistical deviations than the ratio normally formed between the two gates. Some important advantages result from this type of signal processing when applied to the NLL service. First, the statistical accuracy of the log is improved; second, the instrumentation required for implementation of the method is not complicated. Also, the average-pulsetime measurement can be made with either digital or analog equipment, and since it involves only simple arithmetic computations, the method is much simpler to implement than either least-squares or correlation methods.

• Research Organization: Dresser Atlas
• OSTI ID: 5406625
• Journal Information: J. Pet. Technol.; (United States), Journal Name: J. Pet. Technol.; (United States) Vol. 35:7; ISSN JPTJA
• Country of Publication: United States
• Language: English

Related Subjects

440400* -- Well Logging Instrumentation
47 OTHER INSTRUMENTATION
ACCURACY
BARYON REACTIONS
BARYONS
CAPTURE
CROSS SECTIONS
DATA PROCESSING
DECAY
ELEMENTARY PARTICLES
EQUIPMENT
FERMIONS
FIELD TESTS
GEOLOGIC FORMATIONS
HADRON REACTIONS
HADRONS
MATHEMATICS
NEUTRON LOGGING
NEUTRON REACTIONS
NEUTRON-GAMMA LOGGING
NEUTRONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
NUCLEONS
PROCESSING
PULSE RISE TIME
PULSE TECHNIQUES
RADIATION FLUX
RADIOACTIVITY LOGGING
STATISTICS
TESTING
THERMAL NEUTRONS
TIME DEPENDENCE
TIME MEASUREMENT
TIMING PROPERTIES
WELL LOGGING
WELL LOGGING EQUIPMENT