Formation sigma measurement from thermal neutron detection
In a logging system including a sonde for traversing a borehole at a controlled speed between spaced apart elevations in an earth formation, means carried by the sonde for irradiating the formation and generating detector signals indicative of the response of the borehole environment in and around the sonde to the radiation, and data processing means for computing at least one characteristic of the borehole environment from the detector signals, said at least one characteristic including the macroscopic thermal absorption cross section of the formation (formation sigma), the logging method is described using said sonde comprising the steps of: (a) irradiating the formation with a pulsed source of high energy neutrons as the sonde traverses the borehole, whereby the neutrons generated at each pulse interact with the borehole environment to produce a neutron population having a space, time and energy distribution including epithermal and thermal energies; (b) with a detector that has an azimuthally limited angle of receptivity, detecting the time-dependent population of thermal neutrons at an eccentric position in the borehole during a period of time between successive source pulses and generating a thermal neutron detector signal commensurate with said time-dependent population; and (c) from the thermal neutron detector signal, computing the value of formation sigma at the elevation of said eccentric position.
- Assignee:
- Schlumberger Technology Corp., New York, NY (United States)
- Patent Number(s):
- US 5235185; A
- Application Number:
- PPN: US 7-819541
- OSTI ID:
- 6278731
- Resource Relation:
- Patent File Date: 1 Jan 1992
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
47 OTHER INSTRUMENTATION
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
BOREHOLES
NEUTRON-NEUTRON LOGGING
NEUTRON DETECTORS
PERFORMANCE
GEOLOGIC FORMATIONS
IRRADIATION
NEUTRON DETECTION
RESERVOIR ROCK
THERMAL NEUTRONS
TIME DEPENDENCE
WELL LOGGING EQUIPMENT
BARYONS
CAVITIES
DETECTION
ELEMENTARY PARTICLES
EQUIPMENT
FERMIONS
HADRONS
MEASURING INSTRUMENTS
NEUTRON LOGGING
NEUTRONS
NUCLEONS
RADIATION DETECTION
RADIATION DETECTORS
RADIOACTIVITY LOGGING
WELL LOGGING
580000* - Geosciences
440400 - Well Logging Instrumentation
440101 - Radiation Instrumentation- General Detectors or Monitors & Radiometric Instruments