Directional epithermal neutron detector

Patent · Tue Apr 08 04:00:00 EST 1986

OSTI ID:5624812

Givens, W W; Mills, Jr, W R

A borehole tool for epithermal neutron die-away logging of subterranean formations surrounding a borehole is described which consists of: (a) a pulsed source of fast neutrons for irradiating the formations surrounding a borehole, (b) at least one neutron counter for counting epithermal neutrons returning to the borehole from the irradiated formations, (c) a neutron moderating material, (d) an outer thermal neutron shield providing a housing for the counter and the moderating material, (e) an inner thermal neutron shield dividing the housing so as to provide a first compartment bounded by the inner thermal neutron shield and a first portion of the outer thermal neutron shield and a second compartment bounded by the inner thermal neutron shield and a second portion of the outer thermal neutron shield, the counter being positioned within the first compartment and the moderating material being positioned within the second compartment, and (f) means for positioning the borehole tool against one side of the borehole wall and azimuthally orienting the borehole tool such that the first chamber is in juxtaposition with the borehole wall, the formation epithermal neutrons penetrating into the first chamber through the first portion of the outer thermal neutron shield are detected by the neutron counter for die-away measurement, thereby maximizing the directional sensitivty of the neutron counter to formation epithermal neutrons, the borehole fluid epithermal neutrons penetrating into the second chamber through the second chamber through the second portion of the outer thermal neutron shield are largely slowed down and lowered in energy by the moderating material and absorbed by the inner thermal neutron shield before penetrating into the first chamber, thereby minimizing the directional sensitivity of the neutron counter to borehole fluid epithermal neutrons.

• Assignee: Mobil Oil Corp., New York, NY
• Patent Number(s): US 4581532
• OSTI ID: 5624812
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
440101 -- Radiation Instrumentation-- General Detectors or Monitors & Radiometric Instruments
440400 -- Well Logging Instrumentation
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
47 OTHER INSTRUMENTATION
ABSORPTION
AZIMUTH
BARYONS
BOREHOLES
CAVITIES
DETECTION
ELEMENTARY PARTICLES
EPITHERMAL NEUTRONS
EQUIPMENT
FAST NEUTRONS
FERMIONS
GEOLOGIC DEPOSITS
HADRONS
IRRADIATION
MEASURING INSTRUMENTS
MINERAL RESOURCES
MODERATORS
NEUTRON DETECTION
NEUTRON LOGGING
NEUTRON-NEUTRON LOGGING
NEUTRONS
NUCLEONS
PETROLEUM DEPOSITS
POSITIONING
PULSE TECHNIQUES
RADIATION DETECTION
RADIATION DETECTORS
RADIOACTIVITY LOGGING
RESOURCES
SHIELDS
THERMAL SHIELDS
WELL LOGGING
WELL LOGGING EQUIPMENT