Macroscopic Thermal Neutron Capture Cross Section Measurements

The macroscopic thermal neutron-capture cross-section measurement in cased-well bores is discussed. The physical parameter measured is the formation capture cross section which is related to the type of fluid saturating the pore space. This measurement distinguishes between gas and water, gas and oil, and oil and water provided the water is saline. The physics of the measurement and the historical development of the instrumentation are reviewed. Important instrumentation elements are examined. The reasons for the limitation of the measurement to saline connate-water environments of modest to high porosity and simple lithology are listed and quantified. Current hardware and software developments that aim at more-sophisticated data acquisition and reduction are examined in detail. Other important applications such as production monitoring and enhanced-oil-recovery prospects are briefly discussed.