Calibration, checking and physical corrections for a new dual-spaced neutron porosity tool

A new dual-spaced neutron tool has been developed that features high count rates and improved statistical precision and log repeatability. Environmental corrections including borehole diameter, standoff, and lithology are at acceptable levels for DSN-II. The effects of varying source-to-detector spacings and shielding are summarized. Porosity measurement resolution and statistical precision are discussed and it is indicated how tradeoffs between higher count rates and increased environmental corrections must be considered. The absolute calibration of a standard tool is based on its response to limestone test pits, field data, and theoretical calculations. Test data for actual manufactured tools are presented. Shop calibration and wellsite check procedures are discussed. The advantages of multiposition check operations are explained, including reduced sensitivity to check block positioning and external environment. An analysis is presented of errors from tool manufacturing, calibration, and check procedures. A generalized theory of neutron scattering and absorption has been developed to correct dual-spaced neutron logs for unusual minerals and fluids