METHOD OF COMPENSATING FOR THE PHOTOELECTRIC EFFECT IN PULSED, ACCELERATOR-BASED LITHO-DENSITY TOOL

摘要

A method for a pulsed gamma - gamma density tool to simultaneously compensate for interactions due to the photoelectric effect and density variations caused by standoff enables a more precise determination of bulk formation density. This method includes the steps of providing a source of energetic particles and directing those energetic particles at a formation having a known photoelectric factor and electron density and capturing one or more photons either emitted or deflected from the formation either a first detector or a second detector. The first detector is spaced a first distance from the source, the second detector is spaced a second distance from the detector and a third distance separates the first detector from the second detector. Measuring a first total energy of the photons striking the first detector during a time interval and measuring a second total energy of the photons striking the second detector as a function of the time interval and disposing a first filter between the first detector and the formation effective to cause Pe response to match standoff influence thereby compensating for both effects simultaneously. In addition to the first filter, the required compensation may include a second filter between the second detector and the formation as well as adjustments to the respective first distance, second distance and third distance.