A typical well logging configuration. Well logging is widely used in the oil industry. The interpretation of the data is based on benchmark measurements in a known environment, comparison with data from other types of measurements, and computer simulation of the measurements with neutron and gamma-ray transport codes. The computer simulation is done by calculating the response of a tool to a given material using the linear Boltzmann equation and libraries of neutron and photon cross-section data widely available. The ability to calculate responses greatly enhances the ability to design optimum tools and to interpret their response, because different tool designs or material combinations can be investigated with calculations rather than with expensive experiments.
Some tools depend on a time-dependent response, which adds another variable.
The geometry is awkward, because the critical dimensions of the tool are small, but the interaction with the material takes place over quite a large volume. The current practice is to use the Monte Carlo method for these calculations. In Monte Carlo, one takes a random sample of the phase space. This method often makes it possible to get answers to problems that are too complex to solve by more conventional methods. Because a random process is used, all results come with some statistical uncertainty.