Modelling a simple gamma-gamma density well logging tool

We discuss the so-called P1 approach for approximation of the transport equation for gamma photons. We use it to model a simplified gamma-gamma density tool. The model is compared with Monte Carlo simulations. It is shown that the discrepancies between the model and the Monte Carlo simulations can be understood by looking at higher order approximations. This knowledge is used to improve the model which is then applied to a number of standard logging simulations and compared with Monte Carlo simulations.