Mathematical modeling of a gravel-pack logging tool

This report discusses a sophisticated mathematical model of a gravel-pack logging tool that has a gamma ray source and a single gamma ray detector. The authors use a generalized Monte Carlo computer code, called MCNP, to model photon transport in three-dimensional (3D) geometries. This approach includes a technique called variance reduction, which both reduces computational time and increases the precision of the results. The mathematical model is verified by comparison of calculated results with measurements made in laboratory simulations of gravel-pack completions. Laboratory measurements reported previously included a wide selection of fluids of various materials and densities, several screens, tubings, and two casing sizes. Comparison of the modeling results with experimental data reveals excellent agreement, giving a high level of confidence to the model. This study had three major objectives: (1) to expand our understanding of the physical processes involved, (2) to verify and to interpret the laboratory data, and (3) to provide a method by which tool responses can be obtained for a variety of borehole and gravel-pack conditions not measured in the laboratory. Thus, the authors were able to develop a generalized interpretation method that predicts downhole conditions as a function of tool response. A field example showing more » this interpretation procedure is presented. « less