Abstract
In the oil and gas industry, pulse echo measurements have for decades been used in cased holes to estimate the properties of the materials on the outside of the pipe. To investigate the methods used to analyse pulse echo measurements from pipes, we use numerical modelling in COMSOL Multiphysics. While 3D models correctly capture the real geometry, they are computationally heavy and, therefore, not appropriate for simulating a large range of geometric and material variations. Analytic 1D plane wave models are fast to calculate, but we observe large deviations between the 3D and 1D results, showing that corrections to 1D model results are necessary. Therefore, we investigate using 2D and axisymmetric 2.5D models instead and find good agreement between the 2.5D and 3D model results and larger deviations between the 2D and 3D model results. Further, we find that the time explicit formulation works reliably, with an effective absorbing layer, while using the time domain formulation requires more care and a larger domain due to the poorer performance of its perfectly matched layer. Nevertheless, the time domain formulation is preferable when introducing thin domains and additional domain boundaries to keep the computational time at an acceptable level.
