A Robust Empirical Model to Generate Pseudo Sonic Logs from Neutron Porosity Logs

Good well ties are an essential part of any seismic interpretation or reservoir characterisation workflow. This requires accurate and complete density and sonic curves in order to generate a synthetic seismogram. There are a wide variety of published empirical models based upon the work of Gardner et al. (1974) and Faust (1951) that are routinely used to calculate replacement sonic or density curves with varying degrees of accuracy. Using a large and globally distributed set of well logs, we develop a novel empirical model that relates neutron porosity and slowness (compressional sonic) that may be used to calculate a reasonable and accurate pseudo sonic estimate. The method relies on the availability of a neutron porosity log, a type of log that is commonly found in a wide range of log vintages dating back to the late 1940s. Results from multiple basins will be shown to demonstrate the robustness of this method and the corresponding model. We believe that this very simple and effective method will provide the working geophysicist with another useful tool to create pseudo sonic logs suitable for generating synthetic seismograms.