Systematic Evaluation of Stoneley Mobility and Its Petrophysical Application Conditions

Abstract In this study, a comprehensive workflow of estimating formation mobility using Acoustic Stoneley wave was evaluated, with diverse subsurface conditions and drilling environments including hole size, mud type, formation lithology, and formation fluids. The outcome of this exercise aimed to compare inverted Stoneley mobility and that from formation testing. The parameters tested with high significance on Stoneley mobility are mud acoustic slowness, mud acoustic attenuation, and the mud cake membrane stiffness. Analysis applied on these parameters showed a variation of uncertainty as well as sensitivity to mobility, with mud cake membrane stiffness being the most uncertain, and mud acoustic slowness and attenuation being the inputs with high sensitivity. The findings of this study suggest that Stoneley mobility inversion can be used to quantitively estimate a continuous mobility log in clastic formations, a great value with many applications such as optimizing formation testing depths and, on a multiwell scale, in permeability characterization. It is therefore recommended that the Stoneley mobility be integrated in integrated studies for clastic reservoirs, serving as an intermediate measurement between the high resolution and accurate core permeability and formation testing mobility, and that derived from Drill Stem Tests; all are discrete measurements. It is also observed that, when comparing with formation testing results, applying the same Stoneley mobility inversion in heterogeneous carbonate formations seems challenging, an area for further study.