Controlling factors on elastic wave velocities of conglomerate – Experimental and theoretical study

Abstract

As an important type of clastic rocks, the conglomerate has quite different physical properties compared to sandstone due to its strong heterogeneity. Hence, studying the relationship between conglomerate physical properties and elastic wave velocities is essential for the seismic exploration or sonic logging interpretation of conglomeratic reservoirs. In this work, various physical properties and elastic wave velocities of dry conglomerate samples were measured, based on which their relationships were investigated. The results show that the gravel content and porosity are two controlling factors on conglomerate elastic wave velocities. For the studied samples, the content of middle-sized gravels (diameter ≥4 mm) affects the elastic wave velocities greatly due to their high elastic moduli. Besides the gravel content and porosity, the gravel contact patterns and cementation types are key geometrical details that also affect elastic wave velocities significantly. Different gravel contact patterns and cementation types result in notable differences in elastic wave velocities. To further illustrate the effects of geometrical details on elastic wave velocities, a theoretical modelling approach that accounts for gravel contact patterns and cementation types was proposed. The predictions given by this theoretical modelling approach agree well with experimental results, which validates the important roles of gravel contact patterns and cementation types on conglomerate elastic wave velocities. This work provides a basis for inverting conglomerate physical properties from elastic wave velocities, which is helpful for the seismic exploration or sonic logging interpretation of conglomeratic reservoirs.