Microstructure Characterization and S-wave Velocity Prediction in the Barnett Shale Formation

Abstract

Microstructure characterized by pore aspect ratio is a critical parameter which reveals the connectivity of fluid-filled cracks and pores and therefore has a strong influence on permeability in shales. Pore aspect ratio also has a great effect on elastic properties. We use the self-consistent approximation method to build a shale rock physics model for the inversion of pore aspect ratio. Inverted results show that the value of aspect ratio presents much less variety in the Barnett Shale compared to that in surrounding carbonates, which may imply the presence of more complex systems of fractures and cracks in the surroundings. We then investigate the correlations between geomechanical properties and microstructure parameters, and find that the increase in crack density decreases Young's modulus and shear modulus in surrounding carbonates but such correlation is not obvious in the Barnett Shale. In addition, the effect of crack density on Poisson's ratio is weak in all the relevant formations. Another work of this study is to predict S-wave velocity by using the inverted aspect ratio as a constraint. The prediction results indicate good agreements between predicted and real S-wave velocity for all three tight formations.