P- and S-Wave Velocity Calculation Using X-Ray CT Images for Shaly Tight Sandstone

It is an important method to simulate P- and S-wave velocities using digital core obtained from X-ray CT images. However, since it is impossible to differentiate clay and grains, and abundant micro-pores exist in shaly tight sandstones, simulating P- and S-wave velocities using digital core is a challenge. In this study, 2D digital core models are constructed and simulated using finite element method to understand the effect of clay content and distribution, amount of micro-pores on the rock elastic properties. The results will be used to assist the construction of a 3D model that can be used to simulated P- and S-wave velocities of shaly sandstones. The results show that dispersed clay and framework clay have minor effects on the bulk modulus, while interstitial clay shows large effect on bulk modulus. Effects of the different clay distributions on shear modulus are similar. Clay distribution has larger effect on bulk modulus than clay content, whereas clay content has larger effect on shear modulus than clay distribution. Micro-pores related to dispersed clay have minor effect on rock elastic properties, however micro-pores related to framework clay and grain-grain contact clay are sensitive to rock elastic properties. In addition, micro-pores have larger effect on shear modulus than bulk modulus. Based on the above results, a 3D digital core model using 3D watershed method on the X-ray images has been built and the results show good match with the measured velocities.