ELASTIC PROPERTIES OF 3D PRINTED FRACTURE MODEL WITH TRANSVERSELY ISOTROPIC BACKGROUND

In most rock physics models, background anisotropy was neglected which, however, may exists in many fractured formation rocks. Recently, a theoretical model for rock effective elastic properties with penny-shaped cracks embedded in the transversely isotropic (TI) background medium was proposed, whereas no rigorous experimental validation of this theoretical model has been carried out. Hence, to validate this theoretical model, experiments were conducted in this work, for which 3D printing was utilized owing to the advantages against traditional manufacturing: efficient, saving material, and being able to fabricate the complex geometry structures. Firstly, the effective elastic properties of the background medium were measured, by which the elastic properties of fractured rocks with TI background medium can be predicted by the theoretical models. To investigate the suitable printing material and orientation, Antero, Polycarbonate (PC), and Acrylonitrile Styrene Acrylate (ASA) materials were utilized and three different printing directions, vertical, 45°, and horizontal, were considered as well. For manufacturing a series of samples, cylindrical digital models were designed with the inclusion of cracks in different lengths, 10 mm, 15 mm, and 20 mm. The prediction of this theoretical model considering the TI background is closer to the experimental results compared to Hudson's model. The discrepancy between experiments results and theoretical predictions may be caused by the non-unique material properties and 3D printing methods. Additionally, the P- and S-wave velocities were measured under different confining pressure using the AutoLab apparatus to examine the confining pressure effect. This experimental attempt verified the theoretical advancement that background anisotropy has a significant influence on P- and S-wave velocity anisotropy, increasing or decreasing P- and S-wave velocity depending on crack inclination angles. This study also demonstrated the application of 3D printing technology in rock physics experiments, which could be extended in future research.