Characterization and microfabrication of natural porous rocks: From micro-CT imaging and digital rock modelling to micro-3D-printed rock analogs

Tests on standard rock specimens with controlled and identical pore structure are critical to validating the analytical and numerical models. However, it is usually difficult to acquire two natural samples with the same internal structure for the destructive laboratory tests, for the sake of the heterogeneity of natural rock which is caused by the complex diagenetic processes. Three-dimensional (3D) printing technology provides an alternative approach to produce geometry-identical, features-controllable, and lab-testable analogs of natural rock from digital data in a faster and more cost-effective way. This paper presents a customized workflow of 3D-printed rock analogs from micro-CT images combining with digital rock modelling. Three types of natural rock specimens are imaged by micro-CT and processed as inputs for two types of 3D printing techniques. Rock analogs are printed at multiple magnifications from original CT volume in five curable resin materials. Petrophysical parameters of 3D-printed rock analogs are acquired through helium pycnometry (HP) and mercury intrusion porosimetry (MIP). The accuracy of 3D-printed rock analogs is evaluated by comparing the measured results with the benchmark data derived from the digital rock modelling. Both the advantages and the current challenges to reproduce the real pore structure of natural rock by the 3D-printed analogs are discussed. The results indicate that the gypsum-based printed analogs are prior to modelling the surface roughness and wettability properties to natural rock grains, while the resin-based printed analogs owe advantages on reproducing pore structure. As the first effort in literature, this study investigates the inherent relationship between digital rock and 3D-printed rock analogs via comprehensive comparison on petrophysical properties. The results approve that the 3D printing technique is a novel, feasible, and alternative approach for laboratory test to generate rock analogs from the digital model of the natural rock. However, it is still difficult to print the pore structure of the rock at the original dimension.