Microstructure characteristics and fractal analysis of 3D-printed sandstone using micro-CT and SEM-EDS

Replicating sedimentary rocks using three-dimensional (3D) printing can support routine reservoir rock analysis in petrophysical and geomechanical experiments, which is done limited in scope due to lack of suitable printing materials and achievable resolution. Following our previous studies on gypsum powder with binder, a new printing material, silica sand, is used and characterized in this study to demonstrate the microstructure and its similarity to Berea Sandstone. Binder jetting printing system was specifically utilized to bond silica sand particles to create intact cylindrical samples without digital porous model as input. Created samples were first scanned by Backscattered Scanning Electron Microscope (BS-SEM) and Energy Dispersive Spectroscopy (EDS) to identify the particles, the packing mode and cement (binder). Next, micro-computed tomography (CT) was used to determine the microstructure of the samples, including the size and the shape of both particles and pores, in the 3D space. In addition, anisotropy that was found to originate from the pore structures was quantified by comparing the characteristics of pores in different directions. Fractal dimensions from different sample sizes, 6 mm and 12 mm in diameter, were also calculated for pore structure analysis in order to illustrate the effect of sample size on pore heterogeneity in 3D printed samples with silica. The results demonstrated the feasibility of substituting 3D-printed sandstones for natural rocks regarding pore structures for experimental validation of petrophysical models.