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Flow Experiments on 3-D Printed Rock Proxies: Investigating Porosity-Permeability Relationships


Most geoscience experiments and test methods are destructive. 3D printing offers an unprecedented opportunity to perform destructive tests on rock proxies that mimic the original rock sample. Geoscientists can design rock replicas with known material properties and systematically repeat experiments by varying either the rock properties or the experimental parameters. 3D printing will enable advances in fundamental geoscience experiments that cannot be fully achieved with conventional laboratory or computational methods. Pore geometry, fluid chemistry and interfacial physics are primary controls on matrix permeability, yet experimental limitations prevent rigorous investigation of these controls. For example, few studies exist that adequately document the effect of changing pore structure on permeability. Here we present a proof-of-concept workflow for flow experiments on 3D printed replicas of a Berea sandstone core-plug. The geometric arrangement of the pores is identical, however the size of the pores were varied to represent dissolution and precipitating processes. This concept is key in considering how reactive transport and chemical reactions uniformly modify pore networks and therefore change porosity and permeability relationships. A 1.5 inch natural Berea core-plug was first imaged by X-ray CT scan and a 3D digital reconstruction was generated which accurately reproduced the physical pore network geometries. The digital model (400×400×400 voxels) was then modified by shrinking or enlarging the pores by one layer of voxels successively, resulting in 5 digital rock proxies with varying pore volume. Each rock proxy was printed 4 times and stacked to create composite cores that were a total of six inches long and 1.5 inches in diameter. Single phase core-flood experiments were then carried out for each of the composite cores at a confining pressure of 1500 psi for water. Results are then used to evaluate the change in permeability as a function of porosity. While these rock proxies and experiments are not representative of natural reservoir flow behavior, they provide an important first step in constraining the feasibility of these types of experiments. Future investigations involving complex rock textures and reactive transport will allow evaluation pore-scale flow processes and support validation of numerical models currently used to simulate those processes.