HOW TO 3D PRINT POROUS ROCKS MODELS LIKE THE EARTH DOES

One of the most valuable properties of rocks is that they can be porous. Rock pores can store valuable fluids (e.g. water, carbon dioxide, oil, natural gas) or waste streams (e.g. frack water). A rock’s pore size distribution is a useful predictor of how it will perform in concrete pavements.

The usefulness of porous rocks is confounded by their difficulty to study. Pores in reservoir rocks can range from km’s (e.g. Carlsbad Caverns) to nm’s (e.g. organic matter pores in shale). While the average reservoir rock is not this variable, pore sizes can still range over several orders of magnitude. This “wide range of normal” is difficult for any single analytical instrument to probe, be it seismic, well logs, computed tomography, or mercury porosimetry.

3D Printing offers numerous distinct advantages for studying reservoir rocks stemming from its ability to synthesize pore networks in various materials. First, it allows replication of pore networks. A researcher can produce identical copies of a pore network to test different production scenarios or e-mail a pore network to a distant colleague for analysis. Second, it allows the effects of pore network and surface physics to be studied in isolation. A pore network can be printed in different materials or a single material can be used to print different pore networks. Third, it allows a pore system to be upscaled or downscaled. Fourth, it serves as test of digital rock property simulators. While digital simulation results are commonly compared to laboratory analyses on real rocks, the property simulation is being run on a digital pore network model. That digital model can be 3D printed to provide another test of simulation results. Fifth, it allows truly synthetic pore network models to be tested in the lab. These pore network models could be simple geometries (e.g. a cylindrical tube running axially through a cylinder), more complicated mathematics (e.g. periodic minimal surfaces), or stochastically generated (e.g. reverse-engineering a core plug from well cuttings).

The Earth itself is a 3D printer and valuable insights into designing and manufacturing porous rock models can be gleaned from understanding how natural processes and materials create the porous rocks we find so interesting.