Printing Rocks to Experiment with Pore Space
What if we could experiment with pore space and thus build better reservoir models? Petrophysicists and geological modelers both run into difficulties when they attempt pore-scale modeling of earth materials. Petrophysicists cannot easily test hypotheses about the effect of pore space morphology on fluid flow because, in geological materials, it is difficult to establish a control case with which experimental cases can be compared. For example, in limestones one type of pore cannot be "turned off" to see the resultant impact on flow.
Current methodologies for geological modeling and reservoir simulation are overly simplistic. They proscribe the reservoir's geology into a grid, which is seldom if ever geologically accurate, resulting in the edges of geological bodies appearing "pixelated." Whatever geology lies within a cell is approximated by only a few petrophysical values (e.g. porosity, permeability) even though these quantities are known to vary on scales much smaller (microns) than the highest-resolution geological models (meters). If the pore system in a model cell could be characterized beyond simple petrophysical values, the fidelity of static geological models could be increased as well as the accuracy of subsequent reservoir flow simulations.
Three-dimensional, periodic minimal surfaces offer an analytical way to characterize the porous structure of geological materials. Just as a mathematical equation can define a plane that separates two volumes, more complex equations can define more intricately "folded" surfaces separating two volumes. The more intricate these surfaces become, the more they resemble porous materials (the two separate volumes being mineral and porosity). Previously, these surfaces have been used to describe the echinoderm ossicles, which are made of calcite and have porosities up to fifty percent.
In this study, mathematical surfaces have been identified that best represent sedimentary pore systems. These surfaces have been realized as polymer models of one-inch core plugs using a 3-D rapid-prototyping printer and analyzed for their porosity and permeability. In addition, these artificial core plugs have been "scaled up" digitally to eight inches in diameter for teaching purposes. Future efforts will focus on 1) manipulating these mathematical models to test petrophysical properties in different pore systems and 2) printing these models using mineral material (like quartz or calcite).
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013