TESTING THE VIABILITY OF SUPERCRITICAL CO2 AS A FRACKING FLUID BY COMPUTING ITS CHEMICAL INTERACTION WITH VARIOUS MINERALS

Fracking has been of particular interest in Pennsylvania over the last few years. Research has shown that alternative fluids, such as gases or supercritical fluids, produce larger and more complex fractures, making it possible to extract a larger volume of hydrocarbons. Consequently, examining CO₂-shale interaction from a molecular approach may shed light on interfacial interactions that lead to a larger fracture. Supercritical CO₂ (scCO₂) is of particular interest because if carbon sequestration is more widely implemented, scCO₂ will become a much cheaper fracturing fluid. ScCO₂ will also be more economically viable in regions where water is scarce. A lot of research has been done in looking at scCO₂-shale interactions from a molecular approach with regards to carbon sequestration, but not with regards to fracking.

We plan on using molecular modeling to compare water and scCO₂ interactions with illite (a common component of the Marcellus Shale and other shale gas formations). We are deriving the interfacial energies of illite with scCO₂ and water (i.e., the energy of interaction between the two components) from these simulations at pressure and temperature relevant to shale gas extraction (e.g. T=60^oC and P=300 bar). The interfacial energies are important because they can give us a better idea of what creates larger and more complex fractures. For instance, a fluid with a smaller interfacial energy with the shale can be expected to yield a larger fracture network because it would be able to enter the shale more easily and flow throughout the rock. As fluid is added and the pressure in the rock builds up, it would then produce a greater fracture network.

We would expect that the interaction energy between illite and CO₂ will be smaller than the interfacial energy with water. This is because the supercriticality of CO₂ will cause the compound to interact less with the K atoms at the surface of the illite grains. We believe that this lower interfacial tension is the factor that leads to a higher complexity of fractures with scCO₂, because the scCO₂ is better able to diffuse into nanopores and nucleate fractures compared to water.