Alireza Gerami

Abstract Fluid flow in porous rocks is commonly capillary driven and thus, dependent on the surface characteristics of rock grains and in particular the connectivity of corners and crevices in which fluids reside. Traditional microfluidic fabrication techniques do not provide a connected pathway of crevices that are essential to mimic multiphase flow in rocks. Here, geo-material microfluidic devices with connected pathways of corners and crevices were created by functionalising Polydimethylsiloxane (PDMS) with rock minerals. A novel fabrication process that provides attachment of rock minerals onto PDMS was demonstrated. The geo-material microfluidic devices were compared to carbonate and sandstone rocks by using energy dispersive X-ray spectroscopy, scanning electron microscopy (SEM), contact angle measurements, and a surface profilometer. Based on SEM coupled with energy-dispersive X-ray spectrometry (SEM-EDS) analyses, roughness measurements, contact angle, wettability, and roughness were comparable to real rocks. In addition, semivariograms showed that mineral deposition across the different geo-material devices was nearly isotropic. Lastly, important multiphase flow phenomena, such as snap-off and corner flow mechanisms, equivalent to those occurring in reservoir rocks have been visualised. The presented approach can be used to visualise rock-fluid interactions that are relevant to subsurface engineering applications, such as hydrocarbon recovery and CO 2 sequestration.

Geomaterial microfluidics are the next generation of tools necessary for studying fluid flows related to subsurface engineering technologies. Traditional microfluidic devices do not capture surface wettability and roughness parameters that can have a significant influence on porous media flows. This is particularly important for coal seam gas reservoirs in which methane gas is transported through a well-developed system of natural fractures that display unique wettability and roughness characteristics. A coal geomaterial microfluidic device can be generated by etching a fracture pattern on a coal surface by using three-dimensional laser micromachining; however, it is unclear if the resulting surface properties are representative of real coal. In an effort to generate a realistic coal microfluidic device, we characterize coal surface roughness properties from real coal cleats. We then compare these results to the roughness of the patterns, generated from laser etching. Roughness measurements in real coal fractures show that cleats and microfractures are mostly oriented parallel to the coal beddings rather than perpendicular to the bedding, which is important when selecting coal for fabrication of a microfluidic device since we find that the natural microfractures influence the resulting roughness of etched fractures. We also compare resulting coal/brine/gas contact angles under static and dynamics conditions. The contact angle for coal is highly heterogeneous. Surface roughness and pore pressure may influence the contact angle. With the aid of the coal geomaterial device, the effect of these parameters on coal wettability can be explored and a range of possible coal contact angles can be visualized and represented. The geomaterial fabrication, as outlined herein, provides a tool to capture more realistic coal surface properties in microfluidics experiments.