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Understanding how micro porosity effects flow when upscaling to the pore-scale is imperative for accurate predictive modeling of flow in porous media. However, it is not currently possible to image at nanoscale resolutions on larger scales. Furthermore, models with trillions of voxels are computationally expensive, requiring high-performance computing to solve their vast geometries. Carbonate rocks in particular often have complex and multiscale porosity structures that are poorly understood. In this study we use a combined experimental, modeling, and pore space generation methods to tackle the impact of micro porosity on the bulk flow properties of Estalliades limestone. First, a micro core of rock was scanned using x-ray microtomography (μCT) and a representative microporous region was identified. A nano core of rock was then milled using a laser lathe and scanned using x-ray nano tomography (Nano CT). The Nano CT scan was then used as input into the pore space generator and the permeability field was simulated for a range of porosities to create a synthetic Kozeny-Carman porosity-permeability relationship for micro porosity. We found a good match between experimental and simulated Mercury Intrusion Capillary Pressure (MICP) range in the imaged geometry and a good match between the imaged and object generated permeabilities and MICP.
A micro-core of Estaillades was then scanned in the μCT, the differential pressure was measured, and the rock was flooded with highly doped brine to elucidate where themicro porosity was connected and unconnected. The differential contrast between the dry and doped images was then used to assign a porosity to each voxel of connected micro porosity. The flow through the pore space was then solved using a Stokes-Brinkman solver while a second segmented image with no micro porosity was solved a Stokes solver. The differences between the measured permeability and the two computed permeabilities were evaluated. We found that there was good agreement between both the computed permeability of the Stokes and Stokes-Brinkman simulation with the measured permeability. However, there were considerable differences in the velocity fields with the Stokes-Brinkman simulation capturing stagnant regions of the pore space that were not present in the Stokes simulations.
Additionally, we investigated the implications of including microporosity in estimations of relative permeability Nitrogen was experimentally coinjected through the core with doped brine at a 50% fractional flow and imaged to find a single point on the two-phase relative permeability curve. This experimental measurement was then compared with the numerical permeability simulated using both Stokes and Stokes-Brinkman methods with several saturation points along the synthetic MICP injection curve. We found that the Stokes simulation was not able to predict relative permeability with this method due to the major flow paths being impeded by the injected non-wetting phase. However, the Stokes-Brinkman simulations allowed flow in the microporous regions around these blocked flow paths and were able to achieve a relative permeability curve that was a reasonable match to the experimental measurement. This method could be used to predict relative permeability in water wet pore-structures with high microporosity.
About the Speaker: Hannah Menke
Hannah Menke is a Postdoctoral Research Associate at Imperial College London. Her most recent work focusses on investigating the mechanisms controlling the upscaling of pore and nano-scale physicochemical phenomena. Hannah holds a Ph.D. in petroleum and environmental engineering from Imperial College London, a M.S. from the Colorado School of Mines, and a B.S. from Columbia University.
Host: Hang Deng