Geological sequestration of CO2 in the pore space of subsurface rock formations offers a safe and permanent carbon storage solution. In this work, we present the application of a pore-scale flow simulator to the study of CO2 storage in geological formations. We model the rock pore space geometry, extracted from high-resolution X-ray microtomography images of suitable rocks as a network of connected capillaries. Assuming piston-like flow within each capillary and conservation of mass at each network node, a large system of equations can be solved to compute properties like pressure distribution or flow rate at each point in the network. Multi-phase flow simulations track the displacement in time of the fluid interface within each capillary. These dynamic simulations on the high-resolution capillary network representation of the rock are very computationally costly. Alternatively, analysis is carried out on the aggregate results of multiple two-phase flow simulations on several statistically equivalent capillary network models of the rock sample, which retain topological properties of the original at a significantly lower computational cost. We performed a sensitivity analysis with respect to multiple fluid parameters, such as viscosity, interfacial tension, contact angle, pressure, and temperature, and quantify their influence on the infiltration and retention of CO2 inside a capillary network that is representative of an actual rock.
Carbon dioxide capture and storage into underground geological formations is a promising route to reduce emissions into the atmosphere and limit global warming. Geo-sequestration involves the injection of carbon laden solutions directly into the pore space in sedimentary rocks, saline formations, or abandoned oil fields. More scientific research is still needed to understand how the pore structure and material properties of the rock matrix influence the extent to which pressurized fluids can be injected and permeate the pore network. Our research focuses on studying the fundamental mechanics of pore infiltration at micro- and nanoscopic scales to develop a comprehensive model of carbon dioxide sequestration within geological pore networks. We are using single and two-phase flow simulations of fluid injection into the rock pore space, modeled as a network of capillaries representing the geometry extracted from high-resolution X-ray microtomography of suitable rocks. To experimentally validate the simulation results, we have developed a Si/SiO2 lab-on-chip platform for testing porosity models on well-defined geometries at the microscale. The single and multiphase flow measurements performed on the microfluidic chip are monitored with optical microscopy in real time. In this contribution, we will report the progress in our research and development of optical imaging techniques applied to the microfluidic chip. Specifically, we demonstrate how advanced image analysis can be used to extract information about the flow properties. The image analysis results are critical for calibrating high-accuracy flow simulation models for pore scale injection and mineralization of carbon dioxide. The rock-on-chip platform is used also to measure chemical and physical processes governing the carbonate precipitation step of CO2 mineralization. The reaction of CO2 in the microfluidic channels can be detected through crystal formation over time. Fluorescence microscopy and Raman-spectroscopy is used to monitor carbonate precipitation rates directly on chip, to map minerals and track reaction kinetics under different conditions.
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