Pore-Scale Dynamics of Liquid CO\u3csub\u3e2\u3c/sub\u3e–Water Displacement in 2D Axisymmetric Porous Micromodels Under Strong Drainage and Weak Imbibition Conditions: High-Speed μPIV Measurements

Resolving pore-scale transient flow dynamics is crucial to understanding the physics underlying multiphase flow in porous media and informing large-scale predictive models. Surface properties of the porous matrix play an important role in controlling such physics, yet interfacial mechanisms remain poorly understood, in part due to a lack of direct observations. This study reports on an experimental investigation of the pore-scale flow dynamics of liquid CO2 and water in two-dimensional (2D) circular porous micromodels with different surface characteristics employing high-speed microscopic particle image velocimetry (μPIV). The design of the micromodel minimized side boundary effects due to the limited size of the domain. The high-speed μPIV technique resolved the spatial and temporal dynamics of multiphase flow of CO2 and water under reservoir-relevant conditions, for both drainage and imbibition scenarios. When CO2 displaced water in a hydrophilic micromodel (i.e., drainage), unstable capillary fingering occurred and the pore flow was dominated by successive pore-scale burst events (i.e., Haines jumps). When the same experiment was repeated in a nearly neutral wetting micromodel (i.e., weak imbibition), flow instability and fluctuations were virtually eliminated, leading to a more compact displacement pattern. Energy balance analysis indicates that the conversion efficiency between surface energy and external work is less than 30%, and that kinetic energy is a disproportionately smaller contributor to the energy budget. This is true even during a Haines jump event, which induces velocities typically two orders of magnitude higher than the bulk velocity. These novel measurements further enabled direct observations of the meniscus displacement, revealing a significant alteration of the pore filling mechanisms during drainage and imbibition. While the former typically featured burst events, which often occur only at one of the several throats connecting a pore, the latter is typically dominated by a cooperative filling mechanism involving simultaneous invasion of a pore from multiple throats. This cooperative filling mechanism leads to merging of two interfaces and releases surface energy, causing instantaneous high-speed events that are similar, yet fundamentally different from, burst events. Finally, pore-scale velocity fields were statistically analyzed to provide a quantitative measure of the role of capillary effects in these pore flows

Raman-based measurements of greenhouse activity of combustion flue gases

Gases that are capable of absorbing and emitting infrared radiation due to their molecular structure are known as infrared active gases. Infrared activity is the underlying reason for the greenhouse effect. Hence, greenhouse gases are all infrared active. The vibrational/rotational structure that makes the molecule infrared active, also causes the energy exchange and the corresponding wavelength shift during Raman scattering. In this work, Raman scattering spectrum and infrared emission intensity in CO2-containing atmospheric jets at various temperatures and concentrations were measured. The results show that there is a linear relationship between Raman scattering intensity and infrared emission intensity. The linear relationship between Raman signal and infrared emission intensity indicates that Raman scattering can be used as a strong technique for measurement of greenhouse gases

An experimental study of supercritical CO2 flow in pipes and porous micro-models for carbon sequestration applications

The flow of high-pressure, near-critical CO2 in configurations relevant to CO2 sequestration was investigated. The first configuration was CO2 flow in pipes and orifices at pressures and temperatures close to the critical point of CO2 (74 bar, 31°C). A 60-cm-long stainless steel pipe with 2.1 mm inner diameter was used in order to study near-critical CO2 pipe flow. In terms of raw flow data, the results indicated high sensitivity of pressure drop to mass flow rate as well as to inlet conditions; i.e. pressure and temperature. Remarkably though, when friction factor and Reynolds number were defined in terms of the inlet conditions, it was established that the classical Moody chart described the flow with satisfactory accuracy. This was rationalized using shadowgraphs that visualized the process of transition from a supercritical state to a two-phase subcritical state. During this transition, the two phases were separated due to density mismatch and an interface was established that traveled in the direction of the flow. This interface separated the flow in two regions of essentially single-phase flow, which explained the effective validity of the classical Moody chart. Also, Joule-Thomson throttling was studied using a 0.36-mm-diameter orifice. For conditions relevant to carbon capture and sequestration, the fluid underwent Joule-Thompson cooling of approximately 0.5°C/bar. The temperature difference during the cooling increased with increasing inlet enthalpy. Discrepancies with previous computed and experimentally measured values of Joule-Thompson throttling were discussed in detail. In a second configuration, liquid/supercritical CO2 was injected into two-dimensional porous micro-models saturated with water, which mimicked the process of injection and flow into saline aquifers. This flow configuration was studied using fluorescent microscopy and micro-PIV by seeding the water phase with fluorescent tracer particles, and dyeing CO2 with a fluorescent dye. This technique allowed for measurement of the velocity field in the water phase, and tracking the CO2 phase in the porous medium. The results revealed the nature of the flow field during the initial invasion and migration of the CO2 front. In particular, it was established that the front developed growing dendritic features called fingers. During that growth process, velocities 20–25 times the bulk velocity were measured, which occurred in both the flow direction and opposite to it. These velocity jumps support the notion of pressure bursts and Haines jump during pore drainage events. In addition, the variations of the interfacial curvature with time and their connection with water flow field during the growth of fingers were studied. The results revealed the existence of high-momentum pathways in water ahead of growing CO2 fingers. After the passage of the CO2 front, shear-induced flow was detected in the trapped water ganglia in the form of circulation zones near the CO2-water interfaces. The shear from CO2 flow also induced motion in the thin water films covering the surfaces of the micro-model

Near-Critical CO 2 Flow Measurement and Visualization

Near-critical CO 2 flow has been studied because of its potential application in carbon dioxide capture and sequestration, which is one of the proposed solutions for reducing greenhouse gas emission. Near the critical point the thermophysical properties of the fluid undergo abrupt changes that affect the flow structure and characteristics. Pressure drop across a stainless steel tube, 2 ft long with 0.084 in. ID, at different inlet conditions and mass flow rates have been measured. The effects of variations of inlet conditions have been studied. The results show extreme sensitivity of pressure drop to inlet conditions especially inlet temperature in the vicinity of the critical point. Also, shadowgraphs have been acquired to study the flow structure qualitatively