Browsing by Author "Zeng, Yongchao"
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Item A 2-D simulation study on CO2ﾠsoluble surfactant for foam enhanced oil recovery(Elsevier, 2019) Zeng, Yongchao; Farajzadeh, Rouhi; Biswal, Sibani L.; Hirasaki, George J.This paper probes the transport of CO2ﾠsoluble surfactant for foaming in porous media. We numerically investigate the effect of surfactant partitioning between the aqueous phase and the gaseous phase on foam transport for subsurface applications when the surfactant is injected in the CO2ﾠphase. A 2-D reservoir simulation is developed to quantify the effect of surfactant partition coefficient on the displacement conformance and CO2ﾠsweep efficiency. A texture-implicit local-equilibrium foam model is embedded to describe how the partitioning of surfactant between water and CO2ﾠaffects the CO2ﾠfoam mobility control when surfactant is injected in the CO2ﾠphase. We conclude that when surfactant has approximately equal affinity to both the CO2ﾠand the water, the transport of surfactant is in line with the gas propagation and therefore the sweep efficiency is maximized. Too high affinity to water (small partition coefficient) results in surfactant retardation whereas too high affinity to CO2ﾠ(large partition coefficient) leads to weak foam and insufficient mobility reduction. This work sheds light upon the design of water-alternating-gas-plus-surfactant-in-gas (WAGﾠ+ﾠS) process to improve the conventional foam process with surfactant-alternating-gas (SAG) injection mode during which significant amount of surfactant could possibly drain down by gravity before CO2ﾠslugs catch up to generate foam in situ the reservoir.Item A Multiscale Study of Foam: The Phase Behavior, Transport, and Rheology of Foam in Porous Media(2017-12-01) Zeng, Yongchao; Hirasaki, George J.; Biswal, Sibani L.This dissertation provides an in-depth multiscale understanding of the foam flow in porous media for subsurface applications such as gas mobility control, aquifer remediation, CO2 sequestration, water production control etc. In enhanced oil recovery (EOR), gas flooding has superior crude oil displacement efficiency where the gas sweeps. However, the overall oil recovery is often not much better than that of water flooding because of viscous fingering, gravity override, and reservoir heterogeneity. Using surfactant to generate foam in situ the porous media offer promise to simultaneously address all the three issues mentioned. Yet, the successful design of foam projects requires insightful understanding of the phase/component transport and the rheology of foam flow in porous media. The first part of my research investigates the foam transport dependence on its constituent components: the effect of gas types and surfactant structures. An experimental investigation of the effect of gas type and surfactant structure is presented. The effects of gas solubility, the stability of lamellae, the surfactant Gibbs adsorption, and the gas diffusion rate across the lamellae were examined. Our experimental results showed that the steady-state foam strength is inversely correlated with the gas permeability across a liquid lamella, a parameter that characterizes the rate of mass transport. We also calculated the limiting capillary pressure for different foaming surfactants and found that foam stability is correlated with the Gibbs surface excess concentration. My research also advances the understanding of “smart” foam rheology that can improve the sweep efficiency of gas flooding in porous media. Laboratory research work was conducted to capture the effect of heterogeneity on foam using actual reservoir rocks of varied permeabilities. It is observed that foam is more stable in high permeability cores compared to low permeability cores. Such smart rheology was also visualized in a 3-layered heterogeneous micromodel at the pore-level. Foam was shown to respond to the porous media heterogeneity by separating into a relatively dry and wet regime in the high- and low-perm regions respectively. Due to the capillary continuity between the layers of different permeability, the phase separation induced a saturation step change between the layers which resulted in responsive flow resistance. In addition, understanding the foam-oil interaction is crucial to the success of foam EOR projects. In this thesis, foam strength dependence on oil was probed using nuclear magnetic resonance (NMR) imaging technique. Manganese (II) was doped into the surfactant solution to reduce the T_2 relaxation time of water in order to differentiate the NMR response from the oil. The measured apparent viscosity was mapped out with respect to different oil fractional flows and oil saturations. It is found out that the presence of oil can not only weaken the foam strength but also emulsify with the surfactant solution. Unlike the bulk foam column test with oil, the overall apparent viscosity is found to be dependent on both oil saturation (oil fractional flow) and oil composition. Moreover, improved numerical algorithm is developed to estimate foam model parameters based on laboratory-scale experiment for field-scale reservoir simulation. Both dry-out effect and shear-thinning rheology of foam were considered. The algorithm reduced the five-parameter estimation to a few simpler steps, such as linear regression and single-variable optimization, and successfully avoided the sensitivities of initial estimates and the non-uniqueness solution issues. Our improved algorithm was also compared with others reported in literature. The robustness of the algorithm was validated by varied foam systems. Last but not least, the idea of injecting the surfactant with the gas phase (WAG+S, water-alternating-gas-plus-surfactant-in-gas process) has been conceptualized for the next generation CO2 foam EOR. Some novel nonionic or switchable surfactants are CO2 soluble, thus making it possible to inject the surfactant with CO2 slugs. Since surfactant could be present in both the CO2 and aqueous phases, it is important to understand how the surfactant partitioning between the phases influences foam transport in porous media. Foam simulations were conducted in both 1-D and 2-D systems. We conclude that when surfactant has approximately equal affinity to both the CO2 and the water, the transport of surfactant is in line with the gas propagation and therefore the sweep efficiency is maximized.Item Destabilization, Propagation, and Generation of Surfactant-Stabilized Foam during Crude Oil Displacement in Heterogeneous Model Porous Media(American Chemical Society, 2018) Xiao, Siyang; Zeng, Yongchao; Vavra, Eric D.; He, Peng; Puerto, Maura; Hirasaki, George J.; Biswal, Sibani L.Foam flooding in porous media is of increasing interest due to its numerous applications such as enhanced oil recovery, aquifer remediation, and hydraulic fracturing. However, the mechanisms of oil-foam interactions have yet to be fully understood at the pore level. Here, we present three characteristic zones identified in experiments involving the displacement of crude oil from model porous media via surfactant-stabilized foam, and we describe a series of pore-level dynamics in these zones which were not observed in experiments involving paraffin oil. In the displacement front zone, foam coalesces upon initial contact with crude oil, which is known to destabilize the liquid lamellae of the foam. Directly upstream, a transition zone occurs where surface wettability is altered from oil-wet to water-wet. After this transition takes place, a strong foam bank zone exists where foam is generated within the porous media. We visualized each zone using a microfluidic platform, and we discuss the unique physicochemical phenomena that define each zone. In our analysis, we also provide an updated mechanistic understanding of the "smart rheology" of foam which builds upon simple "phase separation" observations in the literature.Item Dynamics of paramagnetic squares in uniform magnetic fields(Elsevier, 2016) Du, Di; He, Peng; Zeng, Yongchao; Biswal, Sibani LisaThe magnetic forces between paramagnetic squares cannot be calculated using a classic dipolar model because the magnetic field distribution is not uniform within square particles. Here, we present the calculation of magnetic forces and torques on paramagnetic squares in a uniform 2-D magnetic field using a Laplace's equation solver. With these calculations, we simulate the variations in equilibrium configurations as a function of number of interacting squares. For example, a single square orients with its diagonal directed to the external field while a system of multiple squares will assemble into chain-like structures with their edges directed to the external field. Unlike chains of spherical magnetic particles, that easily stagger themselves to aggregate, chains consisting of magnetic squares are unable to aggregate due to interchain repulsion.Item Effect of Surfactant Partitioning Between Gaseous Phase and Aqueous Phase onﾠCO2ﾠFoam Transport for Enhanced Oil Recovery(Springer, 2016) Zeng, Yongchao; Ma, Kun; Farajzadeh, Rouhi; Puerto, Maura; Biswal, Sibani L.; Hirasaki, George J.CO2 flood is one of the most successful and promising enhanced oil recovery technologies. However the displacement is limited by viscous fingering, gravity segregation and reservoir heterogeneity. Foaming the CO2 and brine with a tailored surfactant can simultaneously address these three problems and improve the recovery efficiency. Commonly chosen surfactants as foaming agents are either anionic or cationic in class. These charged surfactants are insoluble in either CO2 gas phase or supercritical phase and can only be injected with water. However, some novel nonionic or switchable surfactants are CO2 soluble, thus making it possible to be injected with the CO2 phase. Since surfactant could be present in both CO2 and aqueous phases, it is important to understand how the surfactant partition coefficient influences foam transport in porous media. Thus, a 1-D foam simulator embedded with STARS foam model is developed. All test results, from different cases studied, have demonstrated that when surfactant partitions approximately equally between gaseous phase and aqueous phase, foam favors oil displacement in regard with apparent viscosity and foam propagation speed. The test results from the 1-D simulation are compared with the fractional flow theory analysis reported in literature.Item Insights on Foam Transport from a Texture-Implicit Local-Equilibrium Model with an Improved Parameter Estimation Algorithm(American Chemical Society, 2016) Zeng, Yongchao; Muthuswamy, Aarthi; Ma, Kun; Wang, Le; Farajzadeh, Rouhi; Puerto, Maura; Vincent-Bonnieu, Sebastien; Akbar Eftekhari, Ali; Wang, Ying; Da, Chang; Joyce, Jeffrey C.; Biswal, Sibani L.; Hirasaki, George J.We present an insightful discussion on the implications of foam transport inside porous media based on an improved algorithm for the estimation of model parameters. A widely used texture-implicit local-equilibrium foam model, STARS, is used to describe the reduction of gas mobility in the state of foam with respect to free gas. Both the dry-out effect and shear-dependent rheology are considered in foam simulations. We estimate the limiting capillary pressure Pc* from fmdryvalues in the STARS model to characterize foam film stability in a dynamic flowing system. We find that Pc* is a good indicator of foam strength in porous media and varies with different gas types. We also calculate Pc* for different foaming surfactants and find that foam stability is correlated with the Gibbs surface excess concentration. We compare our improved parameter estimation algorithm with others reported in literature. The robustness of the algorithm is validated for various foam systems.Item Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications(Journal of Visualized Experiments, 2018) Vavra, Eric D.; Zeng, Yongchao; Xiao, Siyang; Hirasaki, George J.; Biswal, Sibani L.Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil. A pattern is first designed using computer-aided design (CAD) software and printed on a transparency with a high-resolution printer. This pattern is then transferred to a photoresist via a lithography procedure. PDMS is cast on the pattern, cured in an oven, and removed to obtain a mold. A thiol-ene crosslinking polymer, commonly used as an optical adhesive (OA), is then poured onto the mold and cured under UV light. The PDMS mold is peeled away from the optical adhesive cast. A glass substrate is then prepared, and the two halves of the device are bonded together. Optical adhesive-based devices are more robust than traditional PDMS microfluidic devices. The epoxy structure is resistant to swelling by many organic solvents, which opens new possibilities for experiments involving light organic liquids. Additionally, the surface wettability behavior of these devices is more stable than that of PDMS. The construction of optical adhesive microfluidic devices is simple, yet requires incrementally more effort than the making of PDMS-based devices. Also, though optical adhesive devices are stable in organic liquids, they may exhibit reduced bond-strength after a long time. Optical adhesive microfluidic devices can be made in geometries that act as 2-D micromodels for porous media. These devices are applied in the study of oil displacement to improve our understanding of the pore-scale mechanisms involved in enhanced oil recovery and aquifer remediation.Item Role of Gas Type on Foam Transport in Porous Media(American Chemical Society, 2016) Zeng, Yongchao; Farajzadeh, Rouhi; Eftekhari, Ali Akbar; Vincent-Bonnieu, Sebastien; Muthuswamy, Aarthi; Rossen, William R.; Hirasaki, George J.; Biswal, Sibani L.We present the results of an experimental investigation of the effect of gas type and composition on foam transport in porous media. Steady-state foam strengths with respect to three cases of distinct gases and two cases containing binary mixtures of these gases were compared. The effects of gas solubility, the stability of lamellae, and the gas diffusion rate across the lamellae were examined. Our experimental results showed that steady-state foam strength is inversely correlated with gas permeability across a liquid lamella, a parameter that characterizes the rate of mass transport. These results are in good agreement with existing observations that the foam strength for a mixture of gases is correlated with the less soluble component. Three hypotheses with different predictions of the underlying mechanism that explain the role of gas type and composition on foam strength are discussed in detail.Item Surface Complexation Modeling of Calcite Zeta Potential Measurements in Brines with Mixed Potential Determining Ions (Ca2+, CO32-, Mg2+, SO42-) for Characterizing Carbonate Wettability(Elsevier, 2017) Song, Jin; Zeng, Yongchao; Wang, Le; Duan, Xindi; Puerto, Maura; Chapman, Walter G.; Biswal, Sibani L.; Hirasaki, George J.This study presents experiment and surface complexation modeling (SCM) of synthetic calcite zeta potential in brine with mixed potential determining ions (PDI) under various CO2 partial pressures. Such SCM, based on systematic zeta potential measurement in mixed brines (Mg2+, SO42−, Ca2+ and CO32−), is currently not available in the literature and is expected to facilitate understanding of the role of electrostatic forces in calcite wettability alteration. We first use a double layer SCM to model experimental zeta potential measurements and then systematically analyze the contribution of charged surface species. Calcite surface charge is investigated as a function of four PDIs and CO2 partial pressure. We show that our model can accurately predict calcite zeta potential in brine containing a combination of four PDIs and apply it to predict zeta potential in ultra-low and pressurized CO2 environments for potential application in enhanced oil recovery in carbonate reservoirs. Model prediction reveals that calcite surface will be positively charged in all considered brines in pressurized CO2 environment (>1 atm). The calcite zeta potential is sensitive to CO2 partial pressure in the various brine in the order of Na2CO3 > Na2SO4 > NaCl > MgCl2 > CaCl2 (Ionic strength = 0.1 M).