1.
Yang, Zhibing, et al.
(författare)
Macro-scale constitutive relationships for CO2 migration in heterogeneous geological formations
2012
Konferensbidrag (övrigt vetenskapligt/konstnärligt) abstract
Numerical models have been developed and applied to migration of geological stored carbon dioxide for site performance and risk assessment studies at the reservoir scale. However, due to the restriction in computational time and resources, reservoir scale models have limitations in accounting for the multi-scale heterogeneities. In order to address the heterogeneity issues, appropriate upscaling methods are needed. In this study, we present macro-scale capillary pressure – relative permeability – saturation relationships for grid-block properties used in the full-scale modeling. We develop a macroscopic percolation model for the upscaling procedures. The macro-scale constitutive relationships are obtained through simulation procedures of CO2 displacing brine in a porous domain with spatially correlated random permeability fields. Sensitivity of the derived constitutive relationships to the statistical parameters representing the local heterogeneity is shown. Comparison of the percolation-based method to other approaches is demonstrated.
2.
Yang, Zhibing, 1982-, et al.
(författare)
Modeling of dense nonaqueous phase liquid entrapment and dissolution in variable aperture fractures
2009
Ingår i: Proceedings of TOUGH2 Symposium 2009. - Lawrence Berkeley National Laboratory, Berkeley, California.
Konferensbidrag (refereegranskat) abstract
This study investigates dense non-aqueous phase liquid (DNAPL) entrapment and dissolution in single, variable-aperture fractures. Log-normally distributed aperture fields with local permeabilities following the cubic law are assumed. Special attention is given to the capillary pressure-liquid saturation function to account for the specific drainage and wetting characteristics of fractures. DNAPL migration and immobilization is modeled by using the iTOUGH2/T2VOC models, and dissolution is simulated using the TMVOC model. Multiple realizations with different sets of aperture statistics and fracture inclination angles are analyzed.The results suggest that the entrapment geometry of DNAPL in a heterogeneous fracture is highly sensitive to the aperture statistics. Larger correlation length or standard deviation produces a wider range of total entrapped DNAPL volume. Modeling of different fracture inclination angles reveals that gravity force plays an important role as well. Subsequent dissolution modeling shows that mass transfer will also be strongly influenced by the different DNAPL entrapment architectures corresponding to the different aperture correlation lengths and standard deviations.
3.
Yang, Zhibing
(författare)
Multiphase Contamination in Rock Fractures : Fluid Displacement and Interphase Mass Transfer
2012
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Multiphase flow and transport in fractured rock is of importance to many practical and engineering applications. In the field of groundwater hydrology an issue of significant environmental concern is the release of dense non-aqueous phase liquids (DNAPLs) which can cause long-term groundwater contamination in fractured aquifers. This study deals with two fundamental processes – fluid displacement and interphase mass transfer – concerning the behavior of the multiphase contaminants in fractured media. The focus of this work has been placed on improving the current understanding of small-scale (single fracture) physics by a combined effort of numerical modeling analysis, laboratory experiments and model development. This thesis contributes to the improved understanding through several aspects. Firstly, the effect of aperture variability, as characterized by geostatistical parameters such as standard deviation and correlation length, on the DNAPL entrapment, dissolution and source-depletion behaviors in single fractures was revealed. Secondly, a novel, generalized approach (adaptive circle fitting approach) to account for the effect of in-plane curvature of fluid-fluid interfaces on immiscible fluid displacement was developed; the new approach has demonstrated good performance when applied to simulate previously published experimental data. Thirdly, the performance of a continuum-based two-phase flow model and an invasion percolation model was compared for modeling fluid displacement in a variable-aperture fracture and the dependence of fracture-scale capillary pressure – saturation relationships on aperture variability was studied. Lastly, through experimental studies and mechanistic numerical modeling of DNAPL dissolution, kinetic mass transfer characteristics of two different entrapment configurations (residual blobs and dead-end pools) were investigated. The obtained understanding from this thesis will be useful for predictive modeling of multiphase contaminant behavior at a larger (fracture network) scale.
4.
5.
Basirat, Farzad, et al.
(författare)
Pore-scale modeling of wettability effects on CO2–brine displacement during geological storage
2017
Ingår i: Advances in Water Resources. - : Elsevier. - 0309-1708 .- 1872-9657. ; 109, s. 181-195
Tidskriftsartikel (refereegranskat) abstract
Wetting properties of reservoir rocks and caprocks can vary significantly, and they strongly influence geological storage of carbon dioxide in deep saline aquifers, during which CO2 is supposed to displace the resident brine and to become permanently trapped. Fundamental understanding of the effect of wettability on CO2-brine displacement is thus important for improving storage efficiency and security. In this study, we investigate the influence of wetting properties on two-phase flow of CO2 and brine at the pore scale. A numerical model based on the phase field method is implemented to simulate the two-phase flow of CO2-brine in a realistic pore geometry. Our focus is to study the pore-scale fluid-fluid displacement mechanisms under different wetting conditions and to quantify the effect of wettability on macroscopic parameters such as residual brine saturation, capillary pressure, relative permeability, and specific interfacial area. Our simulation results confirm that both the trapped wetting phase saturation and the normalized interfacial area increase with decreasing contact angle. However, the wetting condition does not appear to influence the CO2 breakthrough time and saturation. We also show that the macroscopic capillary pressures based on the pressure difference between inlet and outlet can differ significantly from the phase averaging capillary pressures for all contact angles when the capillary number is high ( log Ca > -5). This indicates that the inlet-outlet pressure difference may not be a good measure of the continuum-scale capillary pressure. In addition, the results show that the relative permeability of CO2 can be significantly lower in strongly water-wet conditions than in the intermediate-wet conditions.
6.
Niemi, Auli, et al.
(författare)
Chapter 4: Mathematical Modeling : Approaches for Model Solution
2017
Ingår i: Geologicalstorage Of Co<sub>2</sub> In Deep Saline Formations. - Dordrecht : Springer Netherlands. - 9789402409949 - 9789402409963 ; , s. 129-185
Bokkapitel (refereegranskat) abstract
The governing equations and mathematical models describing CO2 spreading and trapping in saline aquifers and the related hydro-mechanical and chemical processes were described in Chapt.3. In this chapter, the focus is on methods for solving the relevant equations. The chapter gives an overview of the different approaches, from high-fidelity full-physics numerical models to more simplified analytical and semi-analytical solutions. Specific issues such as modeling coupled thermo-hydro-mechanical-chemical processes and modeling of small-scale processes, such as convective mixing and viscous fingering, are also addressed. Finally, illustrative examples of modeling real systems, with different types of modeling approaches, are presented.
7.
Tian, Liang, et al.
(författare)
Effects of permeability heterogeneity on CO2 injectivity and storage efficiency coefficient
2016
Ingår i: Greenhouse Gases. - : Wiley. - 2152-3878. ; 6:1, s. 112-124
Tidskriftsartikel (refereegranskat) abstract
We study the dependency of CO2 storage efficiency coefficient (E) and injectivity index (Iinj) on the geostatistical parameters of the permeability field. CO2 injection simulations are conducted for multiple realizations of log-normally distributed permeability fields parameterized by log permeability standard deviation (?) and dimensionless horizontal correlation length (?). Results show that the injectivity index increases with increasing ?, the magnitude of the effect depending on ?. Increasing ? leads to poorer injectivity for cases with small ?, but improves injectivity when ? is large. Further analysis indicates that the enhancing effect of ? on injectivity can be attributed to cases with channelized flow, while the decrease effect of ? is seen in more dispersive flow regime. The dependence of injectivity on both ? and ? is captured with a linear correlation between Iinj and a parameter group (?/ξ)?, where ξ is a dimensionless scaling parameter. The storage efficiency coefficient, on the other hand, decreases with both increasing ? and ?, and a simple linear fit is found between E and the parameter group ??2, a well-established heterogeneity parameter group describing e.g. macro-dispersivity in solute transport studies. The above relationships provide potentially useful tools for preliminary evaluation of a site. Future studies should address the validity of the relationships in alternative injection scenarios and domain geometries.
8.
Tian, Liang, et al.
(författare)
Integrated simulations of CO2 spreading and pressure response in the multilayer saline aquifer of South Scania Site, Sweden
2016
Ingår i: Greenhouse Gases. - : Wiley. - 2152-3878. ; 6:4, s. 531-545
Tidskriftsartikel (refereegranskat) abstract
An integrated modeling approach/workflow, in which a series of mathematical models of different levels of complexity are applied to evaluate the geological storage capacity of the Scania Site, southwest Sweden, is presented. The storage formation at the site is a layered formation limited by bounding fault zones, and injection is assumed to take place from one existing deep borehole into all layers. A semi-analytical model for two-phase flow is first used to evaluate the pressure response and related parameter sensitivity, as well as the first estimates of acceptable injection rates. These results are then used to guide the more detailed numerical simulations that address both pressure response and plume migration. The vertical equilibrium (VE) model is used to obtain a preliminary understanding of the plume migration with a larger number of simulations. Finally the full TOUGH2/ECO2N simulations are performed for the most detailed analyses of pressure responses and plume migration. Throughout, the results of the different modeling approaches are compared against each other. It is concluded that the key limiting factor for the storage capacity at the site in the injection scenario considered is the fast CO2 migration within the high permeability layer. Future studies can address alternative injection scenarios, including horizontal injection wells and injection to other layers than the high permeability layer.
9.
10.
Wang, Zejun, et al.
(författare)
Pore-Scale Mechanisms of Solid Phase Emergence During DNAPL Remediation by Chemical Oxidation
2022
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:16, s. 11343-11353
Tidskriftsartikel (refereegranskat) abstract
In situ chemical oxidation (ISCO) has proven successful in the remediation of aquifers contaminated with dense nonaqueous phase liquids (DNAPLs). However, the treatment efficiency can often be hampered by the formation of solids or gas, reducing the contact between remediation agents and residual DNAPLs. To further improve the efficiency of ISCO, fundamental knowledge is needed about the complex multiphase flow and reactive transport processes as new solid and fluid phases emerge at the microscale. Here, via microfluidic experiments, we study the pore-scale dynamics of trichloroethylene degradation by permanganate. We visualize how the remediation evolves under the influence of solid phase emergence and explore the roles of injection rate, oxidant concentration, and stabilization supplement. Combining image processing, pressure analysis, and stoichiometry calculations, we provide comprehensive descriptions of the oxidant concentration-dependent growth patterns of the solid phase and their impact on the remediation efficiency. We further corroborate the stabilization mechanism provided by phosphate supplement, which is effective in inhibiting solid phase generation and thus highly beneficial for the oxidation remediation. This work elucidates the pore scale mechanisms during remediation of chlorinated solvents with a particular context in the solid phase production and the associated effects, which is of general significance to understanding various processes in natural and engineered systems involving solid phase emergence or aggregation phenomena, such as groundwater and soil remediation.
