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Editors:
Yitian Xiao, PhD is Senior Geoscience Advisor, ExxonMobil Upstream Research Company, USA.
Fiona Whitaker, PhD is Professor of Earth Sciences, University of Bristol, UK.
Tianfu Xu, PhD is Director of Key Laboratory of Groundwater Resources and Environment, Jilin University, China.
Consulting Editor:
Carl Steefel, PhD is Senior Scientist and Geochemistry Department Head, Earth Science Division, Lawrence Berkeley National Laboratory, USA.
List of Contributors xv
Preface xix
Acknowledgements xxiii
1 Application of Reactive Transport Modeling to CO2 Geological Sequestration and Chemical Stimulation of an Enhanced Geothermal Reservoir 1 Tianfu Xu, Hailong Tian and Jin Na
1.1 Introduction 1
1.2 Fundamental Theories 2
1.2.1 Governing Equations for Flow and Transport 2
1.2.2 Equations for Chemical Reactions 3
1.2.3 Solution Method for Transport Equations 6
1.2.4 Solution Method for Mixed Equilibrium-Kinetics Chemical System 7
1.3 Application to CO2 Geological Storage (CGS) 8
1.3.1 Overview of Applications in CGS 8
1.3.2 Long-Term Fate of Injected CO2 in Deep Saline Aquifers 10
1.3.2.1 Brief Description of CO2 Storage Site in the Songliao Basin 10
1.3.2.2 Conceptual Model 11
1.3.2.3 Results and Discussion 14
1.3.2.4 Summary and Conclusions 21
1.3.3 Evolution of Caprock Sealing Efficiency after the Intrusion of CO2 26
1.3.3.1 Introduction 26
1.3.3.2 Geological Setting 27
1.3.3.3 Conceptual Model 27
1.3.3.4 Results and Discussion 32
1.3.3.5 Concluding Remarks 44
1.4 Reactive Transport Modeling for Chemical Stimulation of an Enhanced Geothermal Reservoir 45
1.4.1 General Description 45
1.4.2 Brief Description of the EGS Site in Songliao Basin 47
1.4.3 Conceptual Model 47
1.4.3.1 Geometry and Boundary Conditions 47
1.4.3.2 Physical Parameters 48
1.4.3.3 Initial Mineral Composition 48
1.4.3.4 Water Chemistry 49
1.4.3.5 Thermodynamic and Kinetic Parameters 49
1.4.4 Results and Discussion 50
1.4.4.1 HCl Preflush 50
1.4.4.2 Mud Acid Main Flush 50
1.4.5 Concluding Remarks 52
1.5 Conclusions and Outlook 54
Appendix A 55
Acknowledgements 56
References 56
2 Modeling Reactive Transport in CO2 Geological Storage: Applications at the Site Scale and Near-Well Effects 61 P. Audigane, Irina Gaus and Fabrizio Gherardi
2.1 Introduction 61
2.2 Short- and Long-term Predictive Simulations of Trapping Mechanisms 65
2.2.1 Sandy Aquifer: Predictions of Long-term Effects of Storage in Sleipner, North Sea, Norway 69
2.2.2 Near-well Effects in Saline Aquifers in Carbonate Formations: Carbonate Dissolution, Drying, and Salt Crystallization in the Dogger, Paris Basin 72
2.2.3 Depleted Offshore Gas Field: Mixing with Methane K12B Field 77
2.3 Studying CO2 Leakage and Well Integrity by Reactive Transport Modeling 80
2.3.1 Near-well Problem in the Paris Basin 81
2.3.1.1 Weathering of Drilling Cement Prior to Injection 81
2.3.1.2 Cement-Reservoir-Caprock Interface 84
2.3.2 The Impact of CO2 Leakage on Groundwater 90
2.4 Discussion and Conclusion 92
References 98
3 Process-based Modelling of Syn-depositional Diagenesis 107 Fiona Whitaker and Miles Frazer
3.1 Introduction 107
3.2 Fundamentals of Syn-depositional Carbonate Diagenesis 108
3.3 Understanding Syn-depositional Diagenesis through RTM 111
3.3.1 Marine Diagenesis 111
3.3.2 Vadose Zone Diagenesis 113
3.3.3 Freshwater Lens Diagenesis 116
3.3.4 Mixing Zone Diagenesis 118
3.4 Challenges in Reactive Transport Modelling of Syn-depositional Diagenesis 120
3.5 Coupled Forward Stratigraphic-Diagenetic Models 124
3.5.1 Stratigraphic Forward Models (SFMs) 124
3.5.2 Carbonate Diagenesis and Sequence Stratigraphy 124
3.5.3 Integrating Diagenesis into SFMs - 1D and 2D Modelling 126
3.5.4 3D Forward Stratigraphic-Diagenetic Models (FSDMs) 128
3.5.5 Application of CARB3D+ to Understanding Carbonate Sedimentation and Syn-sedimentary Diagenesis 130
3.5.5.1 Prediction of Sediment Distribution and Platform Architecture using CARB3D+ 131
3.5.5.2 FSDM - Simulation of Diagenetic Hydrozones 137
3.5.5.3 FSDM - Simulation of Diagenetic Processes 140
3.6 Discussion and Conclusion 145
Acknowledgements 148
References 148
4 Reactive Transport Modeling and Reservoir Quality Prediction 157 Yitian Xiao and Gareth D. Jones
4.1 Fundamental Challenges in Reservoir Quality Prediction 157
4.2 Reactive Transport Modeling Approach 164
4.3 Modeling Dolomitization in Different Hydrogeological Systems 165
4.3.1 Dolomitization and Impact on Carbonate Reservoir Quality: From Reservoir to Outcrop Observations 165
4.3.2 Conceptual Hydrological Models of Dolomitization 168
4.3.3 Geothermal Convection Models 171
4.3.4 Mixing Zone Models 173
4.3.4.1 Traditional Mixing Zone Model 173
4.3.4.2 Ascending Freshwater-Mesohaline Brine Mixing Model: La Molata Miocene Outcrop Case Study 175
4.3.5 Reflux Dolomitization Models 177
4.3.5.1 2D Simulations of Brine Reflux Dolomitization 177
4.3.5.2 3D Simulations of Brine Reflux Dolomitization 181
4.3.5.3 Brine Reflux Dolomitization Case Studies 189
4.3.6 Fault-Controlled Hydrothermal Models 195
4.3.6.1 2D and 3D Conceptual HTD Models 196
4.3.6.2 Fault-controlled Dolomitization at the Benicassim Outcrop in Maestrat Basin, Spain 196
4.3.7 Summary of Dolomite RTM Results 200
4.4 Early Diagenesis in Isolated Carbonate Platforms 200
4.5 Geothermal Convection and Burial Diagenesis 201
4.5.1 Geothermal Convection and Reservoir Quality in Tengiz Field, Kazakhstan 202
4.5.2 Geothermal Convection in South Atlantic Pre-Salt Rift Carbonates 203
4.6 Burial Diagenesis: Fault-Controlled Illitization 208
4.6.1 Illitization and Permeability Reduction in Rotliegendes Play, Germany 208
4.6.2 1D and 2D Reactive Transport Models 208
4.7 Diagenesis and Reservoir Alteration Associated with Oil and Gas Operations 211
4.7.1 CO2 and Acid Gas Injection (AGI) in Siliciclastic and Carbonate Reservoirs 211
4.7.2 Reactive Transport Model Setup 212
4.7.3 Simulation Results: Injection in Siliciclastic Reservoirs 212
4.7.3.1 Feldspar-Rich Sandstone Reservoir 212
4.7.3.2 Quartz-Dominated Sandstone Reservoir 212
4.7.4 Simulation Results: Injection in Carbonate Reservoirs 213
4.7.4.1 Limestone Reservoir 213
4.7.4.2 Dolomite Reservoir 215
4.7.5 Summary of CO2 and Acid Gas Injection and Reservoir Alteration 216
4.7.6 Reservoir Alteration from Steam and Acid Injection 218
4.7.6.1 Case Study: RTM of Steam Flood in Eocene Carbonate Reservoir, Wafra Field 220
4.8 The Present and Future Role of Reactive Transport Models for Reservoir Quality Prediction 221
Acknowledgements 226
References 227
5 Modeling High-Temperature, High-Pressure, High-Salinity and Highly Reducing Geochemical Systems in Oil and Gas Production 237 Guoxiang Zhang, Jeroen Snippe, Esra Inan-Villegas and Paul Taylor
5.1 Introduction 237
5.2 Drivers of the Geochemical Reactions in 4-High Reservoirs During Oil and Gas Production 238
5.2.1 High Temperature 238
5.2.2 High Pressure 239
5.2.3 Salinity, pH and Alkalinity 240
5.2.4 Contrast in Redox Potential 240
5.3 Typical Geochemical Processes in the 4-High Reservoir During HC Production and the Impacts on Production 242
5.3.1 Scaling of Wells and Near Wellbore Formation Rocks by Carbonate Precipitation 242
5.3.2 Well Scaling by Precipitation of Sulfate Minerals 243
5.3.3 Scaling Due to Precipitation of Other Minerals 243
5.3.4 Scaling Due to Combined Precipitation of Multiple Minerals, Solid Solution and/or Fines Migration 244
5.3.5 Souring by Thermochemical Sulfate Reduction (TSR) during HC Production 245
5.3.6 Souring by Bacterial Sulfate Reduction (BSR) During HC Production 247
5.3.7 Scavenging - An Overview of the Sulfur Mass Balance in the HC Reservoir During TSR or BSR 248
5.3.8 Clay Swelling Due to Cation Exchange During Injection of Water 251
5.3.9 Wellbore Cement Corrosion by Acid Attack from Formation Water/Brine 252
5.4 Modeling Approaches and Numerical Simulators 255
5.4.1 Gaps of the Simulators in the Oil and Gas Production Technology Community 255
5.4.1.1 Scale Simulators 255
5.4.1.2 Souring Simulators 255
5.4.2 Clay Swelling Evaluation Approaches 256
5.4.3 Reactive Transport Modeling Simulators Applicable to Petroleum Geochemical Systems 257
5.4.4 Handling High Temperature 259
5.4.5 Handling High Pressure 261
5.4.6 Handling High Salinity 261
5.4.7 Handling Highly Reducing Conditions 263
5.4.8 Numerical Simulators Available for Modeling 4-High Reservoirs 264
5.4.8.1 TOUGHREACT and TOUGHREACT-PITZER 264
5.4.8.2 PHREEQC-based Simulators 265
5.5 Applications of RTM in Evaluating Risks Related to Geochemical Processes in 4-High Reservoirs 266
5.5.1 RTM Evaluation of Well and Reservoir Scaling and Clay Swelling During Waterflood 266
5.5.1.1 Geological, Hydrogeological and Geochemical Setting 266
5.5.1.2 RTM Setup using TOUGHREACT-PITZER and Model Calibration 269
5.5.1.3 Model-Predicted Scaling Risk 272
5.5.1.4 Model-Predicted Clay Swelling Risk 272
5.5.1.5 Summary and Limitations 276
5.5.2 Modeling Reservoir Scaling and Souring by TSR During Waterflood 285
5.5.2.1 Geochemical Setting 286
5.5.2.2 Formation Brine Composition 286
5.5.2.3 Geochemical Reactions Induced by Waterflood 288
5.5.2.4 Temperature-Dependent and Pressure-Dependent Thermodynamic Data 289
5.5.2.5 Handling Solid Reduced Sulfur (Pyrite or Pyrrhotite) Under Reduced Conditions 289
5.5.2.6 TOUGHREACT RTM Phase 1: Screening Phase (Risk Screening) 291
5.5.2.7 TOUGHREACT Validation Model, Phase 2: Anhydrite Leachability Experiment to Validate the Kinetic Parameters of Anhydrite Dissolution 293
5.5.2.8 TOUGHREACT Validation Model, Phase 2: Evaluation Uncertainties in the TSR Rate Constant, Anhydrite Leachability, and Iron-Chlorite Leachability 295
5.5.2.9 TOUGHREACT RTM Phase 3: Prediction 298
5.5.3 RTM Evaluation of Wellbore Cement Corrosion of a Legacy Well in CO2 and CO2/Acid Gas Storage 299
5.5.3.1 Mineralogical Composition and Water Composition of the Wellbore Intervals 300
5.5.3.2 Model Setup 300
5.5.3.3 Modeled Wellbore Cement Corrosion Processes 302
5.5.3.4 Sensitivity Studies 309
5.6 Summary 311
Acknowledgements 311
References 312
6 Multiphase Fluid Flow and Reaction in Heterogeneous Porous Media for Enhanced Heavy Oil Production 319 Xinfeng Jia, Xiaohu Dong, Jinze Xu and Zhangxin Chen
6.1 Introduction 319
6.1.1 Heavy Oil Reserve Distribution 319
6.1.2 Current Exploitation Methods 319
6.1.3 Potential in the Post-Steam Injection Era 321
6.1.3.1 Hybrid Steam-Solvent Processes 321
6.1.3.2 Steam - Solvent - Gas Co-injection Processes 322
6.1.4 Transport Equations 323
6.2 Thermal Recovery Processes 324
6.2.1 Modeling Assumptions 324
6.2.2 Heat Transfer in SAGD 325
6.2.2.1 Gravity Drainage in a Transition Zone 327
6.2.2.2 Boundary Movement 327
6.2.2.3 Boundary Position 327
6.2.3 Heat Transfer in CSS 331
6.2.4 Conductive and Convective Heat Transfer 334
6.2.5 Multiple Phase Flow 334
6.3 Hybrid Thermal-Solvent Process 336
6.3.1 Mass Transfer 336
6.3.2 Coupled Heat and Mass Transfer 337
6.3.3 SAGD vs. ES-SAGD 338
6.4 Thermal-Solvent-Gas Co-injection Process 338
6.4.1 PVT Behaviour 338
6.4.2 MTFs Stimulation Process 341
6.4.3 MTFs-Assisted Gravity Drainage Process 342
6.4.4 Recovery Mechanisms 344
6.5 Uncertainty Analysis for Reservoir Heterogeneity 344
6.5.1 Bottom Water 344
6.5.2 Shale Barrier 346
6.5.3 Lean Zones 346
6.6 Conclusions 348
6.7 Recommendations 349
6.7.1 Effects of Non-Condensable Gases on Heat and Mass Transfer 349
6.7.2 Effects of Reservoir Heterogeneity on Heat and Mass Transfer 349
Acknowledgements 349
References 349
7 Modeling the Potential Impacts of CO2 Sequestration on Shallow Groundwater: The Fate of Trace Metals and Organics and the Effect of Co-injected H2S 353 Liange Zheng and Nicolas Spycher
7.1 Introduction 353
7.2 The Fate of Trace Metals and Organics in a Shallow Aquifer in Response to a Hypothetical CO2 and Brine Leakage Scenario 355
7.2.1 Simulator 356
7.2.2 Model Setup 356
7.2.3 Geochemical Model 359
7.2.4 Metal Release from CO2 and/or Brine Leakage 361
7.3 Impact of Co-injected H2S on the Quality of a Freshwater Aquifer 373
7.3.1 The Simulator 377
7.3.2 Model Setup 378
7.3.3 Metal Mobilization under CO2+H2S Leakage 378
7.4 Summary and Conclusion 381
Appendix A 384
Appendix B 387
Acknowledgements 388
References 388
8 Modeling the Long-term Stability of Multi-barrier Systems for Nuclear Waste Disposal in Geological Clay Formations 395 Francis Claret, Nicolas Marty and Christophe Tournassat
8.1 Introduction 395
8.1.1 Geological Final Disposal of Radioactive Waste 395
8.1.2 The 'Clay Concept' 396
8.1.3 How a Repository System Evolves in Time and Space 396
8.1.4 Modeling How a Repository System Evolves 397
8.2 Modeling Physical and Chemical Processes on Repository Scales 410
8.2.1 Reactive Transport Modeling Principles 410
8.2.1.1 Reactive Transport Constitutive Equations 410
8.2.1.2 Geometry and Space Discretization 410
8.2.1.3 Where Everything Takes Place: the Pore Space 411
8.2.1.4 Kinetic and Thermodynamic Databases 411
8.2.1.5 Initial Conditions 413
8.2.2 Repository Material Properties 414
8.2.2.1 Generalities 414
8.2.2.2 Clay Materials 414
8.2.2.3 Cement Materials 420
8.2.2.4 Iron (Metals) 422
8.2.2.5 Glass 423
8.3 Literature Review 423
8.3.1 Clay/Concrete Interactions 424
8.3.2 Iron/Clay Interactions 426
8.3.3 Clay/Iron/Atmosphere (O2) Interactions 427
8.3.4 Glass Corrosion and its Interaction with Clay 428
8.4 Recent Improvements and Future Challenges in the RTM Approach to Repository Systems 429
8.4.1 Necessary Simplifications in the RTM Approach 429
8.4.2 Modeling Diffusion in Porous Systems with Consideration of Electrostatic Effects 429
8.4.3 Diffusion in Non-saturated Conditions 430
8.4.4 Two-Phase Flow Models 431
8.4.5 Water Consumption and Non-saturated Conditions 432
8.4.6 Reducing Porosity and Coupling with Transport Parameters 432
8.4.7 Accounting for Material Heterogeneities 433
8.4.8 Kinetics versus Local Equilibrium Calculations 433
8.4.9 Modeling Glass Alteration in Clay-rock Environments 434
8.4.10 Coupling Mechanics and Chemistry 435
Acknowledgements 436
References 436
9 Modeling Variably Saturated Water Flow and Multicomponent Reactive Transport in Constructed Wetlands 453 Gunter Langergraber and Jirka simunek
9.1 Introduction 453
9.2 The HYDRUS Wetland Module 455
9.3 The CW2D and CWM1 Biokinetic Models 456
9.3.1 CW2D Biokinetic Model 459
9.3.1.1 Stoichiometric Matrix and Reaction Rates 459
9.3.1.2 Model Parameters 459
9.3.2 CWM1 Biokinetic Model 463
9.3.2.1 Stoichiometric Matrix and Reaction Rates 463
9.3.2.2 Model Parameters 466
9.4 Simulation Results for Vertical Flow Constructed Wetlands Treating Domestic Wastewater 466
9.5 Experiences and Challenges using Wetland Models 474
9.5.1 Description of Water Flow 474
9.5.2 Values of the Biokinetic Model Parameters and Influent Fractionation 475
9.5.3 Clogging Model 477
9.5.4 Models as CW Design Tools 479
9.6 Summary and Conclusions 480
References 481
10 Reactive Transport Modeling and Biogeochemical Cycling 485 Christof Meile and Timothy D. Scheibe
10.1 Introduction 485
10.2 Reactive Transport Model Formulations 486
10.3 The Representation of Microbes 488
10.3.1 Implicit Presence of Microbes 488
10.3.2 Explicit Representations 489
10.3.2.1 Functional Populations 490
10.3.2.2 Trait-based Models 492
10.3.2.3 Bottom-up Approaches 492
10.3.2.4 Metabolic Activity as Ecosystem Response 493
10.3.2.5 Emerging Patterns 494
10.4 Data Integration 495
10.5 Linking Models Across Scales 497
10.6 Summary and Outlook 501
Acknowledgements 502
References 502
11 Effective Stochastic Model For Reactive Transport 511 Alexandre M. Tartakovsky
11.1 Introduction 511
11.2 Pore and Darcy Models for Transport with Bimolecular Reactions 515
11.3 Langevin Advection-Diffusion-Reaction Model 520
11.4 Parameterization of the Stochastic Model 521
11.5 The Langevin Model for Multicomponent Reactive Transport 523
11.6 Rayleigh-Taylor Instability 528
11.7 Summary and Conclusions 529
Acknowledgement 530
References 530
Index 533
Reactive transport modeling is a highly multidisciplinary area of research that has seen rapid advances in the past 20 years. The field encompasses a number of diverse disciplines including hydrology, geochemistry, geology, biology, engineering, environmental and computational sciences. Reactive transport in the subsurface can result in a wide variety of geochemical processes, including rock/mineral alteration in natural diagenetic systems and in response to injection of CO2 and acid gases, enhanced oil and gas recovery, transport and storage of radiogenic and toxic waste products in geological formations, as well as biogeochemical. Reactive transport models are thus important engineering tools which, as this summary of the state of the art demonstrates, have already had significant impact in some disciplines and offer promise in many more. However, at a higher level they also offer the potential to provide the 'dynamic glue' with which to integrate fundamental process-based research into the study of complex natural Earth systems.
This book assimilates contributions from leading experts from universities and national and industrial research institutes around the world, who authoritatively discuss recent applications of reactive transport modeling to a wide range of subsurface and environmental problems. As such, the book is a timely reference and can be used as an advanced text book with relevance to a broad geoscience and engineering audience from both academia and industry. It spans the application of reactive transport models to a range of engineering and environmental fields, from understanding interactions between fluids, solutes and minerals to better manage extraction of energy resources and subsurface storage of waste, to incorporation of geobiology and addressing the challenges of modeling at a range of spatial and temporal scales.
CO2 sequestration and geothermal energy: Large-scale carbon capture and sequestration (CCS) and geothermal energy are potential solutions to reduce CO2 emissions and provide alternative and renewable energy. These processes involve a complex interplay of multiphase flow, capillary trapping, diffusion, convection, and chemical reactions that may have significant impacts on both injection performance and storage security. In Chapters 1 and 2, Xu et al. from Jilin University, China, and Audigane et al. from the French Geological Survey and other institutions in the EU, evaluate the applications of reactive transport modeling to CO2 geological sequestration and the development of geothermal energy. These discussions elucidate the basic theory of reactive transport modeling and its application in understanding interactions among gases, liquids, solutes and minerals, and the implications for CO2 geological sequestration and geothermal energy development. The modeling results help to identify the short- and long-term storage capacities of sedimentary formations and the geochemical processes associated with CO2 leakage during storage, including near-well phenomena and impacts on groundwater, as well as performance issues associated with enhanced geothermal energy. The authors also discuss the current capabilities and limitations of reactive transport models for simulating the geochemical processes associated with CO2 geological storage.
Diagenesis and reservoir quality: The key challenge in reservoir characterization is predicting the spatial distribution of diagenesis, which is often a critical control on reservoir quality heterogeneity and thus producibility of oil and gas. In Chapters 3 and 4, Whitaker from the University of Bristol, UK, Frazer from Chevron, USA, and Xiao and Jones from ExxonMobil, USA, review and discuss a wide range of geoscience applications pertinent to reservoir quality prediction. These include simulation of syn-depositional diagenesis of carbonate rocks controlled by interactions between episodes of submarine deposition of reactive sediment, and rapid changes in hydrological and biogeochemical conditions in response to changes in sea-level. Diagenesis continues to alter reservoir quality during burial, when fault-controlled flows play an increasingly important role, for example in hydrothermal fluid flow and illitization. Finally, at an operational time-scale, reservoirs can be altered by acid gas and steam injection. Reactive transport models are used to examine how key natural variables impact different styles of diagenesis and reservoir porosity evolution, and provide insight on a range of important issues, such as the occurrence and distribution of karstic and dolomite geobodies which can give rise to high permeability 'super-k' zones, calcite and anhydrite cements, and the impact on reservoir quality of fault-controlled fluid flow during both early and burial diagenesis. They are also used to provide rule sets in developing a coupling forward stratigraphic and diagenetic model for carbonate platform development. The authors discuss frameworks and examples to link fundamental geochemical processes, integrate with traditional methods, and calibrate with field and production data that have the potential to significantly improve the ability to predict carbonate and siliciclastic reservoir quality.
Enhanced oil recovery: During petroleum production, enhanced oil recovery (EOR) methods such as CO2 flooding, acid stimulation, steam injection and in situ combustion can cause chemical reactions between the injected fluids and the reservoir rocks (artificial diagenesis) that may be either beneficial or detrimental to enhanced oil recovery. In Chapter 5, Zhang et al. from Shell, USA, discuss enhanced production from conventional hydrocarbon reservoirs which are characterized by high temperature, high pressure, high salinity and highly reducing conditions (4-high). Injection to and/or production from these reservoirs can induce significant geochemical reactions due to the high contrast between geochemical conditions in the reservoir and those of the invading fluids, or between the reservoir and the surface conditions, introducing risks for hydrocarbon (HC) recovery. Risk evaluation and management require thorough understanding and modeling of these geochemical systems. Potential geochemical reactions taking place in 4-high reservoirs during HC recovery are discussed, based on the characterization of the reservoirs. Quantitative description, modeling approaches, tool and examples of real cases are presented in this chapter.
Of the approximately 9?-?11 trillion barrels of crude oil resources in the world, about two-thirds are unconventional heavy oil and bitumen. Thermal processes, using heat to reduce oil viscosity in situ, have been the most successful methods of recovery. In Chapter 6, Jia et al. from the University of Calgary, Canada, cover current modeling approaches to dynamic heat and mass transfer in several heavy oil recovery processes, such as SAGD, hybrid steam-solvent, and steam-solvent-gas co-injection. The respective contribution of conduction and convection to the viscosity reduction of heavy oil is analysed. In addition, the effects of heterogeneous reservoir properties and the impact on heavy oil recovery efficiency are discussed.
Acid gas injection and groundwater contamination: One potential risk of geological storage of CO2 is the leakage of CO2 and deep brines from a deep storage formation into overlying shallow, potable groundwater aquifers. In Chapter 7, Zheng and Spycher from Lawrence Berkeley National Laboratory, USA, discuss results from reactive transport models used to investigate the potential impact of acid gas injection and brine leakage on shallow groundwater, particularly the fate of trace metals and organics and the environmental consequences. Their simulation results provide insight into acid gas injection site selection and operational feasibility to ensure the safety of drinking-water resources near these locations.
Nuclear waste disposal in geological formations: Large amounts of nuclear waste around the world need to be disposed of in repository sites that can ensure the safety and security of the waste for millennia. In Chapter 8, Claret et al. from the French Geological Survey discuss the grand challenge of long-term safe storage of nuclear waste in geological formations. They cover the framework of modeling the long-term stability of multi-barrier systems, which consist of waste overpacks (e.g. metal canisters, concrete), engineered barriers such as bentonite, and natural barriers such as clay rocks. They summarize recent improvements and discuss future challenges in the application of reactive transport modeling to nuclear repository systems in order to understand how a repository system will evolve due to thermal, hydraulic, mechanical, chemical and radiological processes.
Sustainable constructed wetlands: Constructed wetlands are sustainable, environmentally friendly solutions to engineering problems such as wastewater treatment, which involve a large number of physical, chemical, and biological processes. In Chapter 9, Langergraber from the University of Natural Resources and Life Sciences Vienna (BOKU), Austria, and Simunek from the University of California Riverside, USA, discuss their mechanistic modeling approach for saturated/unsaturated water flow and the application of the convection-dispersion equation for heat and solute transport, transformation and degradation processes of the pollutants, plants taking up nutrients and releasing organic matter and nutrients, and clogging that would...
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