This report describes research and development (R&D) activities conducted during Fiscal Year 2022 (FY22) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Energy (DOE). The R&D activities focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. The R&D team represented in this report consists of individuals from Sandia National Laboratories, Lawrence Berkeley National Laboratory (LBNL), Los Alamos National Laboratory (LANL), and Vanderbilt University. EBS R&D work also leverages international collaborations to ensure that the DOE program is active and abreast of the latest advances in nuclear waste disposal.
Thermal-Hydrologic-Mechanical (THM) modeling of DECOVALEX 2023, Task C has continued. In FY2022 the simulations have progressed to Step 1, which is on 3-D modeling of the full-scale emplacement experiment at the Mont Terri Underground Rock Laboratory (Nagra, 2019). This report summarizes progress in Thermal-Hydrologic (TH) modeling of Step 1. THM modeling will be documented in future reports.
This report summarizes the international collaborations conducted by Sandia funded by the US Department of Energy Office (DOE) of Nuclear Energy Spent Fuel and Waste Science & Technology (SFWST) as part of the Sandia National Laboratories Salt R&D and Salt International work packages. This report satisfies the level-three milestone M3SF-22SN010303063. Several stand-alone sections make up this summary report, each completed by the participants. The sections discuss international collaborations on geomechanical benchmarking exercises (WEIMOS), granular salt reconsolidation (KOMPASS), engineered barriers (RANGERS), numerical model comparison (DECOVALEX) and an NEA Salt Club working group on the development of scenarios as part of the performance assessment development process. Finally, we summarize events related to the US/German Workshop on Repository Research, Design and Operations. The work summarized in this annual update has occurred during the COVID-19 pandemic, and little international or domestic travel has occurred. Most of the collaborations have been conducted via email or as virtual meetings, but a slow return to travel and in-person meetings has begun.
The construction of deep geological repositories (DGR) in salt formations requires penetrating through naturally sealing geosphere layers. While the emplaced nuclear waste is primarily protected by the containment-providing rock zone (CRZ), technical barriers are required, for example during handling. For closure geotechnical barriers seal the repository along the accesses against water or solutions from outside and the possible emission paths for radionuclides contained inside. As these barriers must ensure maintenance-free function on a long-term basis, they typically comprise a set of specialized elements with diversified functions that may be used redundantly. The effects of the individual elements are coordinated so that they are collectively referred to as the Engineered Barrier System (EBS).
Novel materials based on the aluminum oxyhydroxide boehmite phase were prepared using a glycothermal reaction in 1,4-butanediol. Under the synthesis conditions, the atomic structure of the boehmite phase is altered by the glycol solvent in place of the interlayer hydroxyl groups, creating glycoboehmite. The structure of glycoboehmite was examined in detail to determine that glycol molecules are intercalated in a bilayer structure, which would suggest that there is twice the expansion identified previously in the literature. This precursor phase enables synthesis of two new phases that incorporate either polyvinylpyrrolidone or hydroxylpropyl cellulose nonionic polymers. These new materials exhibit changes in morphology, thermal properties, and surface chemistry. All the intercalated phases were investigated using PXRD, HRSTEM, SEM, FT-IR, TGA/DSC, zeta potential titrations, and specific surface area measurement. These intercalation polymers are non-ionic and interact through wetting interactions and hydrogen bonding, rather than by chemisorption or chelation with the aluminum ions in the structure.
This report describes research and development (R&D) activities conducted during fiscal year 2021 (FY21) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel and Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Energy (DOE). The R&D activities focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. A primary goal is to advance the development of process models that can be implemented directly within the Generic Disposal System Analysis (GDSA) platform or that can contribute to the safety case in some manner such as building confidence, providing further insight into the processes being modeled, establishing better constraints on barrier performance, etc.
Calcium-silicate-hydrate (C–S–H) represents a key microstructural phase that governs the mechanical properties of concrete at a large scale. Defects in the C–S–H phase are also responsible for the poor ductility and low tensile strength of concrete. Manipulating the microstructure of C–S–H can lead to new cementitious materials with improved structural performance. This paper presents an experimental investigation aiming to characterize a new synthetic polymer-modified synthetic calcium-silicate-hydrate (C–S–H)/styrene-butadiene rubber (SBR) binder. The new C–S–H/SBR binder is produced by calcining calcium carbonate and mixing this with fumed silica (SiO2), deionized water and SBR. Mechanical, physical, chemical and microstructural characterization was conducted to measure the properties of new hardened C–S–H binder. Results from the experimental investigation demonstrate the ability to engineer a new C–S–H binder with low elastic modulus and improved toughness and bond strength by controlling the SBR content and method of C–S–H synthesis. The new binder suggests the possible development of a new family of low-modulus silica-polymer binders that might fit many engineering applications such as cementing oil and gas wells.
Bar-Nes, Gabriela B.; Klein-BenDavid, Ofra K.; Kosson, David K.; Gruber, Chen G.; Taylor, Autumn T.; Brown, Kevin B.; Delapp, Rossane D.; Brown, Lesa B.; Ayers, John A.; Meeusen, Hans M.; Matteo, Edward N.; Jove Colon, Carlos F.; Mitchell, Chven A.; Pyrak-Nolte, Laura J.
Bar-Nes, Gabriela B.; Klein-BenDavid, Ofra K.; Kosson, David K.; Gruber, Chen G.; Taylor, Autumn T.; Brown, Kevin B.; Delapp, Rossane D.; Brown, Lesa B.; Ayers, John A.; Meeusen, Hans M.; Matteo, Edward N.; Jove Colon, Carlos F.; Mitchell, Chven A.; Pyrak-Nolte, Laura J.
The main goal of this project was to create a state-of-the-art predictive capability that screens and identifies wellbores that are at the highest risk of catastrophic failure. This capability is critical to a host of subsurface applications, including gas storage, hydrocarbon extraction and storage, geothermal energy development, and waste disposal, which depend on seal integrity to meet U.S. energy demands in a safe and secure manner. In addition to the screening tool, this project also developed several other supporting capabilities to help understand fundamental processes involved in wellbore failure. This included novel experimental methods to characterize permeability and porosity evolution during compressive failure of cement, as well as methods and capabilities for understanding two-phase flow in damaged wellbore systems, and novel fracture-resistant cements made from recycled fibers.
This report summarizes the 2021 fiscal year (FY21) status of ongoing borehole heater tests in salt funded by the disposal research and development (R&D) program of the Office of Spent Fuel & Waste Science and Technology (SFWST) of the US Department of Energy’s Office of Nuclear Energy’s (DOE-NE) Office of Spent Fuel and Waste Disposition (SFWD). This report satisfies SFWST milestone M2SF- 21SN010303052 by summarizing test activities and data collected during FY21. The Brine Availability Test in Salt (BATS) is fielded in a pair of similar arrays of horizontal boreholes in an experimental area at the Waste Isolation Pilot Plant (WIPP). One array is heated, the other unheated. Each array consists of 14 boreholes, including a central borehole with gas circulation to measure water production, a cement seal exposure test, thermocouples to measure temperature, electrodes to infer resistivity, a packer-isolated borehole to add tracers, fiber optics to measure temperature and strain, and piezoelectric transducers to measure acoustic emissions. The key new data collected during FY21 include a series of gas tracer tests (BATS phase 1b), a pair of liquid tracer tests (BATS phase 1c), and data collected under ambient conditions (including a period with limited access due to the ongoing pandemic) since BATS phase 1a in 2020. A comparison of heated and unheated gas tracer test results clearly shows a decrease in permeability of the salt upon heating (i.e., thermal expansion closes fractures, which reduces permeability).
This report summarizes the FY21 Activities for EBS International Collaborations Work Package. The international collaborations work packages aim to leverage knowledge, expertise, and tools from the international nuclear waste community, as deemed relevant according to SFWST “roadmap” priorities. This report describes research and development (R&D) activities conducted during fiscal year 2021(FY21) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel and Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Energy (DOE). It fulfills the SFWST Campaign deliverable M4SF- 21SN010308062. The R&D activities described in this report focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. A primary goal is to advance the development of process models that can be implemented directly within the Generic Disposal System Analysis (GDSA) platform or that can contribute to the safety case in some manner such as building confidence, providing further insight into the processes being modeled, establishing better constraints on barrier performance, etc. Sandia National Laboratories is participating in THM modeling in the international projects EBS Task Force and DECOVALEX 2023. EBS Task Force, Task 11 is on modeling of laboratory-scale High Temperature Column Test conducted at Lawrence Berkeley National Laboratory. DECOVALEX 2023, Task C is on THM modeling of the full-scale emplacement experiment (FE experiment) at the Mont Terri Underground Rock Laboratory, Switzerland. This report summarizes Sandia’s progress in the modeling studies of DECOVALEX 2023, Task C. Modeling studies related to the High Temperature Column Test will be documented in future reports.
The DOE R&D program under the Spent Fuel Waste Science Technology (SFWST) campaign has made key progress in modeling and experimental approaches towards the characterization of chemical and physical phenomena that could impact the long-term safety assessment of heatgenerating nuclear waste disposition in deep-seated clay/shale/argillaceous rock. International collaboration activities such as heater tests, continuous field data monitoring, and postmortem analysis of samples recovered from these have elucidated key information regarding changes in the engineered barrier system (EBS) material exposed to years of thermal loads. Chemical and structural analyses of sampled bentonite material from such tests as well as experiments conducted on these are key to the characterization of thermal effects affecting bentonite clay barrier performance and the extent of sacrificial zones in the EBS during the thermal period. Thermal, hydrologic, and chemical data collected from heater tests and laboratory experiments has been used in the development, validation, and calibration of THMC simulators to model near-field coupled processes. This information leads to the development of simulation approaches (e.g., continuum and discrete) to tackle issues related to flow and transport at various scales of the host-rock, its interactions with barrier materials, and EBS design concept.
This report summarizes the international collaboration work conducted by Sandia and funded by the US Department of Energy Office (DOE) of Nuclear Energy Spent Fuel and Waste Science & Technology (SFWST) as part of the Sandia National Laboratories Salt R&D and Salt International work packages. This report satisfies the level-three milestone M3SF-20SN010303062. Several stand-alone sections make up this summary report, each completed by the participants. The sections discuss international collaborations on geomechanical benchmarking exercises (WEIMOS), granular salt reconsolidation (KOMPASS), engineered barriers (RANGERS), and model comparison (DECOVALEX). Lastly, the report summarizes a newly developed working group on the development of scenarios as part of the performance assessment development process, and the activities related to the Nuclear Energy Agency (NEA) Salt club and the US/German Workshop on Repository Research, Design and Operations.
Approximately 93% of US total energy supply is dependent on wellbores in some form. The industry will drill more wells in next ten years than in the last 100 years (King, 2014). Global well population is around 1.8 million of which approximately 35% has some signs of leakage (i.e. sustained casing pressure). Around 5% of offshore oil and gas wells “fail” early, more with age and most with maturity. 8.9% of “shale gas” wells in the Marcellus play have experienced failure (120 out of 1,346 wells drilled in 2012) (Ingraffea et al., 2014). Current methods for identifying wells that are at highest priority for increased monitoring and/or at highest risk for failure consists of “hand” analysis of multi-arm caliper (MAC) well logging data and geomechanical models. Machine learning (ML) methods are of interest to explore feasibility for increasing analysis efficiency and/or enhanced detection of precursors to failure (e.g. deformations). MAC datasets used to train ML algorithms and preliminary tests were run for “predicting” casing collar locations and performed above 90% in classification and identifying of casing collar locations.
Approximately 93% of US total energy supply is dependent on wellbores in some form. The industry will drill more wells in next ten years than in the last 100 years (King, 2014). Global well population is around 1.8 million of which approximately 35% has some signs of leakage (i.e. sustained casing pressure). Around 5% of offshore oil and gas wells “fail” early, more with age and most with maturity. 8.9% of “shale gas” wells in the Marcellus play have experienced failure (120 out of 1,346 wells drilled in 2012) (Ingraffea et al., 2014). Current methods for identifying wells that are at highest priority for increased monitoring and/or at highest risk for failure consists of “hand” analysis of multi-arm caliper (MAC) well logging data and geomechanical models. Machine learning (ML) methods are of interest to explore feasibility for increasing analysis efficiency and/or enhanced detection of precursors to failure (e.g. deformations). MAC datasets used to train ML algorithms and preliminary tests were run for “predicting” casing collar locations and performed above 90% in classification and identifying of casing collar locations.
This interim report is an update of ongoing experimental and modeling work on bentonite material described in Jové Colón et al. (2019, 2020) from past international collaboration activities. As noted in Jové Colón et al. (2020), work on international repository science activities such as FEBEX-DP and DECOVALEX19 is either no longer continuing by the international partners. Nevertheless, research activities on the collected sample materials and field data are still ongoing. Descriptions of these underground research laboratory (URL) R&D activities are described elsewhere (Birkholzer et al. 2019; Jové Colón et al. 2020) but will be explained here when needed. The current reports recent reactive-transport modeling on the leaching of sedimentary rock.
Disposal of large, heat-generating waste packages containing the equivalent of 21 pressurized water reactor (PWR) assemblies or more is among the disposal concepts under investigation for a future repository for spent nuclear fuel (SNF) in the United States. Without a long (>200 years) surface storage period, disposal of 21-PWR or larger waste packages (especially if they contain high-burnup fuel) would result in in-drift and near-field temperatures considerably higher than considered in previous generic reference cases that assume either 4-PWR or 12-PWR waste packages (Jové Colón et al. 2014; Mariner et al. 2015; 2017). Sevougian et al. (2019c) identified high-temperature process understanding as a key research and development (R&D) area for the Spent Fuel and Waste Science and Technology (SFWST) Campaign. A two-day workshop in February 2020 brought together campaign scientists with expertise in geology, geochemistry, geomechanics, engineered barriers, waste forms, and corrosion processes to begin integrated development of a high-temperature reference case for disposal of SNF in a mined repository in a shale host rock. Building on the progress made in the workshop, the study team further explored the concepts and processes needed to form the basis for a high-temperature shale repository reference case. The results are described in this report and summarized..
This report describes research and development (R&D) activities conducted during fiscal year 2020 (FY20) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel and Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Energy (DOE). The R&D activities focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. A primary goal is to advance the development of process models that can be implemented directly within the Generic Disposal System Analysis (GDSA) platform or that can contribute to the safety case in some manner such as building confidence, providing further insight into the processes being modeled, establishing better constraints on barrier performance, etc. The FY20 EBS activities involved not only modeling and analysis work, but experimental work as well. Despite delays to some planned activities due to COVID-19 precautions, progress was made during FY20 in multiple research areas and documented in this report as follows: (1) EBS Task Force: Task 9/FEBEX Modeling Final Report: Thermo-Hydrological Modeling with PFLOTRAN, (2) preliminary sensitivity analysis for the FEBEX in-situ heater test, (3) cement-carbonate rock interaction under saturated conditions: from laboratory to modeling, (4) hydrothermal experiments, (5) progress on investigating the high temperature behavior of the uranyl-carbonate complexes, (6) in-situ and electrochemical work for model validation, (7) investigation of the impact of high temperature on EBS bentonite with THMC modeling, (8) sorption and diffusion experiments on bentonite, (9) chemical controls on montmorillonite structure and swelling pressure, (10) microscopic origins of coupled transport processes in bentonite, (11) understanding the THMC evolution of bentonite in FEBEX-DP—coupled THMC modeling, (12) modeling in support of HotBENT, an experiment studying the effects of high temperatures on clay buffers/near-field, and (13) high temperature heating and hydration column test on bentonite.
This report is a summary of the international collaboration work conducted by Sandia and funded by the US Department of Energy Office (DOE) of Nuclear Energy Spent Fuel and Waste Science & Technology (SFWST) as part of the Sandia National Laboratories Salt R&D and Salt International work packages. This report satisfies milestone level-three milestone M3SF-205N010303062. Several stand-alone sections make up this summary report, each completed by the participants. The first two sections discuss international collaborations on geomechanical benchmarking exercises (WEIMOS), granular salt reconsolidation (KOMPASS), engineered barriers (RANGERS), and documentation of Features, Events, and Processes (FEPs).
This report outlines Sandia National Laboratories modeling studies applied to Stage 1 and Stage 2 of the Full-scale Engineered Barriers Experiment in Crystalline Host Rock (FEBEX) in situ test for the SKB EBS Task Force Task 9. The FEBEX test was a full-scale test conducted over ~18 years at the Grimsel, Switzerland Underground Research Laboratory (URL) managed by NAGRA. It involved emplacing simulated waste packages, in the form of welded cylindrical heaters, inside a tunnel in crystalline granitic rock and surrounded by a bentonite barrier and cement plug. Sensors emplaced within the bentonite monitored the wetting-up, heating, and drying out of the bentonite barrier, and the large resulting data set provides an excellent opportunity for validation of multiphysics Thermal-Hydrological (TH), Thermal-Hydrologic-Chemical (THC), and Thermal-Hydrological-Mechanical (THM) modeling approaches for underground nuclear waste storage and the performance of engineered bentonite barriers. The present status of the EBS Task Force is finalizing Task 9, which follows years of modeling studies of the FEBEX test, by many notable modeling teams (Gens et al., 2009; Sanchez et al. 2010; 2012; Samper et al., 2018). These modeling studies generally use two-dimensional axisymmetric meshes, ignoring threedimensional effects, gravity and asymmetric wetting and dry out of the bentonite engineered barrier. This study investigates these effects with use of the PFLOTRAN THC code with massively parallel computational methods in modeling FEBEX Stage 1 and Stage 2 results. The PFLOTRAN numerical code is an open source, state-of-the-art, massively parallel subsurface flow and reactive transport code operating in a high-performance computing environment (Hammond et al., 2014). Section 2 describes the applied partial differential equations describing mass, momentum and energy balance used in this study, considerations derived by assuming phase equilibrium between gas and liquid phases, constitutive equations for granite, cement plug, and bentonite domains, and specific approaches for use inthe PFLOTRAN code. Section 3 describes the geometry, meshing, and model set-up. Section 4 describes modeling results, Section 5 compares modeling results to field testing data, and Section 6 gives conclusions. The Appendix provides detailed information required by the EBSTask Force for final reporting.
This report describes research and development (R&D) activities conducted during fiscal year 2019 (FY19) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel and Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Eneregy (DOE). The R&D activities focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. A primary goal is to advance the development of process models that can be implemented directly within the Genreric Disposal System Analysis (GDSA) platform or that can contribute to the safety case in some manner such as building confidence, providing further insight into the processes being modeled, establishing better constraints on barrier performance, etc.The FY19 EBS activities involved not only modeling and analysis work, but experimental work as well. The report documents the FY19 progress made in seven different research areas as follows: (1) thermal analysis for the disposal of dual purpose canisters (DPCs) in sedimentary host rock using the semianalytical method, (2) tetravalent uranium solubility and speciation, (3) modeling of high temperature, thermal-hydrologic-mechanical-chemical (THMC) coupled processes, (4) integration of coupled thermalhydrologic- chemical (THC) model with GDSA using a Reduced-Order Model, (5) studying chemical controls on montmorillonite structure and swelling pressure, (6) transmission x-ray microscope for in-situ nanotomography of bentonite and shale, and (7) in-situ electrochemical testing of uranium dioxide under anoxic conditions. The R&D team consisted of subject matter experts from Sandia National Laboratories, Lawrence Berkeley National Laboratory (LBNL), Los Alamos National Laboratory (LANL), Pacific Northwest National Laboratory (PNNL), the Bureau de Recherches Géologiques et Minières (BRGM), the University of California Berkeley, and Mississippi State University. In addition, the EBS R&D work leverages international collaborations to ensure that the DOE program is active and abreast of the latest advances in nuclear waste disposal. For example, the FY19 work on modeling coupled THMC processes at high temperatures relied on the bentonite properties from the Full-scale Engineered Barrier EXperiment (FEBEX) Field Test conducted at the Grimsel Test Site in Switzerland. Overall, significant progress has been made in FY19 towards developing the modeling tools and experimental capabilities needed to investigate the performance of EBS materials and the associated interactions in the drift and the surrounding near-field environment under a variety of conditions including high temperature regimes.
The Waste Isolation Pilot Plant (WIPP) is a geologic repository for defense-related nuclear waste. If left undisturbed, the virtually impermeable rock salt surrounding the repository will isolate the nuclear waste from the biosphere. If humans accidentally intrude into the repository in the future, then the likelihood of a radionuclide release to the biosphere will depend significantly on the porosity and permeability of the repository itself. Room ceilings and walls at the WIPP tend to collapse over time, causing rubble piles to form on floors of empty rooms. The surrounding rock formation will gradually compact these rubble piles until they eventually become solid salt, but the length of time for a rubble pile to reach a certain porosity and permeability is unknown. This report details the first efforts to build models to predict the porosity and permeability evolution of an empty room as it closes. Conventional geomechanical numerical methods would struggle to model empty room collapse and rubble pile consolidation, so three different meshless methods, the Immersed Isogeometric Analysis Meshfree, Reproducing Kernel Particle Method (RKPM), and the Conformal Reproducing Kernel method, were assessed. First, the meshless methods and the finite element method each simulated gradual room closure, without ceiling or wall collapse. All three methods produced equivalent room closure predictions with comparable computational speed. Second, the Immersed Isogeometric Analysis Meshfree method and RKPM simulated two-dimensional empty room collapse and rubble pile consolidation. Both methods successfully simulated large viscoplastic deformations, fracture, and rubble pile rearrangement to produce qualitatively realistic results. In addition to geomechanical simulations, the flow channels in damaged salt and crushed salt were measured using micro-computed tomography, and input into a computational fluid dynamics simulation to predict the salt's permeability. Although room for improvement exists, the current simulation approaches appear promising.
The failure of subsurface seals (i.e., wellbores, shaft and drift seals in a deep geologic nuclear waste repository) has important implications for US Energy Security. The performance of these cementitious seals is controlled by a combination of chemical and mechanical forces, which are coupled processes that occur over multiple length scales. The goal of this work is to improve fundamental understanding of cement-geomaterial interfaces and develop tools and methodologies to characterize and predict performance of subsurface seals. This project utilized a combined experimental and modeling approach to better understand failure at cement-geomaterial interfaces. Cutting-edge experimental methods and characterization methods were used to understand evolution of the material properties during chemo-mechanical alteration of cement-geomaterial interfaces. Software tools were developed to model chemo-mechanical coupling and predict the complex interplay between reactive transport and solid mechanics. Novel, fit-for-purpose materials were developed and tested using fundamental understanding of failure processes at cement- geomaterial interfaces. ACKNOWLEDGEMENTS The authors wish to acknowledge the Earth Sciences Research Foundation for their generous support over the last three years. In particular, we thank Erik Webb for his numerous suggestions, comments, feedback, and encouragement over the course of the project. There many who helped bring this project to fruition, including: Dave Borns, Steve Bauer, Pania Newell, Heeho Park, and Doug Blankenship. There are many support personnel who we thank for their valuable contributions to the logistics and business of management side of the project, including: Tracy Woolever, Libby Sanzero, and Nancy Vermillion.
Genedy, Moneeb; Matteo, Edward N.; Stenko, Michael; Stormont, John C.; Taha, Mahmoud R.
Microscale defects (microannuli) at the steel-cement and rock-cement interfaces are a major cause of failure in the integrity of wellbore systems. Microscale defects/microcracks as small as 30 μm are sufficient to create a significant leakage pathway for fluids. In this paper, the authors propose the use of nanomodified methyl methacrylate (NM-MMA) polymer as a seal material for 30-μm microcracks. Four materials were evaluated for their ability to serve as an effective seal material to seal 30-μm microcracks: microfine cement, epoxy, methyl methacrylate (MMA), and NM-MMA incorporating 0.5% by weight aluminum nanoparticles (ANPs). The seal materials' bond strengths with shale were investigated using push-out tests. In addition, the ability to flow fluid through the microcracks was investigated using sagittal microscopic images. Viscosity, surface tension, and contact angle measurements explain the superior ability of MMA seal materials to flow into very thin microcracks compared with other materials. Post-test analysis shows MMA repair materials are capable of completely filling the microcracks. In addition, incorporating ANPs in MMA resulted in significant improvement in seal material ductility. Dynamic mechanical analysis (DMA) showed that incorporating ANPs in MMA reduced the creep compliance and improved creep recovery of NM-MMA. X-ray diffraction (XRD) analysis shows that incorporating ANPs in MMA resin increases the degree of polymer crystallization, resulting in significant improvement in seal material ductility.
In wellbores, cement plays an important role in wellbore integrity. As wells age and are stressed during their life cycle, the cement sheath may deform, altering its permeability and, perhaps compromising its integrity. In this study, we use flow measurements (calculated permeability) to provide real-time insight into damage incurred during triaxial deformation of neat cement. Cracks may be induced during deformation and their linkage may be sensed in the flow measurements. Conversely, cracks and pores may be closed during deformation, arresting fluid flow. We subjected room temperature specimens of neat Portland cement to confining pressures (0.7, 2.1, 13.8 MPa) and measured heliu m flow continuously during triaxial deformation. Axial displacement across a specimen was periodically halted to perhaps assure steady flow rate throughout the sample. We observed the apparent permeability to decrease from 0.8 to 0.7 to 0.2 μD with the imposed confining pressure increase. Each specimen, when subjected to differential stress, exhibited a slight decrease in apparent permeability, implying disconnects of flow paths. For the two lower confining pressures, apparent permeability began to increase just prior to macroscopic failure, suggesting microcrack linkage. For the 2.1 MPa confining pressure test, apparent permeability increased by a factor of three at macrofracture, and for the 0.7 MPa confining pressure test, apparent permeability increased by a factor of thirty at macrofracture. At 13.8 MPa confining pressure, apparent permeability only decreases during triaxial loading, implying that poroelastic compaction restricts flow pathways and connectivity of appropriately oriented cracks for axial flow decreases during deformation. Failure by macrofracture did not occur in this sample. Optical and scanning electron microscopy of deformed specimens indicate that pores and microcracks interact in complex manners, similar microcrack densities are observed in both 0.7 and 13.8 MPa test specimens, and pores represent both microcrack origination and localization sites. Larger pores (entrapped air voids) are sheared, flattened, and sites of crack opening. Micron-scale capillary porosity, determined using SEM image processing, is similar for all specimens. The results from these few experiments indicate that microfracturing of cement during triaxial deformation results in permeabilit y increases at low confining pressures. At the greater pressure, although microfracturing is observed, compaction and lack of microfracture interconnectivity have a greater effect on flow pathways, resulting in a permeability decrease during deformation.
Our results show that a pseudo-boehmite precursor material can be chemically modified with divalent cationic species, for example, Nickel, to create an effective getter for anionic species. The viability of this novel class of materials is established by a variety of characterization methods, including surface area measurements, scanning electron microscopy, elemental analysis, and sorption capacity measurements. We will present the results of sorption capacity and surface area measurements that show the high sorption capacity of this novel class of getter materials. Our study shows that the divalent cation modification can increase the sorption capacity by as much as a factor of two.
This document is a summary of the R&D activities associated with the Engineered Barrier Systems Work Package. Multiple facets of Engineered Barrier Systems (EBS) research were examined in the course of FY18 activities. This report is focused on delvering an update on the status and progress of modelling tools and experimental methods, both of which are essential to understanding and predicting long-term repository performance as part of the safety case. Specifically, the work described herein aims to improve understanding of EBS component evolution and interactions. Utlimately, the EBS Work Package is working towards producing process models for distinct processes that can either be incorporated into performance assessment (PA), or provide critical information for implementing better contraints on barrier performance The main objective of this work is that the models being developed and refined will either be implemented directly into the Genreric Disposal System Analysis platform (GDSA), or can otherwise be indirectly linked to the performance assessment by providing improved bounding conditions. In either the case, the expectation is that validated modelling tools will be developed that provide critical input to the safety case. This report covers a range of topics — modelling topics include: thermal-hydrologic-mechnicalchemical coupling (THMC) in buffer materials, comparisons of modelling approaches to optimize computational efficiency, thermal analysis for EBS/repository design, benchmarking of thermal analysis tools, and a preliminary study of buffer re-saturation processess. Experimental work reported, includes: chemical evolution and sorption behavior of clay-based buffer materials and high-pressure, high temperature studies of EBS material interactions. The work leverages international collaborations to ensure that the DOE program is active and abreast of the latest advances in nuclear waste disposal. This includes participation in the HotBENT Field Test, aimed at understanding near-field effects on EBS materials at temperatures above 100 °C, and the analysis of data and characterization of samples from the FEBEX Field Test. Both the FEBEX and HotBENT Field Tests utilize/utilized the Grimsel Test Site in Switzerland, which is situated in a granite host rock. These tests offer the opportunity to understand near field evolution of bentonite buffer at in situ conditions for either a relatively long timescale (18 years for FEBEX) or temperature above 100 °C (HotBENT). Overall, this report provides in depth descriptions of tools and capabilities to investigate nearfield performance of EBS materials (esp. bentonite buffer), as well as tools for drift-scale thermal and thermal-hydrologic analysis critical to EBS and repository design. For a more detailed description of work contained herein, please see Section 10 ("Conclusions") of this document.
Predicting chemical-mechanical fracture initiation and propagation in materials is a critical problem, with broad relevance to a host of geoscience applications including subsurface storage and waste disposal, geothermal energy development, and oil and gas extraction. In this project, we have developed molecular simulation and coarse- graining techniques to obtain an atomistic-level understanding of the chemical- mechanical mechanisms that control subcritical crack propagation in materials under tension and impact the fracture toughness. We have applied these techniques to the fracture of fused quartz in vacuum, in distilled water, and in two salt solutions - 1M NaC1, 1M NaOH - that form relatively acidic and basic solutions respectively. We have also established the capability to conduct double-compression double-cleavage experiments in an environmental chamber to observe material fracture in aqueous solution. Both simulations and experiments indicate that fractures propagate fastest in NaC1 solutions, slower in distilled water, and even slower in air.
This project plan gives a high-level description of the US Department of Energy Office of Nuclear Energy (DOE-NE) Spent Fuel and Waste Disposition (SFWD) campaign in situ borehole heater test project being planned for the Waste Isolation Pilot Plant (WIPP) site This plan provides an overview of the schedule and responsibilities of the parties involved. This project is a collaborative effort by Sandia, Los Alamos, and Lawrence Berkeley National Laboratories to execute a series of small-diameter borehole heater tests in salt for the DOE-NE SFWD campaign. Design of a heater test in salt at WIPP has evolved over several years. The current design was completed in fiscal year 2017 (FY17), an equipment shakedown experiment is underway in April FY18, and the test implementation will begin in summer of FY18. The project comprises a suite of modular tests, which consist of a group of nearby boreholes in the wall of drifts at WIPP. Each test is centered around a packer-isolated heated borehole (5" diameter) containing equipment for water-vapor collection and brine sampling, surrounded by smaller-diameter (2" diameter) satellite observation boreholes. Observation boreholes will contain temperature sensors, tracer release points, electrical resistivity tomography (ERT) sensors, fiber optic sensing, and acoustic emission (AE) measurements, and sonic velocity sources and sensors. These satellite boreholes will also be used for plugging/sealing tests. The first two tests to be implemented will have the packer-isolated borehole heated to 120°C, with one observation borehole used to monitor changes. Follow-on tests will be designed using information gathered from the first two tests, will be conducted at other temperatures, will use multiple observation boreholes, and may include other measurement types and test designs.
Desirable outcomes for geologic carbon storage include maximizing storage efficiency, preserving injectivity, and avoiding unwanted consequences such as caprock or wellbore leakage or induced seismicity during and post injection. To achieve these outcomes, three control measures are evident including pore pressure, injectate chemistry, and knowledge and prudent use of geologic heterogeneity. Field, experimental, and modeling examples are presented that demonstrate controllable GCS via these three measures. Observed changes in reservoir response accompanying CO2 injection at the Cranfield (Mississippi, USA) site, along with lab testing, show potential for use of injectate chemistry as a means to alter fracture permeability (with concomitant improvements for sweep and storage efficiency). Further control of reservoir sweep attends brine extraction from reservoirs, with benefit for pressure control, mitigation of reservoir and wellbore damage, and water use. State-of-the-art validated models predict the extent of damage and deformation associated with pore pressure hazards in reservoirs, timing and location of networks of fractures, and development of localized leakage pathways. Experimentally validated geomechanics models show where wellbore failure is likely to occur during injection, and efficiency of repair methods. Use of heterogeneity as a control measure includes where best to inject, and where to avoid attempts at storage. An example is use of waste zones or leaky seals to both reduce pore pressure hazards and enhance residual CO2 trapping.
Molecular structures of kerogen control hydrocarbon production in unconventional reservoirs. Significant progress has been made in developing model representations of various kerogen structures. These models have been widely used for the prediction of gas adsorption and migration in shale matrix. However, using density functional perturbation theory (DFPT) calculations and vibrational spectroscopic measurements, we here show that a large gap may still remain between the existing model representations and actual kerogen structures, therefore calling for new model development. Using DFPT, we calculated Fourier transform infrared (FTIR) spectra for six most widely used kerogen structure models. The computed spectra were then systematically compared to the FTIR absorption spectra collected for kerogen samples isolated from Mancos, Woodford and Marcellus formations representing a wide range of kerogen origin and maturation conditions. Limited agreement between the model predictions and the measurements highlights that the existing kerogen models may still miss some key features in structural representation. A combination of DFPT calculations with spectroscopic measurements may provide a useful diagnostic tool for assessing the adequacy of a proposed structural model as well as for future model development. This approach may eventually help develop comprehensive infrared (IR)-fingerprints for tracing kerogen evolution.
This report is a summary of the international collaboration and laboratory work funded by the US Department of Energy Office of Nuclear Energy Spent Fuel and Waste Science & Technology (SFWST) as part of the Sandia National Laboratories Salt R&D work package. This report satisfies milestone levelfour milestone M4SF-17SN010303014. Several stand-alone sections make up this summary report, each completed by the participants. The first two sections discuss international collaborations on geomechanical benchmarking exercises (WEIMOS) and bedded salt investigations (KOSINA), while the last three sections discuss laboratory work conducted on brucite solubility in brine, dissolution of borosilicate glass into brine, and partitioning of fission products into salt phases.
An example case is presented for testing analytical thermal models. The example case represents thermal analysis of a generic repository in bedded salt at 500 m depth. The analysis is part of the study reported in Matteo et al. (2016). Ambient average ground surface temperature of 15°C, and a natural geothermal gradient of 25°C/km, were assumed to calculate temperature at the near field. For generic salt repository concept crushed salt backfill is assumed. For the semi-analytical analysis crushed salt thermal conductivity of 0.57 W/m-K was used. With time the crushed salt is expected to consolidate into intact salt. In this study a backfill thermal conductivity of 3.2 W/m-K (same as intact) is used for sensitivity analysis. Decay heat data for SRS glass is given in Table 1. The rest of the parameter values are shown below. Results of peak temperatures at the waste package surface are given in Table 2.
Douba, A.; Genedy, M.; Matteo, Edward N.; Kandil, U.F.; Stormont, J.; Reda Taha, M.M.
Polymer concrete (PC) is a commonly used material in construction due to its improved durability and good bond strength to steel substrate. PC has been suggested as a repair and seal material to restore the bond between the cement annulus and the steel casing in wells that penetrate formations under consideration for CO2 sequestration. Nanoparticles including Multi-Walled Carbon Nano Tubes (MWCNTs), Aluminum Nanoparticles (ANPs) and Silica Nano particles (SNPs) were added to an epoxy-based PC to examine how the nanoparticles affect the bond strength of PC to a steel substrate. Slant shear tests were used to determine the bond strength of PC incorporating nanomaterials to steel; results reveal that PC incorporating nanomaterials has an improved bond strength to steel substrate compared with neat PC. In particular, ANPs improve the bond strength by 51% over neat PC. Local shear stresses, extracted from Finite Element (FE) analysis of the slant shear test, were found to be as much as twice the apparent/average shear/bond strength. These results suggest that the impact of nanomaterials is higher than that shown by the apparent strength. Fourier Transform Infrared (FTIR) measurements of epoxy with and without nanomaterials showed ANPs to influence curing of epoxy, which might explain the improved bond strength of PC incorporating ANPs.
Genedy, Moneeb; Kandil, Usama F.; Matteo, Edward N.; Stormont, John; Reda Taha, Mahmoud M.
Seal integrity of functional oil wells and abandoned wellbores used for CO2 subsequent storage has become of significant interest with the oil and gas leaks worldwide. This is attributed to the fact that wellbores intersecting geographical formations contain potential leakage pathways. One of the critical leakage pathways is the cement-shale interface. In this paper, we examine the efficiency of a new polymer nanocomposite repair material that can be injected for sealing micro annulus in wellbores. The bond strength and microstructure of the interface of Type G oil well cement (reference), microfine cement, Novolac epoxy incorporating Neat, 0.25%, 0.5%, and 1.0% Aluminum Nanoparticles (ANPs) with shale is investigated. Interfacial bond strength testing shows that injected microfine cement repair has considerably low bond strength, while ANPs-epoxy nanocomposites have a bond strength that is an order of magnitude higher than cement. Microscopic investigations of the interface show that micro annulus interfacial cracks with widths up to 40 μm were observed at the cement-shale interface while these cracks were absent at the cement-epoxy-shale interface. Fourier Transform Infrared and Dynamic mechanical analysis measurements showed that ANPs improve interfacial bond by limiting epoxy crosslinking, and therefore allowing epoxy to form robust bonds with cement and shale.
This research aims to describe the microannulus region of the cement sheath-steel casing interface in terms of its compressibility and permeability. A wellbore system mock-up was used for lab-scale testing, and was subjected to confining and casing pressures in a pressure vessel while measuring gas flow along the specimen's axis. The flow was interpreted as the hydraulic aperture of the microannuli. Numerical joint models were used to calculate stress and displacement conditions of the microannulus region, where the mechanical stiffness and hydraulic aperture were altered in response to the imposed stress state and displacement across the joint interface.
This report summarizes the first stage in a collaborative effort by Sandia, Los Alamos, and Lawrence Berkeley National Laboratories to design a small-diameter borehole heater test in salt at the Waste Isolation Pilot Plant (WIPP) for the US Department of Energy Office of Nuclear Energy (DOE-NE). The intention is to complete test design during the remainder of fiscal year 2017 (FY17), and the implementation of the test will begin in FY18. This document is the result of regular meetings between the three national labs and the DOE-NE, and is intended to represent a consensus of these meetings and discussions.
As the title suggests, this report provides a summary of the status and progress for the Preliminary Design Concepts Work Package. Described herein are design concepts and thermal analysis for crystalline and salt host media. The report concludes that thermal management of defense waste, including the relatively small subset of high thermal output waste packages, is readily achievable. Another important conclusion pertains to engineering feasibility, and design concepts presented herein are based upon established and existing elements and/or designs. The multipack configuration options for the crystalline host media pose the greatest engineering challenges, as these designs involve large, heavy waste packages that pose specific challenges with respect to handling and emplacement. Defense-related Spent Nuclear Fuel (DSNF) presents issues for post-closure criticality control, and a key recommendation made herein relates to the need for special packaging design that includes neutron-absorbing material for the DSNF. Lastly, this report finds that the preliminary design options discussed are tenable for operational and post-closure safety, owing to the fact that these concepts have been derived from other published and well-studied repository designs.
Salt formations represent a promising host for disposal of nuclear waste in the United States and Germany. Together, these countries provided fully developed safety cases for bedded salt and domal salt, respectively. Today, Germany and the United States find themselves in similar positions with respect to salt formations serving as repositories for heat-generating nuclear waste. German research centers are evaluating bedded and pillow salt formations to contrast with their previous safety case made for the Gorleben dome. Sandia National Laboratories is collaborating on this effort as an Associate Partner, and this report summarizes that teamwork. Sandia and German research groups have a long-standing cooperative approach to repository science, engineering, operations, safety assessment, testing, modeling and other elements comprising the basis for salt disposal. Germany and the United States hold annual bilateral workshops, which cover a spectrum of issues surrounding the viability of salt formations. Notably, recent efforts include development of a database for features, events, and processes applying broadly and generically to bedded and domal salt. Another international teaming activity evaluates salt constitutive models, including hundreds of new experiments conducted on bedded salt from the Waste Isolation Pilot Plant. These extensive collaborations continue to build the scientific basis for salt disposal. Repository deliberations in the United States are revisiting bedded and domal salt for housing a nuclear waste repository. By agreeing to collaborate with German peers, our nation stands to benefit by assurance of scientific position, exchange of operational concepts, and approach to elements of the safety case, all reflecting cost and time efficiency.
At the initiation of the Used Fuel Disposition (UFD) R&D campaign, international geologic disposal programs and past work in the U.S. were surveyed to identify viable disposal concepts for crystalline, clay/shale, and salt host media. Concepts for disposal of commercial spent nuclear fuel (SNF) and high-level waste (HLW) from reprocessing are relatively advanced in countries such as Finland, France, and Sweden. The UFD work quickly showed that these international concepts are all “enclosed,” whereby waste packages are emplaced in direct or close contact with natural or engineered materials . Alternative “open” modes (emplacement tunnels are kept open after emplacement for extended ventilation) have been limited to the Yucca Mountain License Application Design. Thermal analysis showed that if “enclosed” concepts are constrained by peak package/buffer temperature, that waste package capacity is limited to 4 PWR assemblies (or 9 BWR) in all media except salt. This information motivated separate studies: 1) extend the peak temperature tolerance of backfill materials, which is ongoing; and 2) develop small canisters (up to 4-PWR size) that can be grouped in larger multi-pack units for convenience of storage, transportation, and possibly disposal (should the disposal concept permit larger packages). A recent result from the second line of investigation is the Task Order 18 report: Generic Design for Small Standardized Transportation, Aging and Disposal Canister Systems. This report identifies disposal concepts for the small canisters (4-PWR size) drawing heavily on previous work, and for the multi-pack (16-PWR or 36-BWR).
At the initiation of the Used Fuel Disposition (UFD) R&D campaign, international geologic disposal programs and past work in the U.S. were surveyed to identify viable disposal concepts for crystalline, clay/shale, and salt host media (Hardin et al., 2012). Concepts for disposal of commercial spent nuclear fuel (SNF) and high-level waste (HLW) from reprocessing are relatively advanced in countries such as Finland, France, and Sweden. The UFD work quickly showed that these international concepts are all “enclosed,” whereby waste packages are emplaced in direct or close contact with natural or engineered materials . Alternative “open” modes (emplacement tunnels are kept open after emplacement for extended ventilation) have been limited to the Yucca Mountain License Application Design (CRWMS M&O, 1999). Thermal analysis showed that, if “enclosed” concepts are constrained by peak package/buffer temperature, waste package capacity is limited to 4 PWR assemblies (or 9-BWR) in all media except salt. This information motivated separate studies: 1) extend the peak temperature tolerance of backfill materials, which is ongoing; and 2) develop small canisters (up to 4-PWR size) that can be grouped in larger multi-pack units for convenience of storage, transportation, and possibly disposal (should the disposal concept permit larger packages). A recent result from the second line of investigation is the Task Order 18 report: Generic Design for Small Standardized Transportation, Aging and Disposal Canister Systems (EnergySolution, 2015). This report identifies disposal concepts for the small canisters (4-PWR size) drawing heavily on previous work, and for the multi-pack (16-PWR or 36-BWR).
This report examines the technical elements necessary to evaluate EBS concepts and perform thermal analysis of DOE-Managed SNF and HLW in the disposal settings of primary interest – argillite, crystalline, salt, and deep borehole. As the disposal design concept is composed of waste inventory, geologic setting, and engineered concept of operation, the engineered barrier system (EBS) falls into the last component of engineered concept of operation. The waste inventory for DOE-Managed HLW and SNF is closely examined, with specific attention to the number of waste packages, the size of waste packages, and the thermal output per package. As expected, the DOE-Managed HLW and SNF inventory has a much smaller volume, and hence smaller number of canisters, as well a lower thermal output, relative to a waste inventory that would include commercial spent nuclear fuel (CSNF). A survey of available data and methods from previous studies of thermal analysis indicates that, in some cases, thermo-hydrologic modeling will be necessary to appropriately address the problem. This report also outlines scope for FY16 work -- a key challenge identified is developing a methodology to effectively and efficiently evaluate EBS performance in each disposal setting on the basis of thermal analyses results.
The purpose of the two projects discussed in this report is to use the cohesive zone method to evaluate fracture properties of geomaterials. Two experimental tests, the push-out test and the notched three-point bend test, were modeled computationally using finite element analysis and cohesive zone modeling to extract load and displacement information and ul- timately determine failure behavior. These results are to be compared with experimental tests when they are available. The first project used the push-out test to investigate the shear bond strength at the cement- shale interface. The second project explored the effects of scaling a notched three-point bend- ing specimen to study fracture toughness characteristics. The bond strength and fracture toughness of a material and its interfaces are important parameters to consider in subsurface applications so that zonal isolation can be achieved.
49th US Rock Mechanics / Geomechanics Symposium 2015
Stormont, J.C.; Ahmad, R.; Ellison, J.; Reda Taha, M.M.; Matteo, Edward N.
Microannuli that develop along the cement-casing interface have been identified as common leakage pathways in wellbores. We have developed an experimental system that allows laboratory testing of wellbore specimens which are comprised of a cement sheath cast on a steel casing. Specimens were produced with a range of flaws including microannuli between the steel casing and the cement. The system allows independent application of confining pressures to 35 MPa and casing pressures to 20 MPa while gas flow is measured through the specimens along the wellbore axis. We present the gas flow results in terms of the hydraulic aperture of microannuli as a function of confining pressure and internal pressure for two different types of microannuli. Hydraulic apertures decrease non-linearly with increasing stress across the microannuli in a manner similar to fractures in rocks and other materials. The hydraulic apertures are more sensitive to changes in confining pressure than casing pressure, consistent with the estimated contact stress that develops across the cement-casing interface.
This paper presents results of three models simulating the hydrological-mechanical behavior of a CO2 injection reservoir and the resulting effects on wellbore system (cement and casing) and seal repair materials. A critical aspect of designing effective wellbore seal repair materials is predicting thermo-mechanical perturbations that can compromise seal integrity. Three distinct computational models comprise the current modeling effort. The first model depicts bench-top experiments of an integrated seal system in an idealized scaled wellbore mock-up being used to test candidate seal repair materials. This model will be used to gain an understanding of the wellbore microannulus compressibility and permeability. The second is a field scale model that uses the stratigraphy, material properties, and injection history from a pilot CO2 injection operation to develop stress-strain histories for wellbore locations from 100 to 400 meters from an injection well. The results from these models are used as input to a more detailed model of a wellbore system. The 3D wellbore model examines the impacts of various loading scenarios on a wellbore system. The results from these models will be used to estimate the necessary thermal-mechanical properties needed for a successful repair material.
Thousands of abandoned wellbores may lie within the aerial extent of a CO2 storage operation. These wellbores represent a potential leakage pathway and a leaky wellbore needs to be re-completed or otherwise repaired to restore seal integrity and ensure containment of the stored CO2. Due to the high cost of recompleting a well, a sufficient economic incentive exists if a viable seal repair technology is available. In this paper, we examine the use of epoxy nanocomposites as potential seal repair materials that have excellent bond characteristics with both steel and cement when cured in the subsurface environment. Test results show Novolac epoxy nanocomposites incorporating nanosilica, nanoclay or nanoalumina to have acceptable flowability that enable injection in wellbore cracks and significantly higher bond strength compared with standard microfine cement.
In the supercritical CO2-water-mineral systems relevant to subsurface CO2 sequestration, interfacial processes at the supercritical fluid-mineral interface will strongly affect core- and reservoir-scale hydrologic properties. Experimental and theoretical studies have shown that water films will form on mineral surfaces in supercritical CO2, but will be thinner than those that form in vadose zone environments at any given matric potential. The theoretical model presented here allows assessment of water saturation as a function of matric potential, a critical step for evaluating relative permeabilities the CO2 sequestration environment. The experimental water adsorption studies, using Quartz Crystal Microbalance and Fourier Transform Infrared Spectroscopy methods, confirm the major conclusions of the adsorption/condensation model. Additional data provided by the FTIR study is that CO2 intercalation into clays, if it occurs, does not involve carbonate or bicarbonate formation, or significant restriction of CO2 mobility. We have shown that the water film that forms in supercritical CO2 is reactive with common rock-forming minerals, including albite, orthoclase, labradorite, and muscovite. The experimental data indicate that reactivity is a function of water film thickness; at an activity of water of 0.9, the greatest extent of reaction in scCO2 occurred in areas (step edges, surface pits) where capillary condensation thickened the water films. This suggests that dissolution/precipitation reactions may occur preferentially in small pores and pore throats, where it may have a disproportionately large effect on rock hydrologic properties. Finally, a theoretical model is presented here that describes the formation and movement of CO2 ganglia in porous media, allowing assessment of the effect of pore size and structural heterogeneity on capillary trapping efficiency. The model results also suggest possible engineering approaches for optimizing trapping capacity and for monitoring ganglion formation in the subsurface.