Publications

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The National Water, Energy and Carbon Sequestration simulation model (WECSsim) is being developed to address the question, 'Where in the current and future U.S. fossil fuel based electricity generation fleet are there opportunities to couple CO{sub 2} storage and extracted water use, and what are the economic and water demand-related impacts of these systems compared to traditional power systems?' The WECSsim collaborative team initially applied this framework to a test case region in the San Juan Basin, New Mexico. Recently, the model has been expanded to incorporate the lower 48 states of the U.S. Significant effort has been spent characterizing locations throughout the U.S. where CO{sub 2} might be stored in saline formations including substantial data collection and analysis efforts to supplement the incomplete brine data offered in the NatCarb database. WECSsim calculates costs associated with CO{sub 2} capture and storage (CCS) for the power plant to saline formation combinations including parasitic energy costs of CO{sub 2} capture, CO{sub 2} pipelines, water treatment options, and the net benefit of water treatment for power plant cooling. Currently, the model can identify the least-cost deep saline formation CO{sub 2} storage option for any current or proposed coal or natural gas-fired power plant in the lower 48 states. Initial results suggest that additional, cumulative water withdrawals resulting from national scale CCS may range from 676 million gallons per day (MGD) to 30,155 MGD depending on the makeup power and cooling technologies being utilized. These demands represent 0.20% to 8.7% of the U.S. total fresh water withdrawals in the year 2000, respectively. These regional and ultimately nation-wide, bottom-up scenarios coupling power plants and saline formations throughout the U.S. can be used to support state or national energy development plans and strategies.

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Mudstone mechanical testing is often limited by poor core recovery and sample size, preservation and preparation issues, which can lead to sampling bias, damage, and time-dependent effects. A micropillar compression technique, originally developed by Uchic et al. 2004, here is applied to elasto-plastic deformation of small volumes of mudstone, in the range of cubic microns. This study examines behavior of the Gothic shale, the basal unit of the Ismay zone of the Pennsylvanian Paradox Formation and potential shale gas play in southeastern Utah, USA. Precision manufacture of micropillars 5 microns in diameter and 10 microns in length are prepared using an ion-milling method. Characterization of samples is carried out using: dual focused ion - scanning electron beam imaging of nano-scaled pores and distribution of matrix clay and quartz, as well as pore-filling organics; laser scanning confocal (LSCM) 3D imaging of natural fractures; and gas permeability, among other techniques. Compression testing of micropillars under load control is performed using two different nanoindenter techniques. Deformation of 0.5 cm in diameter by 1 cm in length cores is carried out and visualized by a microscope loading stage and laser scanning confocal microscopy. Axisymmetric multistage compression testing and multi-stress path testing is carried out using 2.54 cm plugs. Discussion of results addresses size of representative elementary volumes applicable to continuum-scale mudstone deformation, anisotropy, and size-scale plasticity effects. Other issues include fabrication-induced damage, alignment, and influence of substrate.

Mercury intrusion porosimetry (MIP) is an often-applied technique for determining pore throat distributions and seal analysis of fine-grained rocks. Due to closure effects, potential pore collapse, and complex pore network topologies, MIP data interpretation can be ambiguous, and often biased toward smaller pores in the distribution. We apply 3D imaging techniques and lattice-Boltzmann modeling in interpreting MIP data for samples of the Cretaceous Selma Group Chalk. In the Mississippi Interior Salt Basin, the Selma Chalk is the apparent seal for oil and gas fields in the underlying Eutaw Fm., and, where unfractured, the Selma Chalk is one of the regional-scale seals identified by the Southeast Regional Carbon Sequestration Partnership for CO2 injection sites. Dual focused ion - scanning electron beam and laser scanning confocal microscopy methods are used for 3D imaging of nanometer-to-micron scale microcrack and pore distributions in the Selma Chalk. A combination of image analysis software is used to obtain geometric pore body and throat distributions and other topological properties, which are compared to MIP results. 3D data sets of pore-microfracture networks are used in Lattice Boltzmann simulations of drainage (wetting fluid displaced by non-wetting fluid via the Shan-Chen algorithm), which in turn are used to model MIP procedures. Results are used in interpreting MIP results, understanding microfracture-matrix interaction during multiphase flow, and seal analysis for underground CO2 storage.

In an effort to address the potential to scale up of carbon dioxide (CO{sub 2}) capture and sequestration in the United States saline formations, an assessment model is being developed using a national database and modeling tool. This tool builds upon the existing NatCarb database as well as supplemental geological information to address scale up potential for carbon dioxide storage within these formations. The focus of the assessment model is to specifically address the question, 'Where are opportunities to couple CO{sub 2} storage and extracted water use for existing and expanding power plants, and what are the economic impacts of these systems relative to traditional power systems?' Initial findings indicate that approximately less than 20% of all the existing complete saline formation well data points meet the working criteria for combined CO{sub 2} storage and extracted water treatment systems. The initial results of the analysis indicate that less than 20% of all the existing complete saline formation well data may meet the working depth, salinity and formation intersecting criteria. These results were taken from examining updated NatCarb data. This finding, while just an initial result, suggests that the combined use of saline formations for CO{sub 2} storage and extracted water use may be limited by the selection criteria chosen. A second preliminary finding of the analysis suggests that some of the necessary data required for this analysis is not present in all of the NatCarb records. This type of analysis represents the beginning of the larger, in depth study for all existing coal and natural gas power plants and saline formations in the U.S. for the purpose of potential CO{sub 2} storage and water reuse for supplemental cooling. Additionally, this allows for potential policy insight when understanding the difficult nature of combined potential institutional (regulatory) and physical (engineered geological sequestration and extracted water system) constraints across the United States. Finally, a representative scenario for a 1,800 MW subcritical coal fired power plant (amongst other types including supercritical coal, integrated gasification combined cycle, natural gas turbine and natural gas combined cycle) can look to existing and new carbon capture, transportation, compression and sequestration technologies along with a suite of extracting and treating technologies for water to assess the system's overall physical and economic viability. Thus, this particular plant, with 90% capture, will reduce the net emissions of CO{sub 2} (original less the amount of energy and hence CO{sub 2} emissions required to power the carbon capture water treatment systems) less than 90%, and its water demands will increase by approximately 50%. These systems may increase the plant's LCOE by approximately 50% or more. This representative example suggests that scaling up these CO{sub 2} capture and sequestration technologies to many plants throughout the country could increase the water demands substantially at the regional, and possibly national level. These scenarios for all power plants and saline formations throughout U.S. can incorporate new information as it becomes available for potential new plant build out planning.

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Shales and other mudstones are the most abundant rock types in sedimentary basins, yet have received comparatively little attention. Common as hydrocarbon seals, these are increasingly being targeted as unconventional gas reservoirs, caprocks for CO{sub 2} sequestration, and storage repositories for waste. The small pore and grain size, large specific surface areas, and clay mineral structures lend themselves to rapid reaction rates accompanying changes in stress, pressure, temperature and chemical conditions. Under far from equilibrium conditions, mudrocks display a variety of spatio-temporal self-organized phenomena arising from the nonlinear coupling of mechanics with chemistry. Beginning with a detailed examination of nano-scale pore network structures in mudstones, we discuss the dynamics behind such self-organized phenomena as pressure solitons, chemically-induced flow self focusing and permeability transients, localized compaction, time dependent well-bore failure, and oscillatory osmotic fluxes as they occur in clay-bearing sediments. Examples are draw from experiments, numerical simulation, and the field. These phenomena bear on the ability of these rocks to serve as containment barriers.

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Natural helium is a screening tool for identifying the presence or absence of caprock imperfections. Imperfections can be manifested as a variety of features or processes, including insufficiently low permeability, preferential flowpaths such as fractures and faults, and the propensity for capillary breakthrough. Theory and simulations detail how various types of imperfections affect the spatial distribution of natural helium above, within, and below caprock in a single-phase, brine-saturated system. Specifically, the distribution of natural helium can reveal the presence of preferential flowpaths through formations with low matrix permeability. The distribution patterns of helium shed insight on the size, shape, location, and connectedness of imperfections in caprock. We show how imperfections associated with characteristic distributions of natural helium will affect the retention of CO2. We discuss the advantages of natural helium, together with temperature distributions, for revealing imperfections and the optimum locations for sampling the natural tracers. This research is being carried out to support design and interpretation of ongoing field-testing by the Southwest Regional Partnership on Carbon Sequestration. Specifically, we are evaluating seal integrity of the Partnership's Pump Canyon Enhanced Coalbed Methane- CO2 Storage Demonstration, located in the San Juan Basin, New Mexico. The caprock at this site is the Kirtland Formation. This formation is composed of a variety of continental deposits (sandstones, siltstones, mudrocks, and shales) and is ideal for investigating the capability of helium to characterize sealing integrity of a very heterogeneous caprock. We present results of analyses of noble gases and a variety of petrological and petrophysical analyses on core through this caprock. These results are used to investigate the presence of imperfections and their potential impact on CO2 migration and the overall viability of utilizing natural helium as a screening tool. The authors gratefully acknowledge the U.S. Department of Energy and the National Energy Technology Laboratory for sponsoring this project. © 2009 Elsevier Ltd. All rights reserved.