Performance and Safety Screening for the Ohio River Valley CO 2 Storage Site Using Features, Elements, and Processes Database

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A systematic screening procedure was applied to the Ohio River Valley Carbon Dioxide (CO2) Storage site utilizing the Features, Elements, and Processes (FEP) database for geologic storage of CO2 (Savage et al., 2004). The objective was to identify potential risk categories for the long-term geologic storage of CO2 at the Mountaineer Power Plant in New Haven, West Virginia, USA. Over 130 FEPs in seven main classes were assessed based on site characterization information gathered in a geological background study, testing in a deep well drilled on the site, and general site conditions. In evaluating the database, it was apparent that many of the items were not applicable to the Mountaineer site based on its geologic framework and environmental setting. Several FEPs were identified for further consideration for the project. These FEPs generally fell into categories related to variations in subsurface geology, well completion materials, and the behavior of CO2 in the subsurface. Results from the screening were used to provide guidance on injection system design, develop a monitoring program, perform reservoir simulations, and other risk assessment efforts. Initial work indicates that the significant FEPs may be accounted for by focusing the storage program on these potential issues. The screening method was also useful in identifying unnecessary items that were not significant given the site-specific geology and proposed scale of the project. Overall, the FEP database approach provides a comprehensive methodology for assessing potential risk for a practical CO2 storage application. IntroductionConcerns about increasing trends in atmospheric greenhouse gases have prompted research into several CO2 mitigation options. Sequestration in geologic reservoirs has emerged as one of the more viable technologies available to address emissions from large point sources such as power plants, refineries, and other industrial facilities. Experience with natural gas storage, enhanced oil recovery, natural CO2 fields, and hazardous waste injection demonstrate that injection of CO2 emissions into deep rock formations is a safe and practical technology, but there is some risk associated with application of geological storage. To address this potential risk, CO2 sequestration has developed into a storage concept involving monitoring, measurement, and verification of the injected CO2 to prove that the CO2 is safely sequestered. However, a wide range of factors may affect a storage project, and it is difficult to account for all these items in developing a storage and monitoring program. As such, a FEP database was developed by Quintessa to assess safety and performance of geological storage of CO2 (Savage et al., 2004). The database is an extensive list of possible features, events, and processes that should be considered in a storage project. This systems analysis approach has been used for numerous applications, most notably radioactive waste disposal. A FEP screening approach was selected for the Ohio River Valley CO2 Storage Project to aid in design and feasibility evaluation for an injection system at the site. The objective of the screening was to identify the main FEPs needed to be considered for the project. The project itself is aimed at providing an understanding of the viability of carbon capture and sequestration by performing an integrated demonstration of CO2 capture and geologic sequestration at an active power plant in the Ohio River Valley. This region is a significant energy producer in the United States and has a large potential capacity for geologic storage of CO2 (Bergman and Winter 1995). Battelle is leading the project with support from DOE’s National Energy Technology Laboratory to investigate the feasibility of geologic sequestration of CO2 in the Ohio River Valley Region. American Electric Power (AEP), BP, the Ohio Coal Development Office (OCDO) of the Ohio Department of Development, and Schlumberger are providing additional sponsorship and technical input. The site is located just south of New Haven, West Virginia, along the Ohio River at the AEP Mountaineer Power Plant (Figure 1). The plant is a modern 1,300-megawatt coal-fired steam electric generating unit that burns low sulfur coal and is equipped with electrostatic precipitators for particulate emissions control (AEP 1974). The site was selected for investigation in 2002, and a sequential series of characterization tasks were completed to prepare for injection. Initial efforts focused on reviewing the geologic framework of the area as it applies to potential storage reservoirs and caprock (Sminchak et al., 2004). Based on guidelines from this work, a 2,800 m deep well, named “AEP #1,” was drilled on the Mountaineer site. The AEP #1 well had dual purposes: 1. an exploratory boring to characterize geologic storage options; and 2. an on-site injection well for a CO2 capture and storage demonstration for the power plant. Extensive rock core testing, wireline logging, brine sampling, and geomechanical analyses were completed in association with the drilling. A 2-D seismic survey was also performed in two 9 km long transects through the well site (Gupta et al., 2004). Reservoir tests were also completed in the target storage reservoirs and caprock intervals. Risk assessment, public outreach, and reservoir simulations were also included in the project. The next phase proposed in the program is development of a pilot-scale CO2 capture and storage system. This step involves design and evaluation of a system to capture a portion of emissions from the plant, separate the CO2, compress the CO2 into a supercritical liquid, inject this fluid in an injection well, and monitor the fate of the CO2 in the storage reservoir (Figure 2). Injection of less than 0.5% of plant CO2 total emissions per day over a period of approximately 2+ years is the current goal of the design phase (total injection of less than 100,000 metric tons CO2). A smaller scale of injection was selected to allow for flexibility in optimizing the capture process because this is the first project of its kind at an active power plant. Since the program is in a design and planning stage, a FEP screening was considered constructive to guide future activities. MethodsThe general screening method was used to analyze each item in the generic FEP database against the corresponding site-specific conditions at the Mountaineer site. A conceptual model of the site was developed describing the geologic framework, target storage reservoirs, containment units, brine chemistry, environmental conditions, and proposed injection system. This information was then used in a sequential screening process aimed at identifying the main FEPs that apply to the project. FEP DatabaseScreening items were obtained from the “Generic FEP Database for the Assessment of LongTerm Performance and Safety of the Geological Storage of CO2” (Savage et al., 2004). The FEP database is divided into seven main classes, covering events as broad as neotectonics to microscopic processes such as complexation of CO2 with heavy metals. Most FEPs are grouped in the CO2 Properties and Geosphere categories, because these are key topics for CO2 storage reservoirs. The database only addresses geologic storage, and items related to capture and injection are not included. The FEP database is designed to involve a systematic analysis, but it does not prescribe a numeric value to items. An explanation is supplied for each FEP item, but it is up to some interpretation as to whether it applies to a certain site. To account for this uncertainty, a multi-level screening process was employed for the FEP analysis. FEP Screening MethodsA stepwise approach was utilized to identify the FEPs that should be considered for the Ohio River Valley CO2 Storage Project (Figure 2). Screening methods involved the following steps: 1. Compiling characterization data into a site-specific conceptual model 2. Level 1 screening of FEPs for non-applicable or unlikely items 3. Level 2 screening of FEPs that do not apply based on general site conditions and/or site characterization results 4. Level 3 screening using site testing and/or system specifications 5. Providing recommendations on addressing remaining FEPs into system design, monitoring, and application. Initial screening identified items that were non-applicable, programmatic issues related to CO2 storage concepts, or legacy issues beyond the scope of a pilot-scale demonstration. The next level of screening examined the remaining FEP items in relation to general site conditions and site characterization results. If site information convincingly eliminated any concerns regarding the FEP, it was removed from further analysis. Level 3 screening was based on more quantitative information from site testing and/or system specifications. The remaining FEP items were compiled and analyzed to determine how they may affect the CO2 storage project. Lastly, recommendations were made on how system design, monitoring, and storage application may be customized to address the FEPs identified in the screening. Site Conceptual ModelIn the study area, thick sequences of Paleozoic sedimentary rocks form broad basins— the Illinois Basin in the southwest, Michigan Basin in the North, and Appalachian Basin in the southeast— separated by an uplifted Cincinnati Arch region in the Midwestern United States. The study area for this project is located within the Appalachian Basin, where rocks slope toward the southeast. A review of deep wells and wireline logs in the region indicates that the sedimentary rocks are 2,400-3,100 m thick in the immediate vicinity of the study area. The sedimentary rocks overlie dense, metamorphic and igneous basement rocks. The Paleozoic rocks are layered arrangements of shale, siltstone, limestone, dolomite, and sandstone. Rocks dip to the eastsoutheast in the study area at about 20 m/km.