U44A-01 INVITED
Science-Based Risk Assessment for Geologic Storage of CO2
The storage of carbon dioxide in geologic reservoirs offers great potential as an option for mitigation of emissions from fossil fuels. At a meaningful scale, geologic storage will involve large volumes of fluids, requiring numerous storage sites representing a range of geologic characteristics. To be sucessful, storage projects must address a range of potential risks associated with each specific site, ranging from pre- operational factors (such as capacity and injectivity) to post-operational factors (such as long-term fate and impact of the CO2 and other fluids). Hence, a framework for assessing these risks must be capable of handling the range of factors in a diverse set of storage systems, and it must have a strong science base to lend assurance that the equally diverse phenomena that must be considered are sufficiently well addressed. The U.S. Department of Energy has an ongoing effort in its sequestration program to develop the suite of information needed to assess CO2 storage, ranging from small pilot scale investigations to larger scale field tests to regional and national data bases. In addition, the program supports a number of research efforts on key physical and chemical phenomena in storage (including studies related to wellbore integrity). The information from these efforts provides a foundation for developing a science-based framework for assessing potential risks associated with CO2 storage. I will discuss an emerging multiorganizational effort on risk assessment, which is aimed at developing a robust framework and approach for understanding the performance of the storage system. I will also use a specific example related to wellbore integrity in order to illustrate how a fundamental understanding of chemical and physcial phenomena can be used to build the science base for assessing system performance. Specifically laboratory and field studies of cement-CO2- brine interactions are providing insight into the processes that control the evolution of wellbore permeability over time, which can provide a link to the potential role of wellbores in release of CO2 from the reservoir.
U44A-02 INVITED
The Certification Framework: Risk Assessment for Safety and Effectiveness of Geologic Carbon Sequestration
Motivated by the dual objectives of (1) encouraging geologic carbon sequestration (GCS) as one of several strategies urgently needed to reduce CO2 emissions, and (2) protecting the environment from unintended CO2 injection-related impacts, we have developed a simple and transparent framework for certifying GCS safety and effectiveness at individual sites. The approach we developed, called the Certification Framework (CF), is proposed as a standard way for project proponents, regulators, and the public to analyze and understand risks and uncertainties of GCS. In the CF, we relate effective trapping to CO2 leakage risk, where we use the standard definition of risk involving the two factors (1) probability of a particular leakage scenario, and (2) impact of that leakage scenario. In short, if the CO2 leakage risk as calculated by the CF is below threshold values for the life of the project, then effective trapping is predicted and the site can be certified. The concept of effective trapping is more general than traditional "no migration" approaches to underground injection regulation. We achieve simplicity in the CF by using (1) wells and faults as the potential leakage pathways, (2) five compartments to represent where impacts can occur (underground sources of drinking water, hydrocarbon and mineral resources, near-surface environment, health and safety, and emission credits and atmosphere), (3) modeled CO2 fluxes and concentrations as proxies for impact to compartments, (4) broad ranges of storage formation properties to generate a catalog of simulated CO2 plumes, and (5) probabilities of intersection of the CO2 plume with the conduits and compartments. In a case study application of the CF for a saline formation GCS site in the Texas Gulf Coast, analysis with the CF suggested the overall leakage risk to be very small, with the largest contribution coming from risk to the near-surface environment due to potential leakage up abandoned wells, depending on the effective permeability assumed for the wells. This result shows that risk could be drastically reduced by locating and monitoring abandoned wells, along with well or leakage mitigation if necessary. By this means, effective trapping can be predicted with greater certainty because both factors of risk (probability of well leakage, and impact of well leakage) can be reduced significantly through surface monitoring and mitigation, if needed.
U44A-03
Characterization, Monitoring, and Risk Assessment at the IEA GHG Weyburn-Midale CO2 Monitoring and Storage Project, Saskatchewan, Canada.
In July 2000, a major research project was initiated to study the geological storage of CO2 as part of a 5000 tonnes/day EOR project planned for the Weyburn Field in Saskatchewan, Canada. Major objectives of the IEA GHG Weyburn CO2 monitoring and storage project included: assessing the integrity of the geosphere encompassing the Weyburn oil pool for effective long-term storage of CO2; monitoring the movement of the injected CO2, and assessing the risk of migration of CO2 from the injection zone (approximately 1500 metres depth) to the surface. Over the period 2000-2004, a diverse group of 80+ researchers worked on: geological, geophysical, and hydrogeological characterizations at both the regional (100 km beyond the field) and detailed scale (10 km around the field); conducted time-lapse geophysical surveys; carried out surface and subsurface geochemical surveys; and undertook numerical reservoir simulations. Results of the characterization were used for a performance assessment that concluded the risk of CO2 movement to the biosphere was very small. By September 2007, more than 14 Mtonnes of CO2 had been injected into the Weyburn reservoir, including approximately 3 Mtonnes recycled from oil production. A "Final Phase" research project was initiated (2007- 2011) to contribute to a "Best Practices" guide for long-term CO2 storage in EOR settings. Research objectives include: improving the geoscience characterization; further detailed analysis and data collection on the role of wellbores; additional geochemical and geophysical monitoring activities; and an emphasis on quantitative risk assessments using multiple analysis techniques. In this talk a review of results from Phase I will be presented followed by plans and initial results for the Final Phase.
U44A-04
Status Report on the First European on-shore CO2 Storage Site at Ketzin (Germany)
The CO2SINK (CO2 Storage by Injection into a Natural saline aquifer at Ketzin) integrated project
aims to advance the understanding of the science and practical processes involved in underground storage
of CO2 to reduce emissions of greenhouse gases to the atmosphere. The consortium running this EU
project consists of 18 partners from universities, research institutes and industry out of 9 European countries
(www.co2sink.org). It is the first demonstration project for large scale on-shore CO2 storage in Europe.
The storage site near the town of Ketzin, close to Berlin in Germany, includes industrial land and
infrastructure which make it suitable as a testing site for underground injection of CO2 into a deep saline
aquifer. The operation of the CO2 underground storage is regulated under German law according to the
legislation of mining from the state of Brandenburg.
From March to September 2007 one injection well and two observation wells were drilled to a depth of 750 m
to 800 m and completed with "smart" casings at a distance of 50 m to 100 m from each other. The reservoir
characterization was done by cutting and core analysis from the three wells, petrophysical well logs and 3D-
seismics. The Triassic Stuttgart formation consists of siltstones and sandstones interbedded by mudstones
deposited in a fluvial environment. The target formation in 600 - 700 m depth is 80 m thick with sand
channels measuring up to 20 m. Temperature of the formation is around 35 °C. Hydraulic tests revealed
formation productivities of around 0.04 m3 day-1 kPa-1 and 0.06 m3 day-1 kPa-
1, respectively. Based on the thickness of the more permeable zone of the formation this calculates to
permeabilities between 40 and 80 mD.
CO2 from an industrial gas supplier is used for the first injection phase at the Ketzin site. The injection of
CO2 started in June 2008 and is intended to last up to two years. A maximum of about 60.000 t CO2
will be injected. The total amount is going to be adjusted during storage according to scientific and site
specific requirements. Spreading of the CO2 plume will be monitored by a broad range of geophysical
and geochemical techniques: The wells are completed as "smart" wells containing a Distributed Temperature
Sensing (DTS) and Vertical Electrical Resistivity Array (ERT) behind the casing (Schuett et al., AGU Fall
Meeting 08). A gas membrane sensor is used for the continuous analysis of gases (Zimmer et al. AGU Fall
Meeting 08). Before and during injection downhole sampling of fluids for geochemical and microbiological
analysis will be done. Injection of CO2 was interrupted at times for repeated downhole seismic (VSP,
MSP) and cross-hole seismic experiments. Numerical models and risk assessment strategies are going to be
benchmarked via the monitoring results.
In Dezember 2008 results from half a year of storage operation will be available. The geological and the
numerical models will be updated accordingly after compilation and interpretation of the monitoring data.
http://www.co2sink.org
U44A-05
Geologic Carbon Sequestration: Challenges of Mitigation Planning
We present results of our effort to developing meaningful mitigation plans for geologic carbon sequestration. The Southwest Regional Partnership on Carbon Sequestration, funded by the U.S. Department of Energy and managed by DOE's National Energy Technology Laboratory, is assembling science and engineering plans for a commercial-scale geologic sequestration test that will include extensive monitoring and analysis of the fate of injected CO2. Among the principal objectives of the test are to develop effective monitoring methods and risk assessment frameworks for deep injection and sequestration. Effective mitigation plans are an absolutely critical component of commercial-scale geologic carbon sequestration. One fundamental aspect of mitigation engineering design is immediate reduction of reservoir pressure. We developed numerical models of multiphase injection and flow to evaluate pressure reduction as a primary mitigation tool. Model results forecast optimum density and placement of injection and observation wells. Simulation results also suggest that it may be best to engineer observation wells for quick conversion to production (pumping) wells to facilitate immediate pressure reduction, if needed. Results of our reservoir models suggest that immediate pressure reduction will stem geomechanical deformation, stem and/or close crack/fracture growths, shut down "piston-flow" displacement of brines into unintended reservoirs, slow leakage through wellbores, slow leakage of CO2 through faults, and even induce closure of faults. Much like injection wells, the distribution of such observation-pressure-reduction (OPR) wells is critical. Reservoir model results also suggest that OPR wells can be converted to injection wells to maximize capacity and control reservoir pressure. For example, as one portion of the reservoir "fills" and pressure control becomes problematic, the injection well can be converted to an OPR well, and the next well in the series (whether linear or in a grid design) can become the injection well. Finally, simulations suggest that many sites may require water production to create space for injected CO2 and facilitate pressure control. Injection and sequestration in deep saline reservoirs below oil fields is an attractive option for many reasons, among which is the possibility of re-injecting the produced water into existing saltwater disposal wells in shallower formations.
U44A-06
Chemical and Physical Reactions of Wellbore Cement under CO2 Storage Conditions: Effects of Cement Additives
Sequestration of CO2 into geologic formations requires long-term storage and low leakage rates to be effective. Active and abandoned wells in candidate storage formations must be evaluated as potential leakage points. Wellbore integrity is an important part of an overall integrated assessment program being developed at NETL to assess potential risks at CO2 storage sites. Such a program is needed for ongoing policy and regulatory decisions for geologic carbon sequestration. The permeability and integrity of the cement in the well is a primary factor affecting its ability to prevent leakage. Cement must be able to maintain low permeability over lengthy exposure to reservoir conditions in a CO2 injection and storage scenario. Although it is known that cement may be altered by exposure to CO2, the results of ongoing research indicate that cement curing conditions, fluid properties, and cement additives play a significant role in the rate of alteration and reaction. The objective of this study is to improve understanding of the factors affecting wellbore cement integrity for large-scale geologic carbon sequestration projects. Due to the high frequency use of additives (pozzolan) in wellbore cement, it is also essential to understand the reaction of these cement-pozzolan systems upon exposure to CO2 under sequestration conditions (15.5 MPa and 50°C). Laboratory experiments were performed to determine the physical and chemical changes, as well as the rate of alteration of commonly used pozzolan-cement systems under simulated sequestration reservoir conditions, including both supercritical CO2 and CO2-saturated brine. The rate of alteration of the cement-pozzolan systems is considerably faster than with neat cement. However, the alteration of physical properties is much less significant with the pozzolanic blends. Permeability of a carbonated pozzolanic cement paste remains sufficiently small to block significant vertical migration of CO2 in a wellbore. All of the experiments run to date suggest that the cement-pozzolans used will be an effective seal for CO2, as long as the well was properly installed and is initially undamaged.
U44A-07
Field Observations and Geochemical Modeling of CO2 Impacts on Shallow Groundwater Chemistry in Chimayo, New Mexico
One possible environmental consequence of geologic sequestration of CO2 is slow upward leakage through drinking water aquifers. Although CO2 itself is not toxic, elevated CO2 could change the geochemical environment in the aquifer and cause aqueous and/or mineral precipitation/ dissolution reactions that might negatively impact drinking water quality. Here we examine a natural analog site in the Rio Grande Rift, Northern New Mexico, USA, where CO2 is naturally rising along faults and where shallow aquifer chemistry is thought to be affected. Many of the wells have very elevated pCO2 ( > - 1.0); some of the wells also contain a brackish water component. Other than trace elements associated with the brackish water component, we do not see empirical evidence of increased trace element concentrations caused by CO2 influx. We developed a conceptual model of fluid flow and rock/water interactions at the site and numerical models of geochemical reactions and mixing that are consistent with measured variations in major ion concentrations at the site. In particular, our models explain the buffering mechanisms that prevent CO2 dissolution in water from significantly suppressing groundwater pH in this hydrogeochemical setting. This buffering may also partly explain the absence of elevated trace element concentrations, relative to background. Other possible factors include limited or heterogeneous availability of trace elements in aquifer rocks locally, large variability in background concentrations of trace elements, and redox variations unrelated to CO2. We emphasize the potential role that brackish waters, which could leak along with the CO2, could play at CO2 sequestration sites, and discuss the implications for designing effective monitoring strategies.
U44A-08
Laser Based Instruments Using Differential Absorption Detection for Above and Below Ground Monitoring of Carbon Dioxide
Carbon capture and sequestration in geologic formations provides a method to remove carbon dioxide (CO2) from entering the Earth's atmosphere. An important issue for the successful storage of CO2 is the ability to monitor geologic sequestration sites for leakage to verify site integrity. A field site for testing the performance of CO2 detection instruments and techniques has been developed by the Zero Emissions Research Technology (ZERT) group at Montana State University. A field experiment was conducted at the ZERT field site beginning July 9th, 2008 and ending August 7th, 2008 to test the performance of several CO2 detection instruments. The field site allows a controlled flow rate of CO2 to be released underground through a 100 m long horizontal pipe placed below the water table. A flow rate of 0.3 tons CO2/day was used for the entirety of this experiment. This paper describes the results from two laser based instruments that use differential absorption techniques to determine CO2 concentrations in real time both above and below the ground surface. Both instruments use a continuous wave (cw) temperature tunable distributed feedback (DFB) laser capable of tuning across several CO2 and water vapor absorption features between at 2003 nm and 2006 nm. The first instrument uses the DFB laser to measure path integrated atmospheric concentrations of CO2. The second instrument uses the temperature tunable DFB laser to monitor underground CO2 concentrations using a buried photonic bandgap optical fiber. The above ground instrument operated nearly continuously during the CO2 release experiment and an increase in atmospheric CO2 concentration above the release pipe of approximately 2.5 times higher than the background was observed. The underground instrument also operated continuously during the experiment and saw an increase in underground CO2 concentration of approximately 15 times higher than the background. These results from the 2008 ZERT field experiment demonstrate the potential for these instruments to be used for CO2 monitoring of sequestration sites.