H13F-1640
A modeled experiment of gas behavior in aquifer and residual gas formation
National and international concern is rising about the possible effects of greenhouse gases (GHGs) on the climate. Several methods are proposed to reduce the gas in the atmosphere and underground sequestration is recently expected as an effective concept. Especially, residual gas can be the most effective method to store the gas in reservoir. Underground sequestration requires the gas injected into a reservoir. When the gas is injected into a water- saturated aquifer, it pushes water out of the pore space. As the gas bubbles go upward, the gas space is filled with water again, but small gas bubbles are trapped in the pore space by surface force and capillary pressure of water. This is the residual gas formation. Once the residual gas is formed, it seldom moves again from the pore space. Residual gas formation needs neither cap-rock nor structural trap, thus has a potential to be applied to broader regions. The purpose of this study is to examine the fundamental mechanism of residual gas formation and gas migration underground by injecting the gas into a modeled and visualized aquifer. We designed and constructed an experimental apparatus to measure the distribution and the saturation of the residual gas. We used glass beads of 1 or 2mm diameters as porous media to construct some reservoir models that have various porosity, permeability, and wettability. The glass beads packed in our apparatus which has 30cm width, 33.5cm height, and 1cm thickness. It has 1§¤volume in amount. The pore space was filled with viscous liquid, then air was injected from the bottom. Some conditions in the injection time and rate were tested. We observed air behavior and measured the volume of the distribution area of residual gas from its digital photographs, and the volume of residual gas from the amount of water that was pushed out from the apparatus. The experimental results showed that differences of reservoir properties made changes in the gas behavior and residual gas volume. It is also confirmed that air injection rate (injection pressure) was a sensitive property against residual gas volume that can be maximised by selecting a suitable injection rate for each reservoir property.
H13F-1641
Resistivity Variation due to CO2 Migration in Different Temperature and Pressure Conditions
CO2 geological sequestration is one of the effective approaches solving the global warming problem. Captured CO2 is injected to the deep aquifers or depleted oil and gas fields. Injected CO2 migrates thorough the reservoir rock, however, the details behavior of injected CO2 under the ground at super critical phase is not yet fully understood. Migration of injected CO2 will change by the condition of the injected reservoir such as the temperature and pressure. Also density and permeability of the rock may be changed due to temperature or pressure variations. These changes control the migration behavior of injected CO2. In this study, experiments of resistivity measurements were conducted to detect the migration difference of CO2 in different temperature and pressure conditions by using sandstone core samples. Core sample was taken from Berea sandstone and processed to 5cm diameter and 12cm length. For the resistivity measurement, impression electrode was set on the both end and the measurement electrode of ring condition was set on the side of the rock sample. We stetted the core sample in the pressure vessel and recreated the condition of underground reservoir which is high pressure and high temperature. We injected supercritical CO2 in different pressure and temperature for each experiment. Pressure was changed in range of 8 to 11MPa and temperature was changed in range of 35° to 45°. This means that all the experiments were conducted in supercritical phase. From the measured resistivity variation, we verified the migration of CO2 and compared the migration behavior of CO2 in different conditions.
H13F-1642
Seismic Monitoring at the CO2SINK Project Site, Ketzin, Germany: Past, Present and Future
Storage of CO2 in saline aquifers is, perhaps, the most promising and relevant sequestration option for Europe. Saline aquifers are ubiquitous and their storage capacity exceeds that of depleted oil and gas fields. The CO2SINK project, officially started in April 2004, is aimed at developing an "in-situ laboratory" for CO2 storage to fill the gap between numerous conceptual engineering and scientific studies on geological storage and a full- fledged on-shore sequestration demonstration. Major objectives of the project are to (1) advance the understanding of the science and practical processes involved in underground storage of CO2 to reduce emissions of greenhouse gases to the atmosphere, (2) build confidence towards future European CO2 geological storage, and (3) provide operational field experience to aid in the development of harmonized regulatory frameworks and standards for CO2 geological storage. Three boreholes have now been drilled into the target Stuttgart formation on the southern flank of the Ketzin anticline, one injection well and two observation wells. Injection of CO2 at a rate of about 100 tons/day will begin in late 2007 at a depth of about 650 m and continue for about 2 years. An important component of the project, and for geological storage of CO2, is monitoring the movement of injected CO2 using seismic methods. Seismic monitoring methods that will be applied include cross-well, vertical seismic profile (VSP), moving source profiling (MSP), 2D and 3D time lapse techniques. As a first step in the seismic program a 3D seismic survey with about 12 square km of sub-surface coverage was acquired in 2005 with the objectives of providing (1) if possible, an understanding of the structural geometry for flow pathways within the reservoir, (2) a baseline for later evaluation of the time evolution of rock properties as CO2 is injected into the reservoir, and (3) detailed sub-surface images near the injection borehole for planning of the drilling operations. In addition to the 3D survey, seven 2D lines in a "star" configuration were acquired in 2005. During the autumn of 2007, baseline cross-well, VSP and MSP data will be acquired at the injection site. Cross-well seismics will be repeated several times in the early stages of the injection process to map the time evolution of the CO2 plume in the vicinity of the injection well. VSP and MSP acquisition will be repeated twice during the injection period to map migration of the CO2 away from the injection well. Repeat of the 2D "star" will be at the end of the injection period and will allow mapping of possible migration of the CO2 up towards the top of the anticline. Funding for a repeat 3D survey has been applied for and, if successful, will be acquired in 2010. Results from seismic modeling and dynamic modeling of the flow of the injected CO2 will be used when evaluating the time lapse seismics. http://www.co2sink.org
H13F-1643
A Pilot-box injection experiment for monitoring the fate and migration of CO2 for geological sequestration
A three-dimensional CO2 injection experiment was conducted to investigate the capability and applicability of geochemical sampling and electrical resistivity measurements in monitoring the fate and migration of various phase of CO2 for geological sequestration. Two types of CO2 – dissolved and gas phases- and a mineral oil, KF- 20, representing a supercritical CO2 in deep brine aquifers were tested in a series of injection experiments in a pilot-scale box filled with 1-mm diameter glass beads. As well as collecting samples of porewater and gas through 40 sampling ports spatially distributed in the box, time-lapse electrical resistivity measurements were made with 120 electrodes positioned on the front, back and top panels. For reconstructing three-dimensional resistivity images, potential differences were measured at 32 potential dipoles on the top surface of the tank due to two current dipoles on the front and back sides. The resultant resistivity images were compared with the discrete distribution of dissolved CO2 or oil concentrations in each case. It was clearly showed that the three- dimensional resistivity images were successfully able to represent the distribution and migration of CO2 injected in various phases in an artificial aquifer. The experimental results also suggested that the electrical resistivity tomography could be an option for monitoring CO2 injected in deep geological formations for sequestration.
H13F-1644
Cross-well Seismic Tomography to Monitor CO2 Flood Area Using Difference Analysis Method
Capturing CO2 directly from large stationary sources such as thermal power plants and subsequently storing it in a nearby aquifer can be the most efficient way to reduce CO2 emissions into the atmosphere at a lower cost, and monitoring injected CO2 is important to verify practical effectiveness of the CO2 storage. The pilot-scale CO2 sequestration experiment has been undertaken at the Nagaoka gas and oil field, in Niigata Prefecture, Japan and we conducted time-lapse cross-well seismic tomography to detect the spread of injected CO2. When super- critical CO2 spreads into porous media saturated with brine water, the seismic velocity always decreases, which is confirmed theoretically and experimentally. Therefore, CO2 flood area can be estimated from seismic tomography records before and after CO2 injection. However, the tomography records before and after CO2 injection include not only the variation due to CO2 flood, but also differences occurred from the location and property of sources and receivers and they result analysis errors. Thus, in this study, we applyed the differential analysis to cross-well seismic tomography for reducing the difference due to measurement conditions and getting more accurate monitoring results. In the normal procedure, velocity differences are calculated after applying inversion processing to each record separately, but in this differential analysis, first forward modelling is applied using the velocity distribution inverted from one referential record, second the set of first arrival time is obtained from the modelling result and finally the inversion processing is analyzed from the data set of the first arrival time added with the difference of travel-times from the referential record. In the result, we can have an analysis result in which the distribution of CO2 flooding is clearly identified along with cap rock under the inversion analysis with the constrained condition of no velocity enhancement.
H13F-1645
Development of a Fully Coupled Multiphase Thermo-Hydro-Mechanical Numerical Model and Its Application to Geological Storage of Carbon Dioxide
A thermo-hydro-mechanical (THM) numerical model is presented to evaluate groundwater and carbon dioxide flow, heat transport, and land deformation in geologic media due to carbon dioxide injection. This multidimensional numerical model is developed on the basis of the fully coupled multiphase thermoporoealstic governing equations for true anisotropic porous and fractured geologic media, the nonlinear constitutive equations, and the Galerkin finite element method. Two different cases of geologic systems are simulated for the purpose of comparison. One is a three-layer aquifer system, which is composed of two sandstone aquifers separated by a cracked shale aquitard as a cap rock, and another is a single-layer aquifer system, which does not have such an aquitard. The numerical simulation results show that the aquitard has significant effects on the spatial distributions and temporal changes of groundwater pressure and saturation, carbon dioxide pressure and saturation, geothermal temperature, and land displacement vector. Such effects of the shale aquitard are caused by its relatively lower hydraulic permeability and thermal conductivity and relatively higher mechanical deformability compared with those of the sandstone aquifers. Therefore it may be concluded that layered heterogeneity cannot always be ignored if it is observed in actual geologic systems, and thus it must be properly characterized and considered when more rigorous and reasonable predictions of long-term thermo-hydro- mechanical responses of the whole geologic systems to carbon dioxide injection are to be obtained. Further numerical studies of various geological and hydrogeological settings and field applications are recommended to arrive at more general conclusions concerning the effects of layered heterogeneity on multiphase fluid flow, heat transport, and land deformation due to carbon dioxide injection.
H13F-1646
Learning about crustal CO2 migration and leakage using natural analogues
CO2 gas samples and continental carbonates (travertines) were collected in different places of the French carbogaseous province. We performed analyses of noble gases and associated major compounds (mainly CO2) with d13C(CO2) isotopic analyses. We also made d13C and d18O measurements on the travertines present in all different sampled places to determine wether a significant part of the CO2 leaking could be trapped at the Earth surface. We wanted to test if travertines could be an indicator of the history of the system leakage, as they are potentialy datable. The main purpose of this study is to determine, using natural analogues, which context is most favourable for future CO2 storage. We collected seven gas samples from natural bubbling sources and geysers near Sainte Marguerite, Massif central, France. This area is known to present an important heat flow anomaly, due to the probable existence of a mantle plume below. The site exhibits many CO2-rich water wells associated with travertines rocks. We analysed the gas which is composed mainly of CO2 with a d13C (CO2) of around -5‰ compatible with a mantle-derived origin. The noble gas results show helium concentrations in the range of 0.28 to 8.22 ppm, with 5 samples lower than the atmospheric helium concentration of 5.24 ppm. However, within these samples, the 4He/20Ne ratios range from 2.12 to 198 and are all greater than air value of 0.288; thus air contamination can be discarded. The most intriguing result is that all our samples exhibit high and relatively homogeneous values of R/Ra, around 3.5 - 4, implying a large contribution of mantle-derived helium (R/Ra = 8 for the upper mantle) ) to the total budget of this gas. The neon and argon isotopic ratios are close to the atmospheric values, suggesting a small, if any, crustal contribution and an important Air Saturated Water (ASW) contribution, in agreement with the hydrothermalism of the area. To our knowledge, it is the first time that so low helium concentrations combined with so high 3He/4He are measured in crustal fluids. Such low concentrations indicate that He was not dissolved in water at great depth, and thus was not transported by water but migrated as a free gas phase. Our tentative interpretation is that gas comes from a degasing magma at depth, and then migrates toward the surface via faults and fractures. Contact with water should only occur at low depths (aquifers) and should be fast as indicated by the slight isotopic fractionation seen in the neon isotopes together with some elemental ratios enriched in the lightest noble gas isotope. The carbon isotopic composition of the travertines in Sainte Marguerite are consistent with leakage of deep CO2, and should provide new insights to the amount of carbon trapped as carbonates during time. Therefore, travertine precipitation can be regarded as a process trapping part of leaking CO2.
H13F-1647
Mineral Dissolution, Enhanced CO2 Solubility Trapping and Convective Mixing
CO2 injected into an aquifer storage reservoir will tend to migrate upwards towards the cap-rock because the density of supercritical CO2 phase is lower than that of water (aqueous phase). In the upper portions of the reservoir, CO2 dissolution into groundwater will increase pH and induce mineral dissolution and complexing with dissolved ions such as Na+, Ca2+, Mg2+, and Fe2+ to form NaHCO3, CaHCO3+, MgHCO3+, and FeHCO3+. Over time these dissolution and complexing processes will increase CO2 solubility, enhance solubility trapping, and will increase the density of the aqueous phase. Aqueous phase will then move downward due to gravity, giving rise to "convective mixing". We have developed a multi-phase reactive geochemical transport model that accounts for the essential processes of flow, transport and chemistry, including changes in aqueous phase density and viscosity due to changes in dissolved species concentrations. Changes in porosity and permeability due to chemical dissolution and precipitation are also modeled. The process of enhanced solubility trapping and convective mixing was explored through application to a gulf coast sandstone saline aquifer. This work was supported by the Zero Emission Research and Technology project (ZERT) under Contract No. DE- AC02-05CH11231 with the U.S. Department of Energy.
H13F-1648
Reactive Transport Modeling of Supercritical Carbon Dioxide Injection Into Mafic Rock Reservoirs
Technologies to reduce emissions of greenhouse gases and increase the sequestration of CO2 have received increasing attention since the development of the Kyoto protocol. One promising technology is the sequestration of CO2 in geologic formations. The suitability of a fractured basalt reservoir for CO2 sequestration is constrained by three broad categories of issues, which we refer to as physical, technical, and economic constraints. Physical constraints are beyond human control; thus, it is a requirement that a systematic method be developed by which a particular target reservoir may be evaluated to determine if it lies within the bounds required for safe and effective disposal. Technical constraints, on the other hand, are challenges to the ability to design, construct, and/or monitor a sequestration project as a result of limitations on our ability to determine the distribution of properties in the subsurface, our knowledge of the behavior of CO2 in the deep subsurface, and the current state of computational science and subsurface monitoring. Equally important are the heterogeneity of economic costs associated with sequestering CO2 at different sites and within different formations. The work presented here focuses on the technical aspects of CO2 injection, specifically examining reactive transport of CO2 in the subsurface in the vicinity of the injection well using the simulation code TOUGHREACT. Pressure distribution and propagation, kinetics of the geochemical reactions, and resultant changes in permeability/porosity are examined in order to evaluate injection scenarios that maximize the longevity of the injection well and sustainability of the reservoir.
H13F-1649
Hydrodynamics and Geochemical Modelling of CO2 Injection at the K12B Gas Field
This paper presents a numerical simulation study of CO2 injection into the nearly depleted gas reservoir at the K12B field, North Sea, selected as a demonstration site for the Offshore Re-injection of CO2 project. Simulations have been carried out using two different codes: TOUGHREACT for characterizing the geochemical fluid-rock interactions that may occur during the injection period (case A), and TOUGH2EOS7C for simulating the CO2 sequestration coupled with enhanced methane production (case B). The reactive transport modelling predict a rather low geochemical reactivity induced by such injection as the gas reservoir contained initially 13% of CO2 in the gas phase and therefore geochemical equilibrium has been established before injection starts. The simulations of the CH4 recovery estimate due to injection predict a short breakthrough time of 60 days and one year for the two producers, respectively. At the end of the 10 years of injection, CO2 remains at 96% under gas phase and structural trapping remains the main process for geological sequestration at the K12B field.
H13F-1650
Simulations of Carbon Dioxide Leakage from Uncased Boreholes Into Formations Lying Above a Sequestration Reservoir.
We present calculations showing how leakage of CO2 up an uncased section of a borehole can move into formations overlying a sequestration reservoir. Relationships between the invaded formation permeability structure, phase-state of the CO2 in the borehole at the depth of contact, and reservoir pressure are explored. Preliminary results suggest that the most important parameters governing the invasion of borehole CO2 into formations are 1) the pressure gradient between the borehole fluids and the formation waters, and 2) the relative permeability to the available phase that is being transported from the borehole to the surrounding formation. We show that fractured formations overlying a storage reservoir are the most likely to allow significant invasion when leaking boreholes are overpressured with single phase CO2. Finally, we discuss how these results can be abstracted into a system modeling approach during the performance assessment phase of CO2 sequestration site selection.
H13F-1651
Experiment on the influence by supercritical CO2 at the casing cement – sandstone interface
CO2 geological storage is the one of the methods to prevent the global warming. In this method, the most important thing is to prevent leakage of CO2 from the underground reservoir. If CO2 leaks to the surface, it may go up along the casing cement – sandstone interface due to the degradation of the casing cement. Thus we have to understand how CO2 affect the casing cement - sandstone interface. The present work is intended to know what kind of chemical reactions are caused at the casing cement - sandstone interface when exposed to supercritical CO2. Experimental specimens used in the present work are composed of Berea sandstone, Tako sandstone and oil well cement. The sandstones are prepared in the form of cylinder with the diameter of 25 mm and the length of 90 mm, and drilled holes with the diameter of 7 mm at the center. Then oil well cement is put in the holes. These experimental specimens and the distilled water are set in the cambers. Then the chambers are backfilled with CO2. The temperature and the pressure in the cambers are set at 60℃ and 10MPa. In these conditions, CO2 becomes supercritical fluid. These experimental conditions are to be maintained for 3 weeks. After the experiments, the specimens are examined by stereoscopic microscope, polarizing microscope and scanning electron microscope (SEM), and measured by means of X-ray analysis. The water left in the chambers is measured by means of atomic absorption analysis.
H13F-1652
Monitoring of Geologically Stored Carbon Dioxide Using Atmospheric Techniques
Geosequestration (carbon capture and underground storage) is planned as a major global emissions reduction measure and is an essential part of several low CO2 emission energy technologies. The potential escape of the geologically stored CO2 to the atmosphere is one of the main concerns of project operators, regulators, the carbon trade and the public. Although rates of escape large enough to endanger health and safety are extremely unlikely, low leak rates could reduce the effectiveness of geosequestration in controlling emissions. Monitoring geosequestration sites will be a requirement and atmospheric monitoring is part of an overall package, together with subsurface monitoring techniques. Atmospheric monitoring of a CO2 storage site will provide advantages such as relatively low cost and minimal intervention but also presents challenges because of the typically high and variable concentrations and fluxes of CO2 in the atmosphere. Our modeling of hypothetical leaks from CO2 storage and dispersion into the atmosphere suggests that identifying and quantifying emissions to the atmosphere may be possible with a combination of atmospheric techniques. These include the continuous and precise monitoring of CO2, naturally occurring tracers such as CO2 isotopes, and introduced tracers, together with the measurement and modeling of CO2 fluxes and dispersion, over several special scales. Results from the use of these techniques in two projects will be discussed-the CO2CRC's Otway Project in Victoria, and a controlled release experiment near Canberra.
H13F-1653
Simulation of CO2 dispersion in the atmospheric boundary layer using a mesoscale model
The consequences of unexpected releases of CO2 from underground carbon sequestration sites must be understood before large-scale carbon capture and storage projects are implemented. Carbon dioxide gas can migrate through faults, fractures, or abandoned wells that penetrate the subsurface storage site and provide a pathway to the ground surface. Though such leakage is typically slow and in small amounts, CO2 can accumulate at the ground surface because it is denser than the surrounding atmosphere. Such accumulation presents health risks for humans and animals in the vicinity, and can cause damage to crops, trees, and other vegetation. Because atmospheric dispersion of CO2 is driven by gravity and ambient wind conditions, the danger from CO2 is greatest in regions with topographic depressions where the dense gas can pool, or under stably- stratified background atmospheric conditions which further inhibit mixing and dilution of the gas. We are developing a simulation tool for predictions of CO2 releases from underground storage sites in a mesoscale atmospheric model. The model solves the compressible fluid flow equations, and has been modified to account for transport of dense gases. Example simulations from sources of different release strengths over various topography and background atmospheric conditions illustrate the behavior of the model and its utility for risk assessment and certification of carbon sequestration sites.
H13F-1654 INVITED
Using a Process-Based Numerical Model and Simple Empirical Relationships to Evaluate CO2 Fluxes from Agricultural Soils.
Carbon dioxide emissions from an agricultural field in the Sacramento Valley, California, were evaluated using the process-based SOILCO2 module of the HYDRUS-1D software package and a simple empirical model. CO2 fluxes, meteorological variables, soil temperatures, and water contents were measured during years 2004-2006 at multiple locations in an agricultural field, half of which had been subjected to standard tillage and the other half to minimum tillage. Furrow irrigation was applied on a regular basis. While HYDRUS-1D simulates dynamic interactions between soil water contents, temperatures, soil CO2 concentrations, and soil respiration by numerically solving partially-differential water flow (Richards), and heat and CO2 transport (convection- dispersion) equations, an empirical model is based on simple reduction functions, closely resembling the CO2 production function of SOILCO2. It is assumed in this function that overall CO2 production in the soil profile is the sum of the soil and plant respiration, optimal values of which are affected by time, depth, water contents, temperatures, soil salinity, and CO2 concentrations in the soil profile. The effect of these environmental factors is introduced using various reduction functions that multiply the optimal soil CO2 production. While in the SOILCO2 module it is assumed that CO2 is produced in the soil profile and then transported, depending mainly on water contents, toward the soil surface, an empirical model relates CO2 emissions directly to various environmental factors. It was shown that both the numerical model and the simple reduction functions could reasonably well predict the CO2 fluxes across the soil surface. Regression coefficients between measured CO2 emissions and those predicted by the numerical and simple empirical models are compared.
H13F-1655
Comparison of Hyperspectral, Carbon Isotopic, and Soil CO2 Flux Measurements Made During the plant stress part of the July 2007 ZERT CO2 Sequestration Field Experiment conducted at Bozeman MT
We will present the comparison of hyperspectral, carbon Isotopic, and Soil CO2 Flux Measurements Made During the plant stress part of the July 2007 ZERT CO2 Sequestration Field Experiment conducted at Bozeman MT. The hyperspectral measurements of plant stress were done by UC Santa Cruz using a hand held field spectrometer and by Montana State University using an imaging spectrometer. The carbon isotopic measurement were by LANL on the same plants imaged by the hyperspectral instruments. The soil CO2 flux was measured at grid grid points over the entire experimental area. All these measurements were made as a function of time while CO2 was being injected into an underground horizontal well. The results from all these collaborative measurements are consistent with CO2 spreading out in the soil a few meters during the CO2 injection.
H13F-1656
Field System for Extended Range Continuous Monitoring of Near Surface CO2 Gas from Multiple Locations
A novel system was developed for continuous measurement of near surface carbon dioxide gas concentrations associated with the monitoring of carbon dioxide capture and storage in geologic formations. In the current configuration, the battery powered system allows for near surface CO2 gas collection (0-300,000 ppm) from seven (expandable) independently located steady state chambers. Each chamber has an associated pump and metering valve attached to a control manifold that either directs the flow to the analyzer (test chamber) or to exhaust (all others). The uniquely large concentration range in which the system is capable of operating is achieved by using an auto-control system that senses when the LiCor LI-7000 analyzer is approaching saturation and then dilutes the incoming sample using a metered flow of nitrogen gas from the reference gas supply. The dilution is carried out in stages and is capable of increasing or decreasing on the fly to keep the analyzer within range. By reading in the sample flow rate, the dilution gas flow rate, and the output flow it is possible to calculate a dilution scalar that acts as a multiplier for the LiCor analyzer concentration, allowing for immediate read and record of true sampler concentrations. This system was tested and validated during a week of continuous operation and field use, monitoring the seven chambers 24 hours/day with CO2 concentrations ranging from background to over 130,000 ppm.
H13F-1657
Differential Absorption Measurements of Carbon Dioxide for Carbon Sequestration Site Monitoring Using a Temperature Tunable Diode Laser
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 differential absorption measurement instrument based on a continuous wave (cw) temperature tunable distributed feedback (DFB) laser has been developed for measuring atmospheric concentrations of CO2. The tunable DFB laser is capable of tuning across two CO2 absorption features at 2003.50 nm and 2004.02 nm. The measured normalized transmission through the atmosphere is then related to the atmospheric concentration of CO2 through the line strength and normalized line width associated with each absorption feature. A description of this instrument will be presented including the instrument design, operation, and performance characteristics. 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. 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. Two release experiments were performed this past summer with flow rates of 0.1 and 0.3 tons CO2/day. The first release experiment lasted ten days while the second release lasted seven days. Measurements taken with the differential absorption instrument over the horizontal well during these release experiments showed an increase of greater than 300 parts per million (ppm) over the background CO2 concentration. These results indicate the capabilities of the above ground differential absorption instrument for carbon sequestration site monitoring.
H13F-1658
Underground Fiber-Optic Differential Absorption Instrument for Monitoring Carbon Dioxide Soil Gas Concentrations for Carbon Sequestration Site Monitoring
The burning of fossil fuels has resulted in higher carbon dioxide (CO2) concentrations in the atmosphere with potential impacts on the Earth's climate. The use of fossil fuels is predicted to grow over the next several decades with the potential for further increasing the atmospheric concentration of CO2. A proposed method of diminishing the impacts of increased CO2 on the Earth's climate is to capture and store the CO2 in geologic storage sites. One issue with underground sequestration of CO2 is the ability to monitor sequestration sites to verify the integrity of the storage of the CO2. An underground fiber optic differential absorption instrument based on a tunable distributed feedback (DFB) diode laser is being developed at Montana State University to detect small changes in CO2 soil gas concentration in an effort to monitor the overall integrity of the sequestration storage site. The fiber optic instrument exploits the 2003-2006 nm region of the spectrum which contains four CO2 absorption lines. Light from the DFB laser is delivered to an underground absorption cell one meter in length via a single mode optical fiber. The normalized transmission is measured by tuning the DFB diode laser across these four absorption lines and the results are used to determine the CO2 soil gas concentration. A description of this instrument will be presented including the instrument design, operation, and performance characteristics. 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. 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. Two release experiments were performed this past summer with flow rates of 0.1 and 0.3 tons CO2/day. The first release experiment lasted ten days while the second release lasted seven days. Measurements taken with the underground fiber optic differential absorption instrument 2.5 feet below the surface of the soil during these release experiments showed an absolute CO2 soil gas concentration exceeding 100,000 parts per million, an increase by a factor of greater than ten over the background levels of CO2 soil gas concentrations. These results indicate the capabilities of the below ground differential absorption instrument for carbon sequestration site monitoring.
H13F-1659
Modeling Near-Surface Carbon Dioxide Migration from a Shallow Horizontal Well
Simulations of CO2 release from a 70 m-long horizontal well at a depth of 2.5 m were carried out in support of a CO2 shallow-release experiment. The experiment was conceived by the ZERT Project to provide a facility at which researchers can develop capabilities and test approaches for monitoring potential CO2 seepage from geologic CO2 storage sites. The main challenge facing the monitoring community is how to detect small CO2 seepage fluxes potentially arising from CO2 storage sites in the presence of natural background fluxes caused by biological processes. The purpose of the simulation study was to elucidate expected migration processes arising from CO2 release and to provide estimates of surface fluxes to aid in the design of the field experiment. Simulations were carried out using TOUGH2/EOS7CA, a module of the TOUGH2 codes for modeling subsurface migration of water, CO2, and air. The field site is characterized by an organic-rich soil underlain at 1.2 m depth by a sandy cobble. The watertable fluctuates seasonally and was at a depth of 1.6 m during the experiment resulting in a sub-watertable CO2 release. A shallow vertical-well CO2 injection test was carried out to observe injectivity and surface CO2 flux of the soil-cobble system. Accumulation chamber measurements of CO2 flux for this test were used to calibrate the permeability and porosity of the model. Calibrated permeability of the soil was around 5 x 10 -11 m2 (50 Darcy), suggestive of macropores caused by cracks or root casts in the soil. Use of the calibrated properties of the soil and cobble layers in the predictive simulations for the horizontal-well release of 100 kg CO2/day for 10 days resulted in breakthrough times and average fluxes in good agreement with observations. The model shows high concentrations persist near the injection well long after the injection stops, while shallow-soil concentrations dissipate. Acknowledgment: This work was funded by the Assistant Secretary for Fossil Energy, Office of Sequestration, Hydrogen, and Clean Coal Fuels, NETL, of the U.S. Dept. of Energy under Contract No. DE-AC02-05CH11231.
H13F-1660
Vadose Zone Effects on the Signature of a CO2 Leak
Storing CO2 in geologic formations is one of the solutions proposed for reducing CO2 emissions into the atmosphere. The potential risk of CO2 leakage from such reservoirs is a serious matter challenging the merit of this solution. As part of the monitoring, mitigating, and verification (MMV) effort, predicting the characteristics of a leak from a given reservoir has vital importance. Wellbores that penetrate the sequestration reservoir are considered one of the most critical potential leakage pathways. This study focuses on the behavior in the vadose zone of a CO2 plume that has leaked around a wellbore. Parametric studies using the TOUGH2 code have been performed focusing on the following factors: CO2 leak rate, thickness of the vadose zone, permeability of the uppermost soil layer, effect of plant roots, and water table slope. Real data from the Zero Emissions Research Technologies (ZERT) MMV testbed site have been used where possible to confirm model predictions. Also, 3D to 2D scaling issues, domain initialization, and grid requirements for numerical studies are discussed. The implications of this study for the design of future field experiments on leakage are discussed.
H13F-1661
Pressure Propagation and Brine Displacement in CO2 Storage Formations: The Role of Sealing Units
If carbon dioxide capture and storage technologies are implemented on a large scale, enormous amounts of CO2 will be injected and sequestered underground, which means that large volumes of native brines will be displaced. Provided that there is hydraulic communication to shallow formations, such brine displacement from deep storage reservoirs may impact the hydrologic conditions in fresh-water aquifers, for example affecting groundwater table levels or discharge and recharge zones. In some cases, brines or brackish water may also be displaced into the capture zone of fresh-water wells. To explore the conditions important for pressure propagation and brine displacement, we conduct a simulation study investigating the multiphase processes resulting from CO2 injection into a large multi-layer geologic system comprising of a storage formation and the confining low- permeability sealing units. The pressure changes and transport patterns within the storage formation are evaluated as a function of time and distance from the injection point. We are particularly interested in the role of pressure mitigation and vertical brine flow through the upper and lower sealing units. Several sensitivity cases are therefore considered varying the permeability of the upper and lower sealing units within reasonable ranges. Our results suggest that seal conductivities on the order of 0.1 to 0.001 millidarcy may allow for considerable pressure attenuation in the storage formation by interlayer brine migration, while still providing an effective barrier to CO2 leakage (since they serve as capillary and permeability seals). It is thus important to fully understand the multi-layer characteristics of a storage site if the possible environmental impacts of CO2 injection on fresh-water aquifers are to be investigated. In addition to conducting detailed simulations of the multi-phase processes, we also investigate whether existing analytical solutions for well drawdown in leaky aquifers can provide first-order estimates of the expected large-scale pressure conditions during CO2 injection.
H13F-1662
Quick Assessment of CO2 Storage Capacity in Pressure-Constrained Saline Aquifers with Different Hydrogeologic Properties
Abstract: Saline aquifers of high permeability bounded by overlying/underlying seals may be surrounded laterally by low-permeability zones, possibly caused by natural heterogeneity and/or faulting. CO2 injection into and storage in such a "closed" system with impervious seals or a "semiclosed" system with nonideal seals is different from that in an "open" system, from which displaced brine can easily escape laterally. In a closed or semiclosed system, pressure buildup caused by continuous industrial-scale CO2 injection is a limiting factor affecting CO2 storage capacity to avoid geomechanical damage. In this research, a method was developed, under simplifications and assumptions, for quick assessment of CO2 storage capacity and efficiency factor in a pressure-constrained, closed or semiclosed system. This quick-assessment method was based on the fact that accumulated, injected CO2 displaces native brine of an equivalent volume. The equivalent volume was calculated based on (1) additional pore volume of the target formation expanded by pore and brine compressibilities under storage conditions of pressure buildup, (2) expanded pore volume within the seals, and (3) cumulative leakage of displaced brine through the seals. To validate this method, a TOUGH2/ECO2N model was developed, for a two-dimensional radial system, to simulate transient pressure buildup and CO2 plume evolution in response to an industrial-scale CO2 injection. To test the validity range, simulations for various conditions of the formation-seal system were used: (1) radial extent varying from 10 to 100 km, (2) pore compressibility and permeability of the storage formation, and (3) a realistic range of seal's&p permeability from 10-20 to 10-17 m2. Through these detailed numerical simulations, the transient, domain- averaged pressure buildup over the injection period and the storage efficiency for the entire injection period were obtained, and compared with those estimated through the quick-assessment method. The good agreement indicates that the proposed method can produce reasonable approximations for the formation-seal system of various geometric and hydrogeologic properties. This implies that the detailed, two-phase flow conditions, CO2 dissolution, and non-uniform pressure buildup can be neglected in estimating CO2 storage capacity at early stages of site selection and characterization. In addition, the sensitivity of pressure buildup and CO2 plume evolution to the various geometric and hydrogeologic properties of the formation-seal system is presented through the detailed modeling.