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Carbon dioxide capture and geological storage (CCGS) is an emerging technology that is increasingly being considered for reducing greenhouse gas emissions to the atmosphere. Deep saline aquifers provide a very large capacity for CO2 storage and, unlike hydrocarbon reservoirs and coal beds, are immediately accessible and are found in all sedimentary basins. Proper understanding of the displacement character of CO2-brine systems at in-situ conditions is essential in ascertaining CO2 injectivity, migration and trapping in the pore space as a residual gas or supercritical fluid, and in assessing the suitability and safety of prospective CO2 storage sites. Because of lack of published data, the authors conducted a program of measuring the relative permeability and other displacement characteristics of CO2-brine systems for sandstone, carbonate and shale formations in central Alberta in western Canada. The tested formations are representative of the in-situ characteristics of deep saline aquifers in compacted on-shore North American sedimentary basins. The results show that the capillary pressure, interfacial tension, relative permeability and other displacements characteristics of CO2-brine systems depend on the in-situ conditions of pressure, temperature and water salinity, and on the pore size distribution of the sedimentary rock. This paper presents a synthesis and interpretation of the results. [ABSTRACT FROM AUTHOR]

The paper presents a comparison of hydrologic issues and technical approaches used in deep-well injection and disposal of liquid wastes, and those issues and approaches associated with injection and storage of CO2 in deep brine formations. These comparisons have been discussed in nine areas: injection well integrity; abandoned well problems; buoyancy effects; multiphase flow effects; heterogeneity and flow channeling; multilayer isolation effects; caprock effectiveness and hydromechanics; site characterization and monitoring; effects of CO2 storage on groundwater resources. There are considerable similarities, as well as significant differences. Scientifically and technically, these two fields can learn much from each other. The discussions presented in this paper should help to focus on the key scientific issues facing deep injection of fluids. A substantial but by no means exhaustive reference list has been provided for further studies into the subject. [ABSTRACT FROM AUTHOR]

Geologic storage of CO2 is expected to produce plumes of large areal extent, and some leakage may occur along fractures, fault zones, or improperly plugged pre-existing wellbores. A review of physical and chemical processes accompanying leakage suggests a potential for self-enhancement. The numerical simulations presented here confirm this expectation, but reveal self-limiting features as well. It seems unlikely that CO2 leakage could trigger a high-energy run-away discharge, a so-called “pneumatic eruption,” but present understanding is insufficient to rule out this possibility. The most promising avenue for increasing understanding of CO2 leakage behavior is the study of natural analogues. [ABSTRACT FROM AUTHOR]

This paper reports a preliminary investigation of CO2 sequestration and seal integrity at Teapot Dome oil field, Wyoming, USA, with the objective of predicting the potential risk of CO2 leakage along reservoir-bounding faults. CO2 injection into reservoirs creates anomalously high pore pressure at the top of the reservoir that could potentially hydraulically fracture the caprock or trigger slip on reservoir-bounding faults. The Tensleep Formation, a Pennsylvanian age eolian sandstone is evaluated as the target horizon for a pilot CO2 EOR-carbon storage experiment, in a three-way closure trap against a bounding fault, termed the S1 fault. A preliminary geomechanical model of the Tensleep Formation has been developed to evaluate the potential for CO2 injection inducing slip on the S1 fault and thus threatening seal integrity. Uncertainties in the stress tensor and fault geometry have been incorporated into the analysis using Monte Carlo simulation. The authors find that even the most pessimistic risk scenario would require ∼10 MPa of excess pressure to cause the S1 fault to reactivate and provide a potential leakage pathway. This would correspond to a CO2 column height of ∼1,500 m, whereas the structural closure of the Tensleep Formation in the pilot injection area does not exceed 100 m. It is therefore apparent that CO2 injection is not likely to compromise the S1 fault stability. Better constraint of the least principal stress is needed to establish a more reliable estimate of the maximum reservoir pressure required to hydrofracture the caprock. [ABSTRACT FROM AUTHOR]

This paper reports on the regional screening, selection and geological characterisation of a potential on-shore CO2 storage site (saline aquifer) in north-eastern Germany. The main objective of this study was to identify and investigate a candidate storage site, capable to accommodate the total amount of approximately 400 million tons of CO2. Such a volume is produced by a modern, lignite-fired power plant within its operation lifetime of approximately 40 years. Within north-eastern Germany, several saline aquifers of Triassic, Jurassic and Cretaceous age have been evaluated with respect to their regional occurrence, storage potential and basic reservoir properties. Subsequent to a ranking, considering different criteria, the anticlinal structure Schweinrich holding suitable saline aquifers of the uppermost Triassic and lowest Jurassic has been selected from a number of identified candidate sites. According to results of the geological site characterisation, including structural geological investigations and 3D reservoir modelling, the structure Schweinrich seems to be a suitable site for industrial large scale CO2 storage. Further data acquisition (new wells and 3D seismics) and research (more detailed and comprehensive modelling) is needed in order to prove the structural integrity of the storage site and assure long-term safety. [ABSTRACT FROM AUTHOR]

The authors believe that recent global warming of Earth’s atmosphere is not due to an increase in anthropogenic carbon dioxide emission but rather to long-term global factors. The human contribution to the CO2content in the atmosphere and the increase in temperature is negligible in comparison with other sources of carbon dioxide emission. Discussed in this paper are sources, avenues of migration, and the amounts of naturally produced carbon dioxide and methane (greenhouse gases) and long-term changes in the Earth’s climate, which are necessary for understanding the causes of current temperature trends. [ABSTRACT FROM AUTHOR]

Carbon management through the underground injection of CO2 into subsurface brine formations is being actively studied. If there are no technological constraints for implementation, there could be a large number of wells constructed for injecting a large volume of CO2. It is therefore important, in parallel with current scientific studies, to consider the appropriate, science-based regulatory framework for CO2 injection. The Environmental Protection Agency (EPA) Underground Injection Control (UIC) program, authorized under the Safe Drinking Water Act (SDWA), has extensive experience in regulating the injection of mainly liquid wastes into geologic formations in the United States. The federal requirements and permit process implemented by EPA and the Primacy States since 1980 have played a critical role in the safety of subsurface disposal of liquid wastes in the US. Physically and chemically, there are significant differences between CO2 and common liquid wastes. Its viscosity and density are much lower and, under injection pressure in the deep formation, it may be under supercritical conditions. Because of the lower density and viscosity, CO2 leakage through the confining strata may be greater when compared to currently injected liquid wastes. Also, the chemical interactions of CO2 with the geologic formation have their own characteristics. All these scientific factors need to be evaluated to identify new guidelines for appropriate regulatory and monitoring controls. The paper reviews current UIC regulations, injection-well classification scheme and monitoring requirements, and identifies the unique factors related to the physical and chemical processes in the subsurface associated with CO2 injection. Implications of these scientific considerations for regulation development are discussed. [ABSTRACT FROM AUTHOR]

This paper considers the major environmental impacts associated with industrial-scale carbon dioxide sequestration as stable carbonate minerals, material resulting from a study undertaken by CSMA Consultants Ltd. in 1999. The chemical bonding of carbon dioxide, through reaction of two or more products to produce magnesium or calcium carbonate has been suggested as a means to mitigate CO2 from fossil fuel power plants. The study considered six potential methods for sequestering carbon dioxide, notionally captured from fossil fuel burning power stations, as stable mineral carbonates, i.e. magnesite and limestone (calcium carbonate) and as sodium bicarbonate. Four methods were eliminated in the initial screening and two were selected for further detailed consideration. Following this stage the overall environmental costs, including environmental impacts, energy and carbon dioxide balances, meant that all the current technologies amenable to reasoned consideration had to be discarded as currently environmentally unacceptable. [ABSTRACT FROM AUTHOR]

Increase in the use of conservation practices by agriculture in the United States will enhance soil organic carbon and potentially increase carbon sequestration. This, in turn, will decrease the net emission of carbon dioxide. A number of studies exist that calibrate the contribution of various individual, site-specific conservation practices on changes in soil organic carbon. There is a general absence, however, of a comprehensive effort to measure objectively the contribution of these practices including conservation tillage, the Conservation Reserve Program, and conservation buffer strips to an change in soil organic carbon. This paper fills that void. After recounting the evolution of the use of the various conservation practices, it is estimated that organic carbon in the soil in 1998 in the United States attributable to these practices was about 12.2 million metric tons. By 2008, there will be an increase of about 25%. Given that there is a significant potential for conservation practices, which could lead to an increase in carbon sequestration, there are a number of policy options that can be pursued. These include education and technical assistance, financial assistance, research and development, land retirement, and regulation and taxes. [ABSTRACT FROM AUTHOR]

Conventional theory of global warming states that heating of atmosphere occurs as a result of accumulation of CO2 and CH4 in atmosphere. The writers show that rising concentration of CO2 should result in the cooling of climate. The methane accumulation has no essential effect on the Earth’s climate. Even significant releases of the anthropogenic carbon dioxide into the atmosphere do not change average parameters of the Earth’s heat regime and the atmospheric greenhouse effect. Moreover, CO2 concentration increase in the atmosphere results in rising agricultural productivity and improves the conditions for reforestation. Thus, accumulation of small additional amounts of carbon dioxide and methane in the atmosphere as a result of anthropogenic activities has practically no effect on the Earth’s climate. [ABSTRACT FROM AUTHOR]

Field experiments on the CO2 flux of alpine meadow soil in the Qilian Mountain were conducted along the elevation gradient during the growing season of 2004 and 2005. The soil CO2 flux was measured using the Li-6400-09 soil respiration chamber attached to the Li-6400 portable photosynthesis system. The effects of water and heat and roots on the soil CO2 flux were statistically analyzed. The results show that soil CO2 flux along the elevation gradient gradually decreases. The soil CO2 flux was low at night, with lowest value occurring between 0200 and 0600 hours, started to rise rapidly during 0700–0830 hours, and then descend during 1600–1830 hours. The peak CO2 efflux appears during 1100–1600 hours. The diurnal average of soil CO2 efflux was between 0.56 ± 0.32 and 2.53 ± 0.76 μmol m−2 s−1. Seasonally, soil CO2 fluxes are relatively high in summer and autumn and low in spring and winter. The soil CO2 efflux, from the highest to the lowest in the ranking order, occurred in July and August (4.736 μmol m−2 s−1), June and September, and May and October, respectively. The soil CO2 efflux during the growing season is positively correlated with soil temperature, root biomass and soil water content. [ABSTRACT FROM AUTHOR]

Accurate measurements to assess the influence of soil moisture on CO2 flux requires the absolute estimates of soil CO2 flux. Thus, it was constructed a calibration system where CO2 with fixed concentration flowed through the different porous material. Previous to measurement, in order to verify the performance and reliability of a closed dynamic chamber, different discontinuous air-mixing rates and times were tested. The CO2 flux was estimated through sequential lectures and the best fit for flux measurements was obtained taking short readings every 3 min, during a total time of 12 min ( R2 = 0.99). The best mixing rate was attained for 250 mL min−1, allowing 25 s of mixing previous to CO2 extraction for an infrared gas analyzer. The deviation of the measured values for dry sand from the reference CO2 flux (0.097 and 0.071 g m−2 min−1) was 5 and 7%. On dry sandy loam soil (SLS) the deviation was 2%. The measured fluxes decreased 73 and 22% with content moisture of 20 and 10% (sand), and 78% with content moisture of 31% (SLS). This work allowed to estimate how much the measured emission rates deviate from the true ones for the specified chamber and sampling conditions. [ABSTRACT FROM AUTHOR]

Two springs (Cuihua Spring, Shuiqiuchi Spring) in Cuihua Mountain of the Qinling Mountains were observed and sampled monthly during 2004 and 2005 to trace their physical properties and chemical compositions with seasons. Although both pH values and cation (Ca2+, Mg2+, K+, and Na+) contents of Cuihua Spring are higher than those of Shuiqiuchi Spring, seasonal variations in both springs are obvious. The pH values of both spring waters are between 5.69 and 6.98, lower than that of rainwater during summer and autumn. From January to November, the pH values of both springs similarly vary from high to low and then to high again. Variations in electric conductivities of two spring waters are contrary, although their electric conductivities are positively correlative with the cation content respectively. This can be attributed to different water sources of the two springs or different acidic rocks they passed. The contents of HCO3 –, Ca2+, Mg2+, K+, and Na+ are low, indicating a low silicate weathering that the strata in this district are mainly composed of granite and schist of quartz and mica. Differing from change in spring water in karst regions of South China where abundant precipitation and dilution of rainwater cause low pH and electric conductivity in summer and autumn, the seasonal variations in the pH values and the electric conductivities of two springs in Qinling Mountains are attributed to seasonal changes in CO2 produced by microorganisms' activity in soil within respective year, rather than rainfall. The microorganisms' activity in soil produces more CO2 during summer and autumn. Therefore, the water nature of springs in silicate regions chiefly reflects the seasonal changes of CO2 produced by the microorganisms in soil. [ABSTRACT FROM AUTHOR]

A Double Solid Reactant Method was elaborated from a suggestion of Marini (Geological sequestration of carbon dioxide: Thermodynamics, kinetics, and reaction path modeling. Developments in Geochemistry, Elsevier, Amsterdam, 2007) to simulate the release of trace elements during the progressive dissolution of solid phases. The method is based on the definition, for each dissolving solid, of both an entity whose thermodynamic and kinetic properties are known (either a pure mineral or a solid mixture) and a special reactant, that is, a material of known stoichiometry and unknown thermodynamic and kinetic properties. The special reactant is utilised to take into account the concentrations of trace elements in the dissolving solid phase. In this communication, the influence of several trace elements on the Δ G f o, Δ G r o and log K of the minerals considered by Lelli et al. (Environ Geol, 2007) and Accornero and Marini (Geobasi, 2007a; Proceedings of IMWA symposium, Cagliari, 27–31 May 2007b) was evaluated assuming ideal mixing in the solid state. These effects were found to be negligible for albite and the leucite–latitic glass, limited for muscovites and chlorites, and slightly more important for apatites. These influences become progressively higher with increasing concentration of trace elements in these minerals. Based on these deviations in thermodynamic parameters, special reactants should not include oxide components with molar fractions higher than 0.003. [ABSTRACT FROM AUTHOR]

Seismic surveys successfully imaged a small scale CO2 injection (1,600 ton) conducted in a brine aquifer of the Frio Formation near Houston, Texas. These time-lapse borehole seismic surveys, crosswell and vertical seismic profile (VSP), were acquired to monitor the CO2 distribution using two boreholes (the new injection well and a pre-existing well used for monitoring) which are 30 m apart at a depth of 1,500 m. The crosswell survey provided a high-resolution image of the CO2 distribution between the wells via tomographic imaging of the P-wave velocity decrease (up to 500 m/s). The simultaneously acquired S-wave tomography showed little change in S-wave velocity, as expected for fluid substitution. A rock physics model was used to estimate CO2 saturations of 10–20% from the P-wave velocity change. The VSP survey resolved a large (∼70%) change in reflection amplitude for the Frio horizon. This CO2 induced reflection amplitude change allowed estimation of the CO2 extent beyond the monitor well and on three azimuths. The VSP result is compared with numerical modeling of CO2 saturations and is seismically modeled using the velocity change estimated in the crosswell survey. [ABSTRACT FROM AUTHOR]

A screening and ranking framework (SRF) has been developed to evaluate potential geologic carbon dioxide (CO2) storage sites on the basis of health, safety, and environmental (HSE) risk arising from CO2 leakage. The approach is based on the assumption that CO2 leakage risk is dependent on three basic characteristics of a geologic CO2 storage site: (1) the potential for primary containment by the target formation; (2) the potential for secondary containment if the primary formation leaks; and (3) the potential for attenuation and dispersion of leaking CO2 if the primary formation leaks and secondary containment fails. The framework is implemented in a spreadsheet in which users enter numerical scores representing expert opinions or published information along with estimates of uncertainty. Applications to three sites in California demonstrate the approach. Refinements and extensions are possible through the use of more detailed data or model results in place of property proxies. [ABSTRACT FROM AUTHOR]

Careful site characterization is critical for successful geologic storage of carbon dioxide (CO2) because of the many physical and chemical processes impacting CO2 movement and containment under field conditions. Traditional site characterization techniques such as geological mapping, geophysical imaging, well logging, core analyses, and hydraulic well testing provide the basis for judging whether or not a site is suitable for CO2 storage. However, only through the injection and monitoring of CO2 itself can the coupling between buoyancy flow, geologic heterogeneity, and history-dependent multi-phase flow effects be observed and quantified. CO2 injection and monitoring can therefore provide a valuable addition to the site-characterization process. Additionally, careful monitoring and verification of CO2 plume development during the early stages of commercial operation should be performed to assess storage potential and demonstrate permanence. The Frio brine pilot, a research project located in Dayton, Texas (USA) is used as a case study to illustrate the concept of an iterative sequence in which traditional site characterization is used to prepare for CO2 injection and then CO2 injection itself is used to further site-characterization efforts, constrain geologic storage potential, and validate understanding of geochemical and hydrological processes. At the Frio brine pilot, in addition to traditional site-characterization techniques, CO2 movement in the subsurface is monitored by sampling fluid at an observation well, running CO2-saturation-sensitive well logs periodically in both injection and observation wells, imaging with crosswell seismic in the plane between the injection and observation wells, and obtaining vertical seismic profiles to monitor the CO2 plume as it migrates beyond the immediate vicinity of the wells. Numerical modeling plays a central role in integrating geological, geophysical, and hydrological field observations. [ABSTRACT FROM AUTHOR]

Geological storage of CO2 in the offshore Gippsland Basin, Australia, is being investigated by the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) as a possible method for storing the very large volumes of CO2 emissions from the nearby Latrobe Valley area. A storage capacity of about 50 million tonnes of CO2 per annum for a 40-year injection period is required, which will necessitate several individual storage sites to be used both sequentially and simultaneously, but timed such that existing hydrocarbon assets will not be compromised. Detailed characterisation focussed on the Kingfish Field area as the first site to be potentially used, in the anticipation that this oil field will be depleted within the period 2015–2025. The potential injection targets are the interbedded sandstones of the Paleocene-Eocene upper Latrobe Group, regionally sealed by the Lakes Entrance Formation. The research identified several features to the offshore Gippsland Basin that make it particularly favourable for CO2 storage. These include: a complex stratigraphic architecture that provides baffles which slow vertical migration and increase residual gas trapping and dissolution; non-reactive reservoir units that have high injectivity; a thin, suitably reactive, lower permeability marginal reservoir just below the regional seal providing mineral trapping; several depleted oil fields that provide storage capacity coupled with a transient production-induced flow regime that enhances containment; and long migration pathways beneath a competent regional seal. This study has shown that the Gippsland Basin has sufficient capacity to store very large volumes of CO2. It may provide a solution to the problem of substantially reducing greenhouse gas emissions from future coal developments in the Latrobe Valley. [ABSTRACT FROM AUTHOR]

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO2 enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO2 EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO2 EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO2 sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO2 EOR. The second stage provides quick estimates of CO2 EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites. [ABSTRACT FROM AUTHOR]

Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity. [ABSTRACT FROM AUTHOR]

Sedimentary basins are suitable to different degrees for CO2 geological sequestration as a result of various intrinsic and extrinsic characteristics, of which the geothermal regime is one of the most important. Warm basins are less favorable for CO2 sequestration than cold basins because of reduced capacity in terms of CO2 mass, and because of higher CO2 buoyancy, which drives the upward CO2 migration. A set of 15 criteria, with several classes each, has been developed for the assessment and ranking of sedimentary basins in terms of their suitability for CO2 sequestration. Using a parametric normalization procedure, a basin's individual scores are summed to a total score using weights that express the relative importance of different criteria. The total score is ranked to determine the most suitable basin or region thereof for the geological sequestration of CO2. The method is extremely flexible in that it allows changes in the functions that express the importance of various classes for any given criterion, and in the weights that express the relative importance of various criteria. Examples of application are given for Canada's case and for the Alberta basin in Canada. [ABSTRACT FROM AUTHOR]

A numerical study of hydromechanical changes during a deep underground injection of supercritical CO2 in a hypothetical brine aquifer/caprock system is conducted. The injection process is simulated using a newly developed computer model for multi-phase analysis of CO2 and brine water flow, coupled with heat transfer and rock deformations. In this modeling, CO2 is injected at a constant rate over a 10-year period at a depth of 1,300–1,500 m. The injection zone is overlain by a 100-m-thick caprock, located at 1,200–1,300 m, which in one of the studied cases is intersected by a vertical fault. The hydraulic, mechanical as well as hydromechanical responses caused by the injection are studied. This includes the spread of the CO2 plume, effective stress changes, ground surface uplift, stress-induced permeability changes, and mechanical failure analysis. The analysis shows that most hydromechanical changes are induced in the lower part of the caprock near its contact with the injection zone, whereas the sealing mechanism of the upper part may remain intact, despite an injection pressure close to the lithostratic stress value. [ABSTRACT FROM AUTHOR]