Intermediate storage of carbon dioxide in geological formations: A technical perspective

Enhanced oil recovery (EOR) through CO₂ flooding has been practiced on a commercial basis for the last 35 years and continues today at several sites, currently injecting in total over 30 million tons of CO₂ annually. This practice is currently exclusively for economic gain, but can potentially contribute to the reduction of emissions of greenhouse gases provided it is implemented on a large scale. Optimal operations in distributing CO₂ to CO₂-EOR or enhanced gas recovery (EGR) projects (referred to here collectively as CO₂-EHR) on a large scale and long time span imply that intermediate storage of CO₂ in geological formations may be a key component. Intermediate storage is defined as the storage of CO₂ in geological media for a limited time span such that the CO₂ can be sufficiently reproduced for later use in CO₂-EHR. This paper investigates the technical aspects, key individual parameters and possibilities of intermediate storage of CO₂ in geological formations aiming at large scale implementation of carbon dioxide capture and storage (CCS) for deep emission reduction. The main parameters are thus the depth of injection and density, CO₂ flow and transport processes, storage mechanisms, reservoir heterogeneity, the presence of impurities, the type of the reservoirs and the duration of intermediate storage. Structural traps with no flow of formation water combined with proper injection planning such as gas-phase injection favour intermediate storage in deep saline aquifers. In depleted oil and gas fields, high permeability, homogeneous reservoirs with structural traps (e.g. anticlinal structures) are good candidates for intermediate CO₂ storage. Intuitively, depleted natural gas reservoirs can be potential candidates for intermediate storage of carbon dioxide due to similarity in storage characteristics.     

Non-isothermal flow of carbon dioxide in injection wells during geological storage

During sequestration, carbon dioxide within injection wells is likely to be in a dense state and therefore its weight within the wellbore will play an important role in determining the bottomhole pressure and thus the injection rate. However, the density could vary significantly along the well in response to the variation in pressure and temperature. A numerical procedure is formulated in this paper to evaluate the flow of carbon dioxide and its mixtures in non-isothermal wells. This procedure solves the coupled heat, mass and momentum equations with the various fluid and thermodynamic properties, including the saturation pressure, of the gas mixture calculated using a real gas equation of state. This treatment is particularly useful when dealing with gas mixtures where experimental data on mixture properties are not available and these must be predicted. To test the developed procedure two wellbore flow problems from the literature, involving geothermal gradients and wellbore phase transitions are considered; production of 97% carbon dioxide and injection of superheated steam. While these are not typical carbon dioxide injection problems they provide field observations of wellbore flow processes which encompass the mechanisms of interest for carbon dioxide injection, such as phase transition, temperature and density variations with depth. These two examples show that the developed procedure can offer accurate predictions. In a third application the role of wellbore hydraulics during a hypothetical carbon dioxide injection application is considered. The results obtained illustrate the potential complexity of carbon dioxide wellbore hydraulics for sequestration applications and the significant role it can play in determining the well bottomhole pressure and thus injection rate.     

Lessons learned from natural and industrial analogues for storage of carbon dioxide

The deployment of CCS (carbon capture and storage) at industrial scale implies the development of effective monitoring tools. Noble gases are tracers usually proposed to track CO₂. This methodology, combined with the geochemistry of carbon isotopes, has been tested on available analogues.At first, gases from natural analogues were sampled in the Colorado Plateau and in the French carbogaseous provinces, in both well-confined and leaking-sites. Second, we performed a 2-years tracing experience on an underground natural gas storage, sampling gas each month during injection and withdrawal periods.In natural analogues, the geochemical fingerprints are dependent on the containment criterion and on the geological context, giving tools to detect a leakage of deep-CO₂ toward surface. This study also provides information on the origin of CO₂, as well as residence time of fluids within the crust and clues on the physico-chemical processes occurring during the geological story.The study on the industrial analogue demonstrates the feasibility of using noble gases as tracers of CO₂. Withdrawn gases follow geochemical trends coherent with mixing processes between injected gas end-members. Physico-chemical processes revealed by the tracing occur at transient state.These two complementary studies proved the interest of geochemical monitoring to survey the CO₂ behaviour, and gave information on its use.     

An engineering-economic model of pipeline transport of CO2 with application to carbon capture and storage

Carbon dioxide capture and storage (CCS) involves the capture of CO₂ at a large industrial facility, such as a power plant, and its transport to a geological (or other) storage site where CO₂ is sequestered. Previous work has identified pipeline transport of liquid CO₂ as the most economical method of transport for large volumes of CO₂. However, there is little published work on the economics of CO₂ pipeline transport. The objective of this paper is to estimate total cost and the cost per tonne of transporting varying amounts of CO₂ over a range of distances for different regions of the continental United States. An engineering-economic model of pipeline CO₂ transport is developed for this purpose. The model incorporates a probabilistic analysis capability that can be used to quantify the sensitivity of transport cost to variability and uncertainty in the model input parameters. The results of a case study show a pipeline cost of US$ 1.16 per tonne of CO₂ transported for a 100 km pipeline constructed in the Midwest handling 5 million tonnes of CO₂ per year (the approximate output of an 800 MW coal-fired power plant with carbon capture). For the same set of assumptions, the cost of transport is US$ 0.39 per tonne lower in the Central US and US$ 0.20 per tonne higher in the Northeast US. Costs are sensitive to the design capacity of the pipeline and the pipeline length. For example, decreasing the design capacity of the Midwest US pipeline to 2 million tonnes per year increases the cost to US$ 2.23 per tonne of CO₂ for a 100 km pipeline, and US$ 4.06 per tonne CO₂ for a 200 km pipeline. An illustrative probabilistic analysis assigns uncertainty distributions to the pipeline capacity factor, pipeline inlet pressure, capital recovery factor, annual O&M cost, and escalation factors for capital cost components. The result indicates a 90% probability that the cost per tonne of CO₂ is between US$ 1.03 and US$ 2.63 per tonne of CO₂ transported in the Midwest US. In this case, the transport cost is shown to be most sensitive to the pipeline capacity factor and the capital recovery factor. The analytical model elaborated in this paper can be used to estimate pipeline costs for a broad range of potential CCS projects. It can also be used in conjunction with models producing more detailed estimates for specific projects, which requires substantially more information on site-specific factors affecting pipeline routing.     

Coalbed methane reservoir data and simulator parameter uncertainty modelling for CO2 storage performance assessment

Laboratory studies and a number of field pilots have demonstrated that CO₂ injection into coal seams has the potential to enhance coalbed methane (CBM) recovery with the added advantage that most of the injected CO₂ can be stored permanently in coal. The concept of storing CO₂ in geologic formations as a safe and effective greenhouse gas mitigation option requires public and regulatory acceptance. In this context it is important to develop a good understanding of the reservoir performance, uncertainties and the risks that are associated with geological storage. The paper presented refers to the sources of uncertainty involved in CO₂ storage performance assessment in coalbed methane reservoirs and demonstrates their significance using extensive digital well log data representing the Manville coals in Alberta, Canada. The spatial variability of the reservoir properties was captured through geostatistical analysis, and sequential Gaussian simulations of these provided multiple realisations for the reservoir simulator inputs. A number of CO₂ injection scenarios with variable matrix swelling coefficients were evaluated using a 2D reservoir model and spatially distributed realisations of total net thickness and permeability.     

Value of information analysis for adequate monitoring of carbon dioxide storage in geological reservoirs under uncertainty

As monitoring is essential for the proper management of geological storage of carbon dioxide (CO₂), the ability to value information from monitoring is indispensable to adequately design a monitoring program. It is necessary to judge whether the expected improvement in management is worth the cost of monitoring. The value of information (VOI) is closely related to the possible increase in expected utility gained by gathering the information, the concept of which can be applied to such judgement. Although VOI analysis has been extensively studied in the context of decision analysis, its application to the management of carbon dioxide capture and storage (CCS) operations is rare. This paper introduces and discusses the methodology of VOI analyses in the context of monitoring CO₂ storage. A motivating problem with discrete probabilities is used to illustrate the concept of VOI. It is demonstrated that information is not always of value; for information to be worthwhile, monitoring under uncertainty must satisfy certain conditions. This concept is then extended to continuous probability distributions. The effects of prior uncertainty and information reliability on the VOI are examined. It is shown that an excessive improvement in information accuracy yields little value and that the optimal level of reliability can be inferred. VOI analyses provide quantitative insights into the value of information-gathering activities and therefore can be an objective means to adequately design and impartially justify a monitoring program.     

Use of strategic environmental assessment in the site selection process for a radioactive waste disposal facility in Slovenia

The benefits of strategic environmental considerations in the process of siting a repository for low- and intermediate-level radioactive waste (LILW) are presented. The benefits have been explored by analyzing differences between the two site selection processes. One is a so-called official site selection process, which is implemented by the Agency for radwaste management (ARAO); the other is an optimization process suggested by experts working in the area of environmental impact assessment (EIA) and land-use (spatial) planning. The criteria on which the comparison of the results of the two site selection processes has been based are spatial organization, environmental impact, safety in terms of potential exposure of the population to radioactivity released from the repository, and feasibility of the repository from the technical, financial/economic and social point of view (the latter relates to consent by the local community for siting the repository). The site selection processes have been compared with the support of the decision expert system named DEX. The results of the comparison indicate that the sites selected by ARAO meet fewer suitability criteria than those identified by applying strategic environmental considerations in the framework of the optimization process. This result stands when taking into account spatial, environmental, safety and technical feasibility points of view. Acceptability of a site by a local community could not have been tested, since the formal site selection process has not yet been concluded; this remains as an uncertain and open point of the comparison.     

Evaluation of large-scale CO2 storage on fresh-water sections of aquifers: An example from the Texas Gulf Coast Basin

Large-scale injections of CO₂ into subsurface saline aquifers have been proposed to remediate climate change related to buildup of green house gases in the atmosphere. The pressure buildup caused by such injections may impact a volume of the basin significantly larger than the CO₂ plume itself. In areas with hydrological settings similar to the Gulf Coast Basin, the perturbation of the flow-field in deep parts of the basin could result in brines or brackish water being pushed up-dip into unconfined sections of the same formations or into the capture zone of fresh-water wells. The premise of the current study is that the details of multiple-phase flow processes necessary to model the near field evolution of the CO₂ plume are not necessary to describe the impact of the pressure anomaly on up-dip aquifers. This paper quantitatively explores conditions under which shallow groundwater would be impacted by up-dip displacement of brines, utilizing an existing carefully calibrated flow model. Modeling an injection of water, arguably equivalent to 50 million tons of CO₂/year for 50 years resulted in an average water-table rise of 1 m, with minor increase in stream baseflow and larger increase in ground water evapotranspiration, but no significant change in salinity.     

A preliminary cost and engineering estimate for desalinating produced formation water associated with carbon dioxide capture and storage

The risk associated with storage of carbon dioxide in the subsurface can be reduced by removal of a comparable volume of existing brines (e.g. Buscheck et al., 2011). In order to avoid high costs for disposal, the brines should be processed into useful forms such as fresh and low-hardness water. We have carried out a cost analysis of treatment of typical subsurface saline waters found in sedimentary basins, compared with conventional seawater desalination. We have also accounted for some cost savings by utilization of potential well-head pressures at brine production wells, which may be present in some fields due to CO₂ injection, to drive desalination using reverse osmosis. Predicted desalination costs for brines having salinities equal to seawater are about half the cost of conventional seawater desalination when we assume the energy can be obtained from excess pressure at the well head. These costs range from 32 to 40¢ per m³ permeate produced. Without well-head energy recovery, the costs are from 60 to 80¢ per m³ permeate. These costs do not include the cost of any brine production or brine reinjection wells, or pipelines to the well field, or other site-dependent factors.     

Effective communication about complex environmental issues: Perceived quality of information about carbon dioxide capture and storage (CCS) depends on stakeholder collaboration

This experimental research addresses the effectiveness of communication about complex environmental issues, depending on whether the same information is provided by multiple collaborating or by individual organizations (i.e., stakeholders). The information provided pertains to carbon dioxide capture and storage (CCS) technology, as an example of a complex environmental issue. In Studies 1 (N = 75) and 2 (N = 66) we found that participants perceived factual information from collaborating stakeholders to be of higher quality than when the same information was provided by individual stakeholders. As predicted, the expectation of diverse perspectives being represented in the collaborative information mediated this effect. In addition, in Study 3 (N = 79) the perceived dissimilarity of collaborating stakeholders was shown to be an important precondition for the collaboration effect observed in Studies 1 and 2. Finally, these studies indicate that occasional collaboration between different stakeholders does not necessarily harm the perceived credibility of each individual stakeholder.     

Water/acid gas interfacial tensions and their impact on acid gas geological storage

Acid gas geological disposal is a promising process to reduce CO₂ atmospheric emissions and an environment-friendly and economic alternative to the transformation of H₂S into sulphur by the Claus process. Acid gas confinement in geological formations is to a large extent controlled by the capillary properties of the water/acid–gas/caprock system, because a significant fraction of the injected gas rises buoyantly and accumulates beneath the caprock. These properties include the water/acid gas interfacial tension (IFT), to which the so-called capillary entry pressure of the gas in the water-saturated caprock is proportional. In this paper we present the first ever systematic water/acid gas IFT measurements carried out by the pendant drop technique under geological storage conditions. We performed IFT measurements for water/H₂S systems over a large range of pressure (up to P = 15 MPa) and temperature (up to T = 120 °C). Water/H₂S IFT decreases with increasing P and levels off at around 9–10 mN/m at high T (≥70 °C) and P (>12 MPa). The latter values are around 30–40% of water/CO₂ IFTs, and around 20% of water/CH₄ IFTs at similar T and P conditions. The IFT between water and a CO₂ + H₂S mixture at T = 77 °C and P > 7.5 MPa is observed to be approximately equal to the molar average IFT of the water/CO₂ and water/H₂S binary mixtures. Thus, when the H₂S content in the stored acid gas increases the capillary entry pressure decreases, together with the maximum height of acid gas column and potential storage capacity of a given geological formation. Hence, considerable attention should be exercised when refilling with a H₂S-rich acid gas a depleted gas reservoir, or a depleted oil reservoir with a gas cap: in the case of hydrocarbon reservoirs that were initially (i.e., at the time of their discovery) close to capillary leakage, acid gas leakage through the caprock will inevitably occur if the refilling pressure approaches the initial reservoir pressure.     

Effects of increased wood energy consumption on carbon storage in forests of the United States

Large but feasible increases that have been projected for the production of wood energy in the United States can be expected to significantly alter the current carbon storage patterns in US forest vegetation. The 1976 net wood increment left after forest cutting equals about 136 × 10⁶ tons of carbon/year, with about 60% of the increment found in merchantable trees, and the remainder in nonmerchantable components.Achieving 5–10 quads of wood energy beyond 1976 levels by the year 2010 can significantly change current carbon storage patterns with the magnitude of change dependent on the extent of residue harvest to meet energy goals, and the rate of future forest growth. Complete loss of the apparent net wood increment is a possible outcome.Although the future growth and harvest situation cannot be known now, a range of possible scenarios suggests that US forests in the year 2010 will store much less carbon than today, thus significantly changing their role in the global carbon cycle.     

Experimental measurement and modeling of the rate of absorption of carbon dioxide by aqueous ammonia

In this work, the rate of absorption of carbon dioxide by aqueous ammonia solvent has been studied by applying a newly built wetted wall column. The absorption rate in aqueous ammonia was measured at temperatures from 279 to 304 K for 1 to 10 wt% aqueous ammonia with loadings varying from 0 to 0.8 mol CO₂/mol NH₃. The absorption rate in 30 wt% aqueous mono-ethanolamine (MEA) was measured at 294 and 314 K with loadings varying from 0 to 0.4 as comparison.It was found that at 304 K, the rate of absorption of carbon dioxide by 10 wt% NH₃ solvent was comparable to the rates for 30 wt% MEA at 294 and 314 K (a typical absorption temperature for this process). The absorption rate using ammonia was however significantly lower at temperatures of 294 K and lower as applied in the Chilled Ammonia Process. However, at these low temperatures, the rate of absorption in ammonia has only a small temperature dependency.The rate of absorption decreases strongly with decreasing ammonia concentrations and increasing CO₂ loadings.The rate of absorption of carbon dioxide by aqueous ammonia solvent was modeled using the measurements of the unloaded solutions and the zwitter-ion mechanism. The model could successfully predict the experimental measurements of the absorption rate of CO₂ in loaded ammonia solutions.     

Environmental bonds and the challenge of long-term carbon sequestration

The potential to capture carbon from industrial sources and dispose of it for the long-term, known as carbon capture and sequestration (CCS), is widely recognized as an important option to reduce atmospheric carbon dioxide emissions. Specifically, CCS has the potential to provide emissions cuts sufficient to stabilize greenhouse gas levels, while still allowing for the continued use of fossil fuels. In addition, CCS is both technologically-feasible and commercially viable compared with alternatives with the same emissions profile. Although the concept appears to be solid from a technical perspective, initial public perceptions of the technology are uncertain. Moreover, little attention has been paid to developing an understanding of the social and political institutional infrastructure necessary to implement CCS projects. In this paper we explore a particularly dicey issue--how to ensure adequate long-term monitoring and maintenance of the carbon sequestration sites. Bonding mechanisms have been suggested as a potential mechanism to reduce these problems (where bonding refers to financial instruments used to ensure regulatory or contractual commitments). Such mechanisms have been successfully applied in a number of settings (e.g., to ensure court appearances, completion of construction projects, and payment of taxes). The paper examines the use of bonding to address environmental problems and looks at its possible application to nascent CCS projects. We also present evidence on the use of bonding for other projects involving deep underground injection of materials for the purpose of long-term storage or disposal.     

CO2 transportation for carbon capture and storage: Sublimation of carbon dioxide from a dry ice bank

Climate change is being caused by greenhouse gases such as carbon dioxide (CO₂). Carbon capture and storage (CCS) is of interest to the scientific community as one way of achieving significant global reductions of atmospheric CO₂ emissions in the medium term. CO₂ would be captured from large stationary sources such as power plants and transported via pipelines under high pressure conditions to underground storage. If a downward leakage from a surface transportation system module occurs, the CO₂ would undergo a large temperature reduction and form a bank of “dry ice” on the ground surface; the sublimation of the gas from this bank represents an area source term for subsequent atmospheric dispersion, with an emission rate dependent on the energy balance at the bank surface. Gaseous CO₂ is denser than air and tends to remain close to the surface; it is an asphyxiant, a cerebral vasodilator and at high concentrations causes rapid circulatory insufficiency leading to coma and death. Hence a subliming bank of dry ice represents safety hazard. A model is presented for evaluating the energy balance and sublimation rate at the surface of a solid frozen CO₂ bank under different environmental conditions. The results suggest that subliming gas behaves as a proper dense gas (i.e. it remains close to the ground surface) only for low ambient wind speeds.     

Energy and carbon dioxide intensity of Thailand's steel industry and greenhouse gas emission projection toward the year 2050

The purpose of this article is to study the energy and carbon dioxide intensities of Thailand's steel industry and to propose greenhouse gas emission trends from the year 2011 to 2050 under plausible scenarios. The amount of CO₂ emission from iron and steel production was calculated using the 2006 Intergovernmental Panel on Climate Change (IPCC) guidelines in the boundary of production process (gate to gate). The results showed that energy intensity of semi-finished steel product was 2.84 GJ/t semi-finished steel and CO₂ intensity was 0.37 tCO_2eq/t semi-finished steel. Energy intensity of steel finishing process was 1.86 GJ/t finished steel and CO₂ intensity was 0.16 tCO_2eq/t finished steel. Using three plausible scenarios from Thailand's steel industry, S1: without integrated steel plant (baseline scenario), S2: with a traditional integrated BF–BOF route and S3: with an alternative integrated DR-EAF route; the Greenhouse Gas emissions from the year 2011 to 2050 were projected. In 2050, the CO₂ emission from S1 (baseline scenario) was 4.84 million tonnes, S2 was 21.96 million tonnes increasing 4.54 times from baseline scenario. The CO₂ emission from S3 was 7.12 million tonnes increasing 1.47 times from baseline scenario.     

Facilitating access to the algal economy: Mapping waste resources to identify suitable locations for algal farms in Queensland

Algae offer a multiple-benefit opportunity as the products that can result from algal cultivation are numerous and diverse. However, commercial production of algal-derived materials is scarce and in Queensland Australia is virtually non-existent, partly due to challenges around readily available resources. In this work, the potential to regionally recycle waste nitrogen (N), phosphorus (P) and CO₂ to support algal production is considered. A feature of the work is mapping the availability of the three resources for algal cultivation (N, P and CO₂) together with climatic and land use considerations. Mapping resolution is defined by the boundaries of Queensland's (Australia) regional authorities. Layering the maps enables identification of regional hotspots for growing algae. Waste resources are shown to be most abundant in Mackay, Burdekin, Toowoomba, Cassowary and Bundaberg; regions which also have favourable eco-climatic conditions. Waste nitrogen is the limiting waste stream, in these and most other regions however additional requirements can be fixed atmospherically, whereas waste CO₂ is shown to be abundant relative to waste nutrients. It is found that, based on the availability of waste phosphorus, the top 5 most suitable regions have sufficient resources to produce around 1.1 million t/y of algal biomass. This could potentially produce 309 ML of biodiesel which is 5% of Queensland's 2011 diesel oil sales. The outcomes of this work highlight new opportunities for industrial ecology in non-urban regions.     

Household food waste: the implications of consumer choice in food from purchase to disposal

Food and food-related waste is a high priority in terms of waste minimisation in New Zealand. Over the summer of 2012–2013, a survey of 147 participants was conducted on a range of views and practices related to environmental challenges and understandings. The survey, undertaken in Palmerston North, New Zealand, captured a wide socio-demographic. This article focuses on respondents’ food practices from purchase, to plate, to disposal and the environmental implications of these practices. The survey data have allowed an enriched understanding of both individual and structural level challenges as well as incentives towards improving environmental practices in relation to household food waste minimisation. The results indicated that, in keeping with other research in this area, food waste increases according to the number of individuals in a household, and in particular the number of younger people. Also, while the majority of participants were at least “somewhat concerned” about their households’ environmental impact, over three quarters of participant households put food waste into their rubbish bin. Some solutions and directions to further progress research, policy, and practice in this area are offered, and include the need for more direct and personalised communication regarding waste minimisation, along with the provision of kerbside food waste collections. It is clear that individual- or household-level changes are important and must be supported systemically by both local body and state level legislation and initiatives, if there is to be any substantial decline in food waste going to landfill.     

Learning about knowledge management for improving environmental impact assessment in a government agency: the Western Australian experience

How does knowledge management (KM) by a government agency responsible for environmental impact assessment (EIA) potentially contribute to better environmental assessment and management practice? Staff members at government agencies in charge of the EIA process are knowledge workers who perform judgement-oriented tasks highly reliant on individual expertise, but also grounded on the agency’s knowledge accumulated over the years. Part of an agency’s knowledge can be codified and stored in an organizational memory, but is subject to decay or loss if not properly managed. The EIA agency operating in Western Australia was used as a case study. Its KM initiatives were reviewed, knowledge repositories were identified and staff surveyed to gauge the utilisation and effectiveness of such repositories in enabling them to perform EIA tasks.     

Legal and regulatory challenges in the implementation of CO2 geological storage: An Alberta and Canadian perspective

Alberta is the province with the largest CO₂ emissions in Canada, with approximately two-thirds of emissions originating from large stationary sources. Due to the fortuitous association of large CO₂ sources with the storage capacity offered by the underlying Alberta basin, it is expected that large-scale CO₂ geological storage in Canada will occur in Alberta first, and both levels of governments are contemplating measures to facilitate implementation. A review of the current provincial and federal legislation and regulations presented in this paper indicates that the existing legal and regulatory regime is reasonably sufficient, with some modifications, to accommodate the active injection phase of CO₂ capture and storage (CCS) operations, and the early takers of this new technology. However, governments in Alberta and Canada, and likely everywhere, need to address several pressing issues dealing mainly with the CCS post-operational phase. These issues, reviewed in this paper from an Alberta and Canadian perspective, fall into several categories: jurisdictional, property (ownership), regulatory and liability. Because Alberta is a landlocked province, matters relating to CO₂ storage under the seabed will not be addressed here except when discussing matters of jurisdiction and CO₂ classification. Possible models for post-injection liability transfer to the state are also presented. Although this review is focused on western Canada conditions, the issues are broad enough to be of interest in other jurisdictions, which may also adopt parts of the legal and regulatory framework that is quite well developed in Alberta.