Sam Holloway

CO2 storage capacity estimation : methodology and gaps

Abstract Implementation of CO2 capture and geological storage (CCGS) technology at the scale needed to achieve a significant and meaningful reduction in CO2 emissions requires knowledge of the available CO2 storage capacity. CO2 storage capacity assessments may be conducted at various scales—in decreasing order of size and increasing order of resolution: country, basin, regional, local and site-specific. Estimation of the CO2 storage capacity in depleted oil and gas reservoirs is straightforward and is based on recoverable reserves, reservoir properties and in situ CO2 characteristics. In the case of CO2-EOR, the CO2 storage capacity can be roughly evaluated on the basis of worldwide field experience or more accurately through numerical simulations. Determination of the theoretical CO2 storage capacity in coal beds is based on coal thickness and CO2 adsorption isotherms, and recovery and completion factors. Evaluation of the CO2 storage capacity in deep saline aquifers is very complex because four trapping mechanisms that act at different rates are involved and, at times, all mechanisms may be operating simultaneously. The level of detail and resolution required in the data make reliable and accurate estimation of CO2 storage capacity in deep saline aquifers practical only at the local and site-specific scales. This paper follows a previous one on issues and development of standards for CO2 storage capacity estimation, and provides a clear set of definitions and methodologies for the assessment of CO2 storage capacity in geological media. Notwithstanding the defined methodologies suggested for estimating CO2 storage capacity, major challenges lie ahead because of lack of data, particularly for coal beds and deep saline aquifers, lack of knowledge about the coefficients that reduce storage capacity from theoretical to effective and to practical, and lack of knowledge about the interplay between various trapping mechanisms at work in deep saline aquifers.

CO2 storage capacity estimation: Issues and development of standards

Associated with the endeavours of geoscientists to pursue the promise that geological storage of CO2 has of potentially making deep cuts into greenhouse gas emissions, Governments around the world are dependent on reliable estimates of CO2 storage capacity and insightful indications of the viability of geological storage in their respective jurisdictions. Similarly, industry needs reliable estimates for business decisions regarding site selection and development. If such estimates are unreliable, and decisions are made based on poor advice, then valuable resources and time could be wasted. Policies that have been put in place to address CO2 emissions could be jeopardised. Estimates need to clearly state the limitations that existed (data, time, knowledge) at the time of making the assessment and indicate the purpose and future use to which the estimates should be applied. A set of guidelines for estimation of storage capacity will greatly assist future deliberations by government and industry on the appropriateness of geological storage of CO2 in different geological settings and political jurisdictions. This work has been initiated under the auspices of the Carbon Sequestration Leadership Forum (www.cslforum.org), and it is intended that it will be an ongoing taskforce to further examine issues associated with storage capacity estimation.

An overview of the underground disposal of carbon dioxide

Abstract The underground disposal of industrial quantities of CO 2 is entirely feasible. Cost is the main barrier to implementation. The preferred concept is disposal into porous and permeable reservoirs capped by a low permeability seal, ideally, but not necessarily, at depths of around 800 metres or more, where the CO 2 will be in a dense phase. New concepts and refined reservoir models are continually emerging. As more regional estimates are carried out it appears that there will be ample underground storage capacity in the worlds sedimentary basins. Storage will be stable over geological timescales. The (remote) possibility of an escape of CO 2 from a storage reservoir onshore merits further investigation and modelling. It would be highly desirable to learn as much as possible from the operators of the new CO 2 disposal schemes arising from natural gas processing in offshore gas fields, as few such opportunities may arise.

Natural occurrences as analogues for the geological disposal of carbon dioxide

It is now generally accepted that anthropogenic CO2 emissions are contributing to the global rise in atmospheric CO2 concentrations. One possibility for reducing carbon dioxide emissions is to remove it from the flue gases of coal-fired power stations and dispose of it in underground geological reservoirs, possibly offshore in the North Sea. The feasibility of this option has been studied in detail by a consortium of European partners. As part of this study, natural occurrences of carbon dioxide were identified and preliminary information from these was obtained. The best characterised are found in the United States where the carbon dioxide reserves are exploited for use in tertiary enhanced oil recovery (EOR) programs in the Texas oilfields. The carbon dioxide reserves occur in geological structures and lithologies which are similar to those present in the North Sea. As such, these fields offer an ideal natural analogue for the disposal of carbon dioxide, since the interactions with groundwaters and reservoir lithologies have occurred on both spatial and temporal scales relevant to geological processes. Those carbon dioxide fields currently being exploited have already been studied to a limited extent by the oil companies involved. However, further study is required to provide information on the potential effects that disposing of large quantities of carbon dioxide might have on groundwaters and reservoir quality. In addition, more detailed information will be obtained on the interactions which occur during EOR using carbon dioxide. This paper presents data on some of the natural carbon dioxide fields, and compares the effects of these natural fluid-rock interactions with those observed in laboratory experiments performed to establish what reactions occur during the geological disposal of carbon dioxide.

The potential for aquifer disposal of carbon dioxide in the UK

Natural analogues indicate that it is possible to dispose of CO2 underground in closed structures on deep aquifers. Disposal into depleted or exhausted hydrocarbon fields has many advantages, e.g. proven seal, known storage capacity, no exploration costs. Unfortunately there are very few hydrocarbon fields in the UK onshore area, and their total CO2 storage capacity is very low compared to annual UK CO2 production from power generation. The best aquifers for CO2 disposal onshore are the widespread Permo-Triassic sandstones. Further onshore potential exists in younger Mesozoic reservoirs. Offshore, disposal into depleted oil fields (where cost credits from enhanced oil recovery could be beneficial) or the Perno-Triassic gas fields of the southern North Sea, and nearby associated closures of the Triassic Sherwood Sandstone aquifer, appear to provide the best prospects.

Carbon dioxide capture and geological storage

Carbon dioxide capture and geological storage is a technology that could be used to reduce carbon dioxide emissions to the atmosphere from large industrial installations such as fossil fuel-fired power stations by 80–90%. It involves the capture of carbon dioxide at a large industrial plant, its transport to a geological storage site and its long-term isolation in a geological storage reservoir. The technology has aroused considerable interest because it can help reduce emissions from fossil fuels which are likely to remain the dominant source of primary energy for decades to come. The main issues for the technology are cost and its implications for financing new or retrofitted plants, and the security of underground storage.

Safety of the underground disposal of carbon dioxide

The risks associated with the transport and injection of carbon dioxide are reasonably well understood and already borne in the USA. There is a remote possibility that CO 2 disposed of underground could leak from a storage reservoir, either through an unidentified migration pathway or as the result of a well failure. The kind of threat that this might represent may be judged by comparison with naturally occurring volcanic CO 2 emissions. Diffuse CO 2 emissions through the soil or via carbonated springs in volcanic areas do not appear to represent a threat as long as the CO 2 is able to disperse into the atmosphere. However, when CO 2 is able to build up in enclosed spaces it poses a definite threat. Large CO 2 clouds associated with sudden emissions from volcanic vents or craters also pose a lethal threat. However, there appears to be little analogy between such events and any possible leak from a storage reservoir via a natural unidentified migration pathway. Modelling of the development, migration and subsequent dispersal of any CO 2 cloud which might arise from a well failure is recommended.

Flow processes and pressure evolution in aquifers during the injection of supercritical CO2 as a greenhouse gas mitigation measure

ABSTRACT Regional saline aquifers offer the greatest potential for very large-scale underground CO2 storage as a means of mitigating greenhouse gas emissions. Their dynamic storage capacity, in terms of induced increases in formation pressure, will limit the rate at which CO2 can be injected and may ultimately limit the amount of CO2 that can be stored. Generic flow models were generated to examine the effects on pressure evolution of various reservoir parameters (dimensions, permeability, porosity, presence and nature of flow barriers). CO2 injection involves dominantly hydrogeological (single-phase flow) processes in much of the reservoir and surrounding adjacent strata, with additional two-phase flow effects around the CO2 plume itself. Large, thick aquifers with no significant flow barriers can accept high injection rates (c. 10 million tonnes of CO2 per year) without undue pressure effects. However, flow barriers, such as faults, increase induced pressures considerably; for reservoirs with such features, careful site characterization and operational planning will be required for large storage projects. The principles established from the generic modelling were applied to a real aquifer storage operation at Sleipner in the North Sea. Here, CO2 is being injected into the Utsira Sand, a large relatively homogeneous reservoir. Modelling indicates that pressure increase should be negligible. In fact, observed wellhead pressures do show a small rise, but this can be attributed to temperature changes in the fluid column in the wellbore. Pressure changes in the reservoir are likely to be very small.

An overview of the Joule II project ‘The underground disposal of carbon dioxide’

Technicoeconomical study of underground storage of carbon dioxide from fossil fuel-fired power plants for mitigating greenhouse gas emissions

Review of monitoring issues and technologies associated with the long-term underground storage of carbon dioxide

Abstract Large-scale underground storage of CO2 has the potential to play a key role in reducing global greenhouse gas emissions. Typical underground storage reservoirs would lie at depths of 1000 m or more and contain tens or even hundreds of millions of tonnes of CO2. A likely regulatory requirement is that storage sites would have to be monitored both to prove their efficacy in emissions reduction and to ensure site safety. A diverse portfolio of potential monitoring tools is available, some tried and tested in the oil industry, others as yet unproven. Shallow-focused techniques are likely to be deployed to demonstrate short-term site performance and, in the longer term, to ensure early warning of potential surface leakage. Deeper focused methods, notably time-lapse seismic, will be used to track CO2 migration in the subsurface, to assess reservoir performance and to calibrate/validate site performance simulation models. The duration of a monitoring programme is likely to be highly site specific, but conformance between predicted and observed site performance may form an acceptable basis for site closure.