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Conventional Carbon Capture and Storage (CCS) operations use the direct injection of CO2 in a gaseous phase from the surface as a carbon carrier. Due to CO2 properties under reservoir conditions with lower density and viscosity than in situ brine, CO2 flux is mainly gravity-dominated. CO2 moves toward the top and accumulates below the top seal, thus reinforcing the risk of possible leakage to the surface through unexpected hydraulic paths (e.g., reactivated faults, fractures, and abandoned wells) or in sites without an effective sealing caprock. Considering the risks, the potential benefits of the interplay between CO2 and an aqueous solution of formate ions (HCOO¯) were evaluated when combined to control CO2 gravity segregation in porous media. Three combined strategies were evaluated and compared with those where either pure CO2 or a formate solution was injected. The first strategy consisted of a pre-flush of formate solution followed by continuous CO2 injection, and it was not effective in controlling the vertical propagation of the CO2 plume. However, the injection of a formate solution slug in a continuous or alternated way, simultaneously with the CO2 continuous injection, was effective in slowing down the vertical migration of the CO2 plume and keeping it permanently stationary deeper than the surface depth. [ABSTRACT FROM AUTHOR]

Bioenergy with carbon capture and storage (BECCS) can sequester atmospheric CO2, while producing electricity. The CO2 avoidance cost (CAC) is used to calculate the marginal cost of avoided CO2 emissions for BECCS as compared to other established energy technologies. A comparative analysis using four different reference-case power plants for CAC calculations is performed here to evaluate the CO2 avoidance cost of BECCS implementation. Results from this work demonstrate that BECCS can generate electricity at costs competitive with other neutral emissions technologies, while simultaneously removing CO2 from the atmosphere. Approximately 73% of current coal power plants are approaching retirement by the year 2035 in the U.S. After considering CO2 sequestered from the atmosphere and coal power plant CO2 emissions displaced by BECCS, CO2 emissions can be reduced by 1.4 billion tonnes per year in the U.S. alone at a cost of $88 to $116 per tonne of CO2 removed from the atmosphere, for 10% to 90% of available biomass used, respectively. CAC calculations in this paper indicate that BECCS can help the U.S. and other countries transition to a decarbonized electricity grid, as simulations presented in this paper predict that BECCS power plants operate at lower CACs than coal plants with CCS. [ABSTRACT FROM AUTHOR]

Carbon Capture and Storage (CCS) is a very innovative and promising solution for greenhouse gases (GHG) reduction, i.e., capturing carbon dioxide (CO2) at its source and storing it indefinitely to avoid its release to the atmosphere. This paper investigates a set of key issues in the development of specific rules for the application of Life Cycle Assessment (LCA) to CCS. The following LCA-based information are addressed in this work: definition of service type, definition of functional unit, definition of system boundaries, choice of allocation rules, choice of selected Life Cycle Inventory (LCI) results or other selected parameters for description of environmental performance. From a communication perspective, the specific rules defined in this study have been developed coherently with the requirements of a type III environment label scheme, the International EPD® System, according to the ISO 14025 standard. [ABSTRACT FROM AUTHOR]

Geological carbon storage is an effective method capable of reducing carbon dioxide (CO2) emissions at significant scales. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected fluid. Nevertheless, CO2 leakage is a major concern. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow-paths for CO2 to the overburden. Assessment of time-varying leaky wells is a need. In this paper, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of CO2 leakage and corresponding pressure distribution within the storage site and the overburden. Current methods assume instantaneous leakage of CO2 occurring with injection, which is not realistic. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. Fluid and rock compressibilities are taken into consideration, which allow calculating the breakthrough time and the leakage rate of CO2 to the overburden accurately. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is then conducted to assess different CO2 leakage scenarios to the overburden. The developed semi-analytical solution provides a new simple and practical approach to assess the potential of CO2 leakage outside the storage site. This approach is an alternative to numerical methods when detailed simulations are not feasible. Furthermore, the proposed solution can also be used to verify numerical codes, which often exhibit numerical artifacts. [ABSTRACT FROM AUTHOR]

Natural gas is an indispensable resource not evenly distributed in the world. The gas supply chain is characterized by large imbalances between supply and demand, where the underground gas storage (UGS) application plays a key role for creating strategic reserves, taking advantage of geological structures. On the contrary, human activities will require clean energy with near-zero greenhouse gas emissions to be environmentally viable. A key element of this strategy is the carbon capture and storage (CCS) application useful for confining CO2 into the geosphere to reduce anthropogenic emissions. The development of appropriate injection methods and long-term monitoring systems for leak detection of the underground storage of natural gas and CO2 is important to prevent negative effects, such as ground deformations and micro seismic events. In this work, a variety of monitoring applications were gathered and critically analyzed for a total of 60 scientific contributions spanning the world. This bibliographic work shows an analytical and statistical overview of the most common use of UGS and CCS, representing the different goals of these two applications and analyzing the main monitoring techniques used in the gathered contributions. Currently, UGS monitoring requires further development, especially through multidisciplinary approaches useful for identifying possible effects on the surface and gas leaks at depth; meanwhile, CCS solutions are still at the experimental stage, also because of the high costs for large-scale applications that still need specific research. The state of the art of these two very different practices can improve the further development of new monitoring approaches or additional methods. [ABSTRACT FROM AUTHOR]