Sequestration In Aquifers Research Articles

Using NMR displacement measurements to probe CO2 entrapment in porous media

Carbon dioxide sequestration in aquifers is seen as a potential climate change mitigation technique. One physical mechanism by which this could occur is capillary trapping of discrete pore-scale CO2 bubbles (referred to as ganglia) in the pore space. Nuclear magnetic resonance (NMR) techniques were used to quantify the spatial distribution and pore environment of such CO2 entrapment in a model porous medium (random glass bead packing). 3D images revealed a relatively macroscopically homogeneous CO2 entrapment, even though the image resolution is insufficient to resolve individual CO2 ganglia. Quantification of the pore environment of the CO2 ganglia was achieved using NMR displacement propagators (displacement probability distributions), acquired both before and after CO2 entrapment. Lattice Boltzmann (LB) simulations were used to facilitate interpretation of the propagator statistics by considering various pore environments in which CO2 could become trapped. Comparison with the experimental data suggests that CO2 is preferentially entrapped in comparatively larger pores. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Coal energy conversion with carbon sequestration via combustion in supercritical saline aquifer water

The standard idea for deep saline aquifer sequestration is to separate carbon dioxide from a process stream, compress it, and inject it underground. However, since carbon dioxide is less dense than water, even at the high pressures found in aquifers, it is buoyant and will move towards the surface unless trapped by an impermeable seal. Also, significant energy expenditure is required to separate and compress carbon dioxide, even though neat carbon dioxide is not a desired product. These issues may be addressed by combining the idea of fast dissolution at the surface with supercritical water oxidation (SCWO). By burning coal at high pressure in supercritical water drawn from an aquifer, and then sequestering the entire pre-equilibrated effluent, all carbon from the fuel is captured, as well as all non-mineral coal combustion products including sulfur and metals. A possible block diagram of an SCWO-based electric power plant is proposed, including processes to handle salts from the aquifer brine and minerals from coal. The plant is thermodynamically modeled, using an indirectly fired combined cycle to convert energy from hot combustion products to work. This model estimates the overall thermal efficiency that can be achieved, and reveals unanticipated interactions within the plant that have significant effects on efficiency. The assumptions and results of the model highlight design challenges for an actual system.

Diffusive and Convective Mechanisms during CO2 Sequestration in Aquifers

CO2 emissions originated from industrial sources can be captured, transported, and stored in depleted gas/oil fields and deep saline aquifers. The transport mechanisms, occurred during CO2 sequestration in deep saline aquifers, are examined in this study. After injecting CO2 until the tolerable pressure for the aquifer is reached, the wells are closed and CO2 is deposited as free gas and soluble gas in water under the sealing rock. During injection and waiting periods, the concentration profile of CO2 within the aquifer is formed by diffusion and convection mechanisms. The Rayleigh number and mixing zone length concepts are used for investigating the effect of reservoir properties, such as dispersivity, permeability, porosity, and others on the aforementioned mechanisms. The results of convective dominant mechanism in aquifers with 1 md and 10 md permeability values are so near in that diffusion-dominated system. After 10 md, the convection mechanism begins to dominate gradually and it becomes totally convection dominated for 50 md and higher permeability values. These results are also verified by the Rayleigh number and mixing zone lengths.

Coal energy conversion with carbon sequestration via combustion in supercritical saline aquifer water

Abstract The standard idea for deep saline aquifer sequestration is to separate carbon dioxide from a process stream, compress it, and inject it underground. However, since carbon dioxide is less dense than water, even at the high pressures found in aquifers, it is buoyant and will move towards the surface unless trapped by an impermeable seal. Also, significant energy expenditure is required to separate and compress carbon dioxide, even though neat carbon dioxide is not a desired product. These issues may be addressed by combining the idea of fast dissolution at the surface with supercritical water oxidation (SCWO). By burning coal at high pressure in supercritical water drawn from an aquifer, and then sequestering the entire pre-equilibrated effluent, all carbon from the fuel is captured, as well as all non-mineral coal combustion products including sulfur and metals. A possible block diagram of a SCWO-based electric power plant is proposed, including processes to handle salts from the aquifer brine and minerals from coal. An estimate of the overall thermal efficiency that can be achieved is given based on a thermodynamic model. The requirements of a real supercritical water combustor are discussed, and an experimental combustor is described.

Minimizing Risk of Gas Escape in Gas Storage

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 113509, "Minimizing Risk of Gas Escape in Gas Storage by In-Situ Measurement of Gas Threshold Pressure and Optimized- Completion Solutions," by L. Ostrowski, SPE, Baker Hughes, and B. Ulker, RWE Dea A.G., originally prepared for the 2008 SPE Europec/EAGE Conference and Exhibition, Rome, 9-12 June. The paper has not been peer reviewed. Underground gas-storage operations and carbon dioxide (CO2) sequestration in aquifers rely on proper wellbore construction and on the sealing function of the caprock. Potential leakage paths are by migration along the wellbore as a result of poor cementation and flow through the caprock. Capillary pressure data, which are critical for prediction of gas leakage through the caprock, are seldom available and yet are necessary. An in-situ method of determining gas-entry pressure was developed to help reduce uncertainties in gas-leakage predictions. Simulations were performed using this gas threshold entry pressure to investigate the gas leak-age amount through the caprock and along the wellbore for both natural-gas- and CO2-storage models. Introduction Capture and geologic storage of CO2 are being considered to reduce CO2 emissions. Managing geological storage requires an understanding of the processes and risks, including the likely time scales and flux rates involved. Key processes are the migration of CO2 after injection into deep geologic formations, stratigraphic trapping, dissolution, residual-gas trapping, mineralization, and potential leakage. The storage capacity of an underground CO2-storage project must be related not only to the amount of CO2 that can be stored but also to long-term storage effectiveness. Experience with underground natural-gas storage provides useful insight into the geologic storage of CO2. Both methane (CH4) and CO2 are less dense than the usual formation water and thus exhibit a tendency to migrate to the top of the storage formation. Potential leakage of CO2 and CH4 from the storage formation can occur through the caprock, along the wells, and through faults and fractures. In many instances, underground natural-gas- storage projects are operated at pressures exceeding the initial reservoir pressure. Overpressurization usually occurs at the early stages of storage and is essential for increasing storage capacity and gas deliverability. This overpressure can result in pushing water out of the caprock and causing gas to leak from the storage formation. In CO2-storage projects, less is known about the risks of leakage through the caprock because of lack of experience. It is essential to determine the gas-entry pressure into the caprock before proceeding with any gas-storage project.

Numerical simulation of density-driven natural convection in porous media with application for CO 2 injection projects

In this paper we investigate the mass transfer of CO 2 injected into a homogenous (sub)-surface porous formation saturated with a liquid. In almost all cases of practical interest CO 2 is present on top of the liquid. Therefore, we perform our analysis to a porous medium that is impermeable from sides and that is exposed to CO 2 at the top. For this configuration density-driven natural convection enhances the mass transfer rate of CO 2 into the initially stagnant liquid. The analysis is done numerically using mass and momentum conservation laws and diffusion of CO 2 into the liquid. The effects of aspect ratio and the Rayleigh number, which is dependent on the characteristics of the porous medium and fluid properties, are studied. This configuration leads to an unstable flow process. Numerical computations do not show natural convection effects for homogeneous initial conditions. Therefore a sinusoidal perturbation is added for the initial top boundary condition. It is found that the mass transfer increases and concentration front moves faster with increasing Rayleigh number. The results of this paper have implications in enhanced oil recovery and CO 2 sequestration in aquifers.

Sedimentary basins and greenhouse gases: a serendipitous association

There is a natural association of sedimentary basins and fossil fuels. Therefore, we should expect a relation between the sedimentary basin, the exploitation of its fossil fuels, and the resulting greenhouse gas emissions. Carbon dioxide is the dominant greenhouse gas resulting from the burning of fossil fuels, and it comprises more than half of all man-made greenhouse gas emissions. Among the methods proposed for the mitigation of greenhouse gas emissions, specifically carbon dioxide, is disposal into porous formations deep in sedimentary basins. This includes injection into hydrocarbon reservoirs to enhance oil and gas recovery and the long-term sequestration in aquifers. The methodology for proving the latter concept has been developed in the Alberta Basin, Canada. It is now being practiced in the North Sea and considered in Indonesia. A further development is the concept of injecting carbon dioxide, from the burning of fossil fuels, into coal-beds to remove methane. This would have the dual result of increasing the production of methane, a more environmentally friendly fossil fuel than coal or oil, and using waste carbon dioxide to a useful purpose. While burning the recovered methane will result in more carbon dioxide, clearly this additional carbon dioxide can either be used to recover more methane or be disposed of underground in suitable aquifers. There is, thus, a serendipitous association of sedimentary basins, their contained fossil fuels and the means of exploiting or disposing of the greenhouse gases produced from the fossil fuels. This paper expands on this theme, with special effort being made to explain the concepts for those who may not be familiar with the earth sciences.