Application of near critical behavior of equilibrium ratios to phase equilibrium calculations

International audienceWe examine the asymptotic behavior of the equilibrium ratios (Ki) near the convergence locus in the pressure-temperature plane. When the Equation of State (EoS) is analytical, which is the case of most EoS of engineering purpose, Ki tends towards unity or, equivalently, its logarithm lnKi tends to zero, according to a power ½ of the distance to this locus. As a consequence, if lnKi is expressed as a linear combination of pure component parameters with coefficients only depending on mixture phase properties (i.e., reduction parameters), these coefficients obey a similar power law. Deviations from the ½ power law are thus fairly limited for lnKi and for the reduction parameters (at least in the negative flash window between the convergence locus and the phase boundaries), which can be exploited to speed up flash calculations and for quickly determining approximate saturation points and convergence pressures and temperatures. The chosen examples are representative synthetic and natural hydrocarbon mixtures, as well as various injection gas-hydrocarbon systems

CO2 capture by hydrate formation in quiescent conditions: In search of efficient kinetic additives

International audienceAs a preliminary step to the development of a CO2 capture process under high pressure conditions, an experimental kinetic study of CO2 hydrate formation has been carried out in a high-pressure batch reactor, using as water-soluble additives a mixture of tetrahydrofuran (THF) and surfactant (sodium dodecyl sulfate, SDS). Used together and in suitable concentrations, these two additives were found to be very efficient for promoting CO2 capture

CO2 Injectivity in geological storages: an overview of program and results of the GeoCarbone-Injectivity Project

International audienceThe objective of the GeoCarbone-Injectivity project was to develop a methodology to study the complex phenomena involved in the near wellbore region during CO2 injection. This paper presents an overview of the program and results of the project, and some further necessary developments. The proposed methodology is based on experiments and simulations at the core scale, in order to understand (physical modelling and definition of constitutive laws) and quantify (calibration of simulation tools) the mechanisms involved in injectivity variations: fluid/rock interactions, transport mechanisms, geomechanical effects. These mechanisms and the associated parameters have then to be integrated in the models at the wellbore scale. The methodology has been applied for the study of a potential injection of CO2 in the Dogger geological formation of the Paris Basin, in collaboration with the other ANR GeoCarbone projects

Calculation of Joule-Thomson and isentropic expansion coefficients for two-phase mixtures

Joule–Thomson (JT) and isentropic expansion coefficients describe the temperature change induced by a pressure variation under isenthalpic and isentropic conditions, respectively. They are commonly used to model a variety of processes in which either fluid compression or expansion is involved. While a lot of work has been devoted to inferring the JT coefficient from an equation of state when the fluid is a single phase, little attention has been paid to multiphase fluids, where phase equilibrium has to be taken into account; previous work has only addressed the construction on the JT inversion curve. In the present paper, we describe and implement an approach to calculate these two coefficients for multi-component fluid systems, including when they form two different phases, liquid, and vapor, in thermodynamic equilibrium. The only ingredients are an equation of state and expressions for the ideal part of the specific heats of the fluid components. We make use of cubic equations of state, but any thermodynamic model can be used in the proposed framework. Calculations conducted with typical geofluids, some of them containing CO2, show that these coefficients are discontinuous at phase boundaries (where enthalpy and entropy variations exhibit angular points), as expected with any thermodynamic quantity built from first-order derivatives of state functions, and cannot be simply inferred from the coefficients of the liquid and vapor phases

Hydrate growth at the interface between water and CO2/CH4 gas mixtures: influence of pressure, temperature, gas composition and water soluble surfactants

Two major bottlenecks must be overcome when exploiting gas hydrate formation to capture CO2 from natural or flue gases: selectivity, i.e., the CO2 content of the enclathrated gas, which should be as high as possible, and kinetics, which is the focus of this paper. Anionic surfactants such as SDS (sodium dodecyl sulfate) are known to be much more efficient at speeding up gas hydrate formation in the case of methane-rich gases than in the case of CO2-rich gases. To assess the kinetic efficiency of a given surfactant additive, a simple experimental method has been devised, in which hydrate formation is triggered at the top of a sessile water drop by contact with the hydrate phase, and the ensuing hydrate growth is visualized. Depending on the surfactant and gas type, very different gas hydrate growth mechanisms are observed

CO2 enclathration in the presence of water-soluble hydrate promoters: Hydrate phase equilibria and kinetic studies in quiescent conditions

Clathrate hydrates have potential applications in various domains and particularly for CO2 capture where the search for additives able to speed up hydrate formation is of scientific, technological and economical interest. This study investigates the potentialities of two additives used in combination for enhancing CO2 enclathration rates: a surfactant (sodium dodecyl sulphate; SDS) and an organic compound (tetrahydrofuran; THF). Experiments performed in batch and in semi-continuous reactor configuration, reveal that this combination of additives efficiently promotes hydrate formation, allowing a full water-to-hydrate conversion despite the quiescent-forming conditions used. The possible action mechanisms of this combination of additives are analyzed and discussed on the basis of experimental data of hydrate phase equilibria (with and without additives), visual observations, and kinetics experiments

Hydrate growth at the interface between water and pure or mixed CO2/CH4 gases: Influence of pressure, temperature, gas composition and water-soluble surfactants

The morphology and growth of gas hydrate at the interface between an aqueous solution and gaseous mixtures of CO2 and CH4 are observed by means of a simple experimental procedure, in which hydrate formation is triggered at the top of a sessile water drop by contact with another piece of gas hydrate and the ensuing hydrate growth is video-monitored. The aqueous solution is either pure water or a solution of a nonionic or anionic surfactant at low concentration (in the 100–1000 ppmw range). In agreement with previously published data, hydrates formed from pure water and aqueous solutions of non-ionic surfactant grow rapidly as a low-permeable polycrystalline crust along the water/gas interface, which then inhibits further growth in a direction perpendicular to the interface. Lateral growth rates increase strongly with subcooling and CO2 content in the gas mixture. Similar lateral growth rates, but varying morphologies, are observed with the non-ionic surfactants tested. In contrast, the two anionic surfactants tested, sodium dodecyl sulfate (SDS) and dioctyl sodium sulfosuccinate (AOT), promote in the presence of CH4 (but not in the presence of CO2) a rapid and full conversion of the water drop into hydrate through a ‘capillary-driven’ growth process. Insights are given into this process, which is observed with AOT for an unprecedented low concentration of 100 ppmw

Carbon dioxide gas hydrate crystallization in porous silica gel particles partially saturated with a surfactant solution

This paper reports on investigations into the way carbon dioxide (CO2) hydrate forms in porous silica gel partially saturated with pure water or with a surfactant solution. The experiments, conducted at two different temperatures (278.2 and 279.2 K) and under a loading pressure of 3.8 MPa, used silica particles of different nominal pore diameters (30 and 100 nm), saturated at 80% pore volume with pure water or with a 100 ppm solution of either sodium dodecyl sulfate (SDS) or polyoxyethylenesorbitan monoleate (Tween-80). They were run following the “hydrate precursor method” developed in previous works (Duchateau et al., 2009, 2010) to form bulk hydrate under controlled subcooling conditions, and adapted for studying hydrate formation behavior in porous media. The work demonstrated that the successive hydrate formation and decomposition cycles involved in this method do not alter the pore size distribution in the porous media. At the two temperatures investigated, silica gel particles with a nominal pore diameter of 100 nm proved better suited to comparing the CO2-hydrate formation behaviors: higher water-to-hydrate conversions (>90 mol%) were effectively obtained for all the conditions tested making comparison of the results much easier. Of the two surfactants used, only SDS was found to produce a positive effect on both the hydrate formation kinetics and the amount of hydrate formed. Our visual observations of quiescent bulk systems (without porous silica gel) suggest that when SDS is present, CO2 hydrate forms not only at the w/g interface (where it occurs without SDS too), but also in the bulk water phase. This may explain the beneficial effect observed on the porous medium

METSTOR: a GIS to look for potential storage zones in France

International audienceCommunication : http://minh.haduong.com/files/Bonijoly.ea-2008-METSTOR-GHGT9.pdf - Actes : http://web.mit.edu/ghgt9

CO2 Removal from a CO2–CH4 Gas Mixture by Clathrate Hydrate Formation Using THF and SDS as Water-Soluble Hydrate Promoters

This study investigates the use of hydrate formation to separate the CO2 from a CO2–CH4 gas mixture in the presence of water-soluble additives—tetrahydrofuran (THF) and/or sodium dodecyl sulfate (SDS)—at low concentrations. The influence of additive concentration and process operating conditions on the gas enclathration kinetics, the quantity of gas removed, and the selectivity of the separation are studied under quiescent hydrate-forming conditions in a batch reactor. Gas consumption and enclathration occur at high rates only when the two additives are used in combination. Similarly to what has been observed with pure CO2, the proposed mechanism is that a mixed hydrate of structure sII containing THF forms first, which triggers the formation of CO2–CH4 binary gas hydrate of structure sI. However, the gas separation was found not to be selective enough to the CO2 for envisaging any practical application