CO 2 Storage in the Struggle against Climate Change

1 Institut français du pétrole, IFP, 1-4 avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex France 2 BRGM, 3 avenue Claude Guillemin, BP 36009, 45060 Orléans Cedex 2 France e-mail: etienne.brosse@ifp.fr h.fabriol@brgm.fr marc.fleury@ifp.fr s.grataloup@brgm.fr jean-marc.lombard@ifp.fr Oil & Gas Science and Technology – Rev. IFP, Vol. 65 (2010), No. 3, pp. 369-373 Copyright © 2010, Institut français du pétrole DOI: 10.2516/ogst/2010012


D o s s i e r THE CHALLENGE OF CO 2 GEOLOGICAL STORAGE
Over the last fifteen years the storage of carbon dioxide (CO 2 ) in deep geological formations has been considered with increasing attention as one of the major solutions to contribute to the struggle against anthropogenic climate change and ocean acidification.Predicting the part it could play during the 21st century is still a matter of discussion, and should remain so as it depends on many parameters which are poorly known.A stabilization target of concentration of greenhouse gases at 535-590 ppmv eq-CO 2 in the atmosphere (i.e., 440-485 ppmv CO 2 ), a value which represents approximately two times its pre-industrial concentration, should be compatible with a 2.8 to 3.2°C (best estimate) warmer climate on average (IPCC Gp.III, 2007).Compared to the trend that can be extrapolated from the world economy, a stabilization target at ca. 500 ppmv CO 2 would represent a mitigation effort of 600 to 700 Gt CO 2 to be achieved by 2050-2060 (Pacala and Socolow, 2004).If it were assumed that the contribution of geological storage reached 10% of this amount, that would represent the challenge of injecting 60 to 70 Gt CO 2 in appropriate sub-surface sites over 30 to 35 years, i.e., 2600 operations comparable in size to the demonstration project undertaken in 1996 at Sleipner -or 260 operations ten times larger (ca.250 Mt CO 2 ) already achieved by 2050.Some roadmaps are more intensive: for instance IEA (2009) discusses an objective of 19% for the CCS contribution to emissions reduction.Such figures show how high the stakes are for this technology.
Beyond the economic aspect of the question, which is of course vital -and not at present resolved -, an industrial perspective on this scale could materialize only if commitments are taken in many countries, not only by national institutions involved in R&D, and by private companies able to deploy the technical skill, but also and maybe more crucially by the regulating authorities at State level.The huge quantities cited above, and the need to minimize the distance between point sources of CO 2 and storage sites, give rise to an unprecedented interest for deep saline aquifers, present in most sedimentary basins.The degree of exploration of these formations, often linked to surveys undertaken by the oil industry, is extremely variable from one basin to another, and, inside a particular basin, from a given region to another.It will be frequent to address areas where the information is scarce or even non existent.It is also to be expected that prospecting efforts will concern a large variety of sedimentary basins: -basins characterized by simple tectonics and still actively subsiding, such as the North Sea or many Tertiary basins in Southeast Asia, where the chance to find excellent reservoir properties at the adequate burial depth, 1000 to 2000 m, is fair (e.g., the Utsira Sand in the North Sea); -intra-continental basins or marginal basins of older geological age, of more complex tectonics, where the longer and often poly-phased burial and diagenetic history determined an evolution of the reservoir properties which in most cases is detrimental; -basins located offshore, where organizing 3-D seismic surveys is relatively easy; -but also basins located onshore, with densely populated regions, or with protected perimeters, where such surveys could be impossible, with the consequence that monitoring the CO 2 plume migration with 4-D seismic will not be possible in some areas.-PICOREF, on geological investigation and site characterization; -Intégrité, on the continuity and sealing capacity of cap rocks; -Injectivité, on reservoir management close to injection area; -Monitoring, on the performance of monitoring techniques, and; -Carbonatation, on long-term geochemical effects, including biogeochemistry.
The five projects were coordinated under a unique label, Géocarbone, and as much as possible tried to focus their work on the geological features met in the region of the Paris Basin under consideration.
We are pleased to introduce here two successive issues of Oil & Gas Science and Technology -Revue de l'IFP, where a large part of the work achieved by the Géocarbone projects is presented.The reader who would like to complete his/her information is referred to a special issue of Chemical Geology edited by P. Benezeth, B. Menez and C. Noiriel (2009), where articles more specifically dealing with the Carbonatation project were published (Benezeth et al., 2009).
It is out of the scope of this brief introduction to present the concepts of CO 2 geological storage.Many R&D projects have been carried out in several countries, and a huge literature is now available.Several articles and publicly accessible reports can be considered as excellent scientific reviews covering most of the relevant topics: the Canadian IEA GHG Report "Weyburn CO 2 monitoring and storage project" by Whittaker et al. (2004), the "IPCC Special Report on Carbon Dioxide Capture and Storage" (IPCC, 2005, mainly Chapter 5), the European Report "Best practice for the storage of CO 2 in saline aquifers" by Chadwick et al. (2007), the Australian CO2CRC Report "Storage capacity estimation, site selection and characterisation for CO 2 storage projects" edited by Kaldi and Gibson-Poole (2008).The topics addressed in the Géocarbone projects covered most of the aspects considered as important to characterize a potential storage site and to predict the storage behaviour during injection and on the longer term after injection.
In the Paris Basin the deep saline aquifers able to offer large-scale perspectives for CO 2 storage are located in carbonate formations of the Middle Jurassic (the "Dogger"), and in sandstone formations of the Triassic.The Dogger is by far the best known reservoir because it has been the main target for both petroleum E&P and geothermal energy production (Fig. 1).This explains the considerable importance given to carbonate sediments by the Géocarbone projects.From an impressive database of almost 7000 core-sample analyses collected by the petroleum industry over 50 years, Delmas et al. (2010) show that the petrophysical properties of the Dogger are often quite deceiving, and depend on several features (sedimentary fabric, micro-fracturing, stylolitization) which are difficult to predict.The considerations reported above, on the expected quality of reservoirs in relatively old basins, full apply to these formations.At the site scale, understanding the permeability distribution will depend on additional characterization efforts that remain to be made, in particular to improve the connection between facies and diagenesis, and to take more well tests into account.Brosse et al. (2010) present a synthesis from Géocarbone-PICOREF, showing the main geological characteristics of the studied area at the basin scale.The scarcity of structural trapping is a prominent feature, that implies that CO 2 entrapment must be considered as a "hydrodynamic" process, as it is for instance in the Utsira Sand at Sleipner.The paper illustrates the type of data that can be available when exploring an area for site screening, the method followed to select a "sector" area, ca.60 × 60 km, from an initially much larger regional domain, and the building of numerical 3-D "earth models", needed by the simulation work typically required before an application for storage permit.
An overview of Géocarbone-Intégrité, dealing with the sealing efficiency of caprocks, is presented by Fleury et al. (2010).A wide variety of scales and physical mechanisms must be considered.At large scale, the seismic profiles from the Saint-Martin-de-Bossenay field area were reprocessed to focus on the caprock above the Dogger formation.These data as well as well logging data show that no major discontinuity is present and that the thickness of the sealing formation based on a clay content indicator is between 30 and 100 m.Laboratory experiments performed on different facies (dominated either by carbonate or by clays) show low reactivity to CO 2 .Similarly, Bemer and Lombard (2010) show that mechanical properties were not significantly modified after artificial and extreme porosity alteration of low permeability samples.Some general results were also obtained about the lack of modification by CO 2 of wettability, useful to determine capillary entry pressure in the laboratory using standard measurements.Carles et al. (2010) show the uncertainties associated with the different measurement methodologies concerning capillary entry pressure and permeability using samples from a tight interval of the Comblanchien formation (Dogger), dominated by mudstone facies.Berne et al. (2010) also measured by different methods the pore diffusivities applicable for CO 2 and ions.In the paper by Bildstein et al. (2010), numerical simulations are reported that predict the extent of CO 2 migration either by pure diffusion or by two phase flow in the case of capillary breakthrough.It is shown that the migration is limited vertically to less than 10 m of formation over very long periods of time.In addition, this migration produces mostly a decrease of porosity by precipitation, and, only very locally, an increase.
Finally, Rohmer and Seyedi (2010) show that shear fracture reactivation criteria are not reached even for relatively high overpressure due to injection.
The objective of Géocarbone-Injectivité was to develop a methodology to study the complex phenomena involved in the near wellbore region during CO 2 injection.The principles, the main results of the study and some further necessary developments are summarized in Lombard et al. (2010).This methodology is based on experiments and simulations at the core scale, in order to understand (using physical modelling and constitutive laws) and quantify (by the calibration of simulation tools) the mechanisms involved in injectivity variations: fluid/rock interaction, transport mechanisms, geomechanical effects.These mechanisms and the associated parameters have then to be integrated in the models at the wellbore scale.Concerning fluid/rock interaction, the dissolution and precipitation phenomena linked to the acidity of the brine/CO 2 solution have been outlined and different The part of the Paris Basin investigated by the Géocarbone projects is located in the southeast of Paris (orange perimeter).In this area, information on the subsurface is relatively abundant, because of past exploration efforts for petroleum (Dogger and Trias) and, in a circle of ca.50 km radius around Paris, for geothermal heat (Dogger).SMB: Saint-Martin-de-Bossenay -this oilfield structure could be studied because all the data were made available by the successive operators to the Géocarbone projects.
injection scenarios have been studied.Chalbaud et al. (2010) present an experimental study which allowed new brine/CO 2 interfacial tension (IFT) data, necessary for CO 2 storage issues to be acquired, and a correlation with thermodynamical conditions to be proposed.Observations at the pore and core scales have also shown the possible wetting behaviour of CO 2 and the authors propose a discussion of its influence on the storage capacity of the investigated formations.The evolution of transport properties generated by the pore structure alteration of the rock near the well was also studied within Géocarbone-Injectivité.In the study presented in Radilla et al. (2010), both native samples representative of the Dogger formation and samples altered uniformly by an acid solution were characterized.The acidity resulted in a slight increase of permeability and porosity and a decrease of inertial coefficients.Both relative permeabilities and Klinkenberg effects remained unchanged.When no particle displacement takes place, the injectivity of the studied rock was not altered by the acid solution.The poroelastic properties as well as the rupture criteria (induced fracturing) have been measured on native and altered Lavoux and Comblanchien carbonate samples: the already cited Bemer and Lombard's (2010) paper outlines a clear trend of chemically induced mechanical weakening.The experimental data have been compared to the predictions obtained from phenomenological and empirical models.These results are completed by Rimmelé et al. (2010), who measured the evolution of mineral composition and petrophysical properties displayed by Lavoux carbonates and Triassic Adamswiller sandstones during transformation in a closed system in presence of CO 2 (results obtained in the framework of Géocarbone-Carbonatation). Fabriol et al. (2010) give an overview of the results achieved in Géocarbone-Monitoring, and provide recommendations for site monitoring in the specific geological context of the Paris Basin -in particular, for storage hosted in the Dogger carbonates.Regarding monitoring, Becquey et al. (2010) simulated the application of 4-D seismics to the specific site of Saint-Martin-de-Bossenay, using existing logging data.First results indicate that injecting CO 2 will not be easily detectable and that acquisition of more data, particularly downhole seismics, will be necessary.As an alternative to active seismics, geophysical methods based on measuring changes in electrical resistivity could be an option.Bourgeois and Girard (2010) propose a new configuration called "LEMAM" (Long Electrode Mise à la Masse), where current is injected between two deep wells intersecting the reservoir.Their numerical simulations show that, under certain conditions, the CO 2 plume could induce modifications of the electrical potential at the surface, which are above the signal-to-noise ratio and thus measurable.Two papers deal with soil gas and fluids sampling at the surface.Battani et al. (2010) propose an analysis of natural CO 2 emissions at the Sainte-Marguerite site in the French Massif Central.They describe how to predict the origin, processes and evolution of a natural CO 2 leakage.Gal et al. (2010) developed the same techniques at the natural CO 2 reservoir of Montmiral in the French Pre-Alps.The major goals for geochemical study of both sites were to monitor natural concentrations of gas in the soil and to establish their temporal and spatial variability, which could serve as reference values for delivering CO 2 storage permits in similar geological settings.Finally, Pokryszka et al. (2010) present two kinds of tool which were developed in the framework of the project Géocarbone-Monitoring: one for early detection (pre-alert), using analysis of gas samples taken at the bottom of dedicated boreholes drilled from the surface into the intermediate caprock strata; the second to detect and quantify the gaseous flux of CO 2 from the ground to the atmosphere.

RESEARCH WORK AND FIELD PILOTS ARE NEEDED
This short overview of the contribution brought by the Géocarbone projects to a perspective of CO 2 geological storage in the Paris Basin illustrates the variety of topics involved, and their often complex interconnection.Industrial good practice already exists in many of the technical domains concerned, in particular petroleum E&P, natural gas storage, and exploitation of geothermal energy.But none requires so large a panel of skills.In addition, there are specific aspects in CO 2 geological storage which are still poorly covered by already existing industrial approaches, e.g., the need to produce predictive simulations of phenomena that result from coupled mechanisms operating at various space and time scales, including the long term (10 000 years), and that concern sub-surface environments which cannot be described without large uncertainty.
All the above considerations, expressed as a world-scale challenge or as specific difficulties to overcome when focusing on one particular basin (the Paris Basin), show that it would not be reasonable to contemplate any industrial deployment of CCS without a strong involvement of research work associated with pilot-scale operations.

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Figure 1 Nationale de la Recherche), and the activity was split into a set of five connected 3-year projects aimed at investigating a large spectrum of topics linked to CO 2 storage: