Frédérick Gal

The Forez graben, part of the French Hercynian Massif Central, is one of the Oligocene – Miocene graben surrounding the European Alpine belt. It’s contoured by hercynian metamorphic rocks, ranging from schists – micaschists units to gneisses, and by numerous granites (Monts du Forez and Monts du Lyonnais). This graben is filled by clastic rocks (clay, sandy clay and sandstone) and few carbonate beds. Internal geometry tends to deepening eastward, reaching at least 500m deep. Some volcanic rocks are also present within the basin. As for lots of tertiary european grabens, numerous mineral water springs occur in or near the basin’s limits. A majority is CO2-rich and bicarbonate- sodium- rich, whereas other present a thermal bearing. Seven of those springs (both thermal and non-thermal) were studied during two years (monthly step sampling), using stable isotope (O, H and C), radiogenic isotopes (3H and 14C) and ions contents.

ABSTRACT Soil gas and CO2 flux measurements were conducted above and in the vicinity of the Weyburn oil field during the period 2001–2005 and in 2011 to determine baseline values and distributions, and to monitor for surface leaks, above this well-established and intensely studied CO2-Enhanced Oil Recovery (CO2-EOR) project in southern Saskatchewan, Canada. Multiple sites were studied which had sample spacing that ranged from 25 to 200 m, including a 360 point regional grid above the CO2 injection field, a background site off the oil field, and a new site where a landowner claimed CO2 leakage on his property from the storage reservoir. Typically 400–500 points were sampled during each of the seven field campaigns and analysed for a wide range of components, thus yielding a large and varied database collected during different seasons and years. Results show no sign of leakage of the injected CO2. Spatial and seasonal trends and measured values from discrete sampling of soil gas CO2, O2 + Ar, N2, δ13C-CO2, He, Rn, and CH4, from continuous monitoring of soil gas CO2 and Rn, and from discrete sampling of CO2 flux can all be explained by the interplay between near-surface biochemical processes, seasonal environmental conditions, and soil properties. Other light hydrocarbon gases, like C2H4 and C2H6, were generally near or below the instrument detection limit. Lessons learned during the research are described to help improve future near-surface gas geochemistry surveys for site assessment, baseline definition, and leakage monitoring at active CCS sites.

The geochemical monitoring of the Rousse injection pilot, operated by TOTAL Exploration Pproduction France, is presented over a 5- years long time period. The monitoring consisted in the acquisition at regular frequency of soil gas concentrations and fluxes at selected sampling points, coupled with the study of the geochemical parameters evolution of a perched aquifer overlying the storage reservoir through a dedicated 85 m depth borehole. Baseline data were acquired between September 2008 and December 2009 then the monitoring shifted to the surveying of the pilot during the operating phase. This second phase ended in March 2013. Data acquired during these two phases are presented and discussed.

A new sampling system for collecting fluids (water and gas) is presented. It can be advantageously used in CCS applications in order to monitor fluid migration in the storage formation, or to detect small leakages of the storage brine into shallower aquifers. Applications of this sampling technique in different environments are presented.

We performed a gravity survey in the Mont-Blanc and Aiguilles Rouges ranges in order to improve the gravity data coverage of the Alpine crystalline external ranges, and to constrain the deep geometry of a crustal scale thrust. Preliminary results allow us to propose a geometry for the deep structure of the ranges, taking into account a major reverse fault that

Natural analogue sites where geologic CO2 is leaking to the surface provide excellent opportunities to test approaches suitable for monitoring for potential CO2 leakage at carbon capture and storage sites. We tested isotope monitoring approaches for CO2 detection in shallow aquifers and the overlying soil zone at a CO2 analogue site near Sainte-Marguerite in the Massif Central (France). The Sainte-Marguerite area is located in the southern part of the Limagne graben (French Massif Central). The basement, composed of highly fractured granite, outcrops toward the west of the study area, notably around the Saladis spring. An intercalated arkosic permeable interval between fractured granite and Oligocene marls and limestones acts as a stratiform drain for fluid migration while the overlying thick Oligocene interval is impermeable and acts as a seal. The Allier river bed is located near the contact between the basement and the sedimentary rocks. Deep CO2-ladden fluids migrate through the...

... de Lorraine, INPL, 2 avenue de la Forêt de Haye, BP 3, 54501 Vandoeuvre-lès-Nancy - France e-mail: f.gal@brgm.fr - k.lepierres@brgm.fr - m.brach@brgm.fr - g.braibant@brgm.fr - c.beny@brgm.fr - anne.battani@ifp.fr - eric.tocque@ifp.fr - yves.benoit@ifp.fr - elodie.jeandel@ ...

The Pechelbronn oilfield (Rhine Graben, France), where mining activity ended in the 1960s, has been used for waste disposal for twenty years. Since the wastes are varied, work is underway to identify the discharged materials and their derivatives, as well as to locate and quantify potential discharge sites. Two major goals were assigned to the present work. The first was to identify or refine the location of hidden structures that could facilitate gas emanation up to the surface, by studying soil gas concentrations (mainly (222)Rn, CO(2), CH(4) and helium) and carbon isotope ratios in the CO(2) phase. The second was devoted to examining, from a health and safety viewpoint, if the use of the oilfield as a waste disposal site might have led to enhanced or modified gas emanation throughout the area. It appeared that CO(2) and (222)Rn evolution in the whole area were similar, except near some of the faults and fractures that are known through surface mapping and underground observations. These (222)Rn and CO(2) anomalies made it possible to highlight more emissive zones that are either related to main faults or to secondary fractures acting as migration pathways. In that sense, the CO(2) phase can be used to evaluate (222)Rn activities distant from tectonic structures but can lead to erroneous evaluations near to gas migration pathways. Dumping of wastes, as well as oil residues, did not appear to have a strong influence on soil gaseous species and emanation. Similarly, enhanced gas migration due to underground galleries and exploitation wells has not been established. Carbon isotope ratios suggested a balance of biological phenomena, despite the high CO(2) contents reached. Other monitored gaseous species (N(2), Ar, H(2) and alkanes), when detected, always showed amounts close to those found subsurface and/or in atmospheric gases.

ABSTRACT Natural analogue studies have received much interest over past years through the CO2 capture and storage applications. In this paper we focus on one natural analogue in leakage situation in order to describe the nature of the gas leakage, its interaction with surrounding rocks and aquifers and its behaviour over time. Soil gas and water monitoring techniques are used to gather point and continuous records. Leakage occurs along discrete sections relying on the nature of surface formations and the permeability of discontinuities. Main gas vents are perennial, relative proportions of different gas phases (CO2, 222Rn and 4He) being dependent from the interaction with surface deposits and the distance to main tectonic pathways.Mineral waters were also monitored as they represent integrative bodies that exist above nearly all CCS sites. Constraints on chemical processes occurring at depth are brought by the characterisation of the dissolved constituents and by related isotopic systematics. Such determination of mixing processes and their influence is important, as leakage from CCS site may be evidenced through the mixing of the water from the storage complex and overlying aquifers. Longer term monitoring was conducted for physico-chemical parameters highlighting noticeable variations for pH, dissolved oxygen, redox potential and dissolved CO2.