Surface gas measurements and related studies for the characterization and monitoring of geological CO2 storage sites; experiences at Weyburn and in Salah.

Preliminary baseline soil gas data collected in the summer and autumn of 2001 above the Phase 1A injection area of the EnCana Enhanced Oil Recovery project at the Weyburn oilfield in south Saskatchewan was presented at GHGT-6 in Kyoto. Data can now be presented for all three years of the study with conclusions, the predominant one being that the major controls on soil gas levels are seasonal and meteorological with no indications of leakage from depth. In the autumns of 2002 and 2003 further in situ monitoring of CO2, CO2 flux, O2, CH4, radon (222Rn) and thoron (220Rn) was carried out. Soil gas samples were also collected for laboratory analysis of helium, permanent gases, sulphur species and light hydrocarbons. All sampling was repeated over the same 360 point sampling grid and more detailed profiles for both follow-up years. Marked changes in CO2 levels (especially flux) for each of the three-year datasets indicate changes in surface conditions, rather than CO2 from a deeper source. The radon and thoron data was found to be similar for the three years but appears to vary in response to drift composition, and seasonal effects, rather than migration from a deep source. In 2003 further work was agreed in addition to the main grid and profile data. A control area was sampled for the same suite of gases, 10km to the northwest of the oil field. It included similar topography, land use and drift composition to the main sampling grid. There were 35 sample locations on a 7 x 5 point grid with 100m spacing and two additional sites. Early conclusions indicate that the soil gas results in the control area are very similar to those from the main grid, vindicating control site selection and further supporting a lack of deeply sourced CO2 over the injection area. Along with the control site, five zones of possible CO2 leakage were also surveyed and sampled. Two cross a river lineament that may be associated with deep faulting, two were abandoned oil well sites and one site overlays a deep salt dissolution feature. (Unfortunately CO2 flux and gamma measurements were not carried out at these sites.) A northeast/southwest trending lineament, just north of the main grid, was sampled along two profiles perpendicular to the feature, with an increased density of sampling over the feature. The feature generally followed an incised river valley and anomalous CO2 was only detected on the valley floor, where it would be expected as there was lush vegetation in this zone. There were no coincident anomalies for other gases. Soils around two abandoned wells were also sampled. A 16-site grid was surveyed around each well. One well had been completely abandoned and the other was suspended due to failed casing. Such boreholes represent possible points of weakness that may be routes for CO2 migration. The well with failed casing had weakly anomalous CO2 locally to the south, again unmatched for other gases. The fully abandoned well had background CO2 values. Two perpendicular profiles of 10 sites at 25m spacing were sampled for soil gas over the mapped centre of the dissolution feature. Background values were obtained. In 2003 two vertical profiles were performed both indicating an increase in CO2 to a depth maximum of 1.80m; this increase is matched by a corresponding decrease only in O2, indicating biological respiration. Radon concentration indicated no anomalies. Portable gamma spectrometric data was collected in 2003 over the west-centre area of the grid, the profiles and over the control grid. The composition of soils from both areas was found to be very similar.PublishedBerkeley, California4.5. Degassamento naturaleope

Continuous in situ measurements of volcanic gases with a diode-laser-based spectrometer: CO2 and H2O concentration and soil degassing at Vulcano (Aeolian islands: Italy)

We report on a continuous-measurement campaign carried out in Vulcano (Aeolian islands, Sicily), devoted to the simultaneous monitoring of CO2 and H2O concentrations. The measurements were performed with an absorption spectrometer based on a semiconductor laser source emitting around a 2-μm wavelength. The emitted radiation was selectively absorbed by two molecular ro-vibrational transitions specific of the investigated species. Data for CO2 and H2O concentrations, and CO2 soil diffusive flux using an accumulation chamber configuration, were collected at several interesting sampling points on the island (Porto Levante beach- PLB, Fossa Grande Crater – FOG- and Valley of Palizzi, PAL). CO2/H2O values, measured on the ground, are very similar (around 0.019 (± 0.006)) and comparable to the previous discrete detected values of 0.213 (Fumarole F5-La Fossa crater rim) and 0.012 (Fumarole VFS – Baia Levante beach) obtaid during the 1977–1993 heating phase of the crater fumaroles

Runoff control of soil degassing at an active volcano. The case of Piton de la Fournaise, Reunion Island

Airborne atmospheric and in-situ soil gas analyses demonstrate that distal gas leaks are non-existent at Piton de la Fournaise (PF) despite frequent eruptions. Airborne traverses made at a constant altitude indicated that no detectable large-scale CO2 degassing occurs from the volcano. In-situ soil gas traverses (CO2, He-4, Rn-222) across the active riftzones, the summit crater and the caldera rims, show both a lack of positive anomalies and evidence of strong depleted concentrations for He and CO2 with respect to air. Depletions in soil He is explained by intense rain water infiltration. A more unexpected result lies in the very low CO2 concentrations (down to 92 ppm) in bare soils in the summit region. Such a depletion was not previously reported and is attributed to considerable basalt weathering operating as the result of huge runoff. A model has enabled both the runoff and the CO2 consumption occurring within the basaltic layers to be calculated. Data obtained are consistent with values expected from large-scale erosion models and with the local calculated diffusive flux of CO2 in soils. The huge runoff, together with the basaltic lithology of the volcano, are found to be the main factor controlling the soil gas signatures at PF. (C) 2002 Elsevier Science B.V. All rights reserved

Runoff control of soil degassing at an active volcano. The case of Piton de la Fournaise, Reunion Island

peer reviewedaudience: researcherAirborne atmospheric and in-situ soil gas analyses demonstrate that distal gas leaks are non-existent at Piton de la Fournaise (PF) despite frequent eruptions. Airborne traverses made at a constant altitude indicated that no detectable large-scale CO2 degassing occurs from the volcano. In-situ soil gas traverses (CO2, He-4, Rn-222) across the active riftzones, the summit crater and the caldera rims, show both a lack of positive anomalies and evidence of strong depleted concentrations for He and CO2 with respect to air. Depletions in soil He is explained by intense rain water infiltration. A more unexpected result lies in the very low CO2 concentrations (down to 92 ppm) in bare soils in the summit region. Such a depletion was not previously reported and is attributed to considerable basalt weathering operating as the result of huge runoff. A model has enabled both the runoff and the CO2 consumption occurring within the basaltic layers to be calculated. Data obtained are consistent with values expected from large-scale erosion models and with the local calculated diffusive flux of CO2 in soils. The huge runoff, together with the basaltic lithology of the volcano, are found to be the main factor controlling the soil gas signatures at PF. (C) 2002 Elsevier Science B.V. All rights reserved

Soil gas emanations as precursory indicators of volcanic eruptions

International audienceField measurements conducted on several active volcanoes in Italy, the Lesser Antilles, and Indonesia demonstrate the common Occurrence of diffuse soil gas emanations from the volcanic piles, at distances from active craters or fumarolic zones. These emanations consist essentially of carbon dioxide and rare gases and their genetic link with crater fumaroles and/or magma degassing at depth can be verified both chemically and isotopically. We emphasize here the potential use of these fluids for continuous volcano monitoring and eruption forecasting

Structure and CO2 budget of Merapi volcano during inter-eruptive periods

Abstract Soil temperature and gas (CO2 concentration and flux) have been investigated at Merapi volcano (Indonesia) during two inter-eruptive periods (2002 and 2007). Precise imaging of the summit crater and the spatial pattern of diffuse degassing along a gas traverse on the southern slope are interpreted in terms of summit structure and major caldera organization. The summit area is characterized by decreasing CO2 concentrations with distance from the 1932 crater rim, down to atmospheric levels at the base of the terminal cone. Similar patterns are measured on any transect down the slopes of the cone. The spatial distribution of soil gas anomalies suggests that soil degassing is controlled by structures identified as concentric historical caldera rims (1932, 1872, and 1768), which have undergone severe hydrothermal self-sealing processes that dramatically lower the permeability and porosity of soils. Temperature and CO2 flux measurements in soils near the dome display heterogeneous distributions which are consistent with a fracture network identified by previous geophysical studies. These data support the idea that the summit is made of isolated and mobile blocks, whose boundaries are either sealed by depositional processes o

Installazione di una sonda tipo “barasol” a Dagala (Etna) per la misura continua del flusso di radon dal suolo (13 Ottobre 2006)

L’Unità Funzionale Vulcanologia e Geochimica della Sezione di Catania dell’INGV sta sviluppando una nuova tecnologia che permette il monitoraggio in continuo del Radon, un gas che cambia la sua concentrazione in dipendenza del flusso di gas dal suolo. Visto che il tasso di emissione di radon dal suolo è dipendente dalla dinamica sia del magma che delle faglie, si tratta di un parametro che ha una forte potenzialità per la sorveglianza dei vulcani. Per tale motivo l’INGV, nell’ambito della Convenzione 2004-2005 con il Dipartimento della Protezione Civile, ha finanziato un progetto mirato proprio allo sviluppo tecnologico e scientifico di questo tipo di ricerca (progetto V3_6/28 – Etna, coordinatori S. Gresta e P. Papale, resp. M. Neri), la cui prima fase è iniziata il 1° giugno 2005. Questa iniziale fase di lavoro si è concretizzata con l’installazione di una prima sonda tipo “barasol” per la misura continua dell’attività di radon nel suolo presso Torre del Filosofo. Una seconda sonda, acquistata con fondi della Sezione Roma 1 dell’INGV (resp. F. Quattrocchi), è stata installata nei pressi del piano di faglia della Pernicana (quota ~1500 m s.l.m.). Una terza sonda, acquistata con fondi della Sezione Catania dell’INGV, è stata installata nei pressi di Dagala. La presente nota descrive quest’ultima installazione.Istituto Nazionale di Geofisica e VulcanologiaUnpublishedope

Une méthode de modélisation hydrogéologique inverse appliquée à un problème d’ingénierie : l’abaissement du niveau d’un réservoir minier ennoyé dans le bassin ferrifère lorrain

Le bassin ferrifère lorrain est un système hydrodynamique et chimique complexe, formé par la superposition de deux grands aquifères en excellente relation hydraulique : un calcaire fracturé et localement karstique (nappe du Dogger), et un aquifère artificiel constitué de grands vides anastomosés (réservoir minier). Une nouvelle galerie de débordement en cours de création à l’exutoire du réservoir Sud sera achevée en 2003, dans le but d’abaisser de façon définitive le niveau du réservoir de 3,6 m. Cette opération permettra de supprimer les nuisances (inondations chroniques) dues à l’existence de fuites du réservoir vers la plaine alluviale constituant le soubassement de la ville de Moyeuvre-Grande. On présente dans cet article la méthode de modélisation mise en œuvre en 1999, dont l’objectif était de fournir les éléments chiffrés au dimensionnement du nouvel ouvrage. Les résultats de cette première modélisation sont validés par les résultats obtenus avec les nouvelles données acquises depuis lors : nouvel ajustement du modèle en 2001 avec deux années supplémentaires de données, et comparaison aux résultats de mesures obtenus lors de l’opération de pompage à gros débit en 2002. La méthode de modélisation globale inverse mise en œuvre pour résoudre ce problème pratique d’ingénierie civile s’est avérée efficace, économe en temps de calcul comme en temps de mise en œuvre, et bien adaptée au problème posé

Soil gas emanations as precursory indicators of volcanic eruptions

Field measurements conducted on several active volcanoes in Italy, the Lesser Antilles, and Indonesia demonstrate the common Occurrence of diffuse soil gas emanations from the volcanic piles, at distances from active craters or fumarolic zones. These emanations consist essentially of carbon dioxide and rare gases and their genetic link with crater fumaroles and/or magma degassing at depth can be verified both chemically and isotopically. We emphasize here the potential use of these fluids for continuous volcano monitoring and eruption forecasting