1,721,008 research outputs found
Study of the gas migration mechanism in the natural laboratories for the characterisation and monitoring of CO2 geological storage sites
No full textThe greenhouse gas effect and the global warning phenomenon are largely discussed by scientific community and government and, in the next years, a number of actions focused on the reduction of the greenhouse gases emissions have to be finalised. The reduction of greenhouse gas emissions can be achieved in several ways but probably, at the short/mid-term, the only way with an acceptable cost/benefit ratio is to avoid the CO2 emission from the fossil fuel power plant and, in parallel, strongly develop the renewable energies.
A really interesting option for the reduction of CO2 emissions is CCS (CO2 capture and storage). This technique consists of capturing CO2 from power and industrial activities and storing it in deep geological reservoirs having different geological traps. The potential effectiveness of CCS is the reduction of 15% of the emission by 2050.
A critical component of long term geological sequestration of anthropogenic CO2 will be our ability to adequately monitor a chosen site to ensure public and environmental safety. Near surface monitoring is particularly important, as it is possible to conduct sensitive and direct measurements at the boundary between the subsurface and the biosphere (i.e. surface water or atmosphere).
In this work different aspects of direct gas measurements for the control and monitoring of CO2 storage sites were undertaken. In particular: i. the study of some fault systems at the Latera caldera allowed a better understanding of the gas migration mechanisms; ii. soil gas surveys carried out at “Concessione mineraria Monte Sinni” and at Kaniow allowed baseline characterization and the test of this approach for the discontinuous post injection monitoring; iii. the design and development of an innovative and low cost monitoring system that can make possible the use of direct geochemical methods of measurement where the currently required costs make them unsuitable.
The obtained results seem to confirm the potent of the geochemical approach, both in terms of sensitivity and cost/benefit ratio. In fact the discontinuous monitoring applied at Kaniow defined micro-leaks close to the injection site and the monitoring system tested at Panarea Island successfully worked highlighting a good sensitivity and repeatability of the measures.
Finally, in the framework of the CCS activities, it is important to consider the importance of the “public acceptance” of this process. In this regards, although a number of well-tested (i.e. in the oil exploration), indirect geophysical monitoring techniques can be used, the monitoring of the storage site by direct geochemical measurements in the near-surface environment can provide a clearer observation phenomenon and can be easier understood and accepted by local stakeholders
Microscale gas leaks in different geological scenarios in central Italy: Implications for CO2 geological sequestration
No full textStudies into the migration of gas injected at shallow depths: implications for CO2 geological sequestration
No full textSome shallow gas-injection tests were carried out in different Italian geological scenarios. Tests sites are characterised by fractured volcano-sedimentary cover (Latera, Latium), fractured clay cover (Siena basin, Tuscany) and non-fractured clay cover (Dunarobba basin, Umbria). A gas mixture (helium, carbon dioxide and, in the Latera test, also argon) was injected about 20 m below the ground surface through an inclined borehole intercepting the fault plane, into the shallow aquifer. The gas-injection pressure was above hydrostatic plus capillary pressure, but below lithostatic pressure. Soil-gas, soil-exhalation flux and groundwater analyses were carried out to monitor gas breakthrough and behaviour. The experiment simulated gas rising naturally up a fault, where most of the geological boundary conditions were known. Results were different for the different gases, in terms of breakthrough time and location, depending upon the unique physical – chemical properties of each injected gas and the permeability of the sedimentary cover. The gas velocity and migration pattern (namely gas channelling along the fault) were consistent with theoretical models of gas migration. Gas–water partitioning and the evolution of soil gas and groundwater anomalies clearly reflected the conservative behaviour of He and the partial dissolution of CO2 into the aquifer. A general model of gas migration and behaviour is suggested which may have implications in the geological storage of CO2
The study of CO2 natural reservoirs to develop criteria for risk assessment and safety strategy.
No full textDue to the large volumes produced, carbon dioxide (CO2) is the main anthropogenic compound identified as affecting the stability of the Earth’s climate. The injection and storage of anthropogenic CO2 in deep geologic formations (i.e. saline aquifers, hydrocarbon reservoirs, and unmineable coal seams) is a feasible strategy for rapidly reducing CO2 emissions to the atmosphere. However, a lack of public support, due to concerns over risks, could potentially block the widespread implementation of this promising technology. Only by facing these legitimate concerns will we be able to assure the public that (i) the scientific knowledge exists to select the best and safest sites; (ii) the techniques and approaches exist to monitor the safety of these sites during operation and post-injection; and (iii) the technologies exist if it is necessary to remedy a leak. There is the potential to examine some of the many naturally occurring CO2 reservoirs that occur throughout the world, some of which have trapped gas over geologic time periods while others leak due to gas migration along faults and fracture networks. These natural reservoirs occur in volcanic, geothermal, and sedimentary basin settings, and the unique geological and structural characteristics of each site can give important information regarding CO2 migration mechanisms at the required timescales and within complex, heterogeneous geological settings. While well-sealed, natural CO2 reservoirs can help us to understand the processes that isolate CO2, and other gases in the subsurface, leaking sites can be used to study gas migration processes along unsealed fault and fracture zones. In this work we present results from gas migration studies conducted at sites which represent the two extremes of gas leakage found in nature. These two sites are used to highlight how faulting style and near surface geology/hydrogeology can influence the migration of deep origin gases towards the ground surface
A comparison of leaking and non-leaking CO2 reservoirs as natural analogues for geological CO2 sequestration (Sesta and Latera geothermal fields, central Italy),
No full textThe Latera and Sesta areas are two geothermal fields located in central Italy which both exhibit significant quantities of associated CO2 gas. The primary difference between these two sites, however, is that there is large scale leakage of CO2 to the atmosphere in the Latera area while the CO2 at Sesta was only discovered at depth during exploratory geothermal drilling. These sites were thus selected as natural analogues for the geological sequestration of CO2 and were studied with both geophysical and shallow geochemical techniques in order to better understand the differences between a leaking and a sealed CO2 reservoir. The Latera geothermal field is located within the extinct Latera caldera, a large, elliptical, NNE-SSW trending structure which has long been know for carbonate rich springs and CO2-rich gas vents at surface. Sesta, on the other hand, is located within a NNW-SSE trending graben having associated boundary faults and a thick Pliocene clay cover. The CO2 at both sites is believed to be the result of decarbonisation of carbonate minerals due to the local high heat flow. Work conducted on these sites included soil gas surveys to delineate zones of elevated CO2 leakage and gas flux measurements to quantify the amount of CO2 leaking to the atmosphere. In addition electrical tomography surveys were performed at the Latera site to delineate migration pathways (faults and fracture networks). Soil gas results from Latera show CO2 concentrations which range from normal values of 1% up to 95% in gas vents cores. Associated with the elevated CO2 values are anomalous concentrations of trace gases which are transported from depth within the carrier stream, including H2S, He, H2 and CH4. Gas flux measurements range from 3 x 10-7 to 7.7 x 10-5 m3 m-2 sec- 1, with measurements on one gas vent (70 m2) indicating a total mass flux of about 108 kg day-1. In sharp contrast Sesta data showed low CO2 soil gas concentrations, on the order of shallow biological production, and gas flux rates which were 3 orders of magnitude lower than those observed at Latera. Gas migration to surface at Latera thus appears to occur along sub-vertical collapse structures associated with caldera formation, whereas the thick clay sequences at Sesta appear to have prevented large-scale escape of deep gases along the local graben boundary faults. The authors gratefully acknowledge the support of the EC in partly funding this work (EC Nascent project)
The study of CO2 natural reservoirs to develop criteria for risk assessment and safety strategy
No full textGeostatistical Analysis of Soil Gas Data in a High Seismic Intermontane Basin: the Fucino Plain, Central Italy
No full textNumerous soil gas measurements of four gaseous species with very different geochemical behaviors were performed in the Fucino Basin, an area characterized by known and inferred structural discontinuities. A comprehensive statistical and geostatistical treatment of these data followed in order to provide insight into the spatial influence of tectonic discontinuities and geology on deep-seated gas migration toward the surface. The results yielded anomalies with different features, reflecting the different gas-bearing properties of the eastern seismogenic faults related to the 1915 earthquake (Mb = 7.0) and the hidden structural features occurring in the western side of the plain. In particular, this approach demonstrates that soil gas concentration (i.e., Rn and CO2) can identify the simpler normal faults of the eastern sector of the plain. In contrast, the more pervasive fracturing and faulting, as well as the occurrence of coarser deposits, on the western side of the area, make the location of faults less clear. The results show that gases migrate preferentially through zones of brittle deformation by advective processes, as suggested by the relatively high rate of migration needed to obtain anomalies of shortlived 222Rn in the soil pores. Furthermore, a geostatistical study of soil gas data was conducted to quantify the spatial domain of correlation and the gas-bearing properties of faults on the basis of shallow soil gas distribution (i.e., anisotropic behavior). The results provide a clear correlation between the shape and orientation of the anomalies and the different geometry of the faults recognized in the plain
Short and Long Term Gas Hazard: The Release of Toxic Gases in the Alban Hills Volcanic Area (Central Italy).
No full textIn the Alban Hills area, strong areally diffuse and localised spot degassing processes occur. The gas comprises a large proportion of CO2, with minor CH4, H2S and Rn. These advective features are generated by fluid leakage from buried reservoirs hosted in the structural highs of the Mesozoic carbonate basement. Gas migration towards the surface is controlled by fault and fracture systems bordering the structural highs of the carbonate formations (e.g. Ciampino high). Both the sudden and catastrophic, and slow and continuous gas release at surface, of naturally occurring toxic species (CO2, H2S and Rn) poses a serious health risk to people living in this geologically active area. This paper presents data obtained from soil gas and gas flux surveys, as well as gas isotopes analyses, which suggest the presence of a deep origin gas flux enriched in carbon dioxide and minor species (CH4 and H2S), as well as a channelled migration of geogas mixtures having a Rn component which is not produced in situ. In regards to the health risk to local inhabitants, it was found that some anomalous areas had been zoned as parkland while others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil gas CO2 concentrations of over 70% and a CO2 flux of about 0.7 kg m_ 2 day_ 1, as well as radon values of more than 250 kBq/m3. In addition, an indoor radon survey has been conducted in selected houses in the town of Cava dei Selci to search for a possible correlation between the local geology and the radon concentration in indoor air. Preliminary results indicate high indoor values at ground floor levels (up to 1000 Bq/m3) and very high values in the cellars (up to 250.000 Bq/m3). It is recommended that land-use planners incorporate soil gas and/or gas flux measurements in the environmental assessment of areas of possible risk (i.e. volcanic or structurally active areas)
Near Surface Gas Simulator (NSGS): A Visual Basic program to improve the design of near-surface gas geochemistry surveys above CO2 geological storage sites
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