Gas migration along fault systems and through the vadose zone in the Latera caldera (central Italy): Implications for CO2 geological storage

A clear and detailed understanding of gas migration mechanisms from depth to ground surface is fundamental to choose the best locations for C02 geological storage sites, to engineer them so that they do not leak, and to select the most appropriate monitoring strategy and tools to guarantee public safety. Natural test sites (or "natural analogues") provide the best opportunity to study migration mechanisms, as they incorporate such issues as scale, long-time system evolution, and interacting variables that cannot be adequately addressed with laboratory studies or computer models. To this end the present work examines the migration to surface of deep, naturally produced C02 along various buried and exposed faults in the Latera caldera (central Italy) by integrating structural geology and near-surface gas geochemistry surveys. Results show how gas migration is channelled along discrete, high -permeability pathways within the faults, with release typically occurring from spatially restricted gas vents. Size, distribution, and strength of these vents appear to be controlled by the evolution and deformation style of the fault, which is in turn linked to the rheology of the lithological units cut by the fault. As such gas migration can change drastically along strike. Gas migration in the vadose zone around these vents is also discussed, focussing on how the physical-chemical characteristics of various species (C02, CH4, and He) control their spatial distribution and eventual release to the atmosphere. (c) 2008 Elsevier Ltd. All rights reserved

Preliminary results of geological characterization and geochemical monitoring of Sulcis Basin (Sardinia), as a potential CCS site

The Sulcis Basin is an area situated in SW Sardinia (Italy) and is a potential site for the development of CCS in Italy. This paper illustrates the preliminary results of geological characterization of fractured carbonate reservoir (Miliolitico Fm.) and the sealing sequence, composed by clay, marl and volcanic rocks, with a total thickness of more than 900 m. To characterize the reservoircaprock system an extensive structural-geological survey at the outcrop was conducted. It was also performed a study of the geochemical monitoring, to define the baseline conditions, measuring CO2 concentrations and flux in the study site

The mapping and quantification of CO2 leakage and its potential impact on groundwater quality

Il presente lavoro di ricerca è finalizzato allo studio del rilascio in atmosfera di CO2 proveniente da sorgenti sottosuperficiali profonde. Il lavoro riguarda lo sviluppo di un codice dedicato alla modellizzazione delle modalità e densità di campionamento nelle misure di flusso superficiale (utilizzando dati sintetici e reali), al fine di comprendere come tali parametri possano influenzare la capacità di identificare e quantificare il rilascio (leakage) di CO2. Inoltre, nel corso della ricerca, è stato anche valutato il potenziale impatto di tali “perdite” di CO2 sulla qualità delle acque, attraverso l’analisi dell’acqua di falda campionata lungo un transetto che attraversa uno dei maggiori punti di emanazione naturale di CO2 dell’area. I risultati di tale lavoro sono applicabili sia ai sistemi naturali di leakage di CO2 che a quelli antropici (stoccaggio geologico della CO2) dove potenzialmente potrebbe verificarsi una fuoriuscita di tale gas.The present study relates to CO2 leakage from the deep subsurface towards the atmosphere. Work involved writing a computer code to model surface flux measurement strategies and sampling densities (using synthetic and real data) to understand the influence that these parameters have on finding and quantifying leaks, as well as sampling groundwater along a transect through a major natural CO2 leakage area to examine the potential impact of a leak on groundwater quality. This work relates to both natural leaking systems as well as to man-made systems where leakage may hypothetically occur (such as carbon capture and storage, CCS, projects)

Carbon Dioxide and Radon Gas Hazard at the Alban Hill Area (Central Italy).

The sudden and catastrophic, or slow and continuous, release at surface of naturally occurring toxic gases like CO2, H2S and Rn poses a serious health risk to people living in geologically active regions. A detailed geochemical survey was carried out in an area of about 4 km2 in the Ciampino and Marino districts, whereby a total of 274 soil-gas samples were collected and analysed for more than 10 major and trace gas species. Data were then processed using both statistical and geostatistical methods, and the resulting maps were examined in order to highlight areas of elevated risk. General trends of elevated CO2 and Rn concentrations imply the presence of preferential pathways (i.e. faults and fractures) along which deep gases are able to migrate towards the surface. The CO2 and Rn anomalous trends often correspond to and are usually elongated parallel to the Apennine mountain range, the controlling structural feature in central Italy. Because of this fundamental anisotropy in the factors controlling the soil-gas distribution, it was found that a geostatistical approach using variogramanalysis allowed for a better interpretation of the data. With regard to the health risk to local inhabitants, it was found that although some high risk areas had been zoned as parkland, 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 more than 70% and radon values of more than 250 kBq m33. It is recommended that land-use planners incorporate soil-gas and/or gas flux measurements in environmental assessments in areas of possible risk (i.e. volcanic or structurally active areas)

Gas migration from two mine districts. The Tolfa (Lazio, Central Italy) and the Neves-Corvo (Baixo Alentejo, Portugal) case studies

Detailed soil gas surveys were conducted at twomine districts to understand gas migrationmechanisms fromdeposits buried at different depths. The Tolfa (Lazio, Central Italy) and Neves-Corvo (Baixo Alentejo, Portugal) mine districts have different characteristics: the former is relatively shallow (30–100 m) whereas the latter is at a depth of 400–500 m and covered by low-permeability metamorphic rocks. The studied gases included major (N2, O2, CO2) and trace (4He, 222Rn) gases, hydrocarbons (CH4, C2H6 and C3H8) and S compounds (H2S, COS, SO2). The measured concentrations (some examples of max values at Tolfa: Rn 233 Bq/L, CO2 9.5%, CH4 12.3 ppm, COS 3.7 ppm; and at Neves-Corvo: Rn 130 Bq/L, CO2 24.3%, CH4 0.1%) indicate 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 short-lived 222Rn in the soil pores. Considering the different depths of the two ore deposits, obtained results can be considered as features of near-field (Tolfa) and far-field (Neves- Corvo) gas migration

GPR investigations to evaluate the geometry of rock slides and buckling in a limestone formation in northern Italy

Ground Penetrating Radar (GPR) investigations were performed to assess the depth and geometry of rock slides and buckles affecting a dip slope of regularly stratified limestones interbedded with marly-clayey horizons in the south-eastern Alps. This method was chosen because the absence of high cuts in the rock mass and the presence of debris and loosened slabs on the slope did not allow the geometry of the sliding mass to be described solely by means of field mapping. The application of GPR was encouraged by the favourable conditions of the geological "environment". More than 23 medium-frequency GPR lines were performed over compressive and tensile structures as well as over undeformed limestone sequences. Digitally collected data were filtered and processed to enhance deeper reflections, as well as corrected to account for topographic irregularities. GPR was instrumental in assessing the depth of the deformational and failure structures (e.g., buckle folds and tension cracks) induced by the instability phenomena as well as in evaluating deformation continuity along the sliding mass. The GPR surveys confirmed that the layers are continuous over extensive areas (even at the maximum penetration depth of about 6 m) and that deformations involve layer packages which are at least 5 metres thick. The first result indicates the importance of accounting for the mechanical separation of layers when conducting stability analyses while the second points out the inadequacy of common limit-equilibrium/elastic instability analyses. In fact, this type of procedure envisages the instability of much thinner layer packages, thus suggesting that a more complex elasto-plastic deformation analysis of thicker layer packages is more suited to this kind of phenomenon