Modeling composition of Ca-Fe-Mg carbonates in a natural CO2 reservoir

Understanding the physical-chemical features of liquid, gas and solid phases in natural analogue reservoirs of Carbon Capture and Sequestration (CCS) site is fundamental as they can provide key data for building up both conceptual and numerical modeling of reaction path for gas-water-rock interaction in high pCO2 systems. The aim of this work is improve the knowledge about these processes, by employing appropriate methods for compositional data on a case study, focusing on the solid (minerals) phases. In the early eighties, the PSS1 well (Eastern Tuscany, Central Italy), drilled down to almost 5,000 m for oil exploration by ENI (Italian National Agency of Hydrocarbons), intercepted a high pressure (≈700 bar) CO2 reservoir at the temperature of 120 °C. The reservoir rocks in the fertile horizon, located at about 3,800 m, consist of altered volcanic deposits interbedded with gypsumdolomite- bearing evaporites (“Burano Formation”). Surveys for determining the actual paragenesis of volcanic rocks, carried out on the drill core samples, corresponded to the top of CO2 reservoir (3,864-3,871 m depths from surface on the PSS1 bore-well log). Quartz, Ca-Fe-Mg carbonates, clay minerals (illite and chlorite series) and Fe-Ti oxides were found as principal mineralogical phases. Electron Microprobe Analysis on the carbonates has allowed to recognize the presence of ankerite and calcites. Compositional data, related to atomic % content of Ca, Fe, and Mg in carbonates minerals, were transformed by using Isometric Log-Ratio balances, whilst the variability affecting the data pattern was investigated in simple binary diagrams. The stoichiometric substitution processes governing the presence of Ca, Fe and Mg in carbonates were modeled by using regression techniques in the new space defined by ilrs coordinates. Results have evidenced the different role of Fe and Mg in substituting or not Ca in both carbonate minerals of these CO2-bearing reservoir rocks

An approach to the geochemical modelling of water-rock interaction in CO2 storage geological reservoirs: the Weyburn Project (Canada) case study

Geological storage is one of the most promising technologies for reducing anthropogenic atmospheric emissions of CO2. Among the several CO2 storage techniques, sequestration in deep-seated saline aquifers implies four processes: a) supercritical fluid into geologic structure (physical trapping), b) dissolved CO2(aq) due to very long flow path (hydrodynamic trapping), c) dissolved CO2(aq) (solubility trapping), and d) secondary carbonates (mineral trapping). The appealing concept that CO2 can permanently be retained underground has prompted several experimental studies in Europe and North America sponsored by IEA GHG R&D, EU and numerous international industrials and governments, the most important project being the International Energy Agency Weyburn CO2 Monitoring & Storage, an EnCana’s CO2 injection EOR project at Weyburn (Saskatchewan, Canada). Owing to the possible risks associated to this technique, numerical modelling procedures of geochemical processes are necessary to investigate the short- to long-term consequences of CO2 storage. Assumptions and gap-acceptance are made to reconstruct the reservoir conditions (pressure, pH, chemistry, and mineral assemblage), although most strategic geochemical parameters of deep fluids are computed by a posteriori procedure due to the sampling collection at the wellhead, i.e. using depressurised aliquots. In this work a new approach to geochemical model capable of to reconstruct the reservoir chemical composition (T, P, boundary conditions and pH) is proposed using surface analytical data to simulate the short-medium term reservoir evolution during and after the CO2 injection. The PRHEEQC (V2.11) Software Package via thermodynamic corrections to the code default database has been used to obtain a more realistic modelling. The main modifications brought about the Software Package are: i) addition of new solid phases, ii) use of P>0.1 Mpa, iii) variation of the CO2 supercritical fugacity and solubility under reservoir conditions, iv) addition of kinetic rate equations of several minerals and v) calculation of reaction surface area. The Weyburn Project was selected as case study to test our model. The Weyburn oil-pull is recovered from the Midale Beds (1300-1500 m deep) that consist of two units of Mississippian shallow marine carbonate-evaporites: i) the dolomitic “Marly” and ii) the underlying calcitic “Vuggy”, sealed by an anhydrite cap-rock. About 3 billions mc of supercritical CO2 have been injected into the “Phase A1” injection area. The INGV and the University of Calgary (Canada), have carried out a geochemical monitoring program (ca. thrice yearly- from pre-injection trip: “Baseline” trip, August 2000, to September 2004). The merged experimental data are the base of the present geochemical modeling. On the basis of the available data, i.e. a) bulk mineralogy of the Marly and Vuggy reservoirs; b) mean gas-cap composition at the wellheads and c) selected pre- and post-CO2 injection water samples, the in-situ (62 °C and 0.1 MPa) reservoir chemical composition (including pH and the boundary conditions as PCO2, PH2S) has been re-built by the chemical equilibrium among the various phases, minimizing the effects of the past 30-years of water flooding in the oil field. The kinetic evolution of the CO2-rich Weyburn brines interacting with the host-rock minerals performed over 100 years after injection have also been computed. The reaction path modeling suggests that CO2 can mainly be neutralized by solubility and mineral trapping via Dawsonite precipitation. To validate our model the geochemical impact of three years of CO2 injection (September 2000-2003) has been simulated by kinetically controlled reactions. The calculated chemical composition after the CO2 injection is consistent with the analytical data of samples collected in 2003 with a <5 % error for most analytical species, with the exception of Ca and Mg (error >90%), likely due to the complexation effect of carboxilic acid

BARRIER EFFECT IN CO2 CAPTURE AND STORAGE FEASIBILITY STUDY

CO2 Capture & Storage (CCS) in saline aquifer is one of the most promising technologies for reducing anthropogenic emission of CO2. Feasibility studies for CO2 geo-sequestration in Italy have increased in the last few years. Before planning a CCS plant an appropriate precision and accuracy in the prediction of the reservoir evolution during injection, in terms of both geochemical calculation and fluid flow properties, is demanded. In this work a geochemical model will be presented for an offshore well in the Tyrrhenian Sea where the injection of 1.5 million ton/year of CO2 is planned. The dimension of the trapping structure requires to study an area of about 100 km2 and 4 km deep. Consequently, three different simulations were performed by means of TOUGHREACT code with Equation Of State module ECO2N. The first simulation is a stratigraphic column with a size of 110*110*4,000 meters and a metric resolution in the injection/cap-rock area (total of 8,470 elements), performed in order to asses the geochemical evolution of the cap-rock and to ensure the sealing of the system. The second simulation is at large scale in order to assess the CO2 path from the injection towards the spill point (total of about 154,000 elements). During this simulation, the effect of the full coupling of chemistry with fluid flow and a relevant effect in the expected CO2 diffusion velocity was recognized. Owing to the effect of chemical reaction and coupling terms (porosity/permeability variation with mineral dissolution/precipitation), the diffusion velocity results to be 20% slower than in a pure fluid flow simulation. In order to give a better picture of this 'barrier' effect, where the diffusion of the CO2-rich acidic water into the carbonate reservoir originates a complex precipitation/dissolution area, a small volume simulation with a 0.1 m grid was elapsed. This effect may potentially i) have a big impact on CO2 sequestration due to the reduction of available storage volume reached by the CO2 plume in 20 years and/or the enhanced injection pressure and ii) outline the relevance of a full geochemical simulation in an accurate prediction of the reservoir properties

Mineralogy and geochemical trapping of CO2 in an Italian carbonatic deep saline aquifer: preliminary results

CO2 Capture & Storage (CCS) is presently one of the most promising technologies for reducing anthropogenic emissions of CO2 . Among the several potential geologi- cal CO2 storage sites, e.g. depleted oil and gas field, unexploitable coal beds, saline aquifers, the latter are estimated to have the highest potential capacity (350-1000 Gt CO2 ) and, being relatively common worldwide, a higher probability to be located close to major CO2 anthropogenic sources. In these sites CO2 can safely be retained at depth for long times, as follows: a) physical trapping into geologic structures; b) hy- drodynamic trapping where CO2(aq) slowly migrates in an aquifer, c) solubility trap- ping after the dissolution of CO2(aq) and d) mineral trapping as secondary carbon- ates precipitate. Despite the potential advantages of CO2 geo-sequestration, risks of CO2 leakage from the reservoir have to be carefully evaluated by both monitoring techniques and numerical modeling used in “CO2 analogues”, although seepage from saline aquifers is unlikely to be occurring. The fate of CO2 once injected into a saline aquifer can be predicted by means of numerical modelling procedures of geochemical processes, these theoretical calculations being one of the few approaches for inves- tigating the short-long-term consequences of CO2 storage. This study is focused on some Italian deep-seated (>800 m) saline aquifers by assessing solubility and min- eral trapping potentiality as strategic need for some feasibility studies that are about to be started in Italy. Preliminary results obtained by numerical simulations of a geo- chemical modeling applied to an off-shore Italian carbonatic saline aquifer potential suitable to geological CO2 storage are here presented and discussed. Deep well data, still covered by industrial confidentiality, show that the saline aquifer, includes six Late Triassic-Early Jurassic carbonatic formations at the depth of 2500-3700 m b.s.l. These formations, belonging to Tuscan Nappe, consist of porous limestones (mainly calcite) and marly limestones sealed, on the top, by an effective and thick cap-rock (around 2500 m) of clay flysch belonging to the Liguride Units. The evaluation of the potential geochemical impact of CO2 storage and the quantification of water-gas-rock reactions (solubility and mineral trapping) of injection reservoir have been performed by the PRHEEQC (V2.11) Software Package via corrections to the code default ther- modynamic database to obtain a more realistic modelling. The main modifications to the Software Package are, as follows: i) addition of new solid phases, ii) variation of the CO2 supercritical fugacity and solubility under reservoir conditions, iii) addi- tion of kinetic rate equations of several minerals and iv) calculation of reaction sur- face area. Available site-specific data include only basic physical parameters such as temperature, pressure, and salinity of the formation waters. Rocks sampling of each considered formation in the contiguous in-shore zones was carried out. Mineralogy was determined by X-Ray diffraction analysis and Scanning Electronic Microscopy on thin sections. As chemical composition of the aquifer pore water is unknown, this has been inferred by batch modeling assuming thermodynamic equilibrium between minerals and a NaCl equivalent brine at reservoir conditions (up to 135 ̊C and 251 atm). Kinetic modelling was carried out for isothermal conditions (135 ̊C), under a CO2 injection constant pressure of 251 atm, between: a) bulk mineralogy of the six formations constituting the aquifer, and b) pre-CO2 injection water. The kinetic evolu- tion of the CO2 -rich brines interacting with the host-rock minerals performed over 100 years after injection suggests that solubility trapping is prevailing in this early stage of CO2 injection. Further and detailed multidisciplinary studies on rock properties, geochemical and micro seismic monitoring and 3D reservoir simulation are necessary to better characterize the potential storage site and asses the CO2 storage capacity

Permeability and hydraulic condictivity of faulted micashist in the Eastern Elba Island exhumed geothermal system (Tyrrhenian sea, Italy): insights from Cala Stagnone

Estimating values of permeability (k), ef cient porosity (P) and hydraulic conductivity (K) by analysing eld outcrops as analogue of geothermal reservoirs, is a timely theme useful for predictions during geothermal ex- ploration programs. In this paper we present a methodology providing k, P and K values, based on geomet- ric analysis of quartz-tourmaline faults-vein arrays hosted in micaschist exposed in south-eastern Elba Island (Tuscan Archipelago, Italy), considered as the analogue of rock hosting the so-called “deep reservoir” in the Larderello geothermal eld. The methodology is based on the integration among structural geology, uid inclu- sions results and numerical analyses. Through a detailed structural mapping, scan-lines and scan-boxes analy- ses, we have reconstructed three superposed faulting events, developed in an extensional setting and framed in the Neogene evolution of inner Northern Apennines. Geometrical data of the fault-veins array were processed by reviewing the basic parallel-plate-model-equation for k evaluation. Fluid inclusion analyses provided those salinity and pressure-temperature values necessary for de ning density and viscosity of the parent geothermal uids. Then, permeability, density and viscosity were joined to get hydraulic conductivity (K). Permeability is estimated between 5 × 10− 13 and 5 × 10− 17 m2 with variations among the different generation of faults, while the hydraulic conductivity is encompassed between 1.31 × 10− 8 and 2.4 × 10− 13 m/s. The obtained permeabil- ity and hydraulic conductivity values are comparable with those from several geothermal areas, and in particular from the Larderello geothermal eld. The main conclusion is that the proposed integrated approach provides a reliable methodology to obtain crucial values, normally obtained after drilling, for developing numerical ow models of geothermal uid path in active geothermal systems by eld and laboratory analyses of analogue, ex- humed, geothermal systems

Overview of the geochemical modeling on CO2 capture & storage in Italian feasibility studies

CO2 Capture & Storage in saline aquifers is presently one of the most promising technologies for reducing anthropogenic emissions of CO2. In these sites the short-longterm consequences of CO2 storage into a deep reservoir can be predicted by numerical modelling of geochemical processes. Unfortunately a common problem working with off-shore closed wells, where only the well-log information are available, is to obtain physico-chemical data (e.g. petrophysical and mineralogical) needed to reliable numerical simulations. Available site-specific data generally include only basic physical parameters such as temperature, pressure, and salinity of the formation waters. In this study we present a methodological procedure that allows to estimate and integrate lacking information to geochemical modelling of deep reservoirs such as: i) bulk and modal mineralogical composition, ii) porosity and permeability of the rock obtained from heat flow measurements and temperature, iii) chemical composition of formation waters (at reservoir conditions) prior of CO2 injection starting from sampling of analogue outcropping rock formations. The data sets in this way reconstructed constitute the base of geochemical simulations applied on some deep-seated Italian carbonatic and sandy saline aquifers potentially suitable for geological CO2 storage. Numerical simulations of reactive transport has been performed by using the reactive transport code TOUGHREACT via pressure corrections to the default thermodynamic database to obtain a more realistic modelling. Preliminary results of geochemical trapping (solubility and mineral trapping) potentiality and cap-rock stability as strategic need for some feasibility studies near to be started in Italy are here presented and discussed

Modellizzazione delle variazioni composizionali delle specie dell’azoto (NH4 +, NO2 -, NO3 -) nelle acque di falda del Comune di Arezzo (Toscana)♦

Gli elementi chimici disciolti nelle acque continentali provengono dall’alterazione della crosta terrestre. L’acqua erode e dissolve i minerali delle rocce attraverso l’alterazione chimica avvalendosi del contributo dei gas presenti in atmosfera o nel sottosuolo. Il nitrato, una delle sostanze responsabili delle più gravi forme di inquinamento delle acque nei paesi in via di sviluppo, è un nutriente essenziale per la crescita delle piante e rappresenta un anello fondamentale del ciclo biogeochimico dell'azoto, in quanto viene prodotto dai batteri a partire dall'azoto atmosferico. In quantità eccessive il nitrato può essere dannoso per gli uomini e per gli animali. Elevati livelli di nitrato nell'acqua sono causati in larga misura dall'uso di fertilizzanti ricchi di nitrato e dal letame. In questo contesto, le condizioni redox delle acque naturali, che controllano la speciazione dei composti dell’azoto, sono altamente variabili perché controllate prevalentemente dall’attività biologica. In particolare, il bilancio fra i due processi dell’attività biologica, la fotosintesi e la respirazione (o decomposizione della sostanza organica), determina la presenza nel sistema di condizioni ossidanti o riducenti. I composti dell’azoto possono quindi essere considerati utili indicatori dello stato di salute di un acquifero superficiale. In questo lavoro sono analizzati i dati relativi ai tenori delle specie dell’azoto NH4 +, NO2 - e NO3 - relativi ad acque di falda campionate nell’area aretina nel corso della realizzazione dell’Atlante Geochimico delle Acque di Falda e di Scorrimento Superficiale del Comune di Arezzo. I dati sono analizzati proponendo nuove metodologie grafiche e numeriche per visualizzare lo stato del territorio nei confronti della pressione antropica come rilevata dal comportamento spaziale e temporale delle specie suddette

Computational Speciation Models: A Tool for the Interpretation of Spectroelectrochemistry for Catalytic Layers under Operative Conditions

none7In this study,the first coupled FEXRAV and chemical speciation modelling study of the Pd deactivation is presented. Due to the high brilliance of synchrotron light, FEXRAV can investigat edeeply buried surfaces. More specifically, we directly analyzed the evolution of the Pd/C catalytic layer during a voltammetric cycle, through a specifically designed electrochemical cell. Still, we observed a complex interfacial chemistry of Pd, which impairs a straightforward interpretation of FEXRAV data. Exploiting thermodynamic chemical speciation modelling we were able to overcome this issue. The study leads to three main results: 1) the confirmation of the relationship between the change of the Pd/Pd(II) ratio and the change of the Fluorescence intensity 2) the investigation of the deactivation mechanism 3)the identification of the relevant species leading to the electrodissolution of Pd under operative conditions. This study opens new perspectives for the application of the chemical speciation modelling to the study of the deactivation mechanism of Pd in Pd/C catalytic layers under operative conditions in different electrolytes.mixedMontegrossi, G.; GIACCHERINI, ANDREA; BERRETTI, ENRICO; DI BENEDETTO, FRANCESCO; INNOCENTI, MASSIMO; D'Acapito, F.; LAVACCHI, ALESSANDROMontegrossi, G.; Giaccherini, Andrea; Berretti, Enrico; DI BENEDETTO, Francesco; Innocenti, Massimo; D'Acapito, F.; Lavacchi, Alessandr

Closing the knowledge gap on the composition of the asbestos bodies

Asbestos bodies (AB) form in the lungs as a result of a biomineralization process initiated by the alveolar macrophages in the attempt to remove asbestos. During this process, organic and inorganic material deposit on the foreign fibers forming a Fe-rich coating. The AB start to form in months, thus quickly becoming the actual interface between asbestos and the lung tissue. Therefore, revealing their composition, and, in particular, the chemical form of Fe, which is the major component of the AB, is essential to assess their possible role in the pathogenesis of asbestos-related diseases. In this work we report the result of the first x-ray diffraction measurements performed on single AB embedded in the lung tissue samples of former asbestos plant workers. The combination with x-ray absorption spectroscopy data allowed to unambiguously reveal that Fe is present in the AB in the form of two Fe-oxy(hydroxides): ferrihydrite and goethite. The presence of goethite, which can be explained in terms of the transformation of ferrihydrite (a metastable phase) due to the acidic conditions induced by the alveolar macrophages in their attempt to phagocytose the fibers, has toxicological implications that are discussed in the paper