ALBERT

Description: A geochemical survey of thermal waters collected from submarine vents at Panarea Island (Aeolian Islands, southern Italy) was carried out from December 2002 to March 2007, in order to investigate i) the geochemical processes controlling the chemical composition of the hydrothermal fluids and ii) the possible relations between the chemical features of the hydrothermal reservoir and the activity of the magmatic system. Compositional data of the thermal water samples were integrated in a hydrological conceptual model, which describes the formation of the vent fluid by mixing of seawater, seawater concentrated by boiling, and a deep, highly-saline end-member, whose composition is regulated by water-rock interactions at relatively high temperature and shows clear clues of magmatic-related inputs. The chemical composition of concentrated seawater was assumed to be represented by that of the water sample having the highest Mg content. The composition of the deep end-member was instead calculated by extrapolation assuming a zero-Mg end-member. The Na–K–Ca geothermometer, when applied to the thermal end-member composition, indicated an equilibrium temperature of approximately 300 °C, a temperature in agreement with the results obtained by gas-geothermometry.

Description: Istituto Nazionale di Geofisica e Vulcanologia

Description: Submitted

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: JCR Journal

Description: open

Description: EnCana’s CO2 injection EOR project at Weyburn (Saskatchewan, Canada) is the focal point of a multi-faceted research program, sponsored by IEA GHG R&D and numerous international industrial and government partners including the European Community (BGS, BRGM, INGV and GEUS research providers), to find co-optimization of “CO2-EOR Production” and “CO2 -Geological Storage”, addressed to environmental purposes, in the frame of the Kyoto Agreement Policies. The Weyburn oil-pull is recovered from Midale Beds (at the depth of 1300-1500 m). This formation consists of Mississipian shallow marine carbonate-evaporites that can be subdivided into two units: i) the dolomitic “Marly” and ii) the underlying calcitic “Vuggy”, sealed by an anhydrite cap. Presently, around 3 billions mc of supercritical CO2 have been injected into the “Phase A1”injection area that includes around 90 oil producers, 30 water injectors and 30 CO2 injection wells, build up since September 2000. INGV has carried out a geochemical monitoring programme -approximately thrice yearly from pre-injection (“Baseline” trip, August 2000) to September 2004- performing trace element and dissolved gas analysis along with fluids sampling surveys, the latter being performed by the Canadian partners. The experimental data are the base of a geochemical modelling, i.e. the main goal of the present study. In the past, assumptions and gap-acceptance have been made in the literature in the frame of the geochemical modelling of CO2 geological storage, in order to reconstruct the reservoir conditions (pressure, pH and boundary conditions). As these parameters of deep fluids cannot be measured in-situ, all this information must be computed by a a posteriori procedure involving the analytical data. In this work we proposed an approach to geochemical modeling in order to:: i) reconstruct the in-situ reservoir chemical composition (including pH) and ii) evaluate the boundary conditions (e.g. pCO2, pH2S), necessary to implement the reaction path modelling. This is the starting point to assess the geochemical impact of CO2 into the oil reservoir and, as main target, to quantify water-gas-rock reactions. Our geochemical modelling procedure is based on the available data such as: a) bulk mineralogy of the Marly and Vuggy zones; b) average gas-cap composition and c) pre-and post-CO2 injection selected water samples from Midale Beds. The PRHEEQC (V2.11) Software Package was used to reconstruct the in-situ reservoir composition by calculating the chemical equilibrium among the various phases at reservoir temperature (60°C) and pressure (150 bars) conditions by suitable thermodynamic corrections to code database. Then, we identified possible compositions of the initially reservoir liquid phases, always taking into account the case histories of the Marly and Vuggy units. The inverse modelling simulation (IMS) was then performed in order to calculate the amounts of mass transfer of liquid, gas and solid phases that accounted for changes in the water chemistry between the 2000 and 2003 data-sets. IMS calculations suggest that the reservoir underwent mineralogical changes, such as precipitation of chalcedony, gypsum and kaolinite and dissolution of anhydrite and k-feldspar. Calcite dissolution is predicted, but the precipitation of others carbonates (dolomite, dawsonite and siderite) can also occur. Finally, we modelled the geochemical impact of CO2 injection on Weyburn reservoir subjected to both local equilibrium and kinetically controlled reactions. All experimental data and thermo-kinetic modeling of the evolution of the CO2-rich Weyburn brine interacting with host rock minerals performed over 100 years after injection confirm that “solubility trapping” is prevailing in this early stage of CO2 injection. Further and detailed studies on the evolution of the CO2-rich Weyburn brine is one of main aims of this study in the framework of a PhD programme between the INGV of Rome and the Department of Earth Sciences of Florence.

Description: Published

Description: Berkeley, California

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: open

Description: 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.

Description: Published

Description: Rimini, Italy

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: open

Description: In this work we present a new approach to model the effects of CO2 sequestration that has been tested in the Weyburn test site. The Weyburn oil-pull is recovered from Midale Beds (at 1300-1500 m depth). This formation consists of Mississippian shallow marine evaporitic carbonates that can be divided into two units: i) the dolomitic “Marly” and ii) the underlying calcitic “Vuggy”, sealed by an anhydrite cap-rock. Presently, about 3 billions mc of supercritical CO2 have been injected into the “Phase A1” injection area. The aim of our model is to reconstruct i) the chemical composition of the reservoir; ii) the geochemical evolution of the reservoir with time as CO2 is injected and ii) the boundary conditions. The geochemical modeling has been performed by using the code PRHEEQC (V2.11) software package. The “primitive brine” composition was calculated on the basis of the chemical equilibrium among the various phases, assuming reservoir equilibrium conditions for the mineral assemblage with respect to a Na-Cl (Cl/Na=1.2) water, at T of 62 °C and P of 150 bars via thermodynamic corrections to the code database. A comparison between the chemical composition of the “primitive brine” and that analytically determined on water samples collected before the CO2 injection shows an agreement within 10 %. Furthermore, we computed the kinetic evolution of the reservoir by considering the local equilibrium and the kinetically controlled reactions taking into account the CO2 injected during four years of monitoring. The calculated chemical composition after the CO2 injection is consistent with the analytical data of samples collected in 2004, with the exception of calcium and magnesium contents. The results of the Inverse Modeling Simulation (IMS) suggest that the measured Ca and Mg contents are higher than those calculated from the solubility of calcite and dolomite, likely due to the complexation effect of carboxilic acid. The results of the application of the kinetic model lasting 100 years indicate that dissolution of K-feldspar and kaolinite and precipitation of chalcedony affect the Marly and Vuggy units. Furthermore, calcite tends to be dissolved as CO2 solubilises in the reservoir, whereas dolomite dissolution can be considered negligible. Dawsonite precipitates as secondary mineral. The CO2 content from solubility trapping (short/medium-term sequestration) calculation is ~0.8 mol/L.

Description: Published

Description: Pechino, Cina

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: open

Description: CO2 geological storage is one of the most promising technologies for reducing atmospheric emissions of greenhouse gas. The results obtained by a new approach applied to a CO2 storage geochemical model at the Weyburn (Saskatchewan, Canada) test site, where since September 2000 5000 t/day of supercritical CO2 are injected, are presented and discussed. The Weyburn oil-pull is recovered from the Midale Beds (at the depth of 1300-1500 m), consisting of Mississippian shallow marine carbonate-evaporites, that is classically subdivided into two units: i) the dolomitic “Marly” and ii) the underlying calcitic “Vuggy”, sealed by an anhydrite cap-rock. Assumptions and gap-acceptance are commonly made to reconstruct the reservoir conditions (pressure, pH, chemistry, and mineral assemblage), although most geochemical parameters of deep fluids are to be computed by a posteriori procedure due to the sampling collection at the well-head, i.e. using depressurised aliquots. On the basis of the available data at Weyburn, such as: a) bulk mineralogy of the Marly and Vuggy reservoirs; b) mean gas-cap composition at the well-heads and c) selected pre- and post-CO2 injection water samples, we have rebuilt the in-situ reservoir chemical composition and the kinetic evolution after CO2 injection. The geochemical modelling has been performed by using the code PRHEEQC (V2.11) software package; the in-situ reservoir composition was calculated by the chemical equilibrium among the various phases at reservoir temperature (62 °C) and pressure (150 bars) via thermodynamic corrections to the code default database. Furthermore, the “primitive” chemical composition of the pre-injection Marly and Vuggy liquid phase was derived by assuming the equilibrium conditions for the mineral assemblage with respect to a Na-Cl (Cl/Na=1.2) water. A comparison between the chemical composition of the “primitive brine” and that measured before the CO2 injection shown an agreement within 10 % for most analytical species. The second step has been that to compute the geochemical impact of three years of CO2 injection (September 2000-2003) by kinetically controlled reactions. In order to statically validated our geochemical model we have compared the computed and measured data by using the Median Test. The results show that the proposed geochemical model is able to reliably describe (within 5% error) the behaviour of pH, HCO3, Cl, Li, Na, Sr, Si and HS+SO4, with the exception of K, Ca and Mg. Finally, the kinetic evolution of the CO2-rich Weyburn brines interacting with the host-rock minerals, performed over 100 years after injection, has also been modelled. The solubility trapping (short/medium-term sequestration) gives an amount of dissolved CO2 of 0.761moles/L and 0.752 moles/L for Marly and Vuggy units, respectively, whereas the mineral trapping, calculated as difference between dissolved (calcite and dolomite) and precipitated carbonate (dawsonite) minerals, is -0.019 and -5.69x10-5 moles/L for Marly and Vuggy units, respectively. The experimental data-set available and the geochemical modelling intrinsic limitation introduce a large uncertainty in the modelled results and in order to evaluate the dependence of the results from the modeling code, a different thermodynamic approach, such as the modelling software GEM (Gibbs Energy Minimization approach), is required.

Description: Published

Description: Vienna, Austria

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: open