Chemical Characteristics of Deep Groundwater in the Gardermoen Aquifer : Controlling processes and residence times.

Deep groundwaters are normally characterized by long residence times in the aquifer and by being well evolved geochemically. At Gardermoen the estimated average groundwater residence time is in the range of 20-30 years. In this study regional and/or depth related chemical differences in groundwater chemistry have been discussed and related to natural geochemical processes and anthropogenic input, based on a set of groundwater samples. Calcite dissolution is confirmed to be the dominating weathering process and the aquifer may be classified as a Ca2+ and HCO3- system. Most of the dissolution happens in the upper saturated zone, and approximately 48.5% of the bicarbonate may be assigned to calcite dissolution. Geochemical modelling results (by the use of PHREEQC) confirms weathering of silicates along the flowpath to be minor, with plagioclase contributing the most to the groundwater chemistry, followed by chlorite and K-mica (K-feldspar). Deeper groundwater at Gardermoen has reached the post oxic zone, and advanced to manganese or iron reducing conditions. Pyrite oxidation is the only natural source of sulphate within the aquifer. Sulphate reduction was not evident as is expected along with the observed low oxygen saturations, i.e. most of the pyrite oxidation occurs in the oxic upper saturated zone. The observed relationship between bicarbonate and sulphate indicates that protons released from pyrite oxidation do contribute to calcite dissolution, but to a small extent. TLC-FID analyses yielded reliable quantitative estimations of the organic fraction. A tripartite configuration in the peak representing the polar fraction in the chromatograms was observed in all samples, and may be viewed as a characterisation of the distribution among organic acids in the groundwater at Gardermoen, with respect to polarity. Based on this, carboxylic acids are most abundant, followed by phenolic and hydroxylic, respectively. 3H-3He dating performed during this study has not yet been concluded and comprises too few samples in order to establish a regional overview of residence times. The current dataset displays, however, increasing ages relative to the depth below the groundwater table, corresponding to the general assumption on residence times

Using 2D seismic line data to estimate impact of caprock morphology on CO2 migration in the Gassum formation

Poster presented at the Trondheim CCS Conference 2019The Gassum Formation on the Norwegian Continental Shelf serves as the principal case study for the CO2-Upslope project. The top surface of this formation is gently sloping, and characterized by a number of macro-scale structural traps, a few large faults, a large number of small faults, and small-scale depth variations that can be inferred and extrapolated from the seismic data. In the study presented in this paper, we estimate the amount of macro- and sub-scale trapping potential of the formation based on interpreted 2D seismic lines and identified faults. The seismic lines provide the depth of the caprock at each point along straight lateral paths. In the available data, a few dozen such lines cross the study area at various angles. A number of medium and large faults could be explicitly identified and mapped, as they correlate between several of these lines. In addition, hundreds of small-scale faults are only visible as discontinuities along individual lines. The extent and shape of these small faults between the seismic sections cannot be explicitly known from the data. In order to investigate trapping potential, we start out by constructing multiple realizations of the top surface, constructed to be faithful to both large-scale topography and small-scale statistical properties. We use a tensor spline surface approximation to represent the surface trend, with added stochastic small-scale variations consistent with the statistical properties of the line data. Moreover, we include a distribution small-scale faults that are only visible as discontinuities in the seismic lines by adding assumptions on their general orientations and lengths. At the timescales associated with long-term CO2 plume migration, it can generally be assumed that vertical equilibrium has been reached and that the CO2 slowly flows as a thin wedge right under the top surface, driven by gravity forces. Based on this assumption, we apply spill-point analysis and upscaling techniques on our sets of top surface realizations to explore the possible range of values for total structural trapping and plume retardation potential, and how they depend on the assumptions made. We also study the impact of the placement of the injection site, and how much of the total structural storage potential can be actually realized based on the position of the site and the injection strategy.submittedVersio

Estimation of Mutual Solubility of Co2-H2o in Saline Aquifer Systems Using Epc-Saft Equation of State

A primary assessment of mutual solubility of CO2 and water for estimated max and min temperatures and pressures of the prospective reservoir formations of Aurora; Cook (at >2650 m depth) and Johansen (at >2700 m depth) have been done using ePC-SAFT equation of estate. Mole fraction of CO2 in H2O ranges from 0.025 to 0.027, and H2O in CO2 form 0.016 to 0.023 over pressure-temperature ranges of 265 – 283 bar and 95 – 110 °C. The potential for drying out effects (H2O to CO2) is significant, and there would be risk of salt precipitation in the near well area.publishedVersio

On the Distinctiveness of Noble Gases in Injected Co2 from Background Fluids

A comprehensive monitoring program for CO2 storage sites is an integral part of designing CCS projects. Once a CO2 anomaly is observed or suspected, the source of the CO2 may be identified through evaluation of geochemical tracers. Noble gases are one of those geochemical tracers that display unique signatures for the environmental reservoirs involved in the storage site system. The background fluids at storage prospect, such as formation water, hydrocarbons or shallow gases need to be characterized prior to injection. Typical noble gas signatures are of atmospheric, crustal/radiogenic or mantle character. Captured CO2 can contain a large range of noble gas concentrations and ratios with typically significantly lower concentrations than the other background fluids. Here, we collect the noble gas analysis of various environmental fluids in the storage site system relevant to the North Sea, such as hydrocarbons and shallow gases, to narrow down possible observable signatures. If samples are not available realistic values can be inferred from analogue sites/studies. Further, we show that after injection, phase partitioning, hence equilibration, of the injected CO2 with formation water leads to adaption of a radiogenic signature from the formation water. Therefore, the initially low concentrations of the CO2, and their associated elemental and isotopic ratios, are only preserved when remaining almost pure. These signatures can be applied to mixing calculations with the background fluids to rule out if injected CO2 is contributing to an anomaly. Meanwhile, noble gases are one of the environmental tracers that could be cost-effective since they are naturally inherent in the CO2 and the storage reservoir fluids, we also model the addition of artificial noble gas tracers to increase the detectability, i.e. ability to recognize lower contributions of injected CO2 in a background reservoir fluid. These calculations can be fed into cost calculations to estimate the economic impact of such an additional monitoring measure.publishedVersio

Using Reservoir Geology and Petrographic Observations to Improve CO2 Mineralization Estimates; Examples from the Johansen Formation, North Sea, Norway

Reservoir characterization specific to CO2 storage is challenging due to the dynamic interplay of physical and chemical trapping mechanisms. The mineralization potential for CO2 in a given siliciclastic sandstone aquifer is controlled by the mineralogy, the total reactive surface areas, and the prevailing reservoir conditions. Grain size, morphologies and mineral assemblages vary according to sedimentary facies and diagenetic imprint. The proposed workflow highlights how the input values for reactive mineral surface areas used in geochemical modelling may be parameterized as part of geological reservoir characterization. The key issue is to separate minerals both with respect to phase chemistry and morphology (i.e., grain size, shape, and occurrence), and focus on main reactants for sensitivity studies and total storage potentials. The Johansen Formation is the main reservoir unit in the new full-value chain CO2 capture and storage (CCS) prospect in Norway, which was licenced for the storage of CO2 as of 2019. The simulations show how reaction potentials vary in different sedimentary facies and for different mineral occurrences. Mineralization potentials are higher in fine-grained facies, where plagioclase and chlorite are the main cation donors for carbonatization. Reactivity decreases with higher relative fractions of ooidal clay and lithic fragments

Using 2D seismic line data to estimate impact of caprock morphology on CO2 migration in the Gassum formation

The Gassum Formation on the Norwegian Continental Shelf serves as the principal case study for the CO2-Upslope project. The top surface of this formation is gently sloping, and characterized by a number of macro-scale structural traps, a few large faults, a large number of small faults, and small-scale depth variations that can be inferred and extrapolated from the seismic data. In the study presented in this paper, we estimate the amount of macro- and sub-scale trapping potential of the formation based on interpreted 2D seismic lines and identified faults. The seismic lines provide the depth of the caprock at each point along straight lateral paths. In the available data, a few dozen such lines cross the study area at various angles. A number of medium and large faults could be explicitly identified and mapped, as they correlate between several of these lines. In addition, hundreds of small-scale faults are only visible as discontinuities along individual lines. The extent and shape of these small faults between the seismic sections cannot be explicitly known from the data. In order to investigate trapping potential, we start out by constructing multiple realizations of the top surface, constructed to be faithful to both large-scale topography and small-scale statistical properties. We use a tensor spline surface approximation to represent the surface trend, with added stochastic small-scale variations consistent with the statistical properties of the line data. Moreover, we include a distribution small-scale faults that are only visible as discontinuities in the seismic lines by adding assumptions on their general orientations and lengths. At the timescales associated with long-term CO2 plume migration, it can generally be assumed that vertical equilibrium has been reached and that the CO2 slowly flows as a thin wedge right under the top surface, driven by gravity forces. Based on this assumption, we apply spill-point analysis and upscaling techniques on our sets of top surface realizations to explore the possible range of values for total structural trapping and plume retardation potential, and how they depend on the assumptions made. We also study the impact of the placement of the injection site, and how much of the total structural storage potential can be actually realized based on the position of the site and the injection strategy

Estimating Caprock Impact on CO2 Migration in the Gassum Formation Using 2D Seismic Line Data

Realizable CO2 storage potential for saline formations without closed lateral boundaries depends on the combined effects of physical and chemical trapping mechanisms to prevent long-term migration out of the defined storage area. One such mechanism is the topography of the caprock surface, which may retain CO2 in structural pockets along the migration path. Past theoretical and modeling studies suggest that even traps too small to be accurately described by seismic data may play a significant role. In this study, we use real but scarce seismic data from the Gassum Formation of the Norwegian Continental shelf to estimate the impact of topographical features of the top seal in limiting CO2 migration. We seek to estimate the amount of macro- and sub-scale trapping potential of the formation based on a few dozen interpreted 2D seismic lines and identified faults. We generate multiple high-resolution realizations of the top surface, constructed to be faithful to both large-scale topography and small-scale statistical properties. The structural trapping and plume retardation potential of these top surfaces is subsequently estimated using spill-point (static) analysis and dynamical flow simulation. By applying these techniques on a large ensemble of top surface realizations generated using a combination of stochastic realizations and systematic variation of key model parameters, we explore the range of possible impacts on plume advancement, physical trapping and migration direction. The stochastic analysis of trapping capacity and retardation efficiency in statistically generated, sub-seismic resolution features may also be applied for surfaces generated from 3D data

Estimating Caprock Impact on CO2 Migration in the Gassum Formation Using 2D Seismic Line Data

Realizable CO2 storage potential for saline formations without closed lateral boundaries depends on the combined effects of physical and chemical trapping mechanisms to prevent long-term migration out of the defined storage area. One such mechanism is the topography of the caprock surface, which may retain CO2 in structural pockets along the migration path. Past theoretical and modeling studies suggest that even traps too small to be accurately described by seismic data may play a significant role. In this study, we use real but scarce seismic data from the Gassum Formation of the Norwegian Continental shelf to estimate the impact of topographical features of the top seal in limiting CO2 migration. We seek to estimate the amount of macro- and sub-scale trapping potential of the formation based on a few dozen interpreted 2D seismic lines and identified faults. We generate multiple high-resolution realizations of the top surface, constructed to be faithful to both large-scale topography and small-scale statistical properties. The structural trapping and plume retardation potential of these top surfaces is subsequently estimated using spill-point (static) analysis and dynamical flow simulation. By applying these techniques on a large ensemble of top surface realizations generated using a combination of stochastic realizations and systematic variation of key model parameters, we explore the range of possible impacts on plume advancement, physical trapping and migration direction. The stochastic analysis of trapping capacity and retardation efficiency in statistically generated, sub-seismic resolution features may also be applied for surfaces generated from 3D data

Slik kan vi lagre CO2 under havbunnen for alltid

Berggrunnen under Nordsjøen har et stort potensial som felles lagringssted for CO₂ fra industri i hele Nord-Europa.publishedVersio

Estimation of Mutual Solubility of Co2-H2o in Saline Aquifer Systems Using Epc-Saft Equation of State

A primary assessment of mutual solubility of CO2 and water for estimated max and min temperatures and pressures of the prospective reservoir formations of Aurora; Cook (at >2650 m depth) and Johansen (at >2700 m depth) have been done using ePC-SAFT equation of estate. Mole fraction of CO2 in H2O ranges from 0.025 to 0.027, and H2O in CO2 form 0.016 to 0.023 over pressure-temperature ranges of 265 – 283 bar and 95 – 110 °C. The potential for drying out effects (H2O to CO2) is significant, and there would be risk of salt precipitation in the near well area