[Show abstract][Hide abstract] ABSTRACT: Long-term security is critical to the success and public acceptance of geologic carbon storage. Much of the security risk associated with geologic carbon storage stems from CO2 buoyancy. Gaseous and supercritical CO2 are less dense than formation waters providing a driving force for it to escape back to the surface via fractures, or abandoned wells. This buoyancy can be eradicated by the dissolution of CO2 into water prior to, or during its injection into the subsurface. Here we demonstrate the dissolution of CO2 into water during its injection into basalts leading directly to its geologic solubility storage. This process was verified via the successful injection of over 175 t of CO2 dissolved in 5000 t of water into porous rocks located 400–800 m below the surface at the Hellisheidi, Iceland CarbFix injection site. Although larger volumes are required for CO2 storage via this method, because the dissolved CO2 is no longer buoyant, the storage formation does not have to be as deep as for supercritical CO2 and the cap rock integrity is less important. This increases the potential storage resource substantially compared to the current estimated storage potential of supercritical CO2.
International Journal of Greenhouse Gas Control 06/2015; 37. DOI:10.1016/j.ijggc.2015.02.022 · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Geothermal energy is a sustainable and clean energy source. Utilization of high-enthalpy geothermal systems is, however, associated with emissions of geothermal gases like CO2 and H2S. H2S emissions are currently the main environmental problem associated with high enthalpy geothermal energy utilization in Iceland as the Icelandic government has issued a strict regulation on atmospheric H2S concentrations. Reykjavík Energy, the largest geothermal power company in Iceland, is developing innovative methods for capturing CO2 and H2S emissions from its power plants and sequestering the gases as carbonate and sulfide minerals in nearby, subsurface basaltic formations. About 350 tons of CO2 and H2S have been injected into two different storage sites near Hellisheidi geothermal power plant in a pilot capture and sequestration phase. The shallower storage formation lies between 400-800 m depth, is 30-80°C warm and consists of porous, relatively fresh basalts. The deeper storage formation is located below 800 m depth, within the high temperature geothermal system, and consists of fractured, hydrothermally altered basalts with aquifer temperatures around 270°C. Rather than injecting captured gases directly into the storage formations, a technology to dissolve the gases in water prior to injection has been developed. Once dissolved, the gases are no longer buoyant compared to pore fluids, improving considerable security of the injection due to decreased leakage risks. We have demonstrated that the developed method leads immediate to geological solubility trapping of injected gases. A comprehensive monitoring program based on the use of reactive and conservative tracers has furthermore revealed rapid mineral formation of injected CO2 within the shallower reservoir and mass balance calculations suggest over 80% mineralization within less than one year. H2S mineralization is predicted to be even faster but further monitoring will provide more information on the efficiency of H2S mineralization in basalts. Results obtained so far from the pilot injections are in agreement with results from natural analogs, laboratory experiments and reactive transport model simulations, which all indicate CO2 and H2S mineral sequestration in basalt formations to be a viable option in reducing sour gas emissions from geothermal power plants and thereby bringing high enthalpy geothermal energy closer to zero emission energy production. Plans call for up-scaling sour gas capture and sequestration activities at Hellisheidi geothermal power plant in stages. The first up-scale will commence operation in 2014 and involve capture and re-injection of 8,500 tons of CO2-H2S gas mixture on an annual basis. Additional up-scales and potential further separation of CO2 and H2S will follow in coming years.
World Geothermal Congress 2015, Melbourne, Australia, 19-25 April 2015; 04/2015
[Show abstract][Hide abstract] ABSTRACT: In addition to efforts aimed at reducing anthropogenic production of greenhouse gases, geological storage of CO<sub>2</sub> is being explored as a strategy to reduce atmospheric greenhouse gas emission and mitigate climate change. Previous studies of the deep subsurface in North America have not fully considered the potential negative effects of CO<sub>2</sub> leakage into shallow drinking water aquifers, especially from a microbiological perspective. A test well in the Newark Rift Basin was utilized in two field experiments to investigate patterns of microbial succession following injection of CO<sub>2</sub>-saturated water into an isolated aquifer interval, simulating a CO<sub>2</sub> leakage scenario. A decrease in pH following injection of CO<sub>2</sub> saturated aquifer water was accompanied by mobilization of trace elements (e.g. Fe and Mn), and increased bacterial cell concentrations in the recovered water. 16S ribosomal RNA gene sequence libraries from samples collected before and after the
PLoS ONE 01/2015; 10(1-1):e0117812. DOI:10.1371/journal.pone.0117812 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In situ mineral carbonation provides the most effective and permanent solution for geologic CO2 storage. Basaltic rocks have the potential to store large volumes of CO2 as (Ca, Mg, Fe) carbonates . Existing monitoring and verification techniques for geologic CO2 storage are insufficient to quantitatively characterize solubility and mineral trapping in a geologic reservoir. We developed and tested a new reactive tracer technique for quantitative monitoring and detection of dissolved and chemically transformed CO2. The technique involves the active tagging of the injected CO2 with low levels of radiocarbon (14C) as a reactive tracer in combination with the injection of non-reactive tracers such as sulfurhexafluoride (SF6) and trifluoromethylsulphur pentafluoride (SF5CF3). The tracer technique has been applied at the CarbFix pilot injection site in Hellisheidi, Iceland as part of a comprehensive geochemical monitoring program during two injection phases; Phase III and IV. SF6 and SF5CF3 confirm the arrival of the injected CO2 and CO2+H2S solutions at the first observation well HN04, which is 125m west of the injection well at 520 m depth. The initial breakthrough of the migrating dissolved CO2 front occurred 63 and 62 days after injection began as evidenced by an initial peak in the SF6, SF5CF3, 14C, and dissolved inorganic carbon (DIC) concentrations. The major increase in the non-reactive tracer concentrations occurred several months after the initial breakthrough, although no major concentration increase has been observed for 14C and DIC suggesting that mineral reactions are dominant during CO2 injection.
Energy Procedia 12/2014; 63:4180-4185. DOI:10.1016/j.egypro.2014.11.450
[Show abstract][Hide abstract] ABSTRACT: The long-term security of geologic carbon storage is critical to its success and public acceptance. Much of the security risk associated with geological carbon storage stems from its buoyancy. Gaseous and supercritical CO2 are less dense than formation waters, providing a driving force for it to escape back to the surface. This buoyancy can be eliminated by the dissolution of CO2 into water prior to, or during its injection into the subsurface. The dissolution makes it possible to inject into fractured rocks and further enhance mineral storage of CO2 especially if injected into silicate rocks rich in divalent metal cations such as basalts and ultra-mafic rocks. We have demonstrated the dissolution of CO2 into water during its injection into basalt leading to its geologic solubility storage in less than five minutes and potential geologic mineral storage within few years after injection ,  and . The storage potential of CO2 within basaltic rocks is enormous. All the carbon released from burning of all fossil fuel on Earth, 5000 GtC, can theoretically be stored in basaltic rocks .
Energy Procedia 12/2014; 63:4561-4574. DOI:10.1016/j.egypro.2014.11.489
[Show abstract][Hide abstract] ABSTRACT: The CARBFIX project near Reykjavik in Iceland includes is a field-based pilot injection to study the feasibility of permanent CO2 (and H2S) storage in permeable basalt formations . Pure CO2 and CO2/H2S mixtures from the Hellisheidi geothermal power plant were dissolved downhole in groundwater and injected into a permeable confined basalt formation at about 500m depth below ground. We are using non-reactive (sodium fluorescein, SF5CF3, and SF6) and reactive (14C and 13C) tracers in the project to characterize subsurface CO2 transport and in situ CO2-water-rock reactions. In January 2012, 170 tons of pure CO2 tagged with 14C and SF6 were injected followed by 73 tons of a CO2/H2S mixture starting in June 2012. Samples were collected from injection and monitoring wells in evacuated serum glass bottles with butyl stoppers and analyzed by AMS and mass spectrometry for carbon isotopes, by fluorometry for Na-fluorescein and by gas chromatography for SF6 and SF5CF3. Tracer breakthrough curves obtained from the first downstream monitoring well indicate that the injected water arrives in a fast short pulse and a late broad peak. 14C/SF6 and DIC/SF6 ratios are considerably lower in the monitoring wells as compare to the injection well. Evidence for carbonate precipitation was also found in the pump and on the pump lines in the monitoring well. The 14C/12C ratio of the precipitated carbon is the same as that of the DIC during injection and in the monitoring well, but distinct from ambient groundwater background. Mass balance calculations suggest that about 90% of the injected CO2 has been mineralized over a period of only 2 years.
 Gislason et al. (2010), Int. J. Greenh. Gas Con. 4, 537-545.
[Show abstract][Hide abstract] ABSTRACT: The Samail Ophiolite in Oman contains over 10 trillion tons of peridotite undergoing hydration and carbonation reactions at low temperature . The active coupling between subsurface hydrology, geochemistry and microbiology will soon be accessible via targeted drilling by the International Continental Scientific Drilling Program and the Sloan Foundation, among others. In advance, we collected hyperalkaline fluids with millimolar concentrations of H2 and CH4 from 300-meter deep groundwater monitoring wells to characterize low-temperature reaction pathways in the aquifer. We are also conducting low-temperature serpentinization experiments (40°C, 55°C, 100°C) with crushed dunite and harzburgite from Oman to identify rock-derived energy sources for microorganisms. We are measuring H2 production (up to 400nmol/g), aqueous chemical changes and production of acetate and formate (40-80μM). The aqueous geochemical data from Oman fluids and experiments is coupled with detailed mineralogical investigation of natural samples (XRD, QEMSCAN and synchrotron-based x-ray fluorescence spectroscopy of Fe speciation) to identify the operative reaction pathways. The Oman fluids are rich in dissolved H2, but there is an absence of magnetite formation associated with this; instead, we observe extensive serpentine. We are currently investigating the possibility that H2 production is associated with oxidized, Fe3+ in low temperature serpentine. We have enriched stable cultures of methanogenic organisms from deep fluids from site NSHQ04 (pH 10.5, ~1.44 μm/mL CH4). This exciting discovery points to the possibility of deep subsurface life in Oman subsisting under energetic and C limitation. Quantifying the extent of in-situ methanogenesis will be critical to future investigations of microorganisms inhabiting the Oman aquifer to fully understand subsurface carbon cycling and the potential of microbes to control peridotite weathering rates, CH4 production, and carbonate formation. 1. Kelemen & Matter PNAS 2008
[Show abstract][Hide abstract] ABSTRACT: Geologic carbon sequestration has the potential to reduce greenhouse gas concentrations in the atmosphere. However, one barrier to large scale implementation is concern for water quality degradation from leakage of high CO2 fluids into drinking water aquifers. The hydrogeochemical response to simulated CO2 leakage was studied to estimate major and trace element release and to develop criteria for water quality monitoring and risk assessment. In this study, approximately 3100 L aquifer water enhanced with 1 atmosphere pressure CO2 gas was injected into a fracture zone located at 362–366 m below the ground surface in a sandstone/siltstone/mudstone interbedded aquifer in the Newark Basin. This was followed by a 3–6 week long incubation and then continuous monitoring of the hydrogeochemistry in the pumped-back water samples. Relative to background conditions, the recovered aquifer water displayed a decrease of pH, increase of alkalinity, Ca, Mg and Si concentrations, decrease of sulfate and Mo concentrations, and increased concentrations of trace elements including Fe, Mn, Cr, Co, Ni, Cu, Zn, Rb, Sr, Ba and U. These changes in aquifer water geochemistry can be explained by (a) dissolution of silicate and carbonate minerals and (b) trace element release that appear to be dependent on pH and pCO2 and affected by the altered redox conditions in the aquifer. Rapid and simultaneous changes of pH, specific conductance, major and trace metal release in aquifer water could be used as indicators of CO2 leakage from geologic sequestration sites. Hydrogeochemical parameters including pH, total dissolved solids and trace elements, particularly Fe, Mn, and Zn, need to be monitored in compliance with the U.S. Environmental Protection Agency (EPA) drinking water regulations.
International Journal of Greenhouse Gas Control 07/2014; 26:193–203. DOI:10.1016/j.ijggc.2014.04.025 · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The increasing concentrations of CO2 in the atmosphere are attributed to the rising consumption of fossil fuels for energy generation around the world. One of the most stable and environmentally benign methods of reducing atmospheric CO2 is by storing it as thermodynamically stable carbonate minerals. Olivine ((Mg,Fe)2SiO4) is an abundant mineral that reacts with CO2 to form Mg-carbonate. The carbonation of olivine can be enhanced by injecting solutions containing CO2 at high partial pressure into olivine-rich formations at high temperatures, or by performing ex situ mineral carbonation in a reactor system with temperature and pressure control. In this study, the effects of NaHCO3 and NaCl, whose roles in enhanced mineral carbonation have been debated, were investigated in detail along with the effects of temperature, CO2 partial pressure and reaction time for determining the extent of olivine carbonation and its associated chemical and morphological changes. At high temperature and high CO2 pressure conditions, more than 70% olivine carbonation was achieved in 3 hours in the presence of 0.64 M NaHCO3. In contrast, NaCl did not significantly affect olivine carbonation. As olivine was dissolved and carbonated, its pore volume, surface area and particle size were significantly changed and these changes influenced subsequent reactivity of olivine. Thus, for both long-term simulation of olivine carbonation in geologic formations and the ex situ reactor design, the morphological changes of olivine during its reaction with CO2 should be carefully considered in order to accurately estimate the CO2 storage capacity and understand the mechanisms for CO2 trapping by olivine.
[Show abstract][Hide abstract] ABSTRACT: In situ mineral carbonation in mantle peridotite has been proposed as a mechanism for long-term, environmentally benign CO2 sequestration1,2. This process converts peridotite and CO2 to carbonate minerals, like magnesite, in the subsurface, providing permanent and safe storage of the CO2. The volume that can be sequestered in this manner is an open question as peridotite carbonation involves a positive volume change and peridotite aquifers have limited porosity and permeability to accommodate the addition of solid volume. Conversion of peridotite to magnesite results in a volume increase of ~44%, which will fill the existing pore space and could limit the extent of carbonation by reducing porosity and permeability, clogging fluid flow paths, and armoring the reactive surface area. Alternatively, the force of crystallization and changes in fluid pressure from carbonation could act as driving forces for mechanical deformation and fracture propagation within the peridotite, creating new porosity, permeability, and reactive surface area, allowing carbonation to continue3. Natural examples of peridotite that have been entirely converted to magnesite suggest that reactive cracking from mineral carbonation is possible given the right conditions, such as elevated temperature and pCO2 2. Results will be presented from a reactive transport model that has been developed for peridotite carbonation using TOUGHREACT v.24. This model evaluates water and CO2 flow through peridotite fractured at different scales using a multiple continuum mesh. The effect of fluid flow, chemical reactions, and porosity and permeability feedbacks on carbonation rate and extent are explored, as is the effect of temperature. Peridotite carbonation is exothermic, so the release of heat of reaction could be balanced with the fluid injection temperature to maintain the 185oC conditions that facilitate the fastest carbonation rate2. The effect of fluid temperature and flow rate on the rate of carbonation and fracture propagation is investigated, with the goal of establishing the fluid temperatures and injection rates that will optimize the carbonation process. Additionally, pore fluid pressures are monitored as fluid transport and diffusion through fractures drive carbonation; the model then predicts at what extent of reaction progress fluid pressures will exceed the yield strength of the rock and cause fracture propagation. 1Matter and Kelemen, Nat. Geosci., 2009; 2Kelemen et al., Annu. Rev. Earth Planet. Sci., 2011; 3Kelemen and Hirth, Earth Planet. Sci. Lett., 2012; 4Xu, et al., Comput. Geosci., 2011.
American Geophysical Union Annual Meeting, San Francisco, CA; 12/2013
[Show abstract][Hide abstract] ABSTRACT: To mitigate anthropogenically-induced climate change and ocean acidification, net carbon dioxide emissions to the atmosphere must be reduced. One proposed option is underground CO2 disposal. Large-scale injection of CO2 into the Earth's crust requires an understanding of the multiphase flow properties of high-pressure CO2 displacing brine. We present laboratory-scale core flooding experiments designed to measure CO2 endpoint relative permeability for CO2 displacing brine at in situ pressures, salinities, and temperatures. Endpoint drainage CO2 relative permeabilities for liquid and supercritical CO2 were found to be clustered around 0.4 for both the synthetic and natural media studied. These values indicate that relative to CO2, water may not be strongly wetting the solid surface. Based on these results, CO2 injectivity will be reduced and pressure-limited reservoirs will have reduced disposal capacity, though area-limited reservoirs may have increased capacity. Future reservoir-scale modeling efforts should incorporate sensitivity to relative permeability. Assuming applicability of the experimental results to other lithologies and that the majority of reservoirs are pressure limited, geologic carbon sequestration would require approximately twice the number of wells for the same injectivity.
[Show abstract][Hide abstract] ABSTRACT: The peridotite section of the Samail Ophiolite in the Sultanate of Oman offers insight into the feasibility of mineral carbonation for engineered, in situ geological CO2 storage in mantle peridotites. Naturally occurring CO2 sequestration via mineral carbonation is well-developed in the peridotite; however, the natural process captures and sequesters CO2 too slowly to significantly impact the concentration of CO2 in the atmosphere. A reaction path model was developed to simulate in situ CO2 mineralization through carbonation of fresh peridotite, with its composition based on that of mantle peridotite in the Samail Ophiolite and including dissolution kinetics for primary minerals. The model employs a two-stage technique, beginning with an open system and progressing to three different closed system scenarios- a natural system at 30 °C, an engineered CO2 injection scenario at 30 °C, and an engineered CO2 injection scenario at 90 °C. The natural system model reproduces measured aqueous solute concentrations in the target water, signifying the model is a close approximation of the natural process. Natural system model results suggest that the open system achieves steady state within a few decades, while the closed system may take up to 6,500 years to reach observed fluid compositions. The model also identifies the supply of dissolved inorganic carbon as the limiting factor for natural CO2 mineralization in the deep subsurface. Engineered system models indicate that injecting CO2 at depth could enhance the rate of CO2 mineralization by a factor of over 16,000. CO2 injection could also increase mineralization efficiency – kilograms of CO2 sequestered per kilogram of peridotite – by a factor of over 350. These model estimates do not include the effects of precipitation kinetics or changes in permeability and reactive surface area due to secondary mineral precipitation. Nonetheless, the faster rate of mineralization in the CO2 injection models implies that enhanced in situ peridotite carbonation could be a significant sink for atmospheric CO2.
Chemical Geology 11/2012; s 330–331:86–100. DOI:10.1016/j.chemgeo.2012.08.013 · 3.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increasing concentration of CO2 in the atmosphere is attributed to rising consumption of fossil fuels around the world. The development of solutions to reduce CO2 emissions to the atmosphere is one of the most urgent needs of today’s society. CO2 injection into geological formations is one of the CO2 storage options with a large capacity. If non-carbonate minerals such as basalt and olivine exist in the CO2 injection site, the injected CO2 can react with those minerals to form thermodynamically stable solid carbonates. In nature, mineral carbonation takes place via dissolution of the mineral to release Ca/Mg ions followed by precipitation of Ca/Mg in the presence of CO2. The rate limiting step of this carbon mineralization process is considered to be the dissolution of the mineral.A question has been raised regarding the effect of in-situ carbon mineralization on the stability of the geologic storage of CO2. Both the kinetics and extents of mineral dissolution and carbonation reactions within the geological reservoir are important factors to evaluate for the long term stability of the geologically injected CO2.Therefore, this work focuses on understanding CO2-mineral-water interactions at a wide range of reaction conditions (Tmax = 200oC and PCO2, max = 200 bar). Both deionized water and synthetic brine were used as the aqueous reaction media. Minerals such as olivine (Mg2SiO4), labradorite ((Ca,Na)(Al,Si)4O8) and basalt (mixture of silicate minerals), were selected based on their abundance in nature and both dissolution and single-step carbonation experiments were performed to investigate fast and long-term kinetics of mineral weathering. Two different regimes (i.e., surface reaction vs. mass transfer limited regimes) of mineral weathering were identified based on the analyses of the activation energy and reaction kinetics.
[Show abstract][Hide abstract] ABSTRACT: CO(2) capture and storage (CCS) has the potential to develop into an important tool to address climate change. Given society's present reliance on fossil fuels, widespread adoption of CCS appears indispensable for meeting stringent climate targets. We argue that for conventional CCS to become a successful climate mitigation technology--which by necessity has to operate on a large scale--it may need to be complemented with air capture, removing CO(2) directly from the atmosphere. Air capture of CO(2) could act as insurance against CO(2) leaking from storage and furthermore may provide an option for dealing with emissions from mobile dispersed sources such as automobiles and airplanes.
Proceedings of the National Academy of Sciences 07/2012; 109(33):13156-62. DOI:10.1073/pnas.1108765109 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Industrial scale injection of anthropogenic carbon dioxide into the crustal lithosphere has been proposed to reduce atmospheric accumulation. Much of this injection is expected to occur in saline reservoirs. An understanding of two-phase brine- CO2 flow is necessary for predicting storage capacity, fluid migration, and injectivity in geologic reservoirs. Additionally, the chemical reactivity of the rock matrix with CO2(l) affects the transport properties of the rock. A flow system for measuring two-phase transport of CO2 and brine is presented in this paper. The system is capable of displacing brine with either liquid or supercritical CO2. Special effort was taken to circumvent capillary end-effects in these experiments. Drainage end point relative permeability of CO2 displacing brine is found to be in the range of 0.34–0.44, much lower than what is expected for a nonwetting fluid. Such low relative permeabilities would tend to decrease injectivity while increasing displacement efficiency.
Energy Procedia 12/2011; 4:4347-4353. DOI:10.1016/j.egypro.2011.02.386
[Show abstract][Hide abstract] ABSTRACT: In situ mineral carbonation is facilitated by aqueous-phase chemical reactions with dissolved CO2. Evidence from the laboratory and the field shows that the limiting factors for in situ mineral carbonation are the dissolution rate of CO2 into the aqueous phase and the release rate of divalent cations from basic silicate minerals. Up to now, pilot CO2 storage projects and commercial operations have focused on the injection and storage of anthropogenic CO2 as a supercritical phase in depleted oil and gas reservoirs or deep saline aquifers with limited potential for CO2 mineralization. The CarbFix Pilot Project will test the feasibility of in situ mineral carbonation in basaltic rocks as a way to permanently and safely store CO2. The test includes the capture of CO2 flue gas from the Hellisheidi geothermal power plant and the injection of 2200 tons of CO2 per year, fully dissolved in water, at the CarbFix pilot injection site in SW Iceland. This paper describes the design of the CO2 injection test and the novel approach for monitoring and verification of CO2 mineralization in the subsurface by tagging the injected CO2 with radiocarbon (14C), and using SF5CF3 and amidorhodamine G as conservative tracers to monitor the transport of the injected CO2 charged water.
Energy Procedia 12/2011; 4:5579-5585. DOI:10.1016/j.egypro.2011.02.546
[Show abstract][Hide abstract] ABSTRACT: One of the primary objectives for secure CO2 geologic storage
is identifying suitable locations and developing accurate formation
evaluation. Borehole geophysics provides a set of effective techniques
for reservoir and seal characterization at an intermediate scale,
filling the gap between large-scale surface surveys and core-scale
analysis. In this study we analyze borehole geophysical logs obtained
for small-scale CO2 injection experiments in northeastern
Newark basin, transecting Jurassic igneous intrusion (the Palisades
sill) and Triassic lacustrine sediments that both contain fractured-rock
intervals. We present new insights into the Newark basin stratigraphy
and aquifer properties based on these borehole data and discuss the
advantages and limitations of various logging methods for
characterization of fractured reservoirs and seals. High-resolution
logging data have been obtained over a 1500-ft interval in the well,
including caliper, apparent resistivity, gamma ray, and temperature
logs, flowmeter measurements and optical and acoustic televiewer images.
Rock chips were recovered during drilling, but no coring was done. We
analyze these data with a specific focus on reservoir and seal
properties in the fractured sedimentary intervals. Electrical, acoustic,
and nuclear logs are used to evaluate porosity and identify potential
injection reservoirs and impermeable cap rocks. Sharp changes in
borehole fluid resistivity and temperature gradient indicate several
conductive zones potentially suitable for fluid injection and are
confirmed by flowemeter and hydraulic experiments. Analysis of
high-quality optical borehole televiewer (OTV) images provides
structural information about sedimentary bedding and fracture
distribution. The layers dip in northwestern direction at about
10-degree angle. Combined with drill cuttings, OTV images also allow for
reconstruction of a complete lithologic profile. OTV images reveal two
sets of fractures, mostly dominated by large-aperture high-angle
fractures, but they are not directly correlated with hydraulically
conductive zones. Some of the most prominent fractures are obvious flow
pathways, while others are less conductive, and a few do not exhibit any
flow at all. The high-angle fractures strike predominantly in NE-SW
direction, consistent with an extensional stress regime generated during
initial rifting of the Newark basin. Conductive zones are separated by
relatively thick intervals of low-porosity unfractured siltstone that
can potentially serve as caprock for injected fluids.
[Show abstract][Hide abstract] ABSTRACT: Potential leakage of CO2 from deep intervals used for geological
sequestration to shallow aquifers can have important negative impacts on
drinking water resources, thus it is very important to understand the
biogeochemical response to elevated CO2 plumes and develop diagnostic
monitoring systems. An experimental injection, composed of one
atmosphere partial pressure CO2, was conducted in fracture zones in a
sand and clay aquifer in the Newark Basin and incubated for three weeks.
The geophysical logging of the borehole and tracer tests using bromide
and SF6 indicated a weak background ambient flow in the aquifer.
Monitoring of groundwater parameters showed a decrease of pH from 8.2 to
6.1, in addition to silicate and carbonate dissolution, and the release
of 16 trace metals, including iron, manganese, cobalt, zinc, nickel, and
uranium. Changes in bacterial abundance and community diversity were
also tracked in parallel with geochemical transitions. A bench
incubation experiment in the laboratory has been designed to compare the
mineral dissolution and trace metal release rates, as well as the
microbial community' response to 1 and 5 bars of pCO2 under anaerobic
and aerobic conditions. This research will provide criteria for site
selection for geological CO2 sequestration, investigate the
vulnerability of shallow aquifers to CO2 leakage, and develop the
diagnostic testing techniques to assess risk.