CO2 Reservoir Research Articles

CO2 induced changes in Mount Simon sandstone: Understanding links to post CO2 injection monitoring, seismicity, and reservoir integrity

The purpose of this study is to quantify geochemical reactions of CO2 and brine with subsurface samples taken from the Mt. Simon sandstone and identify any potential alterations of the geomechanical rock properties that could lead to changes observable in seismic monitoring or result in changes of micro seismicity such as those observed at the Illinois Basin-Decatur Project (IBDP) site. Two Mt. Simon sandstone samples from 6919.3 feet (2109.0 m) and 6926.1 feet (2111.1 m) depth were exposed to supercritical CO2 (scCO2) dissolved in brine at in-situ reservoir conditions for one month. Geochemical, spectral, scanning electron microscopy, and petrophysical methods were used to analyze the samples before and after the one-month exposure. Significant changes were observed. Multiple geomechanical properties were chosen to form the framework against which to interrogate the petrophysical data: Young’s modulus (E), Poisson’s ratio (ν), lambda·rho (λρ), and mu·rho (μρ). In this study we conclude that framework composition, porosity, heterogeneities, effective pressure, and reactive geochemistry are first order controls on trends in the E-μ and λρ-μρ cross plot spaces. Changes in porosity, permeability, dynamic moduli, and brittleness with exposure to these fluids were observed. No change in ultrasonic P-wave attenuation (QP) was observed. Geochemical alteration causes a distinct shift in λρ-μρ in both samples as well as changes in E, ν , and P and S wave seismic velocity values. These observations could provide insight into subsurface monitoring using seismic methods including amplitude variation with offset (AVO) classification.

Stress field orientation controls on fault leakage at a natural CO<sub>2</sub> reservoir

Abstract. Travertine deposits present above the St. Johns Dome natural CO2 reservoir in Arizona, USA, document a long (>400 kyr) history of surface leakage of CO2 from a subsurface reservoir. These deposits are concentrated along surface traces of faults, implying that there has been a structural control on the migration pathway of CO2-rich fluids. Here, we combine slip tendency and fracture stability to analyse the geomechanical stability of the reservoir-bounding Coyote Wash Fault for three different stress fields and two interpreted fault rock types to predict areas with high leakage risks. We find that these areas coincide with the travertine deposits on the surface, indicating that high-permeability pathways as a result of critically stressed fracture networks exist in both a fault damage zone and around a fault tip. We conclude that these structural features control leakage. Importantly, we find that even without in situ stress field data, the known leakage points can be predicted using geomechanical analyses, despite the unconstrained tectonic setting. Whilst acquiring high-quality stress field data for secure subsurface CO2 or energy storage remains critical, we shown that a first-order assessment of leakage risks during site selection can be made with limited stress field knowledge.

Towards real-time monitoring: data assimilated time-lapse full waveform inversion for seismic velocity and uncertainty estimation

SUMMARYRapid development of time-lapse seismic monitoring instrumentations has made it possible to collect dense time-lapse data for tomographically retrieving time-lapse (even continuous) images of subsurface changes. While traditional time-lapse full waveform inversion (TLFWI) algorithms are designed for sparse time-lapse surveys, they lack of effective temporal constraint on time-lapse data, and, more importantly, lack of the uncertainty estimation of the TLFWI results that is critical for further interpretation. Here, we propose a new data assimilation TLFWI method, using hierarchical matrix powered extended Kalman filter (HiEKF) to quantify the image uncertainty. Compared to existing Kalman filter algorithms, HiEKF allows to store and update a data-sparse representation of the cross-covariance matrices and propagate model errors without expensive operations involving covariance matrices. Hence, HiEKF is computationally efficient and applicable to 3-D TLFWI problems. Then, we reformulate TLFWI in the framework of HiEKF (termed hereafter as TLFWI-HiEKF) to predict time-lapse images of subsurface spatiotemporal velocity changes and simultaneously quantify the uncertainty of the inverted velocity changes over time. We demonstrate the validity and applicability of TLFWI–HiEKF with two realistic CO2 monitoring models derived from Frio-II and Cranfield CO2 injection sites, respectively. In both 2-D and 3-D examples, the inverted high-resolution time-lapse velocity results clearly reveal a continuous velocity reduction due to the injection of CO2. Moreover, the accuracy of the model is increasing over time by assimilating more time-lapse data while the standard deviation is decreasing over lapsed time. We expect TLFWI-HiEKF to be equipped with real-time seismic monitoring systems for continuously imaging the distribution of subsurface gas and fluids in the future large-scale CO2 sequestration experiments and reservoir management.

A hyperbox classifier model for identifying secure carbon dioxide reservoirs

Carbon management technologies such as carbon dioxide capture and storage and direct air capture systems will be needed to mitigate climate change in the coming decades. Both of these technologies will depend on the availability of secure geological storage sites that can permanently hold carbon dioxide with minimal risk of leakage. Machine learning tools that can characterize candidate storage sites based on geological data can aid decision-makers in planning carbon management networks. In this work, a mixed integer linear programming model is developed to generate a binary hyperbox classifier for determining the integrity of a candidate storage site. The model is calibrated and validated using literature data on natural carbon dioxide reservoirs, resulting in a set of IF-THEN rules that are readily interpreted by decision-makers. The approach developed here also includes rule simplification features and the capability to account for statistical Type I (false positive) and Type II (false negative) errors. Different sets of rules can be generated using the model based on user-defined number of hyperboxes. The best set of rules can be selected based on a combination of its performance with the validation data and consistency with expert knowledge. Using the case study for identifying secure CO2 reservoirs, the set of rules which resulted in zero false positives using the validation data was generated using three hyperboxes. However, an alternative set of rules which falsely predicted two out of three insecure sites as positive provides simpler rules indicating CO2 density and reservoir depth as the most important criteria.

Isotopically anomalous organic carbon in the aftermath of the Marinoan snowball Earth.

Throughout most of the sedimentary record, the marine carbon cycle is interpreted as being in isotopic steady state. This is most commonly inferred via isotopic reconstructions, where two export fluxes (organic carbon and carbonate) are offset by a constant isotopic fractionation of ~25 (termed ). Sedimentary deposits immediately overlying the Marinoan snowball Earth diamictites, however, stray from this prediction. In stratigraphic sections from the Ol Formation (Mongolia) and Sheepbed Formation (Canada), we observe a temporary excursion where the organic matter has anomalously heavy C and is grossly decoupled from the carbonate C. This signal may reflect the unique biogeochemical conditions that persisted in the aftermath of snowball Earth. For example, physical oceanographic modeling suggests that a strong density gradient caused the ocean to remain stratified for about 50,000years after termination of the Marinoan snowball event, during which time the surface ocean and continental weathering consumed the large atmospheric CO2 reservoir. Further, we now better understand how C records of carbonate can be post-depostionally altered and thus be misleading. In an attempt to explain the observed carbon isotope record, we developed a model that tracks the fluxes and isotopic values of carbon between the surface ocean, deep ocean, and atmosphere. By comparing the model output to the sedimentary data, stratification alone cannot generate the anomalous observed isotopic signal. Reproducing the heavy C in organic matter requires the progressively diminishing contribution of an additional anomalous source of organic matter. The exact source of this organic matter is unclear.

New palynostratigraphic data of the Irati (Assistência Member) and the Corumbataí formations, Paraná Basin, Brazil, and correlation with other south American basins

This research presents the palynostratigraphy of organic-rich shales from the Irati and the Corumbataí formations, Paraná Basin (PB), Southeastern Brazil, as part of an unconventional hydrocarbon source rock and CO2 reservoir assessment study. Thirty-four samples from the Corumbataí Formation and the Assistência Member of the Irati Formation were collected in the states of Goiás (northern border of the PB), São Paulo and Paraná (eastern and southern border of the PB, respectively). The acquired data allowed to establish a comprehensive palynostratigraphic study across the basin where a total of 18 pollen genera (34 pollen species), seven spore genera, four microplankton genera (1 species), and Chlorophyceae algae species where identified. The palynostratigraphic analysis also reveals a clear dominance of bisaccate pollen grains such as Corisaccites alutas, Lueckisporites virkkiae, and Weylandites lucifer. The Lueckisporites virkkiae zone was identified in the upper part of the Irati Formation (Assistência Member) and the lowermost part of the Corumbataí Formation, indicating a Kungurian to Roadian age for this part of the succession. Differences in the Guttulapollenites hannonicus and Tornopollenites toreutos biostratigraphic ranges, recovered in the Corumbataí Formation, suggest an earlier development of these species in the Paraná Basin during the middle Permian. Therefore, to evaluate the differences in the first occurrences of key species within the Paraná Basin, a close palynostratigraphic correlation between the main Guadalupian-Lopingian South American Gondwana basins is tentatively established.

ASSESSING THE INFLUENCE OF EXTRACTED FLUID AND OPERATIONAL CONDITIONS ON CORROSION OF GAS FIELD EQUIPMENT

Background The main intensifier of corrosion at the objects of the studied oil and gas condensate field is carbon dioxide corrosion (CDC). Aims and Objectives Based on the data from well surveys, analyze the factors affecting the corrosiveness of the media: CO2 partial pressure, temperature, reservoir pressure, pH, salinity, and water composition. After compiling the ion balance and recalculating it to the salts used in the manufacture of model solutions of the salts, make up three model waters corresponding to individual and mixed formations for further testing. Results The main danger in CO2 presence is not general, but local corrosion occurring in the fluid flow under conditions when FeCO3 films, although formed, but at low temperatures characteristic for the studied field, they are not stable enough. The appearance of a crack in the FeCO3 film initiates its cleavage, at this point the CDC begins, creating a carbonate film, which with a certain thickness cracks and chips. Some erosions are formed within the other of corrosive areas. Such local corrosion damages are developing, leading to deep (or through) pitting, to damages occupying the big area in interconnection of separate local corrosion defects on an internal surface of elements of a wellhead. Calculations of corrosion damages depth on a flange from a wellhead after removing the corrosion products testify that corrosion depth damages are from 1.0 to 2.5 mm. As the inspections show, the damages made by CDC are observed not only on a well head, but also in pump-compressor pipes of the wells. Operational tests of various grades of steel in the well media, characterized by high CO2 content (up to 1.7 %), showed that most of them are unstable to CDC, with except the alloy steel 12X18N10T. The rate of general (uniform) corrosion reaches several mm/year, including the low-alloy steel 09G2C used for most elements of the wellhead.

Structural Dynamics of An ELM-11 Framework Transformation Accompanied with Double-Step CO2 Gate sorption: An NMR Spin Relaxation Study

[Cu(4,4'-bipyridine)2(BF4)2] (ELM-11), an elastic layer-structured MOF (metal-organic framework), is expected to be a sophisticated CO2 reservoir candidate because of its high capacity and recovery efficiency for CO2 sorption. While ELM-11 shows a unique double-step gate sorption for CO2 gas, the dynamics of the structural transition have not yet been clarified. In this study, the dynamics of the 4,4'-bipyridine linkers and the BF4- anions were studied by determining 1H spin-lattice relaxation times (T1). The ELM-11 structural transition accompanying CO2 sorption was also examined through the CO2 uptake dependence of the 1H spin–spin relaxation time (T2), in addition to T1. In its closed form, the temperature dependence of the 1H T1 of ELM-11 was analyzed by considering the contributions of both paramagnetic and dipolar relaxations, which revealed the isotropic reorientation of BF4- and the torsional flipping of the 4,4'-bipyridine moieties. The resultant activation energy of 32 kJ mol-1 for the isotropic BF4− reorientation is suggestive of strong (B-F...Cu2+) interactions between Cu(II) and the F atoms in BF4−. Furthermore, the CO2 uptake dependence of T1 was found to be dominated by competition between the increase in the longitudinal relaxation time of the electron spins and the decrease in the spin density in the unit cell.

Authigenic titanite in weathered basalts: Implications for paleoatmospheric reconstructions

The stability of titanite is sensitive to temperature and partial pressure of CO2. The finding of authigenic titanite grains in weathering regolith formed on Paraná basalts, Brazil, under tropical climatic conditions, reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures. Being unusual nowadays, this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area. The tiny grains of 10 ​μm are forming in the microscopic voids in the rock. Also, large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170 ​μm. The titanites of second type often coexist with chalcedony and barite. No carbonate minerals were found in the weathering profile. Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly, increased Al2O3 content and low content of trace elements. Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase. The titanite precipitation is controlled by slow diffusion in poorly-aerated, highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2. However, the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite. We demonstrate a complex feedback between CO2 and soil carbonates. The rise in pCO2 triggers the precipitation of calcite in the weathering regolith, but the greenhouse effect increasing the temperature can cease carbonate deposition. Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.

Analysis of surface gravity and ground deformation responses of geological CO2 reservoirs to variations in CO2 mass and density and reservoir depth and size

The strength and direction of gravity and ground deformation anomaly vectors over normal and tight reservoirs after injection of CO2 depend on the reservoir and CO2 properties. Some of these properties, such as porosity, permeability, and size, define the reservoir type and therefore determine the existence or sign of the anomalies, indirectly. However, some other properties of reservoirs, such as reservoir depth, horizontal extension of CO2 plume, and CO2 mass amount and density, affect the strength of the measurements directly. Gravimetric and geodetic modelling of synthetic CO2 reservoirs can quantify each of the direct effects that represent the expected signals over different geological settings. We present gravity signal as the gravity increase due to CO2 mass attraction, and its combination with the gravity decrease caused by ground uplift. Our results indicate that the reservoir depth and horizontal extension, along with the injected mass, have significant influences on both ground deformation and gravity signals. The results also demonstrate that the horizontal extension of the CO2 distribution decreases the dependency on the depth. In addition, the observed gravity signal over CO2 reservoirs is dominated by the free-air effect from large ground deformation. Finally, the gravity effect over both normal and tight reservoirs and the ground surface deformation over tight reservoirs are highly dependent on the density change of the injected CO2 inside the reservoir as a result of depth dependant changes of pressure and temperature.

Greenhouse gas fluxes from reservoirs determined by watershed lithology, morphometry, and anthropogenic pressure

Human population growth has increased the demand for water and clean energy, leading to the massive construction of reservoirs. Reservoirs can emit greenhouse gases (GHG) affecting the atmospheric radiative budget. The radiative forcing due to CO2, CH4, and N2O emissions and the relative contribution of each GHG in terms of CO2 equivalents to the total forcing is practically unknown. We determined simultaneously the CO2, CH4, and N2O fluxes in reservoirs from diverse watersheds and under variable human pressure to cover the vast idiosyncrasy of temperate Mediterranean reservoirs. We obtained that GHG fluxes ranged more than three orders of magnitude. The reservoirs were sources of CO2 and N2O when the watershed lithology was mostly calcareous, and the crops and the urban areas dominated the landscape. By contrast, reservoirs were sinks of CO2 and N2O when the watershed lithology was predominantly siliceous, and the landscape had more than 40% of forestal coverage. All reservoirs were sources of CH4, and emissions were determined mostly by reservoir mean depth and water temperature. The radiative forcing was substantially higher during the stratification than during the mixing. During the stratification the radiative forcings ranged from 125 mg CO2 equivalents m−2 d−1 to 31 884 mg CO2 equivalents m−2 d−1 and were dominated by the CH4 emissions; whereas during the mixing the radiative forcings ranged from 29 mg CO2 equivalents m−2 d−1 to 722 mg CO2 equivalents m−2 d−1 and were dominated by CO2 emissions. The N2O contribution to the radiative forcing was minor except in one reservoir with a landscape dominated by crops and urban areas. Future construction of reservoirs should consider that siliceous bedrocks, forestal landscapes, and deep canyons could minimize their radiative forcings.

Increased CO2 storage capacity using CO2-foam

Reduction of the CO2 mobility is beneficial during subsurface sequestration of anthropogenic CO2 in saline aquifers and hydrocarbon reservoirs by mitigating flow instabilities leading to early gas breakthrough and poor sweep efficiency. Injection of CO2 foam is a field-proven technology for gas mobility control. Foam generation and coalescence are compared between six commercially available surfactants with a range in CO2 solubility, during unsteady state injection of dense CO2-foam in a long sandstone outcrop core (1.15 m). Foam generation categories and foam decay were defined based on the observed changes in foam apparent viscosity during generation and coalescence. The degree of CO2 solubility influenced apparent viscosity development and peak foam strength for the tested surfactants. Variations in foam peak strength resulted in a range of water saturations at CO2 breakthrough (up to 24 percentage points difference observed experimentally), with implications for the CO2 storage capacity.

Comparison of the Absolute Adsorption of CH4, n-C4H10, and CO2 on Shale

Comprehensive knowledge of absolute adsorption of light hydrocarbons and CO2 is significant for shale reservoir assessment and CO2 stimulation optimization. In this work, excess adsorption isotherm...

Development and surrogate-based calibration of a CO2 reservoir model

Simulation-optimization framework is a widely used approach for numerical model calibrations, though its primary difficulty is its high-demand of computational efforts. In this study, Bagging MARS (BMARS) adapted from Multivariate Adaptive Regression Splines (MARS) algorithm, is used to construct the surrogate of a three-dimensional CO2 reservoir model, which is developed to simulate CO2 injection and migration in a fault-compartmentalized underground reservoir. The BMARS surrogate model is then used in model calibration to estimate specified reservoir model input parameters efficiently. The results demonstrate that the BMARS model can improve fitting stability and predictive accuracy against the ordinary MARS model. Parameter sensitivity analysis, which is efficiently conducted using the BMARS model, suggest that permeability of Fault#10 and caprock dominate the pressure buildup in this fault-compartmentalized reservoir. Hence priority should be given to investment in estimating these two reservoir properties. Overpressure propagation and CO2 migration in the reservoir responding to three years of CO2 injection are also analyzed using the calibrated model. The calibrated water-CO2 flow model could be a useful tool to evaluate the future operation and risk assessment of the reservoir. The results comparison and sensitivity analysis demonstrated the proposed BMARS-based simulation–optimization framework is an efficient and accurate model calibration approach.

Internal Structure and CO2 Reservoirs of Habitable Water Worlds

Abstract Water worlds are water-rich (>1 wt% H2O) exoplanets. The classical models of water worlds considered layered structures determined by the phase boundaries of pure water. However, water worlds are likely to possess comet-like compositions, with between ∼3 and 30 mol% CO2 relative to water. In this study, we build an interior structure model of habitable (i.e., surface liquid ocean–bearing) water worlds using the latest results from experimental data on the CO2–H2O system to explore the CO2 budget and localize the main CO2 reservoirs inside of these planets. We show that CO2 dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO2 if the planet accretes more than 11 wt% of volatiles (CO2 + H2O) during its formation. If the atmosphere holds more than a negligible amount of the CO2 (>0.01% of the planet mass), the planet will not have a habitable surface temperature. We propose a new, potentially dominant, CO2 reservoir for water worlds: CO2 buried inside of the high-pressure water ice mantle as CO2 ices or (H2CO3 · H2O), the monohydrate of carbonic acid. If insufficient amounts of CO2 are sequestered in either this reservoir or the planet’s iron core, habitable-zone water worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

Controls on Gas Domains and Production Behaviour in A High-Rank CSG Reservoir: Insights from Molecular and Isotopic Chemistry of Co-Produced Waters and Gases from the Bowen Basin, Australia

This paper uses hydrochemical and multi-isotope analysis to investigate geological controls on coal seam gas (CSG) saturation domains and gas well production performance in a high-rank (vitrinite reflectance (Rv) > 1.1) CSG field in the north-western Bowen Basin, Australia. New hydrochemical and stable isotope data were combined with existing geochemical datasets to refine hypotheses on the distribution and origins of CSG in two highly compartmentalized Permian coal seams. Stable isotopic results suggest that geographic variations in gas content, saturation and production reflect the extent of secondary microbial gas generation and retention as a function of hydrodynamics. δ13C and δ2H data support a gas mixing hypothesis with δ13C-CH4 increasing from secondary biogenic values to thermogenic values at depth (δ13C −62.2‰ to −46.3‰), whereas correlated methane and carbon dioxide carbon isotope compositions, Δ13C(CO2–CH4) values and δ13CDIC/alkalinity trends are largely consistent with microbial CO2 reduction. In addition, below 200 m, the majority of δ13C-CO2 values are positive (δ13C: −1.2‰ to 7.1‰) and δ13CDIC shows an erratic increase with depth for both seams that is characteristic of evolution via microbial activity. The progression of carbon isotope values along the CO2 reduction fractionation line suggests progressive depletion of the CO2 reservoir with increasing depth. Faults clearly segment coal seams into areas having significantly different production, with results of geochemical analysis suggesting that pooling of biogenic gas and waters and enhanced methanogenesis occur north of a faulted hinge zone.

Numerical simulation of crystal growth of CO2 hydrate within microscopic Sand pores using phase field model for the estimation of effective permeability

Carbon dioxide capture and storage is an efficient technology to reduce CO2 emission. One of the reservoirs of CO2 is an aquifer in the sub-seabed geological formation under a caprock. However, there is a risk of CO2 leakage even though such probability is extremely low. When the water depth of a storage site is large: say, about 400 m or more, leaked CO2 changes its form to gas hydrate, which may block CO2 rise in the sediment. To estimate the sealing potential of CO2 hydrate, it is necessary to evaluate effective permeability of the sediment after CO2 hydrate forms. In this study, a series of numerical models were used to investigate microscopic hydrate distribution that essentially controls the effective permeability. The method consists of packing sand grains within microscopic computational domains, arranging water and CO2 phases in the pore space of the packed sand grains, placing multiple hydrate nuclei, and growing hydrate in the pores of the sand grains. First, we derived a value of the interface mobility of CO2 hydrate by fitting calculated growth rate of a hydrate spherule to a measurement in the literature. Then, CO2 hydrate formation was simulated within microscopic computational domains consisting of sand grains and water-CO2 two phases. Finally, efficient permeability was estimated using the results of the simulation of water flow through the pore space, regarding the formed hydrate as a solid. The calculation results indicated the differences in hydrate distribution in the pore space and in resulting effective permeability, depending on hydrate saturations, initial water saturations, and contact angles of water on the sand surface.

Sr-isotopic ratios trace mixing and dispersion in CO2 push-pull injection experiments at the CO2CRC Otway Research Facility, Australia

Analysis of 87Sr/86Sr ratios and modelling of formation water, injection water and produced water compositions from the CO2CRC Otway Research Facility in Victoria, Australia are used to test tracer behaviour and response in push-pull experiments. Such experiments are an essential pre-requisite to understanding the controls imposed by reservoir heterogeneities on CO2 dissolution rates which may be an important stabilising mechanism for geological carbon storage. The experiments (Otway stage 2B extension in 2014) comprised two sequential tests in which ~100 t of CO2-saturated water was injected with combinations of Sr and Br or Li and Fluorescein tracers, each injection being followed by two staged extractions of ~10 t and a final extraction of ~50 t all spaced at ~10 day intervals. Analysis of the 87Sr/86Sr ratios of the produced fluids from the first injection, spiked with SrCl2 and NaBr, is consistent with Sr behaving conservatively. This contrasts with previous interpretations in which Br was argued to have behaved conservatively while Sr, which dilutes ~three times as fast as Br, was thought to be lost to a mineral phase. Such Sr-loss cannot explain the evolution of 87Sr/86Sr ratios. The analysis of 87Sr/86Sr ratios in the waters produced after the second injection episode, spiked with LiCl and Fluorescein tracers, allows calculation of the fractions of the formation waters and the injection waters from both tests 1 and 2. The Sr, Li and SO4 tracers (the later formed by oxidation of formation sulphide) all indicate similar rates of dilution that is consistent with conservative behaviour. The results of the two injection episodes with spaced extractions are compared with two subsequent push-pull injections in which the produced waters, spiked with methanol, were extracted continuously. These continuous extraction experiments exhibited significantly less dilution over the same range of produced to injected water volumes (up to only ~0.6) than the earlier experiments with spaced extractions. This implies that some process related to the pauses in extraction enhances mixing of injected and formation waters. Achieving the objective of using push-pull experiments to assess reservoir heterogeneities and CO2 dissolution rates will require better assessment of the various tracers to establish which behave conservatively followed a proper understanding of the causes of the variations in mixing as fluids are extracted from the formations.

Rapid Loss of CO2 From the South Pacific Ocean During the Last Glacial Termination

AbstractDuring the termination of the last ice age, atmospheric CO2 rose ~80 ppm, but the origin of this carbon has not been fully resolved. Here we present novel constraints on the patterns and processes of deglacial CO2 release using three marine sediment cores from the southwest Pacific. Carbon isotopes (δ13C) and boron to calcium ratios (B/Ca) of benthic foraminiferal calcite provide records of the δ13C of total dissolved inorganic carbon (DIC) and carbonate ion concentrations ([CO32−]) in seawater, respectively. Together these properties indicate enhanced storage of respired CO2 between 1.2‐ and 2.5‐km water depth during the Last Glacial Maximum (19–23 thousand years ago, ka). The first major rise in atmospheric CO2 during the last deglaciation, at the time of Heinrich Stadial 1, was accompanied by increases in δ13C and [CO32−] at all core depths. The initial increases could be attributed to southward shifted westerly winds driving increased upwelling in the Southern Ocean, sending a signal of enhanced ventilation northward into the Pacific. Our results confirm that southern Pacific interior water masses served as an important reservoir for CO2 during the last glacial period, likely extracted from the atmosphere via the biologic pump. Some abrupt changes in Pacific carbon storage coincide with changes in Southern Ocean pH (Rae et al., 2018, https://doi.org/10.1038/s41586‐018‐0614‐0), upwelling indicators (Anderson et al., 2009, https://doi.org/10.1126/science.1167441), and pCO2 (Monnin et al., 2001, https://doi.org/10.1126/science.291.5501.112), indicating that portions of the deep Pacific carbon pool can be ventilated rapidly to the atmosphere via the Southern Ocean.

Multi-physics modeling of injected nanoparticles effect on remediation of CO2 leakage through cracks

One potential risk in CO2 sequestration is the leakage of carbon dioxide, which can result in contamination of underground water, creating potential threats to existing ecosystems. The common leakage pathway is through the pre-existing fractures or discontinuities within cement in the wellbore, incurred by the environmental conditions imposed on the cement. Injecting nanoparticles into pre-existing cracks is one of the most recently proposed ideas for mitigating fracture propagation in cement CO2 sequestration. To demonstrate the feasibility of this new technology, a numerical approach was taken in this work, as it is challenging to investigate it in a laboratory setting. We proposed a coupled ALE (Arbitrary Lagrangian–Eulerian)–DEM (Discrete Element Method)–peridynamic modeling strategy within the LS-Dyna package to investigate the intertwined interaction among the CO2 fluid flow, native fluid (e.g., brine), particle clusters, and cracks within the cement. The numerical results demonstrate that injected nanoparticles can effectively reduce the pressure exerted on the crack surface. Accordingly, the potential fracture propagation at the crack tip would be reduced compared to corresponding cases without nanoparticels as pressurized by fluid flow. This result verifies the effectiveness of proposed nanoparticle injection technology. Finally, using this established modeling strategy, the effect of filling particles on the fracture mitigation for different crack geometries (e.g. particle cluster patterns, aspect ratio of crack aperture and length) and CO2 reservoir pressure are examined. The result shows that injected particles successfully reduce the fracture propagation in these scenarios.