NMR study comparing capillary trapping in Berea sandstone of air, carbon dioxide, and supercritical carbon dioxide after imbibition of water

Carbon geosequestration (CGS) has been identified as a key technology to reduce anthropogenic greenhouse gas emissions and thus significantly mitigate climate change. In CGS, CO is captured from large point-source emitters (e.g., coal fired power stations), purified, and injected deep underground into geological formations for disposal. However, the CO has a lower density than the resident formation brine and thus migrates upward due to buoyancy forces. To prevent the CO from leaking back to the surface, four trapping mechanisms are used: (1) structural trapping (where a tight caprock acts as a seal barrier through which the CO cannot percolate), (2) residual trapping (where the CO plume is split into many micrometer-sized bubbles, which are immobilized by capillary forces in the pore network of the rock), (3) dissolution trapping (where CO dissolves in the formation brine and sinks deep into the reservoir due to a slight increase in brine density), and (4) mineral trapping (where the CO introduced into the subsurface chemically reacts with the formation brine or reservoir rock or both to form solid precipitates). The efficiency of these trapping mechanisms and the movement of CO through the rock are strongly influenced by the CO-brine-rock wettability (mainly due to the small capillary-like pores in the rock which form a complex network), and it is thus of key importance to rigorously understand CO-wettability. In this context, a substantial number of experiments have been conducted from which several conclusions can be drawn: of prime importance is the rock surface chemistry, and hydrophilic surfaces are water-wet while hydrophobic surfaces are CO-wet. Note that CO-wet surfaces dramatically reduce CO storage capacities. Furthermore, increasing pressure, salinity, or dissolved ion valency increases CO-wettability, while the effect of temperature is not well understood. Indeed theoretical understanding of CO-wettability and the ability to quantitatively predict it are currently limited although recent advances have been made. Moreover, data for real storage rock and real injection gas (which contains impurities) is scarce and it is an open question how realistic subsurface conditions can be reproduced in laboratory experiments. In conclusion, however, it is clear that in principal CO-wettability can vary drastically from completely water-wet to almost completely CO-wet, and this possible variation introduces a large uncertainty into trapping capacity and containment security predictions.

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Section: Measuring Co2–brine–rock Wettabilitymentioning

confidence: 99%

CO₂–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO₂ Geostorage

2017

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“…For x‐ray tomographic imaging techniques with FOVs comparable to standard plug dimensions (several centimeters), the resolution achievable is on the order of millimeters [ Pini and Benson , ; Niu et al ., ]. One alternative approach for studying rock flooding experiments on this length scale is the use of Nuclear Magnetic Resonance (NMR) imaging techniques [ Prather et al ., ; Vogt et al ., ]. Compared to x‐ray methods, NMR imaging has a considerably poorer spatial resolution, and can potentially be compromised when applied to magnetically heterogeneous materials such as sedimentary rocks.…”

Section: Introductionmentioning

confidence: 98%

Capillary trapping quantification in sandstones using NMR relaxometry

Connolly

Vogt

Iglauer

et al. 2017

Water Resources Research

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Capillary trapping of a non‐wetting phase arising from two‐phase immiscible flow in sedimentary rocks is critical to many geoscience scenarios, including oil and gas recovery, aquifer recharge and, with increasing interest, carbon sequestration. Here we demonstrate the successful use of low field 1H Nuclear Magnetic Resonance [NMR] to quantify capillary trapping; specifically we use transverse relaxation time [T2] time measurements to measure both residual water [wetting phase] content and the surface‐to‐volume ratio distribution (which is proportional to pore size] of the void space occupied by this residual water. Critically we systematically confirm this relationship between T2 and pore size by quantifying inter‐pore magnetic field gradients due to magnetic susceptibility contrast, and demonstrate that our measurements at all water saturations are unaffected. Diffusion in such field gradients can potentially severely distort the T2‐pore size relationship, rendering it unusable. Measurements are performed for nitrogen injection into a range of water‐saturated sandstone plugs at reservoir conditions. Consistent with a water‐wet system, water was preferentially displaced from larger pores while relatively little change was observed in the water occupying smaller pore spaces. The impact of cyclic wetting/non‐wetting fluid injection was explored and indicated that such a regime increased non‐wetting trapping efficiency by the sequential occupation of the most available larger pores by nitrogen. Finally the replacement of nitrogen by CO2 was considered; this revealed that dissolution of paramagnetic minerals from the sandstone caused by its exposure to carbonic acid reduced the in situ bulk fluid T2 relaxation time on a timescale comparable to our core flooding experiments. The implications of this for the T2‐pore size relationship are discussed.

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“…The magnitude of the S gr is dependent on multiple factors, such as the rock's porosity/permeability, microporosity, grain shape, pore network structure, wettability (contact angle (θ )), the interfacial tension of the fluid phases (σ ), the mobility ratio, the rate of displacement (or capillary number), the state of the CO 2 phase, the origin of the CO 2 (free phase or exsolved), the connectivity of the nonwetting phase at the start of imbibition, and the initial gas saturation at the start of imbibition 1 (S gi ). [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The relationship between S gr and S gi , is referred to as the initial-residual saturation curve (IR curve) or trapping model.…”

Section: Introductionmentioning

confidence: 99%

Exploring residual CO₂ trapping in Heletz sandstone using pore‐network modeling and a realistic pore‐space topology obtained from a micro‐CT scan

Rasmusson

Tatomir

et al. 2021

Greenhouse Gases

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Geological storage of CO 2 in deep saline aquifers mitigates atmospheric emissions. In situ storage is facilitated by several trapping mechanisms including residual trapping, which plays a major role in the containment of CO 2 . Understanding the underlying mechanisms of residual trapping is crucial for planning storage projects. Of special interest is the relationship between the initial and residual CO 2 saturations-the so-called IR curve, needed for predictive macroscopic-scale simulations. This study aims to improve the understanding of residual trapping in sandstone from the Heletz site, where extensive field experiments have been performed, by using 3D-image analysis on core sample CT-data. This was done to gain knowledge on physical properties (such as radius, coordination number, aspect ratio, shape factor of pores, and pore connectivity) of importance to residual CO 2 trapping. Pore-network flow modeling on a network representation, with the extracted pore-space topology, was employed to estimate the IR curve. The core sample exhibited pores with a large range of coordination numbers, a mean aspect ratio of 1.4, and shape factors mostly corresponding to triangular cross-sections. The estimated IR curve was monotonic, fitting an Aissaoui-type trapping model, displaying a lower sensitivity to the advancing contact angle than previously thought, and indicating a good ability to residually trap CO 2 . This study provides the first report of values for the three above mentioned properties for Heletz sandstone, and the first estimate of an IR curve for CO 2 /brine in Heletz sandstone based on pore-network modeling on a network with a topology retrieved from a core-sample CT-scan.

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NMR study comparing capillary trapping in Berea sandstone of air, carbon dioxide, and supercritical carbon dioxide after imbibition of water

Cited by 18 publications

References 51 publications

CO₂–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO₂ Geostorage

CO₂–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO₂ Geostorage

Capillary trapping quantification in sandstones using NMR relaxometry

Exploring residual CO₂ trapping in Heletz sandstone using pore‐network modeling and a realistic pore‐space topology obtained from a micro‐CT scan

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NMR study comparing capillary trapping in Berea sandstone of air, carbon dioxide, and supercritical carbon dioxide after imbibition of water

Cited by 18 publications

References 51 publications

CO2–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO2 Geostorage

CO2–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO2 Geostorage

Capillary trapping quantification in sandstones using NMR relaxometry

Exploring residual CO2 trapping in Heletz sandstone using pore‐network modeling and a realistic pore‐space topology obtained from a micro‐CT scan

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CO₂–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO₂ Geostorage

CO₂–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO₂ Geostorage

Exploring residual CO₂ trapping in Heletz sandstone using pore‐network modeling and a realistic pore‐space topology obtained from a micro‐CT scan