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The storage of fluids in the subsurface is critical for a broad spectrum of applications including managed aquifer recharge, storage of liquefied carbon dioxide and hydrogen, geothermal heat extraction and exploitation of hydrocarbon. It is surprising then, that there has been relatively little measurement of the vertical distribution of poroelastic storage in geologic formations as compared with permeability. We present experiments in which fluid was injected into an important regional aquifer and the depth‐dependent strain response measured using fiber optic distributed acoustic sensing. The formation expansion and contraction in response to fluid injection were several 100 nanostrain. Strain, and the implied storage distribution, was highly localized in specific strata and demonstrated complex, hydromechanical behavior. This new window into fluid‐geomechanical coupling undermines some typically use models and observations currently in practice, but provides potential for complete representation and prediction of fluid storage in the subsurface. Plain Language Summary: A fiber optic cable was used to measure strain in response to water injection and withdrawal in a sandstone aquifer. The strain was found to be focused in limited strata within the aquifer. In some strata, the formation expanded with injection, and in others the formation contracted with injection. This complex behavior is attributed to the interaction between fluid flow and mechanical strain in the porous rock and is contrary to common models of water storage which predict a proportionate expansion of pore space with injection. These results provide important insight into understanding transient flow response to impulse and oscillatory pressure loading of the well. Key Points: Strain and flow direction was correlated or anti‐correlated with injection head, depending on injection intervalInjection and strain behavior was not simply correlated to geophysical or lithologic logsDynamic injection/withdrawal tests are of limited predictive value to managed aquifer recharge [ABSTRACT FROM AUTHOR]

Unconformity‐related uranium (URU) deposits in the Athabasca Basin, Canada, include the highest grade, large tonnage deposits in the world. Recent studies of the Patterson Lake corridor uranium deposits suggest a deep heat source enhances hydrothermal fluid flow and incursion of basinal brines along brittlely reactivated ductile shear zones. However, the spatial extent of the ore systems and lower crustal features capable of driving the hydrothermal cells remained largely unresolved. Three‐dimensional electrical conductivity models derived from inversion of magnetotelluric data and coincident gravity modeling identified a voluminous conductivity anomaly and corresponding gravity low related to a belt of high‐heat producing intrusions that dips below the deposit. Shallow conductive bodies are identified below the deposits and similarly prospective corridors. The volume and location of the intrusive bodies may have provided a source of radiogenic heat that helped drive remobilization of fluids along reactivated structures, redefining the spatial extent of URU systems. Plain Language Summary: The western Athabasca Basin, straddling the border of Saskatchewan and Alberta in Canada, is home to some of the highest‐grade, large tonnage uranium deposits in the world. Recent studies have suggested a spatial connection between uranium ore systems that are found near the earth's surface and geological processes occurring deep within the crust. However, the processes connecting the lower crust to these shallow deposits is poorly understood. This study used 3D models created from magnetotelluric data, a passive a geophysical technique that measures the earth's natural electric and magnetic fields, to image the earth from surface to a depth of 40 km. We identified a voluminous igneous intrusion that extends from the surface to great depths in the earth's crust. We propose that this intrusion may have contributed to the uranium endowment of the basin, and that radiogenic heat from the large igneous body helped circulate uranium‐bearing fluids through the shallow crust along reactivated geologic structures. The modeling, when combined with other geoscientific datasets, showcases the role of high‐heat producing granitic intrusions in driving the hydrothermal fluid cells that formed the deposits. Key Points: Integrated resistivity—gravity modeling over the Arrow uranium deposit in CanadaMagnetotelluric inversion images deep‐seated thermal source and fluid pathways that formed some of the highest‐grade uranium depositsHolistic ore system model illustrates relationship between crustal ore system and lower crustal resistivity anomalies [ABSTRACT FROM AUTHOR]

Estimating the longitudinal dispersion coefficient DL in flow through heterogeneous porous media is paramount to many problems in geological formations. Moreover, although it is well‐known that DL is sensitive to the morphology of such formations, it has been very difficult to establish a firm link between the two. We describe a novel deep convolutional neural network (DCNN) for estimating DL. The inputs for training of the network are a large and diverse set of data consisting of three‐dimensional images of porous media, as well as their porosity, and the associated DL values computed by random‐walk particle‐tracking (RWPT) simulations. The trained network predicts DL very rapidly, and its predictions are in excellent agreement with the data not used in the training. Thus, a combination of the DCNN and RWPT simulation provides a powerful tool for studying many flow‐related phenomena in geological formations, and estimating their properties. Plain Language Summary: Measuring or computing the dispersion coefficient DL in flow through porous media, a fundamental characteristic of transport in geological formations and risk analysis, is a time‐consuming endeaver. Moreover, although DL is sensitive to the morphology of a pore space, a direct link between the two has been missing. We proposed a deep convolutional neural network for predicting DL, using 3D images of porous media and their porosities. The accuracy of the predictions for the actual data indicates that the ability of the network for estimating the important flow and transport properties of porous media for new input data. The present work was at the core scale, on the order of the physical sizes of the sandstones used in our study. The same approach may be used at the eld scale. In that case, one generates the input data by following the same procedure, except that the data should be generated for models in which the permeability and porosity of the formation vary spatially, and represent correlated fields. Work in this direction is in progress. Key Points: Dispersion coefficientConvolutional neural networkFlow through porous media [ABSTRACT FROM AUTHOR]

Geologic carbon storage is required for achieving negative CO2 emissions to deal with the climate crisis. The classical concept of CO2 storage consists in injecting CO2 in geological formations at depths greater than 800 m, where CO2 becomes a dense fluid, minimizing storage volume. Yet CO2 has a density lower than the resident brine and tends to float, challenging the widespread deployment of geologic carbon storage. Here, we propose for the first time to store CO2 in supercritical reservoirs to reduce the buoyancy‐driven leakage risk. Supercritical reservoirs are found at drilling‐reachable depth in volcanic areas, where high pressure (p > 21.8 MPa) and temperature (T > 374°C) imply CO2 is denser than water. We estimate that a CO2 storage capacity in the range of 50–500 Mt yr−1 could be achieved for every 100 injection wells. Carbon storage in supercritical reservoirs is an appealing alternative to the traditional approach. Plain Language Summary: Geologic carbon storage, which consists in returning carbon deep underground, should be part of the solution to effectively reach carbon neutrality by the middle of the century to mitigate climate change. CO2 has been traditionally proposed to be stored in sedimentary rock at depths below 800 m, where CO2 becomes a dense fluid, minimizing the required storage volume. Nevertheless, CO2 is lighter than brine in the traditional concept, so a rock with sufficient sealing capacity should be present above the storage formation to prevent leakage. Indeed, one of the main hurdles to deploy geologic carbon storage is the risk of CO2 leakage. To reduce this risk, we propose a novel storage concept that consists in injecting CO2 in reservoirs where the pore water stays in supercritical conditions (pressure and temperature higher than 21.8 MPa and 374°C, respectively) because at these conditions, CO2 becomes denser than water. Consequently, CO2 sinks, leading to a safe long‐term storage. This concept, which could store a significant portion of the total requirements to decarbonize the economy, should start being implemented in deep volcanic areas, given that supercritical reservoirs are found at relatively shallow depths between 3 and 5 km. Key Points: We propose a novel geologic carbon storage concept that reduces the buoyancy‐driven CO2 leakage riskBy injecting CO2 in reservoirs where the resident water stays in supercritical conditions, CO2 sinks because it is denser than pore waterSupercritical reservoirs are found at relatively shallow depths between 3 and 5 km in deep volcanic areas [ABSTRACT FROM AUTHOR]

The rate of carbon dioxide (CO2) dissolution in saline aquifers is the least well‐constrained of the secondary trapping mechanisms enhancing the long‐term security of geological carbon storage. CO2 injected into a heterogeneous saline reservoir will preferentially travel along high permeability layers increasing the CO2‐water interfacial area which increases dissolution rates. We provide a conservative, first‐principles analysis of the quantity of CO2 dissolved and the rate at which free‐phase CO2 propagates in layered reservoirs. At early times, advection dominates the propagation of CO2. This transitions to diffusion dominated propagation as the interfacial area increases and diffusive loss slows propagation. As surrounding water‐filled layers become CO2 saturated, propagation becomes advection dominated. For reservoirs with finely bedded strata, ∼10% of the injected CO2 can dissolve in a year. The maximum fraction of CO2 that dissolves is determined by the volumetric ratio of water in low permeability layers and CO2 in high permeability layers. Plain Language Summary: To limit global warming to 2°C, it is likely that large amounts of carbon dioxide (CO2) will need to be stored underground. A significant fraction of the total possible storage space for CO2 is in salt water reservoirs, kilometers beneath the surface. It is important that once the CO2 has been injected underground, it is securely trapped, otherwise, there is a risk that it could leak back to the surface. After the CO2 is injected into these reservoirs, it can dissolve in the surrounding water, greatly reducing the risk of leakage, although complete dissolution of all the injected CO2 may take millions of years. However, preferential flow of CO2 along more permeable layers in geological formations creates a complex front between the water and CO2 which increases the surface area available for dissolution. This study calculates the minimum amount of injected CO2 that can dissolve in such a reservoir and how far it travels. Using injection of CO2 for enhanced oil recovery at the Salt Creek Field in Wyoming as an example, we find that in one year around 10% of the total injected CO2 can dissolve into the surrounding water by this process and become trapped. Key Points: Injection of carbon dioxide into finely bedded reservoirs leads to enhanced contact area with water and hence enhanced dissolution ratesPropagation rates of free‐phase carbon dioxide transition from advection to diffusion dominated as the contact area with water increasesFor injection into the Salt Creek reservoir, Wyoming, nearly 10% of the injected carbon dioxide is predicted to dissolve in one year [ABSTRACT FROM AUTHOR]

The dynamic properties of freestanding rock landforms are a function of fundamental material and mechanical parameters, facilitating noninvasive vibration‐based structural assessment. Characterization of resonant frequencies, mode shapes, and damping ratios, however, can be challenging at culturally sensitive geologic features, such as rock arches, where physical access is limited. Using sparse ambient vibration measurements, we describe three resonant modes between 1 and 40 Hz for 17 natural arches in Utah spanning a range of lengths from 3–88 m. Modal polarization data are evaluated to combine field observations with 3‐D numerical models. We find outcrop‐scale elastic moduli vary from 0.8 to 8.0 GPa, correlated with diagenetic processes and identify low damping at all sites. Correlation of dense‐array measurements from one arch validates predictions of simple bending modes and fixed boundary conditions. Our results establish use of sparse ambient resonance measurements for structural assessment and monitoring of arches and similar freestanding geologic features worldwide. Plain Language Summary: Natural rock arches vibrate under ambient conditions with a unique set of frequencies controlled by geometry, host material, and interactions with nearby bedrock. Recent rockfall events at well‐known arches in Utah have highlighted the need to develop noninvasive assessment methods to better understand how these sensitive landforms evolve. To reduce site impacts, we employed limited instrumentation to measure ambient vibrations of 17 arches across Utah for identification of resonant frequencies. We combine direct observations with predictive numerical models to visualize resonant mode shapes and describe the controlling material properties and structural boundaries. In defining the first three modes of each site, we are able to characterize dynamic properties at arches encompassing several geologic formations and a range of length scales. These results establish a versatile method for structural evaluations of arches and other significant freestanding geologic features. Key Points: Single‐station ambient vibration data and numerical modeling describe the dynamic response of natural arches with limited site accessDense seismic array directly resolves resonant mode shapes, validating predictions of simple bending modes and fixed boundary conditionsSandstone arches in Utah resonate between 1 and 40 Hz, exhibit low damping, and have stiffness that vary with diagenetic conditions [ABSTRACT FROM AUTHOR]

Dynamic topography due to mantle flow contributes to shaping Earth's evolving landscapes by affecting sediment routing, which has rarely been explored in source‐to‐sink contexts. Here we design a generic model to investigate the impact of dynamic topography on both landscape evolution and stratigraphic formations. An imposed wave of dynamic topography propagates laterally under a fixed continent, exerting transient surface uplift and subsidence. We find that a migrating dynamic topography can induce significant drainage reorganizations and affect sediment routing from source to sink. Variations in sediment supply driven by the lateral migrating dynamic topography contribute to the formation of diachronous unconformities along the margin. The predicted sediment flux histories are then put into perspective with the Cretaceous sedimentary records along the Southern African margins. Finally, we demonstrate that correlating offshore depositional hiatuses and unconformities has the potential to constrain the spatiotemporal evolution of past dynamic topography events. Plain Language Summary: Convective motion within Earth's interior result in transient uplift and subsidence of the surface is called dynamic topography. This process slowly shapes landscapes over millions of years and identifying its fingerprints in the rock record remains a challenge. This study uses numerical modeling to investigate the erosional and depositional response of landscapes to sea level change and to mantle flow. We show that unlike sea level change, dynamic topography reorganizes river flows and changes sediment supply to offshore regions, generating various stratal patterns. We model a simple circular landscape that evolves similarly to the southern African landscape between 140 and 66 million years ago and suggest sedimentary fingerprints to link the evolution of the Earth's surface to the dynamics of its deep interior. Key Points: A propagating wave of dynamic topography can induce significant drainage reorganizations and affect sediment routing from source to sinkVariations in sediment supply driven by the migration of dynamic topography can create diachronous unconformities along continental marginsOur model predicts sediment flux histories comparable to that along the Southern African margins during Cretaceous times [ABSTRACT FROM AUTHOR]

Estimating flow and transport properties of porous media that undergo deformation as a result of applying an external pressure or stress is important to a wide variety of processes, ranging from shale formations into which a fracking liquid is injected to CO2 sequestration in geological formations. We propose a novel model for estimating the effective permeability of such porous media. Given the pore‐size distribution (PSD) of a porous medium before deformation, as well as the Young's modulus of its grains, the model uses Hertz‐Mindlin theory of contact between grains to compute the new PSD that results from applying an external pressure P to the medium and utilizes the updated PSD in the effective‐medium approximation to estimate the effective permeability at P. Comparison between the predictions and experimental data for several types of sandstones indicates excellent agreement between the two. Key Point: This demonstrates the first application of the effective‐media approximation to estimating the permeability of deforming porous media [ABSTRACT FROM AUTHOR]

Earthquakes caused by human activities have been observed for decades. Often these are related to industrial activities pumping fluids into deep geologic formations, like with wastewater disposal. The simplest theory connecting these processes to earthquakes is straightforward: injection leads to fluid pressure changes that either reduce the strength of preexisting faults or generate new faults. In practice, the conditions that lead to induced earthquakes are not always clear in ways that can be generalized. Kao et al. (2018, https://doi.org/10.1029/2018GL079288) show how the distribution of induced earthquakes in Western Canada relate to natural rates of deformation in the crust. Using these new results, they discuss an intriguing paradox: induced seismicity can cause short‐term increases in the seismic hazard that are followed by a period of reduced seismic hazard. Such hazard‐reducing scenarios are plausible but hinge upon simplifying assumptions about how the crust stores and releases strain energy in the form of earthquakes. Key Points: Geodetic data indicate a close relationship between crustal strain rates and induced earthquakesInduced earthquakes might reduce the seismic hazard in the long runHazard‐reducing scenarios hinge critically on a few major assumptions [ABSTRACT FROM AUTHOR]