Freshwater Aquifers Research Articles

The Crucial Role of Geothermal Fluids in Reducing the Water and Carbon Footprints of Lithium Mining in Salt Flats Worldwide

ABSTRACT Thermal waters, which often have a high Li concentration, can influence the formation of Li-rich brines in the salt flats. Several studies suggest that geothermal activity accelerates the leaching of Li-rich volcanic rocks in the catchment areas of the closed basins, contributing to higher Li concentrations in brines. Considering that there is no salt flat in Chile or other parts of the world that does not have a present-day (active) or palaeo-geothermal system, there is a need for a holistic geoscientific study of the salt flats to investigate the association between lithium enrichment of brine in the salt flats and geothermal systems present in the host closed basins. The expected results of such studies in different salt flats will help understand the role of geothermal systems in forming economic Li deposits that could be selectively mined sustainably. This is because thermal waters can also concentrate Li in specific horizons, allowing for selective extraction with minimal impact on freshwater aquifers. This would be possible because conductive heating by underlying thermal water could induce circulation (convective overturn) of basin brines within hydrologically connected horizons. Accordingly, this geothermally induced brine circulation may develop a heterogeneous subsurface Li distribution, where thermal waters could be instrumental in forming Li-enriched horizons in subsurface brine. Deciphering and modeling the latter will form a strong and tangible basis for developing environmentfriendly methods for Li mining that will have negligible influence on the groundwater and wetland ecosystems using drilling technologies prevalent in the hydrocarbon industry for extracting particular sedimentary horizons. Further, geothermal systems present in the closed hydrologcal basins could aid in reducing the environmental footprint of Li mining by providing thermal energy for extraction processes and electricity generation using low-enthalpy binary power plants. Considering the focus on direct extraction of Li (DLE) in Chile and neighboring countries, it is necesary to integrate it with geothermal following holistic geoscientific studies involving geological, geochemical and geophysical investigations, validated by exploratory drilling. This will help mitigate environmental challenges associated with current DLE technologies by using geothermal water in the extraction process and expertise from the geothermal industry in brine recharge.

Exploring secondary contamination in river and spring waters: A novel phenomenon arising from seawater intrusion into deep coastal aquifers.

Seawater intrusion, characterized by the infiltration of a seawater wedge into deep coastal freshwater aquifers, poses a significant threat to water quality. Despite extensive research on this hydrogeological phenomenon, monitoring remains challenging, often requiring deep drilling that exacerbates aquifer contamination. This study proposes a novel approach for monitoring seawater intrusion based on hydrogeochemical indicators, specifically focusing on secondary contamination observed in river and spring waters along the Black Sea coast of Russia. Using mass spectrometry, we analyzed the abundance and concentrations of 71 elements, identifying key indicators of secondary contamination influenced by the low hypsometric altitudes of the region. In total, 30 river and spring water samples were analyzed. Notable findings include a positive correlation between excess trace elements and Cl- and SO42-, characteristic of seawater. River waters exhibited lower mineralization compared to spring waters, with consistently higher Mn/Br, Cs/Br, and ∑ rare earth element/Br ratios, serving as reliable indicators of secondary contamination. This study allowed us to propose a geochemical indicator (GIM) GIM=∑ Mn Cs REE/Br which reflects the secondary contamination intensity. The decrease in GMI dynamics indicates an increase in the impact of the secondary contamination process on surface and spring waters. This innovative approach minimizes the reliance on extensive drilling, providing valuable insights for the study and monitoring of seawater intrusion in coastal aquifers.

Review on the Impacts of the Samalas Eruption (1257 CE) to the Hydrogeological Conditions of Mataram, Lombok, Indonesia

This paper examines the local impacts of the 1257 CE Samalas eruption in the Mataram plain in relation to the hydrogeological conditions. Data from several previous studies in the Mataram plain is summarized and then reinterpreted. Data collected from new fieldwork is also presented. This review summarizes hydrogeological conditions into several categories, i.e. stratigraphy, aquifer formation, groundwater quality, and evolution. Two coring data were evaluated, which showed that Mataram plain has a relatively thick alluvial layer with a dominant material of sand mixed with pumice from the reworked deposit of the 1257 CE Samalas eruption. The sediment from this eruption formed a freshwater aquifer layer up to ~18 m deep. Using resistivity data, the aquifer layers in the studied area were characterized as unconfined aquifer, aquitard, and semi-unconfined aquifer. Seven water samples show that the groundwater in the studied area is in good condition, which indicates the bicarbonate water type. The results of the analysis show that the impact of the 1257 CE Samalas eruption on the hydrogeology of Mataram is considered a positive impact, i.e. forming an unconfined aquifer containing freshwater that is good for domestic uses.

Investigation of Saltwater Intrusion into Freshwater Aquifers in Some Estuary Environment in Niger Delta

Investigation of Saltwater Intrusion into Freshwater Aquifers in Some Estuary Environment in Niger Delta

Mathematical modeling of pollution of underground aquifers due to mining of minerals

Purpose. The research aims to create a mathematical model of salt contamination spreading through underground aquifers in the event of depressurization of the hydrocarbon production well crater for further assessment of environmental and economic damage from these processes. Methods. To predict the environmental and economic damage from salt contamination, the distribution of concentrations of harmful substances was investigated, taking into account the number of supply sources and their intensity over time, based on situ studies at the Rybalske Oil Field, Okhtyrskyi District of Sumska Oblast in Ukraine, where there were technological failures wells, accompanied by open fountains with the release of large amounts of highly mineralized water and the formation of craters. Mathematical modelling methods were used to process the data from the study of accidental technogenic pollution of underground aquifers. Findings. Based on real data from the study of the processes of potential salt contamination spread in fresh aquifers as a result of accidents at hydrocarbon production facilities, a mathematical model of salt contamination spreading in drinking groundwater in the event of depressurization of an oil field well crater has been developed. Potential economic losses in case of possible groundwater contamination with highly mineralized solution, which can into drinking groundwater aquifers, are substantiated. It has been established that in connection with the occurrence of an emergency situation due to the release of formation water to the surface in the territory of oil and gas fields, the formation of technogenic meromictic reservoirs is possible, which is confirmed by the example of the Rybalske Oil Field. It is proved that the total mineralization of crater water increases linearly with depth of the reservoir occurrence, and a similar dependence is characteristic of the chloride ion content. Originality. For the first time, a multicomponent mathematical model of mineral salt migration processes in underground freshwater aquifers in the case of depressurization of a meromictic reservoir has been developed. Practical implications. The research results obtained using numerical methods make it possible to predict the processes of spreading harmful substances in drinking underground aquifers as a result of emergencies at oil and gas fields, taking into account the number of sources of pollutants penetrating the study area, the heterogeneity of properties of the environment into which the harmful substance enters, and to assess the dynamics of changes in the concentration of these substances and time with further assessment of environmental and economic damage from these processes.

Quantitative assessment of well leakage, part I: Cement stress evolution

A damaged cement sheath in wells can open a leakage pathway to shallow freshwater aquifers and atmosphere. Quantitative assessment of leakage along wells has become an area of interest for both the industry and the regulatory bodies. The well leakage can be of importance in both active and legacy wells. In order to estimate leakage through cement sheaths, the size of the leakage pathway and the damage in the cement sheath must be estimated. In this work, we have developed a hydro-thermo-mechanically coupled near-well model that aims to calculate the evolution of cement’s stress as it cures. This process takes into account the cement’s gradual increase in stiffness, chemical shrinkage, and the heat of hydration. The results are verified using lab measured cement stress and pore pressure data from the literature. A case study was developed based on a low-enthalpy geothermal doublet in the Netherlands. The results show that during the cold water injection, an outer microannulus may open to 60 µm. The presence of an external source of water and formation stiffness are of significant importance in determining the damage to the cement sheath. The heat of hydration in cement increases the temperature of cement during curing. The subsequent drop in temperature due to drilling or completion reduces the cement stress and exacerbates the damage to the cement sheath. The producer well may not form a microannuli, however shear and cyclical failure may be of higher likelihood. The modelling framework presented here allows for estimation of annular cement stress in the well. The analysis provides quantitative estimates of the size of the leakage pathway along a well that can be used to estimate well leakge. Quantitative estimate of well leakage provides crucial information for quantitative risk analysis and provides a framework to optimize well operations to minimize leakage risk.

Impacts of Sea‐Level Rise on Coastal Groundwater Table Simulated by an Earth System Model With a Land‐Ocean Coupling Scheme

AbstractSea‐level rise (SLR) poses a severe threat to the coastal environment through seawater intrusion into freshwater aquifers. The rising groundwater table also exacerbates the risk of pluvial, fluvial, and groundwater flooding in coastal regions. However, current Earth system models (ESMs) commonly ignore the exchanges of water at the land‐ocean interface. To address this gap, we developed a novel land‐ocean hydrologic coupling scheme in a state‐of‐the‐science ESM, the Energy Exascale Earth System Model version 2 (E3SMv2). The new scheme includes the lateral exchange between seawater and groundwater and the vertical infiltration of seawater driven by the SLR‐induced inundation. Simulations were performed with the updated E3SMv2 for the global land‐ocean interface to assess the impacts of SLR on coastal groundwater under a high CO2 emission scenario. By the middle of this century, seawater infiltration on the inundated areas will be the dominant component in the land‐ocean coupling process, while the lateral subsurface flow exchange will be much smaller. The SLR‐induced seawater infiltration will raise the groundwater levels, enhance evapotranspiration, and increase runoff with distinct spatial patterns globally in the future. Although the coupling process is induced by SLR, we found topography and warming temperature have more control on the coupling impacts, probably due to the relatively modest magnitude of SLR during the selected future period. Overall, our study suggests significant groundwater and seawater exchange at the land‐ocean interface, which needs to be considered in ESMs.

Physicochemical behavior and impact of CO2 and CH4 plumes during gas-rich water leakage in a shallow carbonate freshwater aquifer

Carbon capture and storage (CCS) is a promising technology for reducing CO2 emissions. Significant concerns have emerged about the potential leakage of CO2 into shallow aquifers, highlighting the risk to water quality and environmental safety. This underscores the importance of finding monitoring tools suitable for different geological scenarios. If leakage occurs in the context of depleted reservoirs being used for CO2 storage, residual CH4 from the storage complex will likely be entrained together with CO2. However, few studies have addressed the implications of CH4 presence and its potential as a monitoring parameter during CO2 leakage.To address this gap, we simulated a leakage event by injecting water enriched with CO2 and CH4 into a shallow limestone aquifer. The impact of the injection was monitored using a combination of laboratory measurements on water samples and in-situ sensors located downstream from the injection well.All parameters were affected by the simulated leakage. Some monitoring tools allowed us to differentiate the leakage event from natural variations. A key finding of this study was that at 7 m from the injection well, the CH4 breakthrough occurred roughly one day before the CO2 breakthrough, highlighting the potential of CH4 as an early indicator of CO2 leakage and suggesting interesting prospectives for industrial-scale sites. However, further research is needed to confirm the potential of CH4 as a CO2 leakage indicator at industrial scales, due to potential methane oxidation and loss of the signal with longer times and distances.This study contributes to a better understanding of the potential risks and effective monitoring strategies associated with CO2-CH4 leakage in carbonate aquifers.

Dynamics of Saltwater Intrusion in a Heterogeneous Coastal Environment: Experimental, DC Resistivity, and Numerical Modeling Approaches

Saltwater intrusion (SWI) is a critical concern affecting coastal groundwater sources due to natural and anthropogenic activities. The health of coastal aquifers is deteriorated by excessive SWI, mainly caused by the disturbance of the freshwater–saltwater equilibrium due to the escalating population, climate change, and the rising demand for freshwater resources for human activities. Therefore, gaining insight into the dynamics of SWI is crucial, particularly concerning the various factors that influence the intrusion mechanism. The present study focuses on the experimental simulation of saltwater in freshwater aquifers, considering boundary conditions and density-dependent effects. Two geological scenarios within coastal environments were investigated: First, a uniform, homogeneous case consisting of only sand, and second, a heterogeneous case in which layers of sand, clay, and sand mixed with pebbles are used. During the experiment, DC resistivity sounding data, as part of a widely recognized geophysical method, were collected and subsequently inverted to determine the depth of the freshwater–saltwater interface (FSWI). A finite element analysis was employed to generate numerical models based on experimental feedback. Further, for validation purposes, electrical resistivity tomography (ERT) data were collected from two distinct locations: near the seacoast and an aquaculture area. The ERT results show the presence of salinity intrusion in the study area, attributed mainly to groundwater overpumping and fish farming practices. The experimental findings indicate that the advancement of saltwater is affected by the geological properties of the media they traverse. The porosity (ϕ) and permeability (k) of the geological layer play a crucial role during the passage of saltwater flux into freshwater aquifers. The FSWI deviated along the clay boundary and hindered the easy passage of saltwater into surrounding layers. The alignment of experimental, numerical, and geophysical data suggests that this integrated approach could be valuable for studying SWI and can be applied in different geological settings, including tidal flats and alluvial plains.

Study on the Removal Effect of 3DEPs on Microplastics in Groundwater and Desalination Mechanism

Owing to water scarcity, groundwater quality has become an important constraint on sustainable regional development, especially in coastal areas. Coastal groundwater is subject to natural conditions and intense human activities, and the evolution of water quality is extremely complex, with the possibility of seawater intrusion into the groundwater, leading to the salinisation of freshwater aquifers. At present, the commonly used methods for removing groundwater pollution include coagulation, adsorption, biological method, membrane technology, etc., among which the coagulation method is more commonly used. At present, three-dimensional electrode electrochemical technology is widely used in high salinity organic wastewater and many organic wastewaters, but there are few studies related to microplastic removal by three-dimensional electrode electrochemical technology using metallic aluminium particles as particle electrodes. The treatment of microplastics in coastal groundwater is a relatively novel issue, and with the increasing application of three-dimensional electrochemical technology in the study of desalination, the three-dimensional electrode electrochemical technology will be promising due to the high salinity of coastal groundwater, the increasingly serious pollution of microplastics, and the fluctuation of water quality and quantity.

Aquifer-CO2 leak project. Effect of CO2-rich water percolation in porous limestone cores: Simulation of a leakage in a shallow carbonate freshwater aquifer

Carbon capture and storage (CCS) is a promising technology for reducing greenhouse gas emissions, however, leakage of CO2 constitutes a major concern for aquifers. Despite abundant literature on petrophysical and geochemical changes at storage conditions, few studies address the impact of CO2 leakage on petrophysical and at aquifer-like pressures, flow rates and temperatures. The aim of the paper is to study and quantify at the core scale, the effects of various factors, including flow rates, fluid salinities, CO2 concentrations and limestone carbonate facies, on the petrophysical and geochemical parameters of a carbonate freshwater aquifer during an experimental CO2 leakage. To achieve this, successive CO2-rich water percolation experiments were performed at the core scale, while monitoring changes in petrophysical parameters and water chemistry.During our experiments, initial permeability increments were observed for both rock samples, followed by decreases in later experiments. Evidence of pore clogging and wormholes was also observed. It was found that the transport of particles led to significant porosity creation. The water monitoring sensors were sensible to the experimental leakage conditions, particularly electrical conductivity. The results of this study contribute to the understanding of petrophysical changes in carbonate aquifer systems by anticipating which type of aquifers are more vulnerable to dissolution and to what extent the CO2 leakage conditions modify the petrophysical parameters.

Climate Change Vulnerability Assessment. A Framework for Urban Planning Practitioners in Ilala District, Dar es Salaam City, Tanzania.

Global climate change is a challenge undisputable in the intervening time. The Global South countries are the most vulnerable to global climate change. It is indicated by the prevalence of climate hazards including extreme temperatures leading to urban heat island effects(UHI, prolonged droughts, melting of ice caps, increased extreme weather events such as tropical cyclones, heat waves, urban flooding, sea level rise, and coastal erosion resulting in salty water intrusion into freshwater aquifers. This paper explores a framework for climate change vulnerability assessment in the urban planning process in cities of the Global South. A sample of 95 households was selected purposely for study. Data collection methods involved interviews by structured questionnaires, surveys, focused group discussions, observations, and documentary reviews. Quantitative data analysis was done using a statistical package for social sciences. Qualitative data were analysed by content analysis, narrative analysis, and interpretive phenomenological analysis. Results showed that climate change physical infrastructures, socioeconomic activities and livelihoods and ecosystems were vulnerable to climate change-induced flooding in urban areas. The study concludes that adoption of new urban planning process enhances resilience and sustainable cities and communities in cities of the Global South.

New insights into the flow dynamics of a deep freshwater aquifer in the semi-arid and saline Cuvelai-Etosha Basin, Northern Namibia: Results of a multi-environmental tracer study

Study regionA paleo-megafan system of the Cubango River in the northern parts of the semi-arid Cuvelai-Etosha Basin, shared by Angola and Namibia. It hosts a deep freshwater aquifer, the so-called Kalahari-Ohangwena 2 (KOH-2), with the potential to resolve the imminent regional water supply shortages. Study focusHydrogeochemical and multi-environmental tracer studies incorporating the use of age tracers 14C, 36Cl, 81Kr and 4He to determine the age of groundwater and provide insights into the flow dynamics of the KOH-2. New hydrological insights for the regionStable water isotopes and noble gas thermometry show that in a period with higher rainfall and recharge, temperatures were at least 3 – 4 °C lower than today. Several arguments led to the conclusion that younger groundwater, possibly of an age of 35,000 years, is mixed with ancient saline pore water. These include: 1) the correlation of measured 36Cl and 81Kr ratios, as well as 4He concentrations, using a binary mixing model, and 2) the substantial variation in 81Kr ages, ranging from 40,000 to 170,000 years, over relatively short distances—a phenomenon challenging to explain by advective groundwater flow equations. Consequently, the ages derived from 81Kr measurements serve as indicators of the extent of freshening and therefore describe mixing ages rather than absolute travel times.

Modeling the influence of climate on groundwater flow and heat regime in Brandenburg (Germany)

This study investigates the decades-long evolution of groundwater dynamics and thermal field in the North German Basin beneath Brandenburg (NE Germany) by coupling a distributed hydrologic model with a 3D groundwater model. We found that hydraulic gradients, acting as the main driver of the groundwater flow in the studied basin, are not exclusively influenced by present-day topographic gradients. Instead, structural dip and stratification of rock units and the presence of permeability contrasts and anisotropy are important co-players affecting the flow in deep seated saline aquifers at depths >500 m. In contrast, recharge variability and anthropogenic activities contribute to groundwater dynamics in the shallow (<500 m) freshwater Quaternary aquifers. Recharge fluxes, as derived from the hydrologic model and assigned to the parametrized regional groundwater model, reproduce magnitudes of recorded seasonal groundwater level changes. Nonetheless, observed instances of inter-annual fluctuations and a gradual decline of groundwater levels highlight the need to consider damping of the recharge signal and additional sinks, like pumping, in the model, in order to reconcile long-term groundwater level trends. Seasonal changes in near-surface groundwater temperature and the continuous warming due to conductive heat exchange with the atmosphere are locally enhanced by forced advection, especially in areas of high hydraulic gradients. The main factors controlling the depth of temperature disturbance include the magnitude of surface temperature variations, the subsurface permeability field, and the rate of recharge. Our results demonstrate the maximum depth extent and the response times of the groundwater system subjected to non-linear interactions between local geological variability and climate conditions.

Seawater intrusion assessment in the Bir Guendouz-Boulanoire coastal transboundary aquifers of Morocco and Mauritania

The Bir Guendouz region, situated in Southern Morocco, is affected by saltwater intrusion. The transboundary aquifer is shared by Morocco and Mauritania, and it serves as the primary source of freshwater in this arid region. To differentiate between freshwater and saltwater areas, 750 non-invasive vertical electrical soundings (VES) were utilized along 42 perpendiculars to the coast. Dar-Zarrouk parameters—transverse resistance (Tr), longitudinal conductance (S), and longitudinal resistivity (ρl)— were determined using VES. These techniques remove uncertainties in resistivity interpretation that may arise due to the overlap between freshwater and saline aquifers during the process of suppression and equivalence. The results indicate a significant marine intrusion in the Bir Guendouz-Boulanoire aquifer, with varying degrees of salinization observed in different zones. Freshwater zones are identified by a transverse resistance of over 4450 Ω m2, a longitudinal conductance below 41.7 mho, and a longitudinal resistivity greater than 8.7 Ω m. These characteristics can be used to prevent saltwater intrusion and ensure the sustainable use of groundwater resources. Furthermore, they will aid in improving resource management between the two nations. The study's consequences also involve safeguarding the ecosystem and ensuring the longevity of these transboundary water resources. Therefore, for researchers, professionals, and decision-makers involved in sustainable management of transboundary groundwater, this study serves as a crucial reference.

“You turn the tap on, the water's there, and you just think everything's fine”: a mixed methods approach to understanding public perceptions of groundwater management in Baton Rouge, Louisiana, USA

In Louisiana's Capital Area Groundwater Conservation District (CAGWCD), extensive groundwater withdrawals from the Southern Hills Aquifer System have begun to accelerate the infiltration of saltwater into the aquifer's freshwater sands. This accelerated saltwater intrusion has the potential to reduce the amount of groundwater available for public consumption and other industrial and agricultural uses throughout the region. In response to this threat, the Capital Area Ground Water Conservation Commission has begun development of a long-term strategic plan to achieve and maintain sustainable and resilient groundwater withdrawals from the aquifer system. The development of the strategic plan includes an assessment of public attitudes regarding groundwater and groundwater management in the CAGWCD. This paper presents the results of mixed methods public participatory research to evaluate current and historical views and attitudes around groundwater quality, quantity, and cost in the CAGWCD. The mixed methods approach used in this research employed a sequential explanatory design model consisting of two phases. The first phase involved the implementation of an internet-based survey, followed by a qualitative phase aimed at explaining and enhancing the quantitative results. The qualitative phase employed a combination of one-on-one interviews and focus groups. The research found that the primary governance obstacle that decision-makers may face in managing groundwater is a broad lack of public awareness of groundwater and groundwater issues in the CAGWCD. Despite the criticality of over-pumping and saltwater intrusion into the aquifer system, survey research and subsequent interviews and focus groups have shown that the public is largely unaware of these issues. This research also found a general lack of trust in both industry and government to manage groundwater issues and highlighted the need for groundwater management efforts to be led by unbiased, trusted institutions.

Engineered Materials, Machine Learning Enhance Carbon Storage Well Integrity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214844, “Engineered Materials and Machine Learning for Carbon Storage Well Integrity,” by Jacob Pollock, Oceanit Laboratories, and Hani Elshahawi, SPE, NoviDigiTech. The paper has not been peer reviewed. _ The success of CO2 injection operations, and the endurance of long-term storage, are partially dependent on well design and the materials used for well construction. The authors describe a stack of technologies they have developed that enable enhanced well robustness, monitoring of carbon-storage facilities, and modeling of their performance. The combination of these technologies enables the tracking of downhole and subsurface fluid distribution and flow. Furthermore, the scalable technologies can be used to exploit remaining reservoirs while preventing CO2-plume migration. Introduction Besides site selection and geological features that influence plume migration, well-construction design and materials have a major effect on successful storage. Injection wells are drilled into the storage site and completed with multiple cemented casing strings, with access to the reservoir through perforations or gravel packs. Cement supports and protects the metal casings from corrosive fluids while isolating the storage reservoir from freshwater aquifers by sealing off the wellbore annulus (Fig. 1). Cement integrity and durability are critical to successful carbon capture, storage, and use (CCUS) operations. Despite their importance, current cement-evaluation methods suffer from limited resolution, poor discrimination, and ambiguous interpretation. The authors have developed steel/cement interfacial bonding nanotechnology that enhances both mechanical bonding and acoustic coupling, along with acoustic metamaterials for sensing cement and tracking particles. The acoustic band gap of the materials was demonstrated to improve acoustic contrast and provide information about the cement environment based on frequency and amplitude. Furthermore, data-processing and machine-learning methods have been developed to interpret subsurface readings with more accuracy and deeper insight. Neural networks can be used to interpret the results of smart material detection and sensing, providing new information that was previously unattainable. Engineered Materials for Well Construction New classes of construction components with enhanced properties may be self-healing or passively sensing or may have outstanding physical properties such as mechanical strength. Nanoscale treatments can alter the surface characteristics of materials, endowing them with engineered interfacial behavior. Passive-sensing materials can alter incoming energy waves that can be detected to discern information about material condition and environment. These technologies can improve the properties of well-construction materials for carbon storage, increasing integrity and allowing monitoring of well and reservoir states. The results of successful laboratory and field trials of each technology described in this section are provided in the complete paper.

Coupled Transport, Reactivity, and Mechanics in Fractured Shale Caprocks

AbstractShales are low‐permeability caprocks that confine fluid, such as CO2, nuclear waste, and hydrogen, in storage formations. Stress‐induced fractures in shale caprocks provide pathways for fluid to leak and potentially contaminate fresh water aquifers. Fractured shales are also increasingly considered as resources for CO2 sequestration, enhanced geothermal, and unconventional energy recovery. Injecting reactive fluids into shales introduces chemical disequilibrium, causing an onset of a series of dissolution, precipitation, and fines mobilization mechanisms. The reactions have rapid kinetics and significant impact on porosity and permeability; consequently, flow and storage properties of caprocks. While previous research has explored the separate effects of these reactions, this study aims to uncover their simultaneous occurrence and collective influence. This study unveils these highly coupled transport and reactivity mechanisms by tracking and visualizing the reaction‐induced alterations in the matrix, microcracks, and fractures of shales over time. We conducted brine injection experiments sequentially at pH 4 and 2 in a naturally fractured Wolfcamp shale sample while simultaneously imaging the dynamic processes using X‐ray computed tomography (CT). CT images are validated by finer resolution images obtained using micro‐CT and scanning electron microscopy. We also tracked the sample permeability and fluid chemistry using brine permeability and inductively coupled plasma mass spectrometry, respectively. Findings show that fluid primarily flowed through fractures, dissolving reactive minerals and mobilizing fines on fracture surfaces. Dissolution of fracture asperities under confining stress resulted in the closing of fractures. Clogging in narrow fracture pathways, caused by fines accumulation, diverted fluid flow into matrix pores.

Impact of a CO2 leak on the release of major and trace elements according to groundwater flow conditions in a shallow freshwater carbonate aquifer: In-situ experiments and modelling

To investigate the role of hydrogeological conditions on the release of major and trace elements during CO2 leakage occurring in shallow freshwater aquifers in a CO2 Capture and Storage context, this paper compares the results of two in-situ CO2 leakage experiments. These experiments were carried out in a shallow freshwater carbonated aquifer located in Saint-Emilion, France, during both low and high-water levels periods. In both experiments, 200 L of carbonated water were injected into a well and groundwater monitoring was carried out downstream.Due to the physical heterogeneity of the aquifer at a small scale, the CO2-rich water plume did not follow the same flow path between the two hydrogeological periods, thus highlighting preferential pathways. It was observed that geochemical changes were not of the same intensity. The concentrations of Ca2+, HCO3−, Mg2+, Fe, Mn, As, Co, Cu, Ba, Sr and V increased during the low-water level experiment while the measured concentrations only reflected the dilution of the gasified water injected during the high-water level period.

Imaging freshwater and saline aquifers beneath Bradford County, Pennsylvania, USA, using Audio-Magnetotelluric (AMT) data

We investigate the utility of audio-magnetotelluric (AMT) data for detecting high electrical conductivity zones indicative of fresh and saline groundwater lenses at depths of < ∼1000 m at seven survey sites in the southwestern corner of Bradford County, PA. Dimensionality analysis indicates the AMT data can be interpreted using two-dimensional (2-D) models. 2-D electrical resistivity models obtained from inverting the AMT data reveal conductive zones at depths of <30 m at all sites, between depths of 50–150 m at six sites, and between depths of 400–600 m at one site. The models show slightly lower resistivities (∼15–30 Ω m) in the deeper zones compared to the shallower zones (>30 Ω m). Consistent with well log data from two boreholes in the study area and salinity estimates obtained from the imaged resistivities, we interpret the <30 m deep conductive zone as the freshwater aquifer, and the two deeper conductive zones as salty/briny groundwater lenses. Our salinity estimates for the deeper zones vary from 1 to 380 (unitless Practical Salinity Scale), which agrees well with previous estimates of Appalachian brine salinity of 10–343. We attribute the high-salinity groundwater lenses to Appalachian Basin brine migrating upwards from deeper in the basin via bedrock fracture and fault systems. Our findings indicate AMT surveying can be useful for imaging fresh and saline aquifers at shallow depths (< ∼1000 m), at least within the northeastern section of the Appalachian Basin in Pennsylvania.